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PRODUCTIVITY OF FOUR PASTURE GRAZING

SYSTEMS FOR YEARLING STEERS

By

Edgardo L. Cardozo

A DISSERTATION

Smeitted to
Midhigan State University
in partial fulfillment of the requirement
for the degree of

DOCTOR OF PHILOSOPHY

Department of Animal Science

1983

ABSTRACT

PRODUCTIVITY OF FOUR PASTURE GRAZING
SYSTEMS FOR YEARLING STEERS
By

Edgardo L. Cardozo

Recent reports have suggested that the demand for beef in the
U. S. will continue increasing in the future. This increment will
be a consequence of an increase in the population and to an increase
in meat consumption per capita. At the same time, a high proportion
of the meat actually consumed in Michigan is produced outside of
the state. The utilization of dairy breed steers and cheaper
feedstuffs such as forages will permit to meet the demand for high
quality products at low prices.

Four different pasture mixtures were tested using Holstein
yearling steers: alfalfa-orchardgrass (treatment 1); a combination
of alfalfa-orchardgrass, birdsfoot trefoil-fescue and rye-sorghum
(treatment 2); birdsfoot trefoil-orchardgrass-bromegrass (treatment

3) and Kentucky bluegrass (treatment 4). The first two treatments

Edgardo L. Cardozo

were rotationally grazed, while the last two were used in
continuous grazing.

Treatment effects were statistically significant for
digestibility in both years and for dry matter production only in
year one. No significant treatment effects were observed in yield
per animal, but a high significance was Obtained in production per
hectare. Treatments one and two showed a higher production per
hectare over the other two treatments. At the same time, the former
two treatments outproduced the latter ones in digestibility in both
grazing seasons, and in dry matter production per hectare in the
first year. Liveweight production per animal and per hectare were
higher the second year in all treatments, with a higher increment
observed in treatment two. Intake, selection of the consumed
forage by the steers, legume composition and the rotational grazing
system imposed in treatment two are the main reason for the different
animal performances obtained.

Multivariate linear regression models for the alfalfa-grass
data and the pooled data across treatments were used to predict
forage production. For the alfalfa-orchardgrass treatment, growth
period was the most important variable, followed by evaporation,
forage present at the initiation of the growing period and precipita-
tion. When the pooled data was analyzed, the order of importance
was forage present, growth period, precipitation and evaporation.
Maximum and minimum temperatures were the least important variables

in both models.

ACKNOWLEDGMENTS

The author expresses his deepest gratitude to his entire
guidance Committee. To his major professor, Dr. R. Erickson, for
continual councel, encouragement and friendship during the course
of the graduate study. His constant patience, effort and under-
standing have shown me the meaning of being an outstanding person.
Sincerest appreciation is extended to Dr. K. Wilson and Dr. Frank
Madaski for their constant moral support and interest during my
program, to Dr. H. Ritchie for his invaluable help in the research
project, to Dr. M. Tesar and Dr. G. Schwab for their constructive
criticism in the preparation of this dissertation.

The author is grateful to the Organization of American States
and the Government of Uruguay for their economic support. Thanks
are also extended to Dr. R. Nelson and Dr. W. Magee for the financial
support during the last three months of the program. The interest
and support of Ing. D. Faggi, former Dean of the College of Agricul-
ture in Uruguay is deeply appreciated. His immense commitment to
my program, as a professional and as a friend, assured the success
of it.

Appreciation is expressed to Dr. J. Gill, Dr. C. Anderson, Mr.

ii

M. Villarreal and Mr. J. Liesman for their help with the statistics
and computer analysis of the research data. Thanks are also extended
to Dr. D. Hillman and Dr. W. Thomas for their valuable comments
during the program, and to Dr. R. Emery, Dr. T. Huber and Dr. R. Cook
for the utilization of the laboratory facilities for forage analysis.
Special appreciation is expressed to the members of the Lake City
Research Station Mr. D. Nielsen, Mr. G. McLachlan, Mr. H. McGee and
Mr. H. Boven for their invaluable assistance with the research
project. I am also in debt with Mr. P. Sweeney and Mr. C. Reid for
their willingness to help.

The author is grateful to the Faculty members of the former
Department of Dairy Science. Special gratitude is expressed to the
members of the Breeding and Statistic group of the Department of
Animal Science for considering me for their seminars and workshops:
Dr. W. Magee, Dr. J. Gill, Dr. I. Mao, Dr. L. McGilliard, Dr. T.
Ferris and Dr. C. Anderson.

Sincere appreciation is expressed to all graduate students of
the Department of Animal Science, and specially to Dr. T. Smith,

Mr. J. Forsell, Miss M. L. Lockwood, Mr. D. Kirsch, Mr. B. Hughes,
Miss D. J. Cox, Mr. J. Walter, Mr. D. Banks, Miss D. Lana, Mr. J.
Meyers and Mr. P. Aho.

Special appreciation is expressed to those that contributed
with their honest friendship and moral support: Mrs. and Mr. Bonilla,
Mr. A. Brondani, Mrs. and Mr. Correa, Mrs. and Mr. da Silva, Miss

M. Gjorup, Mrs. and‘Mr. Gonzalez, Mr. A. Hargreaves, Mr. T. Hervas,

iii

Mr. J. Hlubick, Mr. T. Oleas, Mrs. and Mr. Towns, Mrs and Mr. Valdez,
Mrs. and Mr. Villa-Godoy. My special gratitude to Mr. M. Villarreal
for his help and sincere friendship during the entire program. The
author will be always in debt with Mrs. Florence and Mr. F. Madaski
for their friendship and constant support.

Finnally, my deepest appreciation goes to my wife, Mercedes,

for her continual support, sacrifices and love throughout my program.

iv

TABLE OF CONTENTS

LIST OF TABLES . . . . . . . . . .
LIST OF FIGURES . . . . . . . . . .
1. Introduction . . . . . . . . . .
LITERATURE REVIEW . . . . . . . . .

2. Pasture evaluation methods under grazing conditions
2.1 Introduction . . . . . . . . .
2.2 State of the Art of pasture evaluation . . .
2 3 Measurement of dry matter yield and intake: use of
cages . . . . . . . . . .
2 3.1 Cutting equipment . . . . . . . .
2.3.2 Height of cutting . . . . . . . .
2 3

. .3 Herbage accumulation during the grazing period and

measure of growth . . . . . . . . .
2. 3. 4 Measure of intake . . . . . . .
2.4 Sampling methods: accuracy, sample size, number and
distribution . . . . . . . . . .
2.5 Botanical composition . . . . . . . .
3. Gr razing management . . . . . . . . .
3.1 Systems of grazing . . . . . . . . .
3.1.1 Introduction . . . . . . . . . .
3.1.2 Definition of grazing systems . . . . . .
3.2 Management of grazing for forage growth . . . .
3.3 Ecology of grazed pastures . . . . . . .
3.4 Animal-plant relationship . . . . . . .
3.4.1 Stocking rate . . . . . . . . .
3.4.2 Comparisons among grazing systems . . . . .
3.4.3 Conclusions of the relation between systems of grazing
and stocking rate . . . . . . . . .
3.4.4 Trampling . . . . . . . . . . .
3.4.5 Animal excretions . . . . . . . . .
3.4.6 Cycling of nutrients . . . . . . . .
3.4.7 Behavior of grazing animals . . . . . .

Page
viii

xi

mO\O\

11
12

13
16

19
24

27
27
27
28
32

39
39
S3

67
68
7O
72
75

Page

3.4.8 Selection of diet . . . . . . . . 80
3.5 Physiological basis for grazing management . . . 84
3.5.1 Introduction . . . . . . . . . . 84
3.5.2 Pasture growth . . . 84
3.5 2.1 Definition of growth: factors that affect pasture
growth . . . . . . . . . . . 84
3.5.2.2 Mixtures of legumes and grasses . . . . . 85
a. Importance of legumes . . . . . . 85
b. Competition between legumes and grasses . . 95
3.5 3 Pasture growth in relation to the environment . . 98
3.5.4 Organic reserves and growth . . . . . . 102
3.5.5 Frequency and intensity of defoliation in relation
to pasture growth and persistency . . . . . 105
3.6 Control of feed intake . . . . . . . . 114
3.6.1 Introduction . . . . . . . . . 114
3.6.2 Factors that affect intake . . . . . . 114
3.6.3 Mechanisms of control. . . . . . . . 117
3.6.4 Effect of grazing conditions on voluntary intake . 121
4. Measurement of animal performance . . . . . 123
MATERIALS AND METHODS . . . . . . . . . 126
RESULTS 0 O O O O O O O O O O O 143
1. Botanical composition . . . . . . . . 143
2. Dry matter 0 O O O O O O O O O O 148
3. In vitro dry matter digestibility . . . . . 155
4. Intae O 0 O O O O O O O O O O 165
5. Animals . . . . . . . . . . . . 173
DISCUSSION 0 I O O O O O O O O O O 194
1. Botanical composition . . . . . . . . 194
2. Digestibility . . . . . . . . . . 201
3. Animal performance . . . . . . . . . 207
4. Forage growth: a model . . . . . . . . 221
CONCLUSIONS 0 O O O O O O O I O O 229

vi

Page
RECOMMENDATIONS AND FUTURE RESEARCH . . . . . . 233

BIBLIOGRAPHY . . . . . . . . . . . . 236

Vii

Table

10.

11.

12.

13.

LIST OF TABLES

Comparison of the effect of different grazing
systems on performance per animal and per unit
are a O O O O O O I O O O 0

Total herbage production on grass and grass-
legume mixtures . . . . . . . .

Animal performance due to different fertilizer
treatments and comparison of legume-grass versus
grass pas tures O O O O O O O 0

Average body weight and standard errors at the
beginning of the experiment in 1981 and 1982

Animal weigh schedule for year 1 and 2 . .
Average area in acres and hectares per treatment

Mineral composition of trace mineralized salt
blocks . . . . . . . . . .

Means and standard errors for botanical composition
in June 1981 and 1982, Z . . . . . .

Means and standard errors for in vitro dry matter
digestibility at the beginning of the experiment
in both years, Z . . . . . . . .

Legune composition of pastures : means and standard
errors, year 1, Z . . . . . . .

Legume composition of pastures: means and standard
errors, year 2, Z . . . . . . .

Dry matter available per treatment during year one,
means and standard errors, kg per ha . . .

Dry matter available per treatment during year two,
means and standard errors, kg per ha . . .

viii

Page

56

87

92

127
128

132

133

138

139

144

145

149

150

Table Page

14. Dry matter offered for the different treatments
during year one and two, kg per ha . . . 153

15. Means for dry matter offered across treatments
for both years in time one, three and six, kg/ha 154

16. Dry matter offered per treatment in years one
and two and in times one, three and six, kg/ha 156

17. In vitro dry matter digestibility per treatment
during year one, means and standard errors, Z 157

18. In vitro dry matter digestibility per treatment
during year two, means and standard errors, Z 158

19. In vitro dry matter digestibility for the four
treatments in year one and two, Z . . . 162

20. In vitro dry matter digestibility of dry matter

across treatments for times one, three and seven,
Z O O O O O O O O O O O 164

21. Digestibility values for the different treatments
in year one and two, Z . . . . . . 165

22. Intake per steer per day, means and standard errors,
year one, kg of DM . . . . . . 166

23. Intake per steer per day, menas and standard errors,
year two, kg of DM . . . . . . 167

24. Intakes across treatments for times one, three,
six, kg per steer per day . . . . . 171

25. Means for intake for the different treatments in
year one and two, and times one, three and six,
kg of DM per steer per day . . . . . 172

26. Average liveweight per treatment per time in year
one and two, kilograms . . . . . . 177

27. Kilograms of liveweight gain per hectare for the
different treatments, year one, means and standard
errors . . . . . . . . . . 178

28. Kilograms of liveweight gain per hectare for the

different treatments, year two, means and standard
errors . . . . . . . . . . 179

ix

Table

29.

30.

31.

32.

33.

34.

35.

36.

Page
Liveweight gain per hectare for the four treat-
uents during year one and two, kilograms . . . 183
Effect of time of weigh on animal gain, kilograms . 186
Kilograms of liveweight gain per hectare across
treatments at different times during the two experi-
mental periods . . . . . . . . . 187
Liveweight gain per unit area for the different
treatments in times one, three and seven, kg/ha . 191
Stocking rate per treatment during year one . . 208
Stocking rate per treatment during year two . . 209

Linear regression equations for alfalfarorchardgrass
production on several independent variables, 1981-1982 222

Linear regression equations for forage production
(pooled data) on several independent variables,
1981-1982 0 o o o o o o o o o 223

10.

11.

12.

13.

14.

LIST OF FIGURES

Control of feed intake in ruminants with diets
of different qualities . . . . . . .

Map of the experimental area . . . . .

Legume composition of the different treatments,
year one I O O O O O O O O .

Legume composition for the different treatments,
year two 0 O O O O O O O O 0

Dry matter offered for the different treatments,
ye ar one 0 O O O O O O O O 0

Dry matter offered for the different treatments,
year two 0 O O O O O 0 O O

In vitro dry matter digestibility for the differ-
ent treatments, year one . . . . . .

In vitro dry matter digestibility for the differ-
ent treatments, year two . . . . . .

In vitro dry matter digestibility, values are
averages across treatments for each sampling time,
years one and two . . . . . . . .

Daily intake per steer for the different treatments
in year one, in dry matter . . . . . .

Daily intake per steer for the different treatments
in year two, in dry matter . . . . . .

Total liveweight gain per treatment in year one
Total liveweight gain per treatment in year two

Accumulated liveweight gain in year one . .

Page

119

131

146

147

151

152

159

160

163

169

170
174
175

180

Figure Page
15. Accumulate liveweight gain in year two . . . 181

16. Effect of time of weigh on animal gain, values
are averages across treatments for each time in

year one and two . . . . . . . . . 185
17. Liveweight gain per treatment in year one . . . 188
18. Liveweight gain per treatment in year two . . . 189

19. Average liveweight gain per day in year one . . 192
20. Average liveweight gain per day in year two . . 193

21. Proposed relationship between stocking rate and
gain per animal . . . . . . . . . 212

xii

INTRODUCTION

The total land surface of the world is estimated to be around 32.9
billion acres. Approximately 10 Z of it is considered arable land, and
2.5 billion acres (7.6 Z) are used for crop production.lastures (natural
grasslands and sown forages) represent almost 20 Z of the earth's
surface , or 6.4 billion acres (Cook, 1980). According to FAO (1978),
temporary and permanent pastures represent 65 Z of the total agricultural
land in the world. Barnes (1981) reported that up to 56 Z of the total
land in the United States (U.S.) was dedicated to forage production in
1977.

A: the same time, the population in the world is increasing
dramatically. The annual increase has been projected to 1.7 Z, which
represents a total population of 6 billion people by the year 2030.

Meijs (1981a) suggested that because of the extensive areas occupied by

grasslands, we have to put more emphasis in developing them in order to

meet the increasing demands for food by the increasing population. This

idea agrees with two important considerations:

- high quality feeds will have to be diverted to human consumption in
the future (Hoveland, 1975);

- the remaining crop lands in the world will not be able to satisfy
human needs under the present rate of increase in the human population.

Several definitions of grasslands have been proposed by different

authors (Stoddart et al., 1975). I will use the term grassland according
to 't Mannetje (1978a): "it is an ecosystem from.which herbaceous animal
feed is derived". Grassland vegetation may consist of mixture of grasses,
legumes, trees and other plants. Some of them contribute directly to
production of feed for animals, and others, although not important as
feed for grazing animals, play an important role competing with edible

species.

To avoid confusion, I consider it essential to define some of the
terms used in this thesis. Wheeler (1981a) defines forages as the
vegetation eaten by grazing livestock. The same author distinguishes
between native, natural and improved pastures. we are only interested
in improved pastures within the context of this work. He defines
improved pastures as those "communities entirely or principally of sown
species, to which in most cases fertilizer has been applied". This use
conformes the definitions of Moore (1970) and Barnes (1981).

Ruminant livestock in Oceania, America and certain countries of
Europe rely heavily on forages. Tesar (1978b) estimates that native
grasses and grazing lands carry 60 Z of the cattle, 70 Z of the sheep
and 80 Z of the goats in the U. 8. Beef cattle comprise 87 Z of the
total cattle population in the U. S., and 83 Z of all the feed units
consumed is provided by forages (Barnes, 1981). At the same time, this
author established that forages provide 61.2 Z of the feed units to
dairy cattle and 91.1 Z to sheep and goats in the U. S.. In Australia
less than 1 Z of cattle (or approximately 3 Z of the steers over one
year of age ) are lot-fed animals (Wheeler, 1981a). The same author

concludes that most nutrients for dairy cows and sheep are also provided

by forages (grazed and preserved). Meijs (19813) established that
herbage and grassland products (preserved forages) supply approximately
63 Z of the total requirements of sheep and cattle in the Netherlands.
In Argentina, "feedlot operations do not constitute any important
percentage in the beef market" (Inchausty and Tagle, 1980). Escuder
(1976) concludes that beef production in Brazil is based on native

and improved pastures.

Profitable production of slaughter beef on pasture requires forages
with high potential to sustain rapid animal gain and good finish (Hoveland,
1975). Bryan et al. (1964), Shaw et al. (1976a) and Williams et al.
(1976) established the important characteristics sought in pasture
plants to be utilized for animal production:

- ability to grow and persist under several conditions of soil

and climate;

- ability to withstand grazing;

- ability to respond to imporvements in the environment;

- ability to produce high yield and quality of feed;

- absence of toxic compounds that can retard animal gains;

- ease of establishment and gathering reproductive material.

Legumes in general are very important components in pastures due
to their quality such as protein content, digestibility, dry matter
production . Balasko et al. (1974) have indicated the importance of
including legumes in forage programs for beef operations in the North
East United States.

Several reasons support the idea of measuring vegetation.

't Mannetje (1978a) establishes three main purposes: 1) as a way to

describe the vegetation in terms of ground cover, dry matter production,
growth, quality; 2) to distinguish the effect of specific management
practices in terms of changes introduced into the original pasture
ecosystem; and 3) to establish the productive capacity of it. Several
characteristics can be used to evaluate the ability of the vegetation to
produce feed for animals, but all of them depend on the final utilization
of the forages. Reid et al. (1959) established that the main purpose of
forages in the diet of beef cattle is the provision of energy, while

't Mannetje (1978b) maintains that energy, protein, minerals, vitamins
and the absence of toxins and deleterious hormones are the important
factors on which to base quality of forages. Beaty and Engel (1980)
emphasized the importance of considering plants not as uniform material,
but to divide them in their parts, managing them in order to avoid
accumulation of the undesirable plant parts and dead material.

The other important role in the system is played by ruminants. The
projected demand for U. S. beef and feed grains suggests the need for
efficient systems to produce beef from all-forage diets (Baker et al.,
1974). These predictions were based on projections made by Balasko et
al. (1974). These researchers predicted that the demand for beef will
increase, even if the demand per capita remains constant. Beef cow
numbers in Michigan have increased from 132,000 to 195,000 in ten years
(1964 to 1974). There has also been an increase in value of the livestock
from 22 to 52 million dollars (Anonymous, 1974), and these trends will
continue in the near future.

Ferris and Wright (1976) reported that beef consumption in Michigan
is greater than the amount of beef produced in the state. As a result

of that, feedlots in the state have been utilizing animals from other

states. It is likely that future demands will continue to be strong if
beef production can be economically achieved (Helsel et al., 1978).
Beef production would be rapidly expanded by feeding out male
dairy calves that are at present either killed, used for veal production
or sent to the market at different stages of development (Hibbs et al.,
1959). Several studies have shown that dairy-breed calves produce rapid
gains, and feed conversion is relatively efficient, although fat cover
and carcass grades are low when compared to beef-breed steers (Kesler
et al., 1975).
The specific objectives of this study include the following:
- to evaluate the productivity of four pasture systems that vary in
levels of input management;
- to determine the variability and length of productivity of the four

systems.

LITERATURE REVIEW
2. Pasture evaluation methods under grazing conditions

2.1 Introduction

Techniques for evaluation of forages must have reference to animals
in some way. Animals must be used in some part of the system if the
information obtained about forages is to be relevant for plant-animal
systems (Heaney, 1970; Mott and Moore, 1970). Mott (1980) concluded
that yield per animal gives reliable estimates of the forage quality,
providing it is offered ad libitum. On the other hand, animals per area
is a good estimator of forage production when the stocking rate is
near the carrying capacity.

Information on the comparison of pasture yields obtained from
clipping methods and animal methods has increased since the fifties.
Carter (1962) points out that clipping methods tend to overestimate the
yield basically due to unrecovered rejected forage, the effect of the
grazing animals and unmeasured use of nutrients by the animals. At the
same time, other authors have reported that some type of forage analysis
is essential to be able to find relationships between quality parameters
in the pasture and animal responses (Moore, 1981). Mott and Moore (1970),
Myers et al. (1074), Riewe (1980), Mochrie et al. (1981) and Wheeler
(1981b) should be consulted for more detailed information on basic

schedules and protocols for forage evaluation.

Grazing experiments in which animal production is one of the variables
are essential in pasture evaluation programs. Animals are the marketable
product, and since there is a strong interaction between the grazing
animal and the pasture, no accurate pasture evaluation for grazing can
be done without them ('t Mannetje et al., 1976). Spedding (1965) also
established that grazing management should be based on the understanding
of the animal-plant relationship. He claims that it is essential to
understand both the nutritional needs of the animal and the harvesting
effect of the animal on the growth rate of the plants.

The central goal of many plant and animal scientists is the
improvement of forages as feeds for ruminants (Moore, 1981). Burton (1981)
maintains that through genetically improved varieties, farmers can
Obtain more production per animal, a better quality product, and more
efficiency in the system, which will mean more profitability. Based on
these predictions Moore (1981) expressed that more profitability in
livestock enterprises can be obtained if forages are a major part of the
animals' diet, if animal performance increases as a result of the
improvement in forage quality, and if increased income is superior to
increased costs of using better quality forages.

It is also important to evaluate the pastures considering the
general context in WhiCh they will be used ('t Mannetje et al.,

1976). In our experiment we considered two basic aspects:

- the experiment was planned to be used for beef production; and

- we also considered the prevailing conditions in which the forages
will be used. The systems which were used may not represent the most
efficient method of pasture utilization, but they represented methods

that farmers may adopt in the future.

2.2 State of the Art of pasture evaluation

Grazing experiments vary widely in their scope, from studies on
native species (grasses and shrubs) on semi-arid conditions to introduction
of sown species in areas with high rainfall. At the same time, different
completeness of experiments have been achieved from simple analysis of
livestock production to more complete analysis: Chemical analysis of
forages and livestock subproducts, intake, and quantification of the
animal-forage systems (Robards, 1981). Beaty and Engel (1980) concluded
that major improvements have been made on forage production research,
but not on forage intake and digestibility measurements.

Mochrie (1981) presented results from a survey made in the U. S.
on 135 projects under grazing conditions developed throughout the entire
nation from 1975 to 1980. Some of the most important findings can be

summarized as follows:

70 Z of the projects were classified as using humid pastures, 28 Z as
range conditions and 2 Z as irrigated pastures used as supplements to
range.

- 65 Z of the experiments included grasses, 13 Z legumes and 47 Z some
type of legume-grass combinations.

- 73 Z of the projects used beef animals, 13 Z dairy animals, 6.7 Z
sheep-goats and 7.3 Z were a combination of the above. Over 75 Z of
the projects analyzed the response of the pasture using grazing
animals, basically through botanical composition analysis.

- Clipping alone is the most common method used to calculate forage

production (almost 50 Z of the projects); but other methods also used

clipping as part of the analysis.

- Approximately 60 Z of the experiments estimate intake.

- In vivo digestibility comprised only 20 to 25 Z of the experiments,
which indicates a generalized reliance on laboratory techniques.

- The major emphasis is on animal-plant interface. Except when minerals
or metabolic anomalies were the main objective of the experiments, few
soil specialists were included as part of the scientific teams.

Holloway (1980) presents a detailed review of the research in pasture

utilization in the Southern States of the U. 8..

Australian research has some basic differences with the U. S.
systems described above. One of the more important differences is that
sheep is the most important animal specie used in temperate Australian
pasture research (Robards, 1981). Robards (1981) also refers to some
other distinctive characteristics of the plant-animal research systems
in-Australia:

- changes in liveweight are usually the only indicators of available
forage, especially in long term experiments.

- More emphasis has been placed on measuring intake under grazing
conditions, using in vitro methods in combination with fistulated
animals or other in vitro techniques.

- Australian researchers have employed the fecal index technique under
grazing conditions to increase the accuracy of intake and digestibility
measures (Langlands, 1975). This is one technique with great potential
to evaluate nutritional status of grazing animals under extensive

conditions (Holloway et al., (1980).

2.3 Measurement of dry matter yield and intake: use of cages

 

Several types of techniques have been used to measure dry matter

yield and intake by grazing animals. Maclusky (1959) reports that large

v1

an»

10

discrepancies have been reported in the literature between the pasture
output and animal production when herbage sampling techniques and animal
requirements are used as the basis of the estimation. Those discrepancies
are based on pasture sampling errors which do not precisely show what
animals consume. Ahlgren (1947) concluded that the use of livestock
provides the most accurate results because it considers not only the
effect of the pasture on the animal but the animal effect on the forage
as well. However, good clipping techniques may give more precise
information on pasture yield than methods using animals due to the large
variability among them (Anonymous, 1952).
The main purposes of measuring dry matter yield and intake can be
summarized as follows:
- to determine the amount of dry matter feed available for the grazing
animals (Bransby et al., 1977);
- to plan the use of fertilizers, herbicides, choice of grazing methods
or stocking rates ('t Mannetje, 1978b);
- to calculate growth (Bransby et al. (1977), utilization by animals and
their effect on the pasture: trampling, urination and defecation
('t Mannetje, 1978b). The procedure used also depends on several other
factors: specie of animals used, specie of plants and their combination
in mixtures or pure stands, scale of the investigation, size of the
plots to be sampled, available resources and facilities (Anonymous,
1952).
The quantity of forage available in any pasture can be measured
by mechanical methods (destructive) and by non-destructive procedures
(visual or electronic means) (Burns, 1980). In the destructive method,

representative forage samples are cut from the pastures. The non-destructive

11

procedures are based on the utilization of one or more variables related
to quantity, and harvesting a small amount of the available forage for
further analysis. Several non-destructive methods are described in the
literature: visual estimation (Hutchinson et al., 1972), height (Whitney,
1974), density (It Mannetje, 1978b), and measurements of non-vegetative
attributes such as electronic capacitance (Neal and Neal, 1973), beta-
attenuation and spectral composition of reflected light ('t Mannetje,
1978b). The basic idea behind the non-destructive procedures is to
reduce labor and equipment costs (Burns, 1980), and sometimes-as a way
to overcome the problem that samples take a large proportion of the
available forage on small plots ('t Mannetje, 1978b). Corbett (1981)
suggests that a capacitance meter to measure dry matter before and after
grazing is a promising method to increase the ease and accuracy of the
"difference" method. With the destructive technique (cutting and weighing)
a representative sample of the available forage is harvested and several
analysis can be performed to have a more accurate estimation of the
elements available to the grazing animals (Bransby et al., 1977).

Bransby et al. (1977) developed the idea of using a combination of
forage attributes (height, density and compressibility) to be measured
together by a disk. The new term was called "forage bulk" by the authors
and has the advantage of its accuracy and speed. The level of precision
measured on tall fescue pure stands seems to be relatively insensitive
to the diameter of the disk and to the amount of forage present on the
field.

2.3.1 Cutting equipment

 

Several hand harvesting devices for forages are available: scissors,

12

shears, curved knives, etc. The major advantages of this type of
equipment is their adaptability to small or irregular sample quadrats
and their controlability of sample height. Their main disadvantage is
the high labor input which make them less used ('t Mannetje, 1978b).
Researchers now use power-driven equipment and special machines to
increase the efficiency of sample collection. Machines permit large
samples to be taken quickly and a larger area can be sampled (Shaw et
al., 1976b).

The principal disadvantage of the power-driven equipment is the
variability in cutting height. For Meijs (1981a) the choice of the
Inachine is based on the cutting height which has to be controllable.
2.3.2 Hegighftof cutting

Two systems of height cutting can be used: ground level and above
gground level. As we mentioned earlier, hand cutting systems are more
ziccurate in controlling height level. Meijs (1981a) found differences
111 cutting height using lawn-mower and motor scythe with a mixture
ciomposed predominantly of perennial ryegrass (Lolium perenng). He also
f(Fund significant differences among persons cutting the same forage

mllxture which supports the need for the same person to cut all the
Samples.

One way to avoid errors due to variable height cutting levels is
hai‘rvesting to ground level. However cutting to ground level has certain
disadvantages :

“ it may damage the vegetation and introduce another factor that affects
regrowth. 't Mannetje (1978b) emphasized the importance of avoiding
samples from the same location over short periods of time.

‘ Samples may be highly contaminated with soil, litter and dung

13

(Anonymous, 1961). This tends to overestimate dry matter production
and includes another source of error in chemical analysis. Johnson
(1978) indicates some methods to overcome this problem.

- It is essential that collection of material to analyze animal intake
represents what animals actually eat. If the whole plant is harvested,
underestimation of digestibility and concentration of minerals and
other components will occur as a result of the selectivity of animals
(Johnson, 1978).

However, Walters and Evans (1979) concluded that ground level cutting

systems are more applicable, unless the species used have prostrate

liabits.‘Maclusky (1959) reported several experiments done at the Hannah

Research Institute clipping to ground level.

The other possible cutting height is above ground level. Meijs
(L1981a,b) using a motor scythe reported differences in cutting height
before and at the end of the grazing period, the latter being higher.
However he did not find any difference using a lawn-mower.

2.L3.3 Herbage accumulation during the grazing period and measure of

growth

Herbage accumulation during the grazing period is a function of
the following factors (Meijs, 1981a):

length of the grazing period;
Cflharacteristics outside the pastures: season, temperature, rainfall,
Irutrient levels of the soil;
grazing intensity: herbage allowance, stocking rate.
Different procedures have been used to measure dry matter production
aJud consumption by grazing animals. In general these methods can be

grouped in two different categories: direct harvest technique represented

14

by technique number one of Boyd, and the "difference" method with various
modifications (Boyd, 1949). Lineham (1952) and Lineham et al. (1952)
reviewed the different techniques included in the so called "difference
method". Klingmen et al. (1943) distinguish between two methods to
estimate yield:

- through measuring consumption by the grazing animal, and

- measuring annual growth of herbage.

When the grazing period is short, a good indication of the available
forage is obtained by cutting samples at the beginning of the grazing
period. When animals are moved out, another sample can be taken and
consumption is calculated by the difference between the two (Harris et
al., 1977). This system can be used under range conditions (Cook et al.,
1948) or sown pastures (Holmes, 1980). Even though it needs twice as much
sampling as the non-destructive methods, it provides estimates of yield
and intake (Cooke, 1969). Growth during rest periods is obtained by the
difference in forage available at the beginning of the next grazing
period and the forage left uneaten during the last grazing period
('t Mannetje, 1978b).

When the grazing period is less than three days, there is no need
to correct intake of the grazing animals by pasture growth (Lineham, 1952;
Lineham et al., 1952; Anonymous, 1961; Carter, 1962; Pigden and Minson,
1969; Walters and Evans, 1979). Green (1949) suggested two days as a
maximum, and Holmes (1980) used two to four days as a grazing interval
without correcting for plant growth.

Long-cycle rotational or continuous grazing requires the utilization
of protected areas or enclosures to correct for the growth of the pasture
(Carter, 1962). Bosch (1956) distinguishes between gross and net yield.

Gross yield is determined by direct measurement, and as a result, it

15

involves a large error. Net yield is calculated by indirect methods,
using the number of grazing days, milk yield and growth of the livestock.
Lineham (1952) established that within certain limits, pasture growth is
a function of the existing forage on the field: the higher the remaining
forage present on the field the higher is the rateof plant growth.
Mitchell (1970) defines growth as the increment in plant size and fresh
weight due to cell division and enlargement.

Several authors have established that some bias is introduced in
the evaluation due to the fact that a special microclimate is created
within the enclosure (Maclusky, 1959). This bias is increased when the
grazing period is extensive (Lineham, 1952), and with dense stands of
high and prostate species (Mitchell, 1970). Cowlishaw (1951) reported
that 16.2 Z more green matter and 11 Z more dry matter is produced inside
the cages due to lower wind velocity, higher relative humidity and as a
result lower dry matter percentage and transpiration losses. Peterson et
al. (1965) working with alfalfa pastures reported a 20 Z decrease in dry
matter production outside the cages due principally to soil compaction.
Cowlishaw (1951) also mentions the effect of defoliation, trampling,
dung and urine outside the cages as being responsible for lower growth
rates.

At the beginning of the grazing period, homogeneous sampling sites
are chosen. At each sampling site two sampling units similar in yield
and composition are defined: one is out before animals start grazing to
measure yield (0Y1) and other predefined characteristics, and the other
area is protected from grazing. At the end of the grazing period its
yield is estimated (CY2) by cutting procedure. Growth (Cl) is then

calculated as G1 a CY2 - 0Y1. For successive periods the formula is

16

n
AG = 2: ( CYn - OYn_1 ) ('t Mannetje, 1978b).
1

2.3.4 Measure of intake

 

Van Soest (1982) defines intake as the amount of feed an animal
consumes and it is expressed as the weight of that feed ingested in a
given time period. However due to the imprecision of this system,

't Mannetje (1978b) uses utilization instead of intake. It refers to
intake by grazing livestock and other herbivores plus decomposition and
hebage spoiled by trampling, dung and urine. These effects can not be
easily separated from true intake and as a consequence, utilization,
consumption and intake are often used as synonymous (Anonymous, 1961).

Herbage intake by grazing animals can be estimated by measurements
on the pasture (Brown, 1954; Peterson et al., 1956; Carter, 1962;
Shepherd, 1962; Meijs, 19813) or by measurements on animals themselves
(Anonymous, 1952, 1961; Harris, 1962; Woolfolk, 1962; Pigden and Minson,
1969; Harris et al., 1977; Walters and Evans, 1979). In general, animal
techniques are prefered because they are more accurate (Maclusky, 1959;
Raymond, 1969) since they can be based on individual-animal basis
(Walters and Evans, 1979). Within the last few years the chromic oxide
technique has been considered as a very useful and precise tool to
measure intake. Raleigh et al. (1980) present an up—to-date review
about the use of this technique.

Meijs (1981a) establishes the basis for the potentiality of the
"sward method" to provide reliable estimates of forage intake:

- the accuracy in maintaining a constant cutting height before and
after the grazing period. It also has to reproduce the grazing

behaviour of the animals and recover deteriorated material by

Ru.

3

 

as.
.5
N t

O‘-

h...»

u-
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17

trampling or other factors.

- The precision in assessing the pasture growth throughout the grazing
period.

- The exactness of the estimation of the forage intake by the grazing
animals.

Peterson et al. (1956) compared chromogen and clipping methods to
measure consumption of total dry matter and digestible nutrients by
steers on alfalfa pastures under two grazing systems. Based on these
results, they concluded that the clipping method does provide an
acceptable method for preliminary evaluation of pastures. The same main
conclusion is reported by Anonymous (1952) and Walters and Evans (1979).

Corbett (1978) presents a review of techniques used to estimate
intake of animals under grazing conditions. His discussion deals with
the labor requirements and sources of error, two of the most critical
areas in pasture research. The same author presents a supplement paper
in 1981.

To calculate animal consumption under long grazing periods, Lineham
et al. (1952) used a formula that takes into account the growth of the
pasture during the grazing period. The formula is:

Amount of grass nutrients (log D - log F)

=(C-F)
consumed by steers (log C - log F)

 

where C is the amount of pasture nutrients at the beginning of grazing,

D is the quantity of pasture nutrients in cages at the end of the grazing
period, and F is the quantity of pasture nutrients left uneaten on the
grazing area at the end of the grazing period. These authors found a

correlation coeficient of 0.95 using this formula and a method of intake

18

calculated from maintenance and weight changes of the animals during
a four year year period. Lineham (1952) reports a 1 Z difference using
this formula relative to the "animal method". The animal method is
based on actual measured liveweight gain of 464 bullocks in 46,748
grazing days.

Bosch (1956) simplified the previous formula to:

Amount of grass nutrients
= ( C - F ) + ( D - C )
consumed by livestock 2

where C, D, and F are the same parameters defined by Lineham et al.
(1952). Using a series of observations from Lineham, Bosch (1956)
compared the results using both formulas. He found that both procedures
gave practically the same results, and as a consequence he recommended
his formula because it is simpler to use.

schultz et al. (1959) established a curvilinear relationship
between forage consumption and beef production per acre. However,
Carter (1962) suggested that this effect could be true under continuous
grazing for long periods of time; but we have to expect a linear
relationship when short grazing periods are used and maximum intake is
assured. This is to diminish the maintenance proportion with respect
to total weight gain. MacluSky (1959) also found a linear relation
between yield per acre and intake on a ryegrass pasture. However the
same author reported that a curvilinear relation could be found if the

increase in yield per acre was due to maturity instead of to soil

fertility, and if a wide range of yield was considered.

 

 

s .-
‘I "b
4

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19

2.4 Sampling:methods: accuracy,g3ample size, number and distribution

Different sampling systems have been used to calculate forage yield

(Carter, 1962). McIntyre (1978) reviews the different sampling systems
used in planned experiments and the degree of accuracy obtained.

we will reproduce the definition of the two sampling units that
fit in our experiment. Stratified random sampling is when a plot is
subdivided into subplots and these are subsampled regularly (McIntyre,
1978). Systematic sampling are plots sampled at regular intervals
(McIntyre, 1978).

The number of cages required depends on the precision desired,
type and uniformity of the pasture, and the size of the cages (Wilson,
1969). Fewer cages are required where growth of the mixture plants are
vigorous or when stoloniferous species are used. On the other hand,
more cages are required when conditions do not promote a vigorous
growth (Wilson, 1966). Klingman et a1. (1943) concluded that with very
uniform herbage the same number of cages is required regardless of the
size of the pasture. Carter (1962) reports that the literature is very
limited regarding the size and number of cages per pen. However two
conclusions can be drawn (Wilson, 1966):

- several small samples give a more precise estimate of yield than few
larger samples for the same area;
- fairly intensive sampling is required if accuracy is to be achieved.

Much has been done on direct methods during the 1940's and 1950's.
There has not been any big improvement in that area since then, because

researchers have emphasized indirect techniques for pasture evaluation.

Different sizes and number of cages per pen are used. Carter (1962)

reported that the standard 4 by 4 foot cages are most often used;

20

but he also cited other authors who recommend different type and or
size of cages to achieve better sampling procedures. Carter (1962)
presents a good review of these points.

Carter et al. (1960) compared the effectiveness of using two
quadrats versus one in sampling forage before and after grazing with
three different pastures: alfalfa, brome and sudan. They concluded that
there was not any difference between forage yields in the two quadrats
and that a series of yield measures from both quadrats resulted in a
highly significant correlation (>>0.79). They also reported that the
two quadrats system removed excessive forage from the 1,200 square feet
available for the three sheep maintained in the pen. Based on these
facts the authors concluded that one quadrat is sufficient to sample
forage unless a larger daily rationed pasture has to be used. Due to
higher correlation coefficients between the chromic oxide technique
and the estimation of the intake using a 2 by 3 foot quadrat, these
authors recommend using this quadrat size instead of the 1 by 1 foot
size.

When the "difference method" is used, the number of pair of
sampling units cut during a rotation period has to be approximately 16
per treatment, for all replicates, if the sample area is between 1 and
2 square yards. With smaller areas, the number of sampling units tend
to increase (Anonymous, 1961). The authors do not mention size of the
plots, shape of the sample or grazing periods in the same pen.

Cooke (1969) establishes a guide for number of samples per
treatment according to the number of replicates, in order to obtain an

expected coefficient of variability of 20 Z. He also makes a

21

differentiation between dense sown pastures and natural grasslands, the
latter having twice as many cages per plot. In case of 3 replicates, he
recommends 6 cages per plot but he mentions neither the size of the pens
nor the size of the samples.

Green et al. (1952) reported that coefficient of variation between
sample yields varies between 20 and 35 Z when a sample unit of 1 or 2
square yards is used, and the yield of dry matter per acre lay between
1,000 and 2,500 lbs.. However, it rises to 60 or 80 Z with only 500 lbs.
of dry matter yield per acre. Green (1952) found a negative linear
regression between the coefficient of variation expressed in yield and
the logarithm of sampling unit size. Based on these findings, Green et
al. (1952) concluded that it is more convenient to use sampling units
of about 3 to 6 square feet rather than the more common size units of
1 or more square yards. It is also important to consider the fact that
the convenience of using smaller sampling unit size increases with
increase in the level of variability.

Klingman et a1. (1943) studied the best system to allocate cages,
and the number of 4 by 4 foot cages required to obtain different levels
of precision (expressed in pounds of dry matter per acre). They used
a twelve acre pasture of legume-grass with a mean dry matter yield per
acre of 700 lbs.. For a precision of 200 lbs. of dry matter per acre,
at 5 Z level of probability, 20 single cages are required. With increasing
level of accuracy more cages are needed.

Some researchers have used duplicate and triplicate cages. This
means placing pairs or trios of cages closely. Klingman et al. (1943)
concluded that for a fixed number of cages the error of estimation

increased with more cages put together instead of singly. Or, in other

22

words, to achieve the same sampling error it is necessary to use 2.26
and 1.63 times as many cages with trios and pairs respectively, than
when cages are placed individually.

Green et al. (1952), assuming a 15 Z coefficient of variation of a
plot yielding 2,000 lbs. per acre and 25 Z for sampling variation,
concluded that only three units per plot (25/15)2 are required to
reduce the sampling error to the level of plot error.

' Maclusky (1959) used 8 to 10 samples per pen in an experiment with
dairy cows on ryegrass. The size of the pens were small enough to keep
one cow with daily rotation. This procedure gave statistical precision
in calculating intake per animal per day. It should be mentioned that
the pastures were much more intensely sampled than in other experiments
reported, considering the number of sample units per pen, the size of
the pens, and the fact that cows were rotated on a day by day basis
which eliminates the error introduced by the growth of the forage.

A representative sample unit of a pasture may only come from a
random sample. The procedure to obtain pasture samples from "before"
and "after" grazing was mentioned previously. Klingman et a1. (1943)
established a method to obtain samples when cages are used. The system
is similar to the procedure defined by 't Mannetje (1978b), but a third
site similar to the two chosen is then located. More accurate results
are obtained when the cage site is chosen at random and a similar site
is selected for harvesting instead of choosing it also in a random
fashion (Klingman et al., 1943). A third site is randomly chosen outside
the cages and harvested at the end of the grazing period. Green et al.
(1952) reported that the immediate area to the cages becomes deteriorated

due to excessive trampling and to other factors, and that makes more

23

difficult the close pairing of cages.

All the reports presented are good guides to the number of sites
required to sample a given sward in an adequate manner, but they do not
conSider the effect of repeated sampling of the pasture on a repeated
sequence over a grazing period, nor do they suggest how many pastures
should be sampled in a rotational grazing system. Wilson (1969) suggests
that with six or more rotation fields with similar productivity, it is
not essential to sample all of them. For any given number of sampling
sites a very reliable estimate of yield is obtained if only half of the
pens are sampled at double intensity. It is best to sample in an alternate
fashion, starting either with the first or second pen (Wilson, 1966).

Wilson (1966) used six 2-acre blocks subdivided in 4 half-acre
plots seeded with 4 different herbage mixtures. He used a rotational
system within each mixture: each half-acre plot was subdivided in 4 1/8
acre paddocks. The author concluded that the coefficient of variability
for sample harvest yield was 28-56 Z and 15-46 Z for total annual yields.
In order to obtain a coefficient of variability of 12.5 Z (between plots),
four cages of 3 by 6 foot per paddock are required.

The shape of sample units can be very diverse: square, rectangular
and circular. To reduce edge effects, the perimeter of the sample unit
has to be as small as possible in relation to the size of the unit
(Meijs, 1981a). To reduce this problem, Van Dyne et a1. (1963) proposed
the utilization of circular samples. The problems with circular samples
increase with high pastures ('t Mannetje, 1978b). To overcome this
problem Kennedy (1972) proposed the use of a stake that when pushed
into the ground forms the center of the quadrat. The author mentions

several advantages attributable to the device: decrease bias in quadrat

24

placement, less problems with perimeters, higher precision in clipping
at different height above the soil surface, and less time consuming.
Another possibility to overcome the problem of boundary definition is

to use an open ended square or rectangular quadrat ('t Mannetje, 1978b).
McIntyre (1978) favors the use of rectangular shape for statistical
reasons: less variation exists using a long and narrow sample shape
compared to the square shape. Larger samples (1.5 by 12 fOOt), if the
number is kept constant, decrease the variability between samples
(Anonymous, 1952).

2.5 Botanical composition

 

The type of vegetation at any time is the direct consequence of
the interrelationship of several factors: climate, grazing system,
stocking rate and stocking pressure, etc. Some of them depend on the
management practices applied to it: number of animals maintained on a
given area, size and physiological conditions of them. There are some
other factors independent of the management: rainfall, temperature,
sunlight (Loomis et al., 1971).

A complete interpretation of grazing experiments requires a
knowledge of the botanical compOsition of the pastures as well as a
full understanding of the changes that occur over time. Species differ
in their value for animal production, their response to changes in the
environment and management factors ('t Mannetje et al., 1976). Animal
production is highly correlated with the species composition of the
pasture, especially those with legume content (Norman, 1970; 't Mannetje,
1974).

A botanical composition analysis has to be made at least once a

year, but preferably more often. The basic objectives of the analysis

 

v
.1.

25

are to recognize specific aspects related to the method of grazing

and/or clipping techniques, application of fertilizers, stocking rate,
duration of the trial, and as a way to determine the relative contribution
of each plant species to the forage consumed by the animals (Anonymous,
1952).

Tothill (1978) suggests that botanical composition implies the
gathering of information of species composition about areas of vegetation
in such a way to present a coherent framework pertinent to the purpose
of the study. Several previous reviews on this topic are also cited by
this author.

There are four types of properties of vegetation extensively used
in vegetation description and measurement: physiognomy, structure,
function and composition. They are usually grouped into two groups:
physiognomy, structure and function in one group and composition in a
second group (Tothill, 1978).

Composition can also be expressed in different ways: number or
density, area (cover) and weight (Branson, 1962; Greig—Smith, 1964).
Brown (1954) adds two more categories to this classification: pattern
and frequency of occurence. Weight expresses the importance of the
different species on the bases of relative production (Tothill and
Peterson, 1962). Yield of the species components (weight) is the most
important measure because it is directly related to animal performance
('t Mannetje et al., 1976). Its principal disadvantages are the amount
of labor involved when hand separation of the species is used (Tothill
and Peterson, 1962), human error (Theurer, 1976), and the spoiling of
herbage (Tothill, 1978). Persistency (study through changes in composition

over time) is the most important attribute of the vegetation to be

26

considered (Leach et al., 1976).

Several reviews have been published on methods available to study
botanical composition (Sears, 1951; Anonymous, 1952; Brown, 1954;
Theurer, 1970; Ward, 1970; Theurer et al., 1976; Harris et al., 1977).
Theurer et al. (1976) grouped those methods into four categories: visual
appraisal, manual separation with weight or volume analysis, micro-
histological methods and microscope point techniques. The last two
methods are more accurate when samples from fistulated animals are used
(Theurer, 1970).

Visual appraisal is the more rapid and less costly method, but a
great deal of innacuracy is involved. It can be applicable in those cases
where cover or density are the characteristics to be analyzed. It cannot
be used when samples from fistulated animals need to be analyzed (Theurer
et al., 1976).

Tothill and Peterson (1962) enumerate four different methods to
obtain weight: cutting and weighing, cutting and estimating visuals, eye
estimation of weight in the field and estimation of weights in the field
by plots. The authors agree on the fact that the first one is the more
accurate method and the other three are approximations to be used only
in surveys. Branson (1962) established that hand separation in the field
is the more accurate method of range vegetation, where species yield
are generally small but there may be several species per unit area,

which makes it more time consuming.

27

3. Grazing management

3.1 Systems of grazing_

 

3.1.1 Introduction

 

Independently of the method used to evaluate grasslands, they must
be judged according to their ability to sustain animal production.
Unfortunately, when data from animals are used to evaluate grasslands,
it is not always clear whether we are evaluating the pastures, or the
system of grazing under use, or the animals themselves (Maclusky, 1959).

The grazing system involves several factors that interact with one
another: soil, climate, animals, sward, parasites and diseases. This
supports the idea of the complexities involved in any grazing system.
Several decisions are involved in management of grazing systems (Morley,
1981):

- decisions that involve plants: species to use, use of fertilizers
and irrigation, subdivision of the pastures, resting periods;

- decisions that involve the animals: composition of the grazers,
marketing dates, disease control, stocking rate.

The growth rate of awards varies greatly throughout the year.
Climate and soil characteristics play an essential role in that
variation, as well as species used in the sward and the management
system (Murphy, 1977).

‘McMeekan (1956) and Beranger (1977) consider that grazing
management consists basically of three components controlled by the
farmer: stocking rate, the grazing method and the kind of grazing animals
used. They indicate three basic objectives of the grazing management:

to stimulate grass growth, to stimulate the optimum use of the grass,

28

and to use it very efficiently for animal production. The Arizona
Interagency Range Committee (1973) adds two additional objectives to
those three mentioned early: to reduce supplemental feeding and minimize
labor cost. Shiflet and Heady (1971) state that the major goals are to
improve or maintain the grazing resource and to increase livestock
production. According to Holmes (1980), an adequate grazing management
procedure must provide a low cost supply of nutritious herbage through
the growing season, avoid any waste of herbage and maintain the
productivity of the sward.

3.1.2 Definition of grazing;systems

 

The name of a grazing system does not always explain the design of
the system. When we define a system as rotational we are refering to
animals being moved from one pen to the next, and the pasture receives
a rest period and a successive utilization period. But very little is
said about animals maintained per unit area, animal-days per pen, and
duration of the rest period. These basic ideas led Heady (1970) to
conclude that unless writers give more detailed information about their
systems, it is impossible for readers to understand that specific
system by just knowing the name.

For that reason I will define several terms to be used in this
report, according to Heady (1970), Shiflet and Heady (1971), Stoddart
et a1 (1975):

Grazing season: portion of the year when grazing is feasible. The
grazing season is just a part of the vegetative growing season. Swards
start their growing season well in advance of the time animals start
grazing. It should be understood that we will stop the grazing trial

before the growing season is ended.

29

Grazing period: part of the grazing season during which grazing takes
place.

Continuous grazing: unrestricted livestock access to any part of the
pasture throughout the grazing period. It is also called free or
uncontrollable grazing.

Rotational grazing: animals are moved from one treatment pen to the next
on scheduled basis. In this system pens are allowed to rest before
animals are moved back in for another grazing time. It is also called
intermittent grazing.

Grazing time: period of time animals graze a specific pen in a rotational
grazing system.

Deferred pasture: part of a pasture treatment (pen) not grazed during
certain time within the grazing period.

't Mannetje et al. (1976) established that three main variables are
needed to define grazing methods: number of animals, time they spend in
any paddock and the interval between grazings. Considering those three
variables they define the following grazing methods: continuous set
stocking rates, continuous variable stocking rates, rotational set
stocking rates, rotational variable stocking rates and strip grazing.

Continuous set stocking rate is the least variable of all systems
in terms of the interpretation. However, McMeekan (1961) reports three
different possibilities within this system: the use of a simple field
grazed by all stock during the entire grazing period, or a diurnal shift
between a day and a night paddock, or the use of these two systems in
conjunction with a young stock or dry stock area.

The rotational system is much more variable in definition. It may

30

be used as a system where animals are rotated on monthly, weekly or
daily basis, or any other combination in between. Semple et al. (1942)
defined the rotation system in two groups: alternate rotational when
only 2 paddocks are involved in the system, and rotation grazing when

3 or more paddocks are used. Campbell (1961) defines rotational grazing
as those which cover a multitude of systems from daily shifts to monthly
shifts, from 3 to 30 paddock systems.

Up to now we have considered rotation system as a subdivision of
one type of pasture. Semple et al. (1942) defined the rotation system
formed by different pure sward species, or combination of species in
the pasture. These authors emphasized the importance of careful planning
in order to have the animals on each pasture when they can obtain the
most from it without reducing its productive capacity in the future.

A multitude of combination systems have been created too. Under
range conditions Merrill (1954) defined the "deferred rotation grazing
system". In this system, the total area is divided in four pens, and
each paddock is grazed during 12 months and then rested four months.
Merrill (1973a,b) adapted two new modifications of the different
rotation systems: intensive and non-intensive deferred rotation grazing.

Another modification of the rotative system was developed in
Germany in 1916 specially for dairy operations: "Hohenheim system".

It is basically a division of the pasture into 4 to 8 paddocks of
similar size and the utilization by the grazing animals in a gradual
way: high producers are the head of the sequence, followed by low
producers and dry cows at the end. The original Hohenheim plan called

for a heavy application of fertilizer, especially nitrogen (Woodward et

(3‘

-H

ll'

.-

.5

5..

(h

.3.

31

al., 1938). This plan was the origin of another rotational method used

in dairy operations called "leaders and followers" (Leaver, 1970;

Campling, 1975), or "top and bottom grazers" (Blaser et al., 1959).

Some of the most relevant experiments in the last two decades have
been the tendency to simplify the grazing systems in use, and at the
same time increase their efficiency in terms of animal output. The new
methods have been tested basically with dairy cows for two reasons:

- milk production is a more intensive type of operation than beef;

- it is also more sensitive to any change in the system: quantity of
forage, variation in specific forage components such as protein
content or mineral composition.

Three intensive grazing methods have been under evaluation in the
last two decades in Europe:

- strip grazing: it consists of moving animals once or twice a day.
When twice a day is used, the electric fence is moved after every
milking (for dairy cows) to allow animals to graze fresh forage
(Logan et al., 1960).

- The "wye College System": it consists of four paddocks, each one
grazed during one week and rested during three weeks, high stocking
rate and nitrogen fertilizer applications. It is also possible to
subdivide the paddock under grazing and use it in combination with
strip grazing (Castle and Watson, 1975; Holmes, 1980).

- Alternation of cutting and grazing: the basic idea behind this system
is to reduce wastage and increase intake of forage. It is a modification
of the zero grazing system in which the forage is mechanically harvested

and fed to animals (Journet and Demarquilly, 1979).

32

There are some additional combinations that are not mentioned in
this review. Kothman (1980) uses a different classification system based
on intensity and frequency of utilization because it gives a higher
degree of flexibility under range conditions. For additional information
on this subject, the Arizona Interagency Range Committee (1973) published
a very detailed work on grazing systems for Arizona ranges.

Authors do not agree on what system is more advantageous in terms
of animal production; but they are in general agreement that the system
of grazing and stocking rates are two variables that exert their effects
in a parallel mode (Campling, 1975; 't Mannetje et al., 1976; Holmes,
1980). For this reason I will analyse the advantages and disadvantages

of the different systems mentioned in the stocking rate section.

3.2 Management of ggazing for forage growth

 

Subdivision of the grazing area is necessary for research as well
as for production purposes. It is recognized that subdivision of
grasslands influence animal performance in at least five different ways
(Morley, 1978):

- pasture can be rotated to preserve food for times when it is short;

- growth of pasture can increase, so more forage is available on a
total basis;

- the botanical composition can be modified to change the proportion
of certain species, and as a consequence, the relative proportion
of specific constituents: protein, dry matter, digestibility;

- reduction of waste material;

maintain a better health condition of the herd.
In this case, subdivision means that the forage is utilized in a

rotational grazing form. In such a way, those could be the theoretical

33

advantages of the rotational grazing over continuous system.

One of the most important advantages cited above is the higher
growth of the pasture under the rotational system. Several mechanisms
have been proposed to explain this situation: leaf area index, losses
from decay and variation in the relationship between the use of reserves
and production of new reserves. This latter point will be discussed
later.

Loomis and Williams (1969) established that the density of the
canopy is the most important feature related to crop growth. Riewe (1976)
reported that the maximum growth is obtained at near maximum light
interception, provided other factors (temperature, water, soil nutrients)
do not limit growth. This is based on the fact that the light passing
through the canopy to the ground is wasted.

The leaf area index concept (LAI) is a more functional parameter
to measure light interception, and according to Watson (1947), the
variation in it is the main factor associated with differences in yield.
Watson (1947) defines leaf area index as the number of unit area leaves
per unit area of ground surface. Watson (1947), Brougham (1956), and
Koter (1977) among others, established that:

— LAI and dry matter growth are positively correlated;

- the LAI during growth should be sufficient to intercept as much of
the radiation as possible;

- above optimum LAI creates situation of parasitism, where the lower
leaves use the carbohydrates to a higher extent of their capacity of
synthesis;

- the LAI changes according to species, type of production,season within

years and among years.

I“ _

5|.

ru

34

The optimum LAI is species dependent. Hrabe (1977) reported a
different optimum LAI for species and for season within species. For
alfalfa the LAI that produces maximum yield per hectare is 5 to 6 in
the spring, and 4 to 5 after the first cut, due to an increase in
radiation during summer. For white clover, he reported 4 to 5 and 3 to
4 per square meter of ground respectively. Koter (1977) found an optimum
LAI for ryegrass equal to 8 and for alfalfa equal to 7 with an alfalfa
density of 250 plants per square meter. Brougham (1958) reported values
of 7.1 for ryegrass, 3.5 for white clover and 4.5 for mixed stands.
Brown and Blaser (1968) also reported lower optimum LAI for clovers
than for grasses.

Watson (1958) established the relationship between LAI and net
assimilation rate (NAR or E). When LAI increases over an optimum, NAR
declines. This relationship is very important because crop growth rate
(C) (net dry matter production) depends on these two variables (Loomis
and Williams, 1969): C = LAI x mean rate of net photosynthesis of all
leaves. Sometimes a lower leaf surface than maximum for complete light
interception is required in order to maintain a high quality standard
of the forage harvested (Riewe, 1976). In those cases a compromise-
between maximum forage yield and adequate quality must be reached.

The relationship between C, LAI and mean rate of net photosynthesis
is not clear. For some authors (Watson, 1958; Sibma et al., 1977), C
increases with LAI up to a maximum.point called optimum LAI (Lop), above
which further increase in LAI produces lower C. On the other hand, other
authors (Brougham, 1956; Williams et al., 1965) have found that C
increases with LAI up to a point where it is kept constant in spite of

continuous increments in LAI. Stoy (1969) explains that difference in

35

the different capacity of the species used to intercept light, and to
the differences in environmental factors such as light intensity and
plant density.

The distribution pattern among leaves is another important factor
to consider. Even when a full cover could be provided by one continuous
layer of leaves, LAI equal to 3 is needed to achieve a complete light
interception (Loomis and Williams, 1969). Monteith (1965) indicated
that LAI larger than 3 is needed for 95 Z interception of light with a
sun elevation above 60 degrees. Brougham (1956, 1958) measured light
intensity, LAI and height of the defoliated pasture. He found that a
clover-ryegrass pasture defoliated to 1 inch of height requires 24
days of regrowth to intercept 95 Z of the light, while only 4 days are
needed if it is defoliated to 5 inches. Pastures defoliated to 5 inches
produced 20 Z more dry matter than the same mixture defoliated to 1
inch, but during the first 14 days of regrowth the difference was
almost 100 Z.

The leaf angle to the horizontal (oz) is another important factor
to be considered. In case of very dense swards, erect leaves are much
more efficient in terms of light interception; however when LAI is
small, horizontal leaves are more advantageous (Duncan, 1969). Alfalfa
plants are erect, and as a consequence their leaves are distributed in
a vertical way, with larger 04 values (Warren Wilson, 1965, 1967).
When LAI is less than 3, photosynthesis increase with a more prostrate
leaf arrangement, but with a larger LAI than 5, photosynthesis increases
with more erect leaves (Monteith, 1965).

The angle of the leaves to the horizontal changes throughout the

36

season. Sibma et al. (1977) found that the production of carbohydrates

decreased 30 Z when the leaf position of LoliumLperenne changed from

 

erectophile to planophile. After defoliation or cutting, leaves were
replaced in the original erectophile position and proportional recovery
of carbohydrate synthesis occured. These authors concluded that one of
the causes of lower production in the later part of the growing season
could be the leaf position of the stands.

Monteith (1969) suggested that for the most common leaf indices
found in the field (4 to 8 in mature stands), the leaf angle is not so
crucial in determining photosynthesis rate. At large leaf areas (8 to
12), different models predict a more efficient utilization of the
light for erectophile stands. Stoy (1969) reports that the different
inclination of leaves of the species used for research is the major
factor that can explain the lack of agreement among authors in terms
of the true relationship between growth rate, leaf area index and rate
of net photosynthesis.

Beevers (1969) introduced the concept of "metabolic sinks" to
express those cases where the products of photosynthesis are utilized
within the plant. New leaves are a metabolic sink since they need
photosynthetates produced in any other parts of the plant to complete
their growth. Old and shaded leaves from the bottom of the plant are
considered sink too, not because they import sugars from other parts
of the plant, but because they use their own photosynthetates (Beevers,
1969).

It is not clear what the final balance is between the utilization
and synthesis of photosynthetates by old, lower shaded leaves of plants.

Riewe (1976) reports that respiration rates may exceed photosynthesis.

37

However, King and Evans (1967), among other authors, demonstrated that
shaded bottom leaves of alfalfa and other species have a lower respiration
rate than leaves from the top of the canopy. Stoy (1969) concluded that
lower shaded leaves do not reduce the amount of assimilates produced

by the upper leaves.

3.3 Ecology of ggazed pasture

 

Grazed pastures develop complex interrelations with other components
of the environment. Snaydon (1981) defines the ecosystem as a complex
interacting system between the grazing animals, the pastures they graze,
the associated microorganisms, the soil and the climatic conditions in
a given area. The term ecosystem was first used by Tansley (1935) in
order to describe the relationship between the living organisms and the
environment, but as Stoddart et al. (1975) establish, the idea of the
ecological complex is much older.

The ecosystem can be divided in different ways. One way is to
distinguish between biotic and abiotic components. The biotic part of
the ecosystem is formed by the animals, microorganisms and plants.

They develop complex interactions among them: animals affect plants
through defoliation, cycling the nutrients and trampling. On the other
hand, plants affect animals through the quantity and quality of the
forage produced and seasonality of the production. Microorganisms
impose different actions over the other biotic components of the
system: plant and animal diseases, decomposition of plant residues,
active role in nitrogen fixation.

Stoddart et al. (1975) divide the biotic component in four

categories:

38

- producers: represented by plants, and they are the only ones in the
ecosystem to produce food for consumers.

— consumers: animals that consume and redistribute the energy captured
by producers. There are two types of consumers: primary or herbivores
and secondary or carnivores.

- reducers: decompose and rearrange organic matter from the producers
and consumers.

- manipulators: manipulate the other factors in the ecosystem to their
benefit (man) .

It is also essential to consider the interactions that exist
between the biotic and abiotic components of the system. Soil and
environment are the integral elements of the abiotic component of the
ecosystem. Animal-soil interaction can be seen in two ways: the direct
effect of the animals on the soil through compaction and nutrient
cycling, and the indirect effect of soils on animals through forage
production.

Plant-environment relations are diverse. Light, temperature, water,
and carbon dioxide concentration are the most important environmental
factors that affect plant performance. Carbon dioxide supply interacts
extensively with light intensity to determine the rate of the
photosynthetic process. Hesketh (1963) working with four commercial
crops established light saturation curves with different concentrations
of carbon dioxide.

I only tried to specify in this chapter that complex relationships
exist between the plant and the other components of the ecosystem.

Further discussion will deal with the animal-plant relationship, the

39

relationship between pasture and minerals, as well as between species
of pastures.

Stoddart et al. (1975) present an excellent review on this topic.
Williams (1966) presents an example where energy flow and productivity
in a range ecosystem is analyzed. Even though these two publications
deal with range situations, the basic principles are applicable to

sown pastures.

3.4 Animalfiplant relationship

 

3.4.1 Stocking rate

 

Maximum production from.pastures is obtained only when the needs
of the animals and the productive capacity of the pasture are in
equilibrium. It is in this respect that stocking rate plays an important
role in pasture utilization, in terms of consumption of the feed
available and in determining the productive life of the sward.

It is well known that pastures for beef production are more
extensively managed than dairy pastures. As a result, beef production
per unit area and efficiency of pasture utilization are generally
lower than for dairy production. There is enough research information
to support the idea of a more intensive management system in beef
operations, but this is seldom used on commercial farms.

Optimum systems of grazing management cannot be generalized for
all situations because climatic conditions play an essential part on
the system, directly on the animals and indirectly through the type of
plant species or mixture of those species that can be used. Enough
information is available about sown pastures in temperate areas, but

in general there is a shortage of knowledge in semiarid regions as well

40

as in high altitudes.

In general, when management is modified by the adoption of new
techniques, the amount and quality of the pasture is also changed. The
addition of legumes to a grass dominated pasture, fertilization,
subdivision of the land are examples of modifications of the management
practices. As a consequence of those modifications, production per
animal and per unit area also changes. This phenomenon led McMeekan
(1961) to conclude that stocking rate is the most important determinant
variable of pasture production. 't Mannetje et al. (1976) established
that under most research conditions it is essential to use different
stocking rates. Axelson and Morley (1968) indicated that variety of
plant could be the most important determinant of economic responses,
especially at optimum stocking rates. This conclusion is drawn from
the fact that these authors worked with-a very high stocking rate
(7 and 9 sheep per acre or 17 and 22 sheep per hectare) for more than
five years. But the supreme importance of high stocking rate in
determining output per acre was recognized by many authors: Holmes,
1962; Wheeler,1962; Bone and Tayler, 1963; McMeekan and Walshe, 1963;
Gordon, 1973; Hutton and Parker, 1973; Leaver, 1974; Macleod, 1976;
and others.

Since the first experiments in mid 1950's, increased stocking
rates have, in most cases, led to an increased output per unit area.
Castle et al. (1972) observed that in 19 years (1951-1970) the factors
that affected milk production at the Hannah Institute were basically
two: the stocking rate and variation in milk production of the herd as
a whole. Journet and Demarquilly (1979) present a review of the main

results obtained in New Zealand, Australia and Great Britain showing

41

the effect of stocking rate on milk production per cow, per acre and

changes in body weight. Owen and Hinders (1962) using an alfalfarbrome

and alfalfa-orchard pasture with a daily strip system, compared the
effect of increasing stocking rates on different parameters. High
stocking rates produced more milk on alfalfa-brome (10 Z), while low

stocking rate was more effective with alfalfa-orchardgrass (17 Z).

Bryant et al. (1965) found a higher average daily gain of steers on

Kentucky bluegrassdwhite clover mixtures under low stocking rates.

The differences in average daily gain were only significant when

extreme stocking rates were used.

Hart (1980) details the different steps required to establish
the proper stocking rate for grazing experiments:

— define what is the measurement system to use in order to evaluate
the experimental results: maximum liveweight gain per animal or per
unit area, maximum profit per animal or per unit area, maximum
utilization of the available forage, or most rapid improvement of
pasture conditions;

- if it is possible, establish a mathematical relationship between
the stocking rate and animal and/or plant response;

- calculate the stocking rate needed to obtain the level of response
desired;

- analyze all the other constraints that could limit the results to be
obtained from the experiment.

Morley (1978) established the needs for estimating responses to
stocking rates under research conditions. He mentions three main

purposes:

42

- to estimate production per animal: it includes physical production
as well as financial results;

- to determine total costs per head including deaths, extra labor and
supplementary feed;

- to assess stability of pastures: it is an important point since the
farmer not only requires physical and economical results, but to be
able to use the same pasture for as long as it can survive and be
productive.

Several curves relating production per head and per unit area with
different stocking rates have been postulated. As Morley (1978)
suggested, if there were complete agreement between the different
authors it would be possible to determine one's position on the curve
by using two stocking rates and sometimes even one. The different
curves and their supportive concepts will be examined.

Under grazing conditions, the output per unit area is the most
common measure of animal production. Morley and Spedding (1968)
suggest that this occurs as a result of the relationship that exists
between production per unit area and total production per farm, or per
unit rainfall or even total energy. In those areas where the price of
land is higher than the price of animals, it is economically justifiable
to express physical and financial production in terms of unit of land
and not per animal basis. Mott (1959) established a mathematical
function to relate product per acre (2), animal days per acre (x) and
performance per animal per day (Y), assuming all the animals are similar
in rate of consumption and performance: production per acre is equal

to animal days per acre times performance per animal per day.

43

We have to define certain terms in order to unify their meanings
since not all the authors use them in the same context:

- stocking rate: total area of land alloted to each animal—unit year
(Kothman, 1974), or number of animals per unit area of land (Holmes,
1980);

- grazing pressure: Animal-forage ratio at a specific time (Kothman,
1974);

- carrying capacity: stocking rate at the optimum grazing pressure
(Mott, 1960) .

Mott (1960) was the first author to present generalized curves to
relate grazing pressure and production per animal and per unit area.

He established that the equation relating animal production per head

(y) and stocking rate (x) is as follows:

y = k - abx
where k, a and b are constants. Using data from the literature he
calculated the values for those three constants: 1.1214, 0.0014 and
84.54, respectively. It is important to consider that the first
assumption made to calculate those values is that if the stocking rate
is 1.0, then the value of gain per animal is also 1.0. With an increment
of 50 Z in the stocking rate the steers do not gain any weight because
the feed is in such a short supply that steers can only maintain
themselves: y = 0. This is true for steers averaging 1 to 2 years of
age; other constant values must be used with older steers where a greater
proportion of the feed intake is used for maintenance. Similar results
were obtained by Alder (1969, 1970). He obtained from 620 to 860 grams

per calf per day using half the area per head than other authors, but

44

his calves weighed between 55 and 70 kg. while calves from comparable
experiments were 4 and 5 times heavier: 200 to 300 kg..
‘Mott (1960) established a mathematical equation to relate product

per acre (2) and stocking rate (x):

z = x (k - abx)

Expressing z, y and x as a ratio with respect to optimum grazing pressure

(2', y', x'), it is possible to plot both curves on the same scale. In

such a case, the optimum stocking rate is below the maximum production

per acre, but over-grazing and under-grazing are avoided.

Riewe (1961) using data from 14 different experiments throughout
the U. 8. established a highly negative linear correlation between gain
per animal and stocking rate. At the same time a higher gain per acre
was obtained with the stocking rates used. In order to study the
interactions between replication-stocking rate and species-stocking
rate, Riewe (1961) performed an experiment on gulf ryegrass using
yearling steers on three different stocking rates: 0.86, 1.14 and 1.43
steers per acre, over five months. From that experiment he developed
a curve from which the following conclusions were made:

- maximum gain per animal was 230 lbs with 0.86 animals per acre;

- maximum gain per acre was 225 lbs with 1.14 animals per acre;

- a significant negative correlation between stocking rate and gain per
animal was found, but gain per acre was increased with a higher
grazing intensity. However, with 1.43 steers per acre, gain per steer
and per acre were smaller than 1.14. If the curve proposed by Mott
(1960) is usable, 1.43 steers per acre is an excessive stocking rate

to increase production per unit area.

'r.)

LT)

45

Riewe et al. (1963) compared two different species, gulf ryegrass
and tall fescue under three different stocking rates and three replications
per pasture to predict grazing production curves and optimum stocking
rates. The stocking rates were different for the two species and also
different between years for the same specie. The conclusions to be
obtained from this experiment are as follows:

- maximum gain per steer was higher on ryegrass. This could be
explained by a lower digestible energy intake on fescue compared with
ryegrass, which agrees with previous reports (Mc Cullough, 1953).

- Gain per steer decreased more rapidly on ryegrass with higher
stocking rates. The authors found a larger decrease in digestible
energy intake of steers on ryegrass than on those grazing fescue.

- At the point of maximum gain per acre, gain per steer and per acre
were higher on ryegrass. However tall fescue pastures had a higher
stocking rate.

From the curves drawn, it is possible to observe that maximum gain per

acre can be obtained with 1.5 steers per acre on fescue and with only

0.90 on ryegrass.

Hildreth and Riewe (1963), using the same pastures as Riewe et a1.
(1963) established an economic optimum stocking rate. The economic
optimum stocking rate increases with a positive margin and with increase
in animal gain. On the other hand, negative margin and increase in total
costs different than the pastures themselves make the economic optimum
stocking rate decrease. McCartor and Rouquette (1977) proposed a formula
that relates stocking rate with maximum profitability per hectare.

These authors found that the stocking rate which maximizes net profit

per hectare changes slightly, depending on the difference between

46

purchase price and selling price of the forage. Riewe (1961) established
that the highest gross return is obtained with the stocking rate
producing maximum gain per acre. However, with a decrease in the price
of the pound of beef (negative margin) the highest gain per animal
(lower stocking rate) results in the least loss. Jones (1981)
established that in general, stocking rate for maximum economic

return is lower than for the maximum gain per unit area and per animal
because costs and risks are lower than at higher stocking rates. Hart
(1980) presents a series of formulas for calculating gross return, net
return per unit area, and maximum net return with different stocking
rates.

Jones and Sandland (1974), using beef cattle continuously grazing
tropical pastures, developed a simple linear model to relate production
per animal (y) and stocking rate (x):

y = a - bx
where a = 1.999 and b = 0.999 (not significantly different than 2 and
1 respectively). High values for a and low for b reflect a high
quality and very stable pastures (Roberts, 1980). On the other hand,
low a and large b are indicative of a low quality pasture, very sensitive
to a high stocking rate (Jones, 1981). Linearity was established on
the range 0.18-2.0 times the optimum stocking rate (Jones and Sandland,
1974). Several other authors also demonstrated linear relatiOns between
gain per animal and stocking rate: Cowlishaw (1969); Hart (1972);
Conway (1974); Jones (1974). Hart (1972) used four different forage
yields (6, 9, 12, 15 tons per hectare) of Coastal bermudagrass and
found that average gain per day decreases linearly with increasing

stocking rate (from 2 animals per hectare and above), but the rate of

47

decrease becomes less as forage yield increases. Conway (1974) accepts
a linear decrease in gain per animal with higher stocking rates, but
he suggests a constant animal gain below the critical value. Peterson
et al. (1956) also found a constant gain with very low stocking rates.
On the other hand, Morley and Spedding (1968) maintain that linearity
can be proved only in the region of optimum stocking rate, but it is
unlikely to be true over a wide range of stocking rates. Using the
formula developed by Jones and Sansland (1974), it is possible to
predict negative values for liveweight gain per animal when stocking
rate is twice the optimum.but not 50 Z as Mott (1960) suggested.
Authors did not study the relationship between stocking rate and
gain per unit area with the same detail as they did in gain per animal
and intensity of grazing. However, some authors established a ‘
curvilinear relation (Mott, 1960; Jones, 1974). Owen and Ridgman (1968)'
using sheep and different stocking rates confirmed this theory. Jones
and Sandland (1974) established the following quadratic equation to

measure gain per hectare (yh) with stocking rate (x):

yh=2x-x2
Sandland and Jones (1975) analyzed two more linear models (Conniffe
et al., 1970, 1972; Owen and Ridgman, 1968) and compared them with the
linear models of Cowlishaw (1969) and Jones and Sandland (1974). They
concluded that the linear relation between animal gain and stocking
rates is a good approximation even for grazing intensities beyond the
critical stocking rate. This idea is in opposition with Morley and
Spedding (1968) who suggested a probable curvilinear relation in that

area, and with Conniffe et al. (1970) who suggested a gain plateau at

48

low stocking rates and a sigmoid curve with increasing slope which fits
better with stocking rates over the critical value. Connolly (1976) also
suggests that there is a constant gain per animal with low stocking rate,
but above the critical stocking rate there is a quadratic curve with
increasing slope. Petersen et al. (1965) established that above the
critical stocking rate the gain per animal decreases hyperbolically.

Hart (1978) established a model for grazing on rangelands. He
suggested that under rangeland conditions, gain per animal is very
nearly constant at low stocking rates, and it decreases linearly with
stocking rates above the critical value. He developed different linear
regression equations for the different months of the grazing season
based on the fact that the quantity and quality of forage and the needs
of the animals change during the season. The model can be used to
determine the economic stocking level, and to compare different pasture
improvement practices.

Jones (1981) proposes a model with four different areas of the
curve. The first part of the curve is a situation where gain per animal
and per hectare increase with an increase in stocking rate. This is due
to an increase in legume percentage, suppression of maturity or patch
grazing. The second area of the curve is defined as a constant gain per
animal, but gain per area still increases lizearly. The third situation
occurs where gain per animal decreases as a result of a decline in food
supply per animal. The author suggests that this part of the curve is
linear or near linear. Finally the last part of the curve is characterized
by a sharper decline in gain per animal as a result of an increase loss
of this legume species in the mixture due to an excessively high stocking

rate .

49

At very low stocking rates and high soil fertility, grasses may
dominate in the mixture. Wolfe (1972) reported that under such
conditions grasses may constitute up to 90 Z of the pasture. As
stocking rates are raised, lower-growing and prostrate species
(legumes specifically) are favoured as a result of less shading
(Rossiter, 1969). This supports the idea of Jones (1981) with respect
to the first section of his model.

For a given pasture, the optimum stocking rate varies with the
season. Beranger (1977) established that with a set stocking system
the optimum stocking rate has to be low. This is a consequence of the
effect of the high stocking rate on the growth of the pasture:
excessive high stocking rate has a large reducing effect on the
pasture growth at the last part of the grazing season. Conway (1963b)
obtained a significant decrease in liveweight gain of beef cattle
during the first 10 weeks of grazing over a two year period, when
stocking rate was increased from 1 to 2.5 bullocks per acre (average
weight 560 lbs). However when the increment in stocking rate was to
1.75 bullocks per acre, the reduction in gain was only 8 Z and was
observed after 20 weeks of grazing. Conway (1968) reported that when
2 animals per acre were maintained during the first part of the
experiment (16 to 19 weeks), and the stocking rate was reduced to 1
per acre thereafter, yield per unit area was similar to the treatment
with constant stocking rate of 2 bullocks per acre. However, these two
treatments produced more liveweight per acre than the treatment with
only 1 bullock per acre: 48 and 55 Z more respectovely. Beranger et al.

(1970) and Beranger (1977) concluded that stocking rate has to be

50

adjusted according to the growth of the pasture. For a perennial
ryegrass, the author suggested that the optimum stocking rate at theenui
of the summer is about 50 to 60 Z of the level in spring and early
summer.

Blaser et al. (1969) report two experiments done with adjusted
stocking rates according to the growth of the pasture during the season.
In the first experiment they worked with bluegrass with 2 average
stocking rates: 1.4 and 3.0 steers per acre, specified as medium and
heavy stocking rates respectively. With the medium rate, average daily
gain was 1.77 lbs and production per acre 380 lbs, while it was 0.92
and 432 lbs respectively, for high intensity. The difference in average
daily gain was attributed to a higher pasture yield per steer, which in
consequence led the steers to a higher level of selectivity. In the
second experiment, bluegrass-white clover pastures were stocked with
yearling heifers (700 lb average) at three different stocking rates. The
difference between medium and heavy was only 7 percent on a per head
basis in favor of medium,‘while it was 23 Z on a per acre basis in favor
of heavy intensity.

Some authors have supported the idea of using constant stocking
rates in experiments: Wheeler, 1962; 't Mannetje et al., 1976; Morley,
1978. With this system, the number of animals per unit area remains
unchanged throughout the grazing season. Under this system it is
recognized that the quantity and quality (Beranger, 1977; Hart, 1978)
as well as seasonal distribution (Morley and Spedding, 1968) vary
throughout the grazing season and depends upon plant genotype (Morley

and Spedding, 1968). Wheeler et al. (1973) suggested that this fact led

51

researchers to the idea of using different stocking rates according to

the pasture production: "appropiate rate". Under specific circumstances
this subjective method resulted in treatment effects that were proportional
to the stocking rates under use (Wheeler, 1962). Using response surface
design it is possible to find the optimum response in animal output

from the combination of the two variables: stocking rate and pasture
production (Gill, 1978b).

The "put and take" system is a variation of the variable stocking
rate method (Blaser et al., 1956), and was first described by Mott and
Lucas (1952). It allows for the adjustment of stocking rate in
accordance with the fluctuation of feed available to the livestock
(Greenhalgh et al., 1972; Matches and Mott, 1975). Mott and Lucas
(1952) also suggested that the same objectives can be achieved using
the same number of animals and adjusting the area to adjust for the
differences in pasture growth. This system is a good method of animal
and plant evaluation according to the theory proposed by Ivins (1959).
He suggested that in order to evaluate "grass potential" it is
required to increase the stocking rate to a maximum and use animals
with a very high productive capacity. When animals do not provide
enough response to the pasture available (the limitation is imposed
by the animals), the author suggests using dry matter yield as the
most valuable estimate of grassland productivity, closely followed by
the maximum stocking capacity which permits animals to express their
potential. As a guide, 3.5 gallons of milk per cow per day and 2.5 lbs
of gain per day are the limiting production levels at which animals

are insensitive to grassland treatments.

52

Different methods of computing yield per acre were proposed by Mott
and Lucas (1952) using the "put and take system", where the number of
animals are changed according to the availability of herbage. For method
one, the following measures are needed: total product produced by all
animals per acre, total animal days per acre and average daily gain of
all animals. Product per acre is then defined as the product of animal
days per acre and average daily gain. For method two, animal days from
all animals on the pasture and average daily performance from testers
(animals that remained on the pasture for the entire grazing period)
are computed. Output per acre is the product between animal days per
acre and average daily performance of testers. The third method involves
the utilization of some feed unit such as total digestible nutrients
(T.D.N.). It requires a double step procedure: tester animal days is
first calculated dividing T.D.N. yield per acre by average T.D.N.
consumption per day of testers. The second step is to calculate the
tester product per acre, as the product between tester animal days and
daily performance of average tester.

Matches and Mott (1975) analyzed the "put and take method" and
indicated its advantages when pastures of different potentialities are
compared. If the researcher does not graze all pastures at their
optimal, a source of bias is introduced to the system. With undergrazing
the estimate of animal days per unit area is too low and the potential
production of animal product per acre is not reached. With overgrazing,
performance per animal is reduced and potential production of animal
product is underestimated. Based on these facts, the authors proposed

the use of the put and take system as the way to estimate the potential

53

of different-pasture treatments: production per head, output per acre
and carrying capacity. The whole grazing system then may be evaluated
under a fixed stocking rate which is more comparable to the general
situation under farm conditions.

Burns et al. (1970b) also support the idea of using the put and
take system under research conditions. The stocking rate that provides
maximal per unit performance, output per animal product and maximum
forage productivity are in general not the same for all pastures. The
optimum stocking rate to achieve maximum performance does not always
agree with the stocking rate to obtain maximum profit. Because
economic patterns change rapidly, researchers and farmers have to
estimate animal and pasture performances over a wide range of
stocking rates.

3.4.2 Comparisons amonggggazingTsystems

 

Before the merits of the different systems of grazing management
can be analyzed, the parameters for comparisons must be selected. If
the primary objective is to reduce labor, machinery and fence costs,
the continuous system may have advantages over rotational and zero
grazing. However, if the primary objective is to increase the stocking
rate only, it is possible to choose the rotational grazing because it
offers more advantages under that circumstance (Marsh, 1976).

Output per animal and/or per unit area are the parameters
generally chosen for evaluating animal production under different
grazing systems, since they are closely related to the financial
behavior of the enterprise. Based on the different models presented,
it is possible to conclude that performance per head and per unit

area have to be considered together to obtain an optimum relationship

54

with stocking rate.

The herbage production is the most crucial factor resulting from
the manipulation of the stocking rate. Jones (1981) established how
herbage production in terms of quantity and species composition, varies
with different stocking rates. Marsh (1976) mentioned nitrogen
fertilization and defoliation practice as the two more important factors
affecting herbage yield in the British Isles. We will concentrate on
stocking rate in this section, since fertilization will be reviewed
later.

Several authors have established the influence of the grazing
system on herbage yield. In general, those who indicate a higher dry
matter production under rotational grazing, rely on the fact that longer
rest periods are necessary for that to occur. Hodgson (1966), Hodgson
and Ollerenshaw (1969) and Morris (1969) studied the frequency of
defoliation of ryegrass and cocksfoot swards in a continuous grazing
system. They reported a range of 19 to 36 days as the number of days
between consecutive defoliation, with a stocking rate from 19 to 32
sheep per acre (medium and high stocking rate respectively). Under
heavy stocking rate, defoliation of tillers occured every 7 to 8 days
while under medium intensity every 11 to 14 days. Twenty seven percent
of the green leaf length (GLL) of tillers were removed under high
intensity (Hodgson, 1966), and 24 Z was the mean GLL of cooksfoot
removed for all stocking rates (Morris, 1969). Spedding (1965) and
Hodgson (1966) suggested that frequent and severe defoliation of all
plants in a continuously grazed award is unlikely, except under a

severe overstocking condition. Greenwood and Arnold (1968) confirmed

55

what Spedding and Hodgson established. They reported that under high.
stocking rates where herbage available cannot support any gain, between
85 and 97 Z of the plants were grazed at least once a week. When the
stocking rate was decreased to let sheep have an average daily gain

of 1.3 kg, only 44 Z of those plants were grazed once a week. Under
severe stocking rate, rotational grazing can impose a longer growth
period between grazings, and as a consequence of that, higher herbage
yield can be obtained (Marsh, 1976).

Spedding (1965) suggested that it should be possible to utilize
forages under a continuous grazing condition without damaging the
pasture. He introduced a new concept: "correctly stocked continuous.
grazing". It is defined as a situation where the amount of forage
produced is equal to the amount consumed by the animals. Morris (1969)
proposed a change of this definition: the amount of material removed
per day by the animals is equal to the amount grown daily minus the
amount lost by decay. This new concept introduces the idea that optimum
LAI coincides with maximum herbage growth but with lower maximum
consumption, due to death and decay of some material.

In Table 1, a comparison between different grazing systems and
their effects on animal performance is presented. The comparisons were
made using different pasture mixtures and animal species to be able
to arrive at common conclusions. Also presented are experiments that
differ in stocking rate, duration of the trials and area of the world,
to analyze the validity of the comparisons on a broader base.

From Table 1, it is possible to conclude that not all authors
agree in which grazing system produces the most output per animal or

per unit area. In spite of this lack of agreement, several authors have

56

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61

shown a stocking rate by grazing system interaction CMchekan, 1956,
1961; McMeekan and Walshe, 1963; Riewe et al., 1959; Robinson and
Simpson, 1975; Riewe, 1976).

Some authors have claimed greater differences in favor of
continuous grazing for gain per animal and per unit area with light
stocking rates than with heavy grazing pressure. Riewe et al. (1959)
observed differences in favor of continuous over rotational grazing
for yearling steers on clover-grass mixtures over a three year period.
Similar observations were made by Hull et al. (1967) when rotational
and continuous grazing where compared at a stocking rate of 7.25
steers per acre on a grass—clover mixture over three years. Blaser et
al. (1969), in a study with three stocking rates on orchardgrass,
found that continuous grazing produced more gain per steer with low
and medium grazing intensity, being much higher with low intensity.
The same behavior was found in production per acre: 428 and 395, 435
and 392 lbs for low and medium stocking rate for rotational and
continuous, respectively. Blaser et a1. (1959) reported a 32 Z better
performance per day using continuous system.when the stocking rate
was kept at 12 lambs per acre on a bluegrass-white clover pasture.
Using steers, the same authors found an 11 Z better performance on a
daily basis on the continuous system on a bluegrass-orchardgrass-
clover pasture. Raguse et a1. (1971) reported higher average daily
gains (12 Z) and more plant cover using continuous grazing than
rotational grazing over a 4 year period.

Other authors have reported an advantage for rotational system

over continuous grazing. McMeekan and Walshe (1963) found that

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62

rotational grazing produced more milk per cow and per acre on a grass-
clover mixture. In a four year period, the percentages over the
continuous high stocking rate (assumed 100 Z) their findings for
rotational low, rotational high and continuous low can be summarized
as follows:

- Fat corrected milk per cow: 125.25 Z, 116.50 Z, 119.50 Z;

Fat production per cow: 125.89 Z, 117.75 Z, 120.40 Z;
- Fat percentage per cow: 101.41 Z, 103.39 Z, 102.04 Z;

- Fat corrected milk per acre: 101.73 Z, 114.84 Z, 91.69 Z;

Fat production per acre :102.16 Z and 92.30 Z.

Comparing continuous and rotational, both at the same stocking rate,
it is possible to observe that rotational system always produced more
fat corrected milk and fat than continuous. Under continuous and
rotational grazing, low stocking rate produced more fat corrected milk
per cow but less per acre, indicating that independently of the system,
when more milk or fat per cow is the final objective, low stocking
rate rotational system is better than high intensity of grazing.
However, when the objective is to maximize fat corrected milk or fat
production per unit area, high stocking rate rotational grazing is
advisable to be used.

Some other experiments also found advantages for the rotational
over the continuous system. Harrison et al. (1941) found a 7 Z higher
production per acre using sheep on alfalfa—brome at a high stocking
rate. Hull et a1. (1967) using 11 steers per hectare reported a 22 Z
more animal days per hectare and 13 Z more kilograms of beef produced

per unit area on a rotational system, in spite of a 7 Z lower production

63

per steer on a daily basis. Peart (1968) reported a 50 Z mortality on
an alfalfa pasture under continuous grazing with 12.5 wethers per
hectare, while no deaths were reported when 8 pens were used in a
similar grazing intensity.

The number of paddocks in a rotational system plays an important
role in the system too. Meyer et al. (1956) found a 14 Z higher average
daily gain using a rotational system where steers grazed alfalfa
during seven days than when daily rotational was practiced. However,

3 Z more beef was produced per acre with the strip rotational. Itner

et a1. (1954) reported a higher average daily gain and pounds of beef
per acre on strip grazing over rotational using 4 pens and 8 to 12

days for grazing. Average daily gain was only 6 Z more on strip grazing,
but output per acre was 39 Z higher. Ruane and Raftery (1964) found

23 Z more cows grazing days per acre and 26 Z more milk per acre with
20 pens over 2 pens rotational at a stocking rate of 1.4 cows per acre.
Peart (1968) found similar results in terms of wool production (3.5 and
3.4 kg of wool per head) using 8 pens with a grazing period of 5 days
and 4 pens with 12 days of grazing. However, he reported only 6 Z of

a reduction in the alfalfa population on the former, while it was 17 Z
on the latter system.

There is another rotational system where two groups of animals
graze the same pasture. The first group (leaders or top grazers)
consume about half of the pasturage, and then the second group
(followers or bottom grazers) are moved in. Top grazers obtain more
available forage, and as a consequence, they can select what they
consume. Blaser et al. (1969) reported a 24 Z more forage consumed by

leaders which in turn produced more. Using orchardgarss and nitrogen,

64

and fescue and nitrogen, the top grazers produced 54 Z and 45 Z more
liveweight gain per day, respectively. Using these two species with
legumes, top grazers produced 34 Z and 70 Z more average daily gain,
respectively. When they compared the rotational systemrwith leaders
and followers with a rotational system using one group of steers at
similar stocking rates, total liveweight per acre and average daily
gain of both systems were not statistically different. Using fattening
steers as leaders and cows as followers, this system could stimulate
a higher average daily gain for those categories that need a more
succulent and palatable diet (Blaser et al., 1975). Archibald et al.
(1975) compared the leaders and followers system with the rigid
rotational with dairy cows and did not find any difference. Castle
and Watson (1975) found similar results using very highly productive
dairy cows .

Some additional aspects have to be considered also when comparisons
between rotational and continuous systems are made: carrying capacity,
feed consumption, forage production, changes in botanical composition
of the forage and other minor related aspects. Bryant et al. (1961a,b)
found important differences in carrying capacity for the mixtures he
compared, but all of them in favor of the rotational system: 30 Z,
18.9 Z and 21.6 Z more for alfalfa-orchardgrass, ladino-orchardgrass,
and bluegrass~white clover-trefoil, respectively. These authors reported
a higher growth of legumes and grasses under the rotational grazing,
as well as less weed infestation. Sharrow and Krueger (1979) observed
the same phenomena.working with subterranean clover and ryegrass; and

Hayman and Saville (1981) with a grass-clover mixture over a 3 year

65

period. Based on the results, the authors concluded that rotational
system has a definitive advantage on the growing season because it
stimulates higher forage yield. Lucas and MCMEekan (1959) reported
that 25 Z of the total area could be cut under strip grazing, whereas
surplus cut could be harvested under the rotational system. Brundage
and Petersen (1952) comparing strip and continuous grazing found that
only under strip grazing some surplus forage could be harvested.

Differences in feed consumption is also another theory that is
used to explain the higher values of performance obtained in certain
systems. Meyer et al. (1956) obtained the following percentages of
pounds of beef per acre: 57 Z, 24 Z, 7.25 Z more on zero grazing,
hayling and strip grazing over a 5 day rotational system on alfalfa
pure stands. However, the feed consumption percentages on the 5 day
rotation were 107.91 Z, 136.69 Z, and 92.09 Z respectively. It is
clear from those values that feed consumption does not explain the
superiority or inferiority of any system.by itself. Penning anleibb
(1979) found that lambs grazing perennial ryegrass ad libitum consumed
more than similar lambs fed indoors. The difference diminished with
the age of the lamb. Bartholomew et al. (1981) compared herbage
consumption with two different periods of regrowth: 20 and 35 days.
They did not find differences in net herbage allowance between the
two growing periods, but they found that 2 out of 3 years, intake was
lower on the 35 day rotation, which in turn supported a higher efficiency
for the 20 day rotation period.

Changes in botanical composition is also an important factor to be

considered when comparisons are made. Logan et al. (1960) found a

66

slightly higher increase in the legume percentage of the mixture using
mechanically grazed fields compared with strip grazing during the first
two years of the experiment, but once the mixture was established, no
difference was found. Kennedy et a1. (1960) reported that with longer
rest periods, shorter and close defoliation (more pens in the system),
alfalfa can persist as well as under zero grazing conditions. Dennis
et al. (1959) found that yields of alfalfa obtained from plots cut at
4 and 6 week intervals were greater than those from more frequent
cutting: 1 to 2 weeks. Similar results were obtained by Peart (1968)
comparing alfalfa pastures under two different rotational systems: 4
and 8 pens. Hildebrand (1939), Davis and Davis (1956) and Blaser et al.
(1969) also reported higher persistency of the alfalfa plants with
longer cutting frequencies.

The number of cuttings during the first year play an essential
role in the persistency of the alfalfa. Alfalfa cut four times in the
first year post emergence gave lower production on the second year
(Davis et al., 1953) and on the four years (Davis and Davis, 1956).
Pure stands of alfalfa also persist better than alfalfa-grass mixtures
when four cuts are performed after emergence (Davis and Davis, 1956).

Birdsfoot trefoil under grazing has received less attention than
alfalfa. Mott et al. (1953), Davis and Klosterman (1959) using beef
cattle, and Davis and Bell (1957) using sheep, studied the importance
of including trefoil as a normal component of legume-grass pastures.
Van Keuren and Davis (1968), and Van Keuren et al. (1969) studied a
mixture of birdsfoot-bluegrass under continuous and rotational grazing
with sheep and cattle. They concluded that like alfalfa, birdsfoot

trefoil has to be rotationally grazed to obtain a long-life stand in

67

the pasture. Empire, a prostate variety of birdsfoot, had a slightly
better persistency than Viking, a more erect variety. This agrees with
the statement of Riewe (1976): "continuous grazing with proper stocking
rate, favors the growth of plants that are semi-prostate morphologically,
or those that become semi-prostate under grazing, such as bluegrass,
orchardgrass, ladino clover, ryegrass and other species with similar
growth habits".
3.4.3 Conclusions of the relation between system ofiggazing and
stockinggrate

a) Three major factors affect efficiency of animal production under

grazing conditions:
- grazing method;
- kind of forage species and livestock;
- stocking rate.

b) Rate of stocking is by far the most powerful factor of the three
influencing efficiency on a per unit area basis (McMeekan, 1956)

c) On a per acre basis, extreme differences in grazing methods are
associated with relatively small effects on efficiency of pasture
utilization (McMeekan, 1961).

d) Significant interactions between stocking rate and grazing method
have been widely reported.

e) Optimum stocking rate under rotational grazing occurs at a level
5 to 10 Z higher than under continuous grazing. A depression of about
10 to 12 Z in output per animal with increase in grazing intensity
corresponds to an optimum stocking rate, independent of the grazing
system (McMeekan and Wlashe, 1963). The authors suggest that this is

a guideline when comparisons between the two systems are made.

68

3.4.4 Trampling
Trampling is an inevitable consequence of grazing. The use of high

levels of fertilizers have produced larger forage yields with a parallel
increase in stock density to harvest the surplus yield. At the same
time, increasing utilization of more productive forages with a longer
growth period, has also imposed an additional stress on the soils, more
marked under wet conditions.

Brown and Evans (1973) quote the fundamental concept developed by
Edmond that "all treading damages pasture independently of the type of
soil, moisture level, species of plants under consideration or species
of animals that produce the traffic". Treading has direct and indirect
effects on the productivity of the sward. The direct effect is produced
through crushing of the foliage, tillers,growing points and other parts
of the plants. Under a wet environment, the hoofs of the grazing animals
produce trampling of the plant parts in the soil. Under such conditions
entry of diseases throughout the broken forage structures is facilitated
and decrease in production is the more likely consequence (Leach et al.,
1976).

The most common indirect consequence is the negative effect of
treading on the soil structure. Several studies have demonstrated the
effect of treading on the soil, especially under wet conditions: Edmond
(1970), Federer et a1 (1961), Gradwell (1960, 1968), Mullen et al. (1974,
1977), Charles (1979). These authors reported a loss in porosity, pan
formation and a perched water table as a consequence of excessive animal
traffic on wet soils. In such situations, plant roots do not develop
properly and do not penetrate below the formed-pan, depending on the

nutrients and humidity remaining in the soil portion located between the

69

pan and the soil surface. Edmond (1958) showed that the soil pan is
formed at 4 to 6 centimeters in depth, which in time deteriorates to
extreme situations where the livestock pull up the plants when grazing,
producing death of the plants and sward deterioration (Charles, 1979).
Frame (1976) distinguishes two stages of deterioration: short-term
because growth is reduced, and long-term because botanical composition
is altered.

Pasture species differ in their reaction to animal treading
(Edmond, 1958, 1962, 1963, 1966, 1970; Carter and Sivalingan, 1977).
Damage is more reduced in tall species compared with short habit species
(Brown, 1968). Edmond (1964) ranked 10 species in their behavior with
respect to treading. 0f the 10 species used, perennial ryegrass and
kentucky bluegrass were the most resistant species, while dactylis was
one of the least. The basic reason behind reduction of pasture yield
is the decrease in the number of tillers and nodes due to traffic
destruction.

Season has a marked influence on species capacity to resist
treading. Ryegrass is more resistant in winter than in any other
season, while red clover is more resistant in summer time. This led
Edmond to conclude that active growth reduces the intensity of the
treading effect. Quinn and Hervey (1970) confirmed this conclusion
under range conditions.

The species physiology is another factor that has to be considered.
Kentucky bluegrass develops rhizomes which makes this species more
tolerant, while dactylis has its growing points more elevated and, as

a result, is more susceptible (Edmond, 1964). Ryegrass tends to set its

70

tillers below the surface of the soil. which protects the meristematic
tissues of the plant. The tillers are capable of producing roots as well
as short stems, which travel below the soil surface giving this species

a high resistance to animal trampling (Mitchell, 1960).

3.4.5 Animal Excretions

 

The acceptability of the forage by the grazing animals is affected
by defecation and urination of the animals. The daily production of
feces from grazing animals varies with the factors that affect intake.
Holmes (1980) reports an average of 2.5 to 3.5 kg of dry matter per
day for dairy cows, 1.2 to 2.0 kg for young cattle, and 0.3 to 0.6 kg
for sheep. In terms of area covered, adult cattle feces may repreSent
0.05 to 0.07 square meters and 0.45 to 1.10 square meters for individual
dung patches and total area receiving dung per day respectively, with
proportionately less area for smaller categories and sheep (Petersen
et al., 1956a; Maclusky, 1960; MacDiarmid and Watkin, 1972b).

The marked characteristic of contaminated pasture by cattle dung
and urine is the rejection of the herbage in that area. Marsh and
Campling (1970) reported that the actual rejected area is bigger than
the area covered by manure, but some of the herbage above and surrounding
the patches are consumed by cattle. Maclusky (1960) calculated that the
area affected is six times the area of the dung. Wolton (1979) reported
that the rejection is dependent on the grazing pressure: with a higher
intensity less forage is rejected. Greenhalgh et a1. (1969) compared
the effect of fouling and stocking intensity. While both factors have
equal effect on organic matter intake, stocking intensity has a larger
effect on digestible organic matter intake. MacDiarmid and Watkin

(1972b) presented a diagram where it is shown that under intensive

71

stocking rate rejection is almost zero.

Several theories have been proposed to explain the causes of
rejection. Norman and Green (1958) reported that the first cause of
forage rejection was the dung itself; but then the forage ungrazed
increased in maturity and became less palatable being the more important
reason of the animals' rejeCtion. A good way to diminish the rejection
period is to cut that forage so the regrowth is more palatable and
digestible. Garner (1963) reported two reasons to explain forage
refusal contaminated with dung: lack of palatability of the forage
itself and smell of the dung. Plice (1951, 1952) concluded that the
high content of nitrogen and low content of phosphorus in cows' dung
produces a phosphorus/nitrogen imbalanced intake by plants and, as a
consequence, less sugar is formed causing plants to decrease in
palatability. Plice (1951) reports several experiments where cows show
a marked preference for sweetened material. Marten and Donker (1964a)
described a different behavior of steers grazing brome stands and
alfalfarbrome mixture, the former being more rejected. Marten and
Donker (1964b) observed that high phosphorus fertilization did not
increase the consumption of contaminated pastures with cows' dung
which proves that Plice's theory is not valid. As a result of their
studies, these authors (1966) concluded that the most likely reason
of intake depression is smell. Arnold (1981) reported that smell is
one of the important senses the animals use to select diets, confirming
What was previously established by Marten and Donker. For a more
complete discussion on the forage-animal complex in forage palatability,
Marten (1978, 1981) and Burns (1978) present a detailed review on the

subject.

72

The deleterious effect of dung and urine decreases with time.
Norman and Green (1958) reported that the rejection of urine-contaminated
pasture lasts only a short time, and cattle may graze it preferentially
on the next rotational period. This confirms the conclusion of Maclusky
(1960) that urine causes herbage rejection for a short time only.
Garstang and.Mudd (1971) found a decrease in the proportion of herbage
rejected by dairy cows from 28 Z in year 1 to 10 Z in year 3. However,
Reid et al. (1972) reported an increment in percentage of herbage
rejected over a 3 year period from 13 Z to 24 Z on control cows and to
20 Z on cows conditioned to consume hay with manure. The increment in
forage rejected in this experiment can be due to a decrease in grazing
intensity which permited cows a larger degree of selection. Boswell
(1971) reported herbage intake of clean and fouled pastures at two
different stocking rates and 8 different herbage allowances. In all
combinations forage intake was larger in clean pastures, except when
the stocking intensity was high and herbage allowance low. In this
case, cows on fouled pastures consumed 10 Z more than cows on clean
pastures. The only explanation for this to happen is that animals may
become conditioned to the fecal material on feed (Garstang and Mudd,
1971). This idea was also developed by MacDiarmid and Watkin (1972b)
who found that cows become acclimatized after 2 or 3 years of
intensive grazing on contaminated pastures with feces and urine.

3.4.6 Cyclingiof nutrients

The nutrients required for plant production pass through a cycle
where animals, microorganisms, plants and soil play an important role.
Under stable grasslands, there is an active equilibrium between the

inputs from the environment and the losses from.the system. Under

73

intensive grassland utilization, however, the equilibrium is broken as
a result of a higher extraction from the system compared to the inputs.
This has created the needs for fertilizers, irrigation, etc as a way

to overcome the removal of soil nutrients under more intensive soil
utilization. In this case, the normal recycling of the nutrients cannot
counteract for all the nutrients extracted. Mott (1974) preSents a
complete review of the subject.

A nutrient cycle can be defined as the uptake, utilization,
release and reutilization of the nutrients throughout different methods
present in the system (Till, 1981). Hutchinson and King (1980) present
a diagram for the cycling of nutrients in intensively grazed pastures.
The more important factors controlling the process are the flow rates
of nutrients between the different parts of the system: plants, animals,
microorganisms, and other consumers (Till, 1980).

Plants obtain their nutrients as inorganic ions (Till, 1981) or
labile ions (Hutchinson and King, 1980) from the soil solution. The
soil solution itself constitutes a small portion of the total available
pool, considering that the soil fixes certain anions and cations within
its structure. Till (1980) presents a diagram showing inputs and
outputs and their relationship with the available pool. Mitchell (1970)
presents a summary discussion on the external and internal factors that
affect absorption of soil and nutrients by plants.

The amount of dung and urine are important sources of nutrients to
the soil environment. Many workers have reported an increase in forage
production due to the recycling of nutrients under grazing conditions.

Herriot and wells (1963) reported a 24 Z increase in yield of dry matter

74

when the excreta.was returned to the pasture. Frame and Hunt (1971)
observed 15 and 40 Z higher yields of organic matter and crude protein,
respectively, on a grass award over two years. Other authors have also
reported higher yields under grazing conditions: Norman and Green (1958);
Wolton (1963); Cuykendall and Marten (1968); Calder et a1. (1970);
MacDiarmid and Watkin (1971).

In general, authors agree that particularly urine is the most
important recycling factor that produces higher forage yield under
grazing compared to cutting. Urinary return with its high content of
nitrogen and potassium.produces a greater effect on grass swards than
on grass-clover pastures; and its effect is larger for those grass
pastures not fertilized with nitrogen. Urinary return produces a decrease
in nitrogen fixation by the legume (Wheeler, 1958). Mundy (1961) reported
that about 70 Z of the total nitrogen and nearly all the potassium
excreted by animals is through urine. Blue (1980) found that between
50 and 80 Z of the nitrogen applied is recovered through animals'
excretion. These two reports support the idea of negative influence
of the nitrogen excretion on the legume from the mixture.

Excretal nitrogen seems to be more effective once the grass dominance
is achieved. Frame (1976) reports a higher crude protein, organic matter
and digestible organic matter the second year of the experiment where
ryegrass was 90 Z of the herbage in grazed awards. The same results were
previously reported by Frame and Hunt (1971) and Walton (1963). Richards
(1973) found that although the rate of nitrogen in dung patches is high
(1 to 5 Z of dry matter), part of it is in organic forms (basically
microbial) and resistant to decomposition. This means that approximately

25 Z of the dung nitrogen can be used during the year of the deposition,

75

and a higher percentage is available during the second year.

If dung patches remaing unchanged on the field for several days,
important changes occur underneath of them.‘MacDiarmid and Watkin (1971)
reported that clover stolons and grass tillers underneath the affected
area die rapidly, and recolonization comes from plants in the surrounding
areas. Under normal climatic conditions, 60 Z of the weight of the patch
is lost by evaporation in 13 days, but even that is not rapid enough to
prevent tillers and stolons death (MacDiarmid and Watkin, 1972a). Under
rainy conditions, the speed of decomposition is increased mobilizing
nutrients more rapidly in order to be used by other members of the
system. Under dry conditions the opposite occurs (MacDiarmid and Watkin,
1972b), causing more plants to be killed. Lotero et al. (1965) reported
that nitrogen from urine is lost more than nitrogen from dung. In a five
day period, 4.7 Z of the nitrogen from the dung (equivalent to 25 lbs
of nitrogen per acre) is lost as ammonia (MacDiarmid and Watkin, 1972a).
Norman and Green (1958) observed a higher increase in crude protein
production of the pasture from dung and urine in spring than in fall,
basically due to larger losses of nitrogen in fall through leaching.
3.4.7 Behavior of;grazingianimals

Ruminants divide their times on pastures between three main
activities: grazing, ruminating and resting (Campbell et al., 1969).

The quantity and quality of the available forage determines the amount
of time spent on each activity. However, other factors also affect

the behavior of cattle: temperature, humidity, size of pasture, number
of animals in the herd and their social interaction. Due to the number

of factors and the complex interactions between them, Arnold and

76

Dudzinski (1967a,b) could only explain a small part of the variation-of

grazing time of sheep. Livestock can adjust their routine in order to
compensate for the adverse effects that these factors can cause (Harker
et al., 1961). In this respect, Minson et al. (1976) stated that the
study of grazing behavior of ruminants can be very valuable as a guide
to the nutritive value of the grazed pasture. King (1962) established
that forage intake provides the best single index of the reaction of
grazing animals to the environment.

The grazing behavior concept involves three main considerations:
grazing time, number of bites and size of bites. Grazing time reflects
the ease of livestock for harvesting forages, and it is influenced by
the quantity and quality of the herbage (Minson et al., 1976). Cattle
graze an average of 6 to 8 hours in abundant and good quality pastures
(Hutdhinson et al., 1962), and about 12 hours per day when herbage is
short or sparse (Campbell et al., 1969). Cattle prefer to graze during
the day (King, 1962) divided in two major periods: early in the morning
and late in the afternoon (Holmes, 1980), with three to four grazing
periods between the morning and afternoon milkings and one to two after
the evening milking (King, 1962). As days get shorter, the breaks
between grazings decrease until in midwinter in latitudes of 20 degrees
or more, where grazing is almost continuous during the day (Arnold,
1981).

Authors do not have a general agreement on which period is more
important in terms of number of animals grazing at one time. Hancock
(1953) established that the morning grazing is the more important one
and it begins before sunrise, and for milking cows soon after the

morning milking. However, Sheppard et al. (1957) observed that 71 Z of

77

the steers were grazing between 4 and 8 P.M., while only 55 Z were
doing it between 6 and 8 P.M.. Several other authors have demonstrated
that the eating activity of free-feeding feed lot steers occurs mainly
between 6 A.M. and 6 P.M., with peaks during early morning and late
afternoon (Putnam and Davis, 1963; Putnam et al., 1967, 1968; Chase
et al., 1976).

The quantity and quality of the available forage are important
factors that affect the grazing behavior of animals. Arnold and
Dudzinski (1967a,b) eatablished that when feed is short, animals spend
more time grazing because they harvest less forage per bite. Grazing
time increases when the available dry matter per acre drops below
1,000 lbs in dense swards such as alfalfa-grass mixtures, or below
500 lbs on open grass pastures (Campbell, 1963). Grazing time also
increases with high and coarse pastures because of the extra time
required to select the diet (Brundage and Sweetman, 1956; Holder,
1960). Charcon and Stobbs (1976) observed a continuous decrease in
intake of forage per bite as the pasture is eaten down. However,
grazing time, total number of bites and rate of biting increase at
first and then decrease. Under these circumstances, a higher percentage
of the consumed energy has to be used for work and a lower amount is
used for production (Campbell et al., 1969). Hancock (1952), using
identical twin dairy cows, observed an increase in grazing time with
lower possibilities of selecting the diet, due to a lower availability
of grass per cow and per unit area. Using ten sets of identical heifers,
Hancock (1954) found an increase in total time for grazing and for

ruminating: grazing time increases with scarcity and poor quality of

78

forage while ruminating time is extended by low quality forage. However,
Cowan (1975) reported an increase in grazing time with higher pasture
yields up to 3,000 kg of dry matter per hectare. With forage production
over 3,000 kg, total grazing time tended to decrease.

The climate exerts direct and indirect effects on the grazing
behavior of animals. The indirect effects are produced through changes
in quantity and quality of the available forage, while direct effects
are due to the influence of temperature, rainfall and day length.

Under tropical conditions, Cowan (1975) found an average grazing time
of Friesian cattle of 600 minutes for the entire year with no
significant differences between summer and winter. In summer, cows
spend more time grazing between the afternoon and morning milking,
with a consequent reduction of grazing time during the day. These
results agreed with other reports under similar conditions (Payne et
al., 1951; Arnold and Dudzinski, 1978).

Other climatic considerations are temperature, humidity and
rainfall. Within the 0 to 34 degrees centigrades range, temperature
and grazing time are not related under conditions of low humidity.
However, with warm and humid climates, total grazing time decreases
with temperatures above 26 degrees centigrade (Arnold and Dudzinski,
1978). Humidity is a very important factor since most of the heat
loss occurs through the skin and the lungs of the animals (Huffman,
1959). Seath and Miller (1946), using Jersey and Holstein milking
cows, observed that 75 Z of the grazing time occurs at night, and
only 25 Z during the day with temperatures above 100 degrees Farenheit.

When rain is accompanied by wind, cattle graze following the wind

79

direction first, and cease grazing when rain and wind are prolonged
for a long period of time (Arnold, 1981).

There are some other factors influencing grazing time: size of
the animals, level of production, level of supplementation and social
behavior. Brumby (1959) found a greater grazing time required for
Jersey cows when compared to Holstein cows, and this is the result of
smaller amount of forage harvested each time by small animals (Jersey).
When the fat corrected milk of the two breeds was the same, the author
observed negligible differences in grazing time between the two breeds.

The social interaction of grazing animals has been studied also,
because it has an important effect on the grazing behavior. Bailey et
al. (1974) demonstrated the effect of supplemented steers grazing in
conjunction with unsupplemented ones. Steers without supplementation
reduced the grazing time, and this was attributed to social influences
by the steers receiving some grain. Hodgson and Wilkinson (1967)
observed that cows and calves eat more when they graze together than
when they do it separately. Holder (1962) reports the same behavior
with sheep.

Number and size of bites are also important considerations
of the grazing behavior. Stobbs (1973b) established that the intake
by grazing animals is proportional to the time spent grazing and the
rate of grazing, which in turn depends on the rate and size of biting.
Biting rate of cattle can range from 70 to 80 bites per minute at the
beginning of the grazing, to 40 to 50 bites per minute at the end
(Minson et al., 1976). Bite size varies from 0.05 to 0.80 grams of

organic matter, depending on the structure of the canopy and on the

80

availability of the forage (Stobbs, 1973b; Minson et al., 1976). Stobbs

(1973a) defined a critical size of bite equal to 0.3 grams of organic
matter. Bite sizes below this critical value were recorded using
tropical forages.

3.4.8 Selection of diet

 

It is well documented that in most circumstances ruminants graze
selectively on rangelands as well as on sown pastures for different
reasons (Voigtlander and Voss, 1977). Diet selection is a function of
the animal as well as pasture attributes. Among the animal attributes,
species, class of animals, productive function and prior experience
are the most important factors to consider, which in sum determine
the "preference"."Palatability" is the term used to group forage
characteristics and involves chemical and physical properties such as
percentage of crude protein and fiber, digestibility, presence of hair
and spines, structure of the canopy, and stem to leaf ratio (Kothman,
1980a). There are also some external factors to the animal-plant
complex that affect selection of the diet: topography, water sources,
social behavior of the animals and soil characteristics. Arnold (1964)
presents a detailed diagram of the different factors involved in diet
selection by the grazing livestock.

Different parts of the plants are not consumed in the same form.
This phenomenon depends on several factors, but stocking rate is one
of the most important ones (Pieper et al., 1959; Blaser et al., 1962;
Cook and Harris, 1968a; Cook, 1973; Riewe, 1981). When availability
of high quality forage decreases due to maturity of the herbage or
excessive stocking rate, ruminants adjust their diets, consuming less

acceptable species or parts of plants (Watkin and Clements, 1978).

81

Several authors have reported a marked preference of sheep and cattle
for young and green material over old and more mature material (Cook
and Harris, 1950; Cowlishaw and Alder, 1960; Arnold, 1963; Willoughby,
1970). Alder and Minson (1963) observed that cattle select the top

and leaves of alfalfa, and the end of leaves and stems of orchardgrass.
Over a two year period these authors found a reduction on percent
composition (on dry matter basis) of flower buds and leaves of alfalfa
of 95 and 50 Z respectively, while the increase in stem percentage

was 48 Z.

Some evidence relating selection of forage by livestock and the
chemical composition of the forage has been presented. The material
consumed is generally higher in protein and lower in fiber (Hardison
et al., 1954; Pieper et al., 1959; Weir and Terrell, 1959; Arnold,
1960; Coleman et al., 1971). Several authors have confirmed the fact
that the digestibility of the ingested material is superior to the «
available forage (Hardison et al., 1954; Pieper et al., 1959; BlaSer
et al., 1960; Bryant et al., 1961a; Fontenot and Blaser, 1965), and
also the phosphorus content of the consumed forage is significantly
higher (Cook et al., 1963). Cook and Harris (1950), and Pieper et al.
(1959) observed a higher consumption of gross energy by grazing
livestock. Cook and Harris (1968a,b) theorize that this is due to a
higher intake of grasses on rangelands which have a higher content
of energy-yielding constituents than browse and forbes.

The selctivity of the ruminants changes throughout the grazing
season and it is dependent on the species composition of the pasture

and on the previous experience of the animals. Hardison et al. (1954)

82

reported that specific characteristics of the forage utilized (kind

of plants, stage of growth, accessibility of the plant parts) influence
the selectivity of grazing ruminants. Coleman et al. (1971) observed

a higher selectivity for protein in June and July, and for acid
detergent fiber in August, in two mixtures of legume-grass. The authors
attributed the difference in selectivity to a greater production of
forage in May-June-July compared to later in the season. Similar
results were found by Cook and Harris (1950, 1968a,b) on rangelands.

The difference in chemical constituents of the herbage consumed
and available on the pasture are plant species dependent. Single
chemical constituents can explain difference in preference by grazing
animals when ecotypes or single cultivars of individual species are
compared (Arnold, 1964). Coleman et al. (1971) found a larger difference
in crude protein and digestibility on a fescue-lespedeza mixture than
on an orchardgrass-clover. Coleman and Barth (1973) reported similar
results. Blaser et al. (1960) found a much larger difference in protein
content of an alfalfa-orchardgrass mixture than a bluegrass-clover
with advance of the grazing season, which in turn affects the protein
consumption by the grazing animals.

Selection is determined by the different animal senses: sight,
touch, taste and smell. These senses interrelate their effects in such
a way that it is difficult to prove which one specifically plays a
more important role in the diet selection. Arnold (1966a) showed that
sheep with and without sight do not differ in the diet they select.
This led Arnold and Dudzinski (1978) to conclude that sight helps

sheep to recognize plants but not to select the diet. Arnold (1966b,

83

1970) confirmed the interaction between taste, smell and touch in an
experiment with sheep and different pastures. Goatcher and Church
(1970a,b,c,d) analyzed the effect of taste on sheep, goats and cattle.
The authors concluded that cattle have a larger degree of discrimination
than sheep. At the same time, bitter is the most effective stimulant
in terms of selection, while sweet is the leats and sour and salty
tastes intermediate.

Some other factors affect the selectivity of grazing ruminants:
soil moisture and fertility, topography, physiological needs of the
animals, animal breeds, morphological and physical aspects related
to plant species, plant diseases, antiquality components related to
forages. Some of these factors can affect the selectivity by
ruminants in a direct form, but some others can do it indirectly,
producing pasture deterioration and causing animals to concentrate
more on certain species while grazing. For more detailed information
on the different aspects related to diet selection by sheep and
cattle, the reader is refered to other authors: Ivins (1952, 1955),
Jones (1952), Donelly (1954), Buckner (1960), Blaser et al. (1962),
Kare and Ficken (1963), Arnold (1964, 1981), Heady (1964), High and
Hobbs (1966), O'Donovan et al. (1967), Goatcher and Church(1970e),
Marten (1970, 1973, 1978), Arnold and Hill (1972), Marten et al.
(1973), Marten and Jordan (1974), Stoddart et al. (1975), Williams
(1975), Watkin and Clement (1978), Breese (1979), Carr (1979),
Copemmn (1979), Matthews and Kilgour (1980). Marten (1970b) presents
an excellent review of the plant and animal factors related to
palatability, and Burns (1980) discusses the most recent information

about antiquality constituents of forages.

84

3.5 Physiological basis for grazing management

 

3.5.1 Introduction

One of the main objectives of researdh in pasture-animal
complexes is to provide maximum production of forage of an acceptable
quality. Three approaches with regard to pastures are stated by
Booysen (1966): physiological, genetical and ecological. The
physiological approach is based on the concept of pasture growth
which in turn is a consequence of characteristics associated with the
plant species themselves and with the grazing animals. Leach et al.
(1976) and Ludlow (1976) review the physiology of growth and ecology
of pastures in detail.
3.5.2 Pasture growth
3.5.2.1 Definition ofggrgwth: factors that affect pasture gggwth

Pasture growth is not easy to define because it involves different
aspects of the canopy structure. Mitchell (1970) defines growth as the
increase in weight of plants due to cell division and enlargement.
However, Hunt (1978) not only considers growth as the irreversible
change in size of the plants, but also the change in number of plants
in a specified area, and the differentiation of plant tissue in its
different parts. This author then considers that the most important
aspect of plant growth is not the absolute gain in weight but the
relative growth rate (RGR) defined as the increase in plant material
per unit of time. Some other authors have proposed the use of unit leaf
rate (ULR) or nate assimilation rate (NAR) which is defined as the net
gain in weight per unit of leaf area (Evans, 1972). Booysen (1966)

defines the term crop growth rate: increment in dry weight per unit

85

period of time per unit area of land, and is the product of leaf area
index and net assimilation rate.

Leaf area index was defined by Watson in 1947. His definition
was provided previously in this review. In newly—germinated pastures
the leaf area index is less than one. As the pasture develops, the
area of the leaves increases, reaching different values depending on
the species. The optimum leaf area index depends on the species, being
higher for those species for tuber or grain production. Net assimilation
rate is defined as the dry weight increment with respect to the area
of the leaves (Watson, 1956, 1958).

The basic process that governs plant growth is photosynthesis.

As a result of this, all the factors involved in the photosynthetic
reactions exert their effects on plant growth: light intensity,
temperature, concentration of carbon dioxide, minerals, soil moisture,
organic reserves, pigment composition and concentration. We will
discuss only those factors related to the animal-plant relationship
and those climatic elements more related to our experiment, since the
photosynthesis process goes beyond the scope of our research.

3.5.2.2 Mixtures of leggmes and ggasses

A.- Importance of legumes

Legumes have several influences on the soil-plant complex. The
beneficial effects of growing legumes in mixtures with grasses can be
summarized as follows (Hodgson, 1952; Williams, 1970; Burton, 1976;
Templeton, 1976; Thompson, 1977; Watson, 1978):

- increase in crop yield per unit area and higher animal performance;
- reduction of the nitrogen fertilizer required for similar yields

under pure stands of grasses;

86

- improvement of the soil texture;

- increase in protein, calcium, palatability of the pasture;

- increase in yield of the crops used in rotation with legume-based
pastures;

— decrease in weed invasion of the pasture;

- more even distribution of the pasture throughout the grazing season;

— higher carotene content of the pasture, and as a result a higher
vitamin A value of the milk.

Rowland and Bumpus (1952) analyze the place of legumes in grass awards

for animal production. Thomson (1979) reviews the literature concerning

the advantages of legume-grass mixtures under European conditions.

Kalmbacher (1979) discusses the future importance of legumes in forages

as essential elements for feeding ruminants.

The influence of legumes on total forage yield, animal performance
and percentage of protein available to grazing animals are the points
to be considered in this review. The effect of legumes on grass stands
is very clear. Authors agree on the positive effect of legumes when
added to grasses. The increase in dry matter production per unit area
varies with the legume specie used, but in general goes from 5 to 50
percent (table 2). The capacity of legumes to fix nitrogen from the
atmosphere is the main factor responsible for increasing dry matter
production of pasture mixtures over pure grass stands (Lazenby and
Swain, 1972). Tesar (1978b) summarizes the factors that affect the
amount of nitrogen fixed by different legume species, but in general
oscilates between 80 lbs per acre for red clover to 300 lbs for 3 to

4 year old stands of alfalfa. When awards are composed of 25 Z legumes

87

 

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88

 

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89

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90

and 75 Z grasses, nitrogen fixation is much lower and may not supply
the required amount for maximum growth (Mulder, 1952). Simpson and
Stobbs (1981) reported annual rates near 1,100 lbs per acre for pure
stands of alfalfa under mowing in temperate environments. The authors
present an excellent review of the possible mechanisms of nitrogen
transfer from legumes to grasses.

From the experiments included in table 3, it seems that the
differences in animal performance grazing grass pure stands and grass-
legume mixtures are important and consistent. Different mixtures were
considered to prove that the advantages of including legumes are not
restricted to a few species. Animal performance using only grasses
and grass-legume mixtures were also included to analyze animal
responses under different conditions. The addition of nitrogen to
grass stands produce an increase in average daily gain, steer days
per acre and total gain per acre (Spooner and Ray, 1969, 1972; Tesar
et al., 1973; Scholl et al., 1974; Mott and Moore, 1975). Similar
results can be obtained with sheep and cattle when legume-grass
mixtures are compared to pure stand of grasses (Blaser et al., 1960;
Hobbs et al., 1965; Hamilton et al., 1969; Harris et al., 1972; Matches
et al., 1975; Mott and Moore, 1975). Anthony and Harris (1976)
summarize additional information on the effect of legumes on performance
of grazing animals. Kaiser and Cmarik (1976) review the latest researCh
information on finishing slaughter cattle on pastures. Reed (1981)
presents a complete review on agronomic studies and animal production
of legume based and nitrogen fertilized pastures for sheep and beef

cattle.

91

 

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93

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94

Some experiments have been done comparing grasses in pure stands
with grass-legume mixtures using different fertilizer levels. When the
level of nitrogen added to the mixture is above 100 lbs, there is a
decrease in average daily gain, but more steer days and gain per acre
are obtained (High et al., 1965; Burns et al., 1970a; Spooner and Ray,
1972). This can be explained by a decrease in legume percentage of the
mixture due to excessive nitrogen available. Templeton (1976) mentions
the possible causes for higher gains on legume-grass mixtures: higher
intake, a more rapid rate of digestion and efficiency in nutrient
utilization. Intake is reduced when insufficient protein is present
in the forage (Minson, 1967; Orskov, 1976), and values below 8.5 Z
were recorded as critical (Blaxter and Wilson, 1963). Minson (1976)
points out the importance of the protein component in the pasture to
obtain good animal performances. Thornton and Minson (1973) concluded
that the lower retention time of legume species in the rumen is
responsible for larger consumption of these species over grasses.

Reed (1972) presents a detailed review about the performance of sheep
grazing different types of pastures.

Leaves have a large capacity to synthesize and store protein and
non-protein nitrogen. In young leaves, protein can represent up to
50 Z of the total dry matter present. Because of the higher nitrogen
content of legume leaves when compared with grasses, animals ingest
very high protein material when grazing a legume dominant sward
(Davies, 1952). Protein is located in photosynthetic cells and non-
protein nitrogen in large vacuoles surrounded by those cell (Hogan

and Hemsley, 1976). This system of nitrogen distribution is important

95

in those species with a high content of non-protein nitrogen such as
of those of leguminosae (Brady, 1976). Johnson and Nichols (1969)
compared 11 grasses in single stands and in association with alfalfa.
Under these conditions, it was necessary to add 100 lbs per acre of
nitrogen to obtain a higher protein percentage from the grasses in
pure stands than in the mixture. Botanical composition of the mixtures
were not reported. Lee (1976) presents an excellent review of the
biological differences between storage proteins in legumes and cereals.
Lyttleton (1973) reviews the protein and nucleic acids composition in
herbage.

The distribution of seasonal production is an important factor
to consider. Matches et al. (1975) obtained a higher production for
fescue-legume mixtures than for fescue stands after the first cut.
Schmidt and Tenpas (1965) observed a more uniform distribution of
forage yield of grass-legume mixtures when compared with grasses
pure stands. The differences in seasonal yield distributions were
more marked with less favorable rainfall pattern. Similar results were
previously reported by Wagner (1954). 0cokoljic and Velickovic (1970)
observed that in spring, with high precipitation and low temperatures,
orchardgrass and bromegrass dominated the pasture in mixture with
birdsfoot trefoil. However, the latter specie increased from 22.29
to 51.09 Z throughout the season (decrease in rainfall and increase
in temperature).
B.- Competition between legumes an§_gr_asses

Pasture plants growing together interact and compete with one

another. Grime (1973) defines competition as the tendency of the

96

different plants of a forage community to utilize the same space,
molecule of water, quantum of light or mineral available for growth.
Leach et al. (1976) discuss the different research techniques used

to study interaction between plants of commercial crops and of

pastures as well. Leach (1967) comments on the specific characteristics
alfalfa has to adapt to different conditions. Those characteristics

can be generalized to include other species:

tolerance to dry conditions;

activation of growing points by factors such as soil moisture,

temperature and water relations within the plant;

tolerance to a wide range of temperatures and humidities;

tolerance to short photoperiods;

high photosynthetic capacity;

resistance to diseases.

Matheson (1972) offers a detailed comment on these aspects with
respect to different pasture species. Hall (1978) and Harper (1978)
review the competitive and non-competitive interrelations among the
most commonly used pasture species.

The growth pattern of legume and grasses is not the same. The
growing points in grasses is near the soil surface, and as a
consequence, they are rarely damaged by defoliation. Legumes have
the growing points as buds, and a large proportion of the axillary
buds are also located near the soil surface. Red clover and alfalfa
have a perennating tap root with visible crown of stem.buds and short
shoots that cannot be reached by the grazing animal. Regrowth from
these species is originated from the crown buds and axillary buds.

Grasses originate their new leaf tissue from leaf primordiumnwhose

97

meristematic tissue remains very close to the ground (Mitchell, 1970;
Williams, 1980).

The growth of the plant populations can be represented by a
sigmoid curve. At first, the increase in biomass is slow and after the
size of plants increase, growth enters to an exponential phase. The
plant community reaches a stage where plants start competing for the
available resources and the maximum potential growth cannot be
maintained (Hutdhings and Budd, 1981). Mitdhell (1970) reviews other
theories that explain the pasture growth: theory of Blackman, law of
diminishing returns of Mitscherlich, and the theory of Macy.

The competitiveness of the species is important when mixtures of
2 or more species are seeded. The mixture of several species is very
difficult to manage in order to create conditions for the maintenance
of all the species. This led Blaser et al. (1952) to proposed a plan
using different legume—grass mixtures with only 2 or 3 species. Using
this scheme, the specific mixtures can be planned to produce forage
through the grazing season considering the particular environmental
conditions and the main objectives of the livestock enterprise. Calder
(1952) presents a similar scheme for New Zealand conditions based on
subterranean, white clover and different grasses. Since legumes have
important contributions in mixtures, the efforts have been concentrated
in discovering the main constraints that these species have to
overcome under grazing conditions in England (Davies, 1952), Australia
(Griffiths Davies, 1952), France (Hedin and Rebischung, 1952), and the

U. S. (Sprague, 1952).

98

3.5.3 Pasture ggowth in relation to the environment

 

The importance of green plants as food prducers for ruminants is
dependent on the conversion of radiant energy to chemical energy by
photosynthesis. Several factors influence the photosynthetic process
but light is the primary input. Based on this principle, Loomis et al.
(1971) have suggested that the efficiency of crop production can be
measured in terms of conversion of solar energy into useful products.
Laude (1972) presents a review of the external factors that affect
growth of grasses, and Denmead (1972) analyzes the microclimate
phenomena that occur within the grass community.

Three main components of light have to be distinguished: quality,
intensity and duration. Mitchell (1970) defines quality as the
available and active wavelength that can be used in the photosynthetic
process. Loomis and Williams (1963) reported that between 5 and 7 Z
of the total visible light (400-700 mn of wavelength) is utilized in
the process. Hesketh (1963) compared the photosynthetic efficiency of
9 species, and observed that regardless of the differences between
species in their behavior, the concentration of chlorophyll did not
vary greatly among them. The author concluded that the differences
among species must be due to differences in mesophyll diffusion and
to the dark reaction of the photosynthetic process.

Intensity and duration of light are important components to
consider. Plants are divided in two main groups according to the
photorespiration level: 4-carbon plants (C4) and 3-carbon plants (C3),
with little or no photorespiration, and with high rates of

photorespiration respectively (Wittwer, 1974). Sorghum is an example

99

of the former group, while the majority of the legumes and grasses used
for grazing belong to the latter. The importance of the C4 group is
that light saturation is not achieved even at full sunlight, and as a
result they may be considered to be more efficient in using carbon
dioxide from the air at low concentrations (Berry, 1975). Wilson (1973)
presents a complete review on the physiological basis of light
utilization in plant communities. Evans (1980) discusses the important
differences between C4 and C3 plants in relation to plant physiology
and environmental factors that influence the efficiency of light
utilization.

Light has important effects on forage growth, seedling growth,
weight of plants, and nodulation as well. Peterson and Loomis (1949)
observed an increase in shoots development of Kentucky bluegrass with
short days (11 hours). The authors also reported an increase of
prostrate habit of this specie as a result of short days. Wolf and
Blaser (1972) studied the effect of light intensity on stem height
and weight of alfalfa pure stands. With decreasing light intensity,
the authors observed an increase in stem elongation but a decrease in
stem weight. This experiment may resemble what happens in the lower
layers of leaves in dense stands of alfalfa. McKee (1962) reports the
efect of daylength on several Characteristics of birdsfoot trefoil.
With increasing daylength from 9 to 10 hours to a maximum of 24 hours,
the author observed a change in leaf color to lighter green tones,
higher and more erect plants with greatly elongated internodes.
Nodulation as measured by nodule number, color, size and mass was
inferior at 9, 11 and 24 hours of light when compared to normal

Photoperiod: 13-15 hours. The practical implication of these findings

100

is based on the fact that at the end of the grazing season, birdsfoot
trefoil plants are in greatly disadvantage due to their lower capability
to grow and fix nitrogen. Cooper (1966) compared the behavior of
alfalfa and trefoil under different levels of shade. The author
concluded that regardless of a lower relative growth rate, alfalfa has
a greater assimilation rate which makes it less susceptible to be
shaded under field conditions. Ludlow (1978), and Rhodes and Stern
(1978) can be consulted for additional aspects on light competition.
Temperature is another factor that affects plant growth. Increase
in temperature over 20 degrees centigrade (C) produces an increase in
respiration but a decrease in apparent photosynthesis. True
photosynthesis increases with temperature until it levels off around
25 to 30 degrees C (Mitchell, 1970). El-Sharkaway and Hesketh (1964)
analyzed the effect of temperature on 4 different crops. They
concluded that optimum temperature is directly correlated with net
photosynthetic rate, which in turn is a measure of exchange of carbon
dioxide between the leaf and the surrounding air. Sorghum (C4 plant)
shows an optimum temperature around 40 degrees (El-Sharkaway and
Hesketh, 1964), while for most temperate grasses such as ryegrass and
orchardgrass it is approximately 20 to 23 degrees C (Vickery, 1981).
Smith (1969) obtained higher yields of Vernal alfalfa in warm
temperatures (32 degrees C during the day and 24 at night) than in
cool conditions (18 and 10 degrees). However, Vough and Marten (1971)
found higher yields at low temperatures (16 and 10 degrees) than at a
higher regime (27 and 21 degrees). Jensen et al. (1967) observed

different behavior of alfalfa strains: hardy strains yielded equally

101

under hot (81 degrees) and cool temperatures (61 degrees Farenheit),
but the intermediate and non hardy strains produced significantly more
forage under low temperatures. Baker and Jung (1970) studied the
temperature effects on 4 grasses: timothy, orchard, brome and bluegrass.
High temperature stress affects more the growth of timothy and
bluegrass than the other 2 species. The former species were found to
contain less RNA and DNA per unit dry weight of tissue. The authors
theorize that the high temperature stress could be exerted on nucleic
acid composition which in turn results in reduced growth.

Geographic origin of species is the major determinant of the
optimum temperature for particular ecotypes, but in general, growth
occurs between 10 and 25 degrees C. Growth decreases with temperatures
below 10 degrees C and above 25 degrees C for temperate grasses, and
usually ceases at 5 and 30 to 35 degrees C (Vickery, 1981). Peterson
and Loomis (1949) observed a marked effect of low temperatures (55.8
and 65.4 degrees Farenheit) on carbohydrate accumulation, but cool
temperatures and short photoperiods together produced the greatest
carbohydrate storage in bluegrass. McWilliam (1978) makes a thorough
review on response to plants to temperature.

Soil moisture is also important to be considered in forage growth.
Shallow-rooted forages sudh as bluegrass, orchardgrass or red clover
are more affected by low rainfall than deep root system plants such as
alfalfa (Smith and Rohweder, 1977). El-Sharkaway and Hesketh (1964)
observed that net photosynthetic rate was depressed under water
deficit for visible wilted leaves of the 4 species analyzed. The authors

concluded that the closing of the stomata was responsible for such

102

behavior, and no specie differences were found in this respect. Similar
stomata resistance between C3 and C4 plants were reported by other
authors (Bull, 1969). However, Berry (1975) maintains that C4 plants
are more efficient in absorption of carbon dioxide under low
concentration of this gas in the atmosphere, and can absorb a larger
amount of it at any diffusion limitation than alfalfa. McKee (1961)
commented on the importance of soil moisture to obtain an adequate
nodulation of legumes. The author concluded that birdsfoot trefoil
is more susceptible than alfalfa and red clover to low moisture
conditions based on the fact that 137 days after emergency, different
seed sources of this specie did not nodulate under moisture stress.
3.5.4 Qgganic reserves and growth

Organic reserves are an essential factor to obtain rapid regrowth
at the beginning of the growing season and after each harvest. They
also play an important role in winter survival of the different species.
Weinmann (1952) defines reserve substances as organic materials
synthesized by plants and stored in different organs which will be
utilized as a source of energy or as building materials. Perennial
species store reserve materials in rhizomes, crowns, roots, stems,
and leaf sheaths, while annual species rely on materials stored in
seeds (Mitchell, 1970). The major storage areas are the lower regions
of stems and stem basis, and non-structural carbohydrate reserves of
the grass roots are probably not used to stimulate growth (White,
1973). On the other hand, legumes accumulate and use reserves from
roots (Smith, 1962; Reynolds, 1971). Hodgkinson (1970) showed that tap
root of alfalfa is the main source of elements for plant growth.

Pearce et al. (1969) have shown the distribution of carbon 14 before

103

and after defoliation of alfalfa plants. Sheard (1972) presents a
detailed review on organic reserves and plant regrowth.

There are different types of reserve carbohydrates and the
relative importance of them depends on the geographical origin of the
species under consideration. Glucose, fructose, sucrose and the
fructosans are the most common types in temperate grasses (Matches,
1969). On the other hand, those grass species from trapical or semi-
tropical origins seem to store starch in conjunction with sucrose
(Smith and Grotelueschen, 1966). The total non-structural carbohydrates
in alfalfa are principally starch and sugars. Glucose, fructose and
sucrose make up the total sugar fraction in alfalfa (Smith, 1975).
Okajima and Smith (1964) reported a high concentration of fructosans
in orchardgrass, timothy, canarygrass and Kentucky bluegrass, but very
low levels in bromegrass. Their results agree with what Phillips et al.
(1954) previously reported. However, Jung et a1. (1974) obtained
different results working with 8 grasses. The authors concluded that
the variation between the different reports is due to the extractants
used which obscure the real content of fructosans in bromegrass. This
hypothesis corresponds with the findings of Smith and Grotelueschen
(1966). These authors classify grass species according to the percentage
of carbohydrates extracted with different concentrations of ethanol:
timothy and orchardgrass contain a whole series of fructosans and with
timothy having high amounts of long-chain fructosans; canarygrass and
bluegrass with long-chain fructosans as well, but with smaller units
being changed to larger units as shown by the reactions with 50 and
65 Z ethanol. The third group is conformed by bromegrass and tall fescue

where large concentrations of short-chain fructosans were detected.

104

Smith (1967) later reported a change in the length of fructosan chains
with growth stage in timothy, but confirmed that short-chain fructosans
are present in bromegrass regardless of the anatomical part of the
plant or growth stage analyzed. Subsequent reports confirmed the fact
that bromegrass and tall fescue are short-chain fructosan accumulators
(Smith, 1972).

The accumulation of carbohydrate reserves is a dynamic process
with daily and seasonal fluctuations (White, 1973). Jung et al. (1974)
obtained 55 and 66 Z more total non-structural carbohydrates of 8
grasses in Spring and Autumn than in Summer respectively. Tall fescue
and bromegrass showed the highest values, while bluegrass was the specie
with lowest concentrations of reserves. Lopez et al. (1967) showed
lowest reserves in July and August for fescue, an increase of 174 Z
between August and November when it leveled off until January, and
finally a 30 Z decrease occurred between January and February. Reynolds
and Smith (1962) observed that reserves in alfalfa, brome and timothy
under no cutting decrease in Spring and then start increasing to reach
a peak in June-July. For alfalfa, the maximum peak was reached near
full-bloom (late June), but for the two grasses it occurred in mid-
July which corresponds to seed formation in brome and to the period
from anthesis to the dough stage in timothy. After that peak, reserves
decline slightly and remain constant for the entire season. Similar
results were reported for alfalfa, red clover and birdsfoot trefoil
(Smith, 1962), and for alfalfa and sainfoin (Cooper and Watson, 1968).
Holt and Hilst (1969) studied the daily variation of carbohydrate

content in 1 legume and 3 grass species. They found that non-structural

105

polysacharide content followed an increasing linear pattern in the day-
time for the 3 grasses but not for alfalfa which had a most rapid
increase in the afternoon. Non-structural polysacharide content
increased faster in brome and fescue than in Kentucky bluegrass.
3.5.5 Frequency and intensity of defoliation in relation togpasture
growth and_persistency

The effect of herbage removal on plant regrowth has been grouped
in 3 main categories: (1) depletion of carbohydrate reserves,
(2) reduction in root growth, and (3) reduction of leaf area. Frequency,
intensity and timing are the 3 parameters to consider in order to
quantify the effect of defoliation (Harris, 1978). Grazing and clipping
practices have have produced different results when used to evaluate
pastures. Close defoliation and removal of stubble can explain part
of the lower yields obtained under grazing conditions (Sprague and
Sullivan, 1950). Other reasons for sudh differences are soil compaction,
decrease in soil aeration and water infiltration, injured of the plants
by hoofs, and a more rapid removal of reserves (Bryant and Blaser, 1961).
Wilman (1977) obtained similar results grazing and cutting 3 times per
year an alfalfa-orchardgrass mixture. In order to show general principles
related to pasture growth, I will use information from cutting trials
due to the lack of published material of grazing experiments with species
such as alfalfa.

The adaptability of the forage species to withstand defoliation
depends on the anatomy and physiology of their growth. Culmed grasses
(meristems at the top of the plant) are more susceptible to the influence

of cutting and grazing than culmless grasses(meristems in basal positions)

106

(Hyder, 1972). Legumes also differ in their growth behavior. Alfalfa
maintained uncut produce more than one growth from the crown, while
birdsfoot trefoil arises only the first growth from the crown.
Additional growths depend on branches derived from axillary buds
from old shoots (Smith, 1968; Nelson and Smith, 1968). The importance
of the crown of alfalfa under continuous grazing was emphasized by
Kehr et al. (1963).

Root growth of most species is reduced by defoliation. Pearce
et al. (1969) demonstrated the mobilization of carbon reserves from
alfalfa roots after defoliation. Legumes in pure stands (Smith, 1962;
Bryant and Blaser, 1963; Jensen et al., 1967; Cooper and Watson, 1968;
Reynolds, 1971) and in combination with grasses (Reynolds and Smith,
1962; Bryant and Blaser, 1964) were studied to evaluate root growth
under different defoliation practices. Authors concluded that root
weight decreases with the number of cuttings practiced during the
growing season. Jensen et al. (1967) showed that non hardy varieties
of alfalfa are less affected by the cutting frequency than hardy and
intermediate varieties. Smith (1962) observed a different behavior
analyzing alfalfa, red clover and birdsfoot trefoil. Alfalfa maintained
the highest level of carbohydrate reserves and birdsfoot trefoil the
lowest, regardless of the fact that the three legumes showed a regular
cyclic pattern in storage and utilization of the root reserves.
Fulkerson (1970) demonstrated the negative effect of fall harvesting
of alfalfa in three locations in Canada. The greatest losses occured
with thin stands and short early spring growth. Davidson (1978)

reviews the most important aspects that regulate the root growth in

107

pastures.

Cutting schedule also affects carbohydrate reserves of grasses.
Reserve carbohydrates in grasses are located in different parts of the
plants, but their concentration is greater in the stubble than in the
roots or leaves (Davidson and Milthorpe, 1965; Matches, 1969; Sprague
and Sullivan, 1950). Paulsen and Smith (1968) compared the accumulation
of carbdhydrates at the base of the stems of fescue plants harvested
3 and 5 times from April through August at 5 centimeters (2 inches)
height. The authors did not find significant differences in the
reserves accumulated due to the cutting treatments. Reynolds and
Smith (1962) reported a greatest range of fluctuations in carbohydrate
reserves for timothy than for brome under 3 cutting systems from June
to August. Youngner (1972) reviews the literature on this topic and
concludes that cutting affects growth and development of all parts of
plants, mainly as a direct consequence of the reduction in the amount
of the phtosynthetically active tissue.

Total yield during a growing season is affected by the number of
cuttings. Washko and Price (1970) indicated the importance of harvest
frequency on total yield and persistance of alfalfa. The authors
concluded that 35-day harvest schedule offers the best alternative for
dry matter yield, persistance and quality. Several studies in the
Northern states have shown that highest yields of alfalfa pure stands
are obtained with three cuttings per year at early-flower stage
(Jackobs and Oldemeyer, 1955; Kust and Smith, 1961; Smith, 1965). Four
cuttings in the same area have proved to increase winter damage (Smith
et al., 1968). However, Bryant and Blaser (1963) showed that a higher

yield of alfalfa is obtained with 4 cuts, the first one at bud stage

108

and the other 3 at 1/10 bloom. It is important to consider that these
authors compared 4, 5 and 6 cutting schedules. For Michigan conditions,
Tesar (1978b) recommends 4 cuttings to obtain maximum yield maintaining
good stands of alfalfa. Keoghan (1967) presents an excellent review on
the effect of number of harvest, yield of alfalfa stands and reduction
of winter hardiness. Dotzenko and Ahlgren (1951) compared the effect
of cutting frequency on total yield of an alfalfa-bromegrass mixture.
The authors obtained the highest yields when only 2 cuttings were
performed. Folkins et al. (1961) and Sprague et al. (1964) showed that
late summer defoliation is very important to assure persistance of
alfalfa, especially when seeded with orchardgrass. Jung et al. (1969)
observed that autumn grazing of alfalfa in West Virginia produced an
early flowering in Spring of the following year and the authors
suggested that it was due to lower reserve levels. Under Virginia
conditions, Bryant and Blaser (1964) recommend making fall cuttings
of alfalfa late in the season to avoid plant growth and depletion of
reserves. Weir et al. (1960) obtained a higher alfalfa yield with 4
weeks defoliations under warmer conditions in California. Under
British conditions, 3 cuttings of alfalfa were also proved to produce
higher yields (Davies et al., 1953; Dent, 1955; Davies and Davies,
1956; Davies and Tyler, 1962). However, Davies et al. (1960) obtained
higher results when 2 cuttings were practiced due to a higher alfalfa
persistency. The authors suggested that the unfavorable conditions
were responsible for the low persistency of alfalfa with 3 cutting
systems.

The height of cutting has an important effect on the regrowth of

legumes. Ridgman (1960) established that cutting at ground level can

109

cause the death of alfalfa plants. Leach (1970) Observed that regrowth
of alfalfa depends on the number of shoots and the time they start to
elongate. The author concluded that the leaves retained after
defoliation and the root reserves do not play an essential role
immediately after cutting. However, the active basal leaves that
remained after defoliation could be the mechanism that triggers the
regrowth process (Leach, 1968). Smith (1962), and Smith and Nelson
(1967) reported that a leafy stubble is required in trefoil for high
rates of regrowth, but only with six cuts per year in alfalfa. The
difference in management is based on the fact that trefoil does not
restore its reserves during the growing season such as alfalfa (Smith,
1962; Nelson and Smith, 1968, 1969). These results support the
conclusions made by Beardsley and Anderson (1960) that birdsfoot
trefoil can be harvested frequently but not closely, and alfalfa
closely but not frequently in order to maintain a good persistency.
Intervals between defoliations and height of cutting are very
important in grass pastures because they affect depletion of reserves,
removal of growing points, stubble and leaf area left. Teel (1962)
established the importance of cutting height in bromegrass. The author
found that regrowth of bromegrass after the shoot primordia was
destroyed by defoliation must arise from basal buds. As a consequence,
grazing and cutting must be done in such a way to avoid depletion of
reserves and destruction of the basal buds. Reynolds and Smith (1962)
studied the growth pattern of bromegrass under 3 cutting systems. The
authors found that poor recovery after the first harvest was obtained

because low carbohydrate levels as well as inactive basal buds were

110

present, when 3 harvests were made the previous year. These findings
agree with results from Paulsen and Smith (1968, 1969). Wright et al.
(1967) noted that height of cutting does not have a generalized effect
when 1.5 and 3.5 inches were used in 12 different locations in the
Northeastern region of the U. S. Knievel et al. (1971) observed that
bromegrass yielded more, with a 4 centimeter than, with a 10
centimeter stubble height. Burger et al. (1958) obtained higher
production from brome-clover mixtures cut at 1 inch than at higher
heights, but the percentage of brome showed a steady downward trend.
Winch et al. (1970) suggested to harvest pure bromegrass stands
immediately after the majority of the heads have emerged in order to
obtain a more uniform material in protein and digestibility contents.
Carter and Law (1948) showed the detrimental effect of cutting at less
than 30 day intervals on root and top production. The authors concluded
that the negative effect of cutting every 15 days was much greater
than the decrease in top production, and as a consequence, less
productive plants were produced. In summary, bromegrass is a specie
that needs to be cut at 4 centimeter height. When seeded alone, more
cuttings per year can be practiced because it more rapidly stores
reserves. Under mixtures with alfalfa, the rest period must be longer
because it stores less reserves (Paulsen and Smith, 1968), and to
obtain a more uniform production of protein (Winch et al., 1970).
Orchardgrass produces many sterile shoots and, as a result, a
rapid regrowth is obtained. Under long resting periods, there is an
excessive elongation of the sheath from sterile shoots and close
harvesting produces leaves to be cut through the sheath rather than

through the lamella, and severe damage can occur (Teel, 1962). Washko

111

et al. (1967) observed that the trends in food reserves were highest
when cut at the early vegetative stage or early heading, and for plants
harvested at 3.5 inches compared to 1.5 inches. Yield of the different
varieties of orchardgrass varied with their cycle: Potomac produced
more when cut at 1.5 inches while late maturing varieties produced
more at 3.5 inches height. Griffith and Teel (1965) report a 57 Z
reduction in stands when orchardgrass was clipped at 2 centimeters
height. Hart et al. (1971) suggested that under grazing conditions
close defoliation (5 centimeters height) beginning before tiller
elongation and at monthly intervals seem to give the best yields.
This management practice makes orchardgrass a good grass to be seeded
with legumes such as alfalfa that requires similar grazing management.
Tall fescue yield is also affected by timing, frequency and
height of cutting. Yeh et al. (1976) observed that tall fescue in the
Southern Corn Belt area produces most of its vegetative growth in
Spring and Autumn. They noted that even when buds are present in
midsummer, no appreciable elongation of buds into tillers is observed
due to high concentration of auxin in stem bases as a result of high
temperatures. Under conditions of accumulated growth, number of tillers
of fescue plants increase from June to July and remain fairly constant,
while the number of buds continue increasing up to September. Under
such conditions, it seems like summer growth is originated from tillers
and not from buds (Lopez et al., 1967). Similar results were reported
by Beaty et al. (1978a). Matches (1969) studied the importance of
height of cutting on the energy reserve status of tall fescue pure
stands, and their regrowth capability. He concluded that height of cut

should never be less than 3 centimeters, but 6 and 9 centimeters

112

appear satisfactory. Burger et al. (1958) recommended 1 inch for
higher dry matter production on fescue-ladino clover mixtures, and
Hoveland et al. (1978) suggested 10 centimeters as the optimum
cutting height for fescue-bahiagrass mixtures, if dry matter and a
high percentage of fescue in the mixture are desired. Vartha et al.
(1977) studied the effect of frequency of defoliation on dry matter
production under grazing conditions. The authors did not find
significant results under continuous grazing and rest cycles of 20
and 30 days during Spring and Summer. However, more herbage production
was observed in the 30 days rest period during fall. Matches (1979)
presents a complete review of fescue management under cutting and
grazing conditions to maximize dry matter production.

Sorghum is generally seeded in May in the Northern states of
U.S. and in England. Growth is very slow for the first month after
germination, but it increases rapidly in July, August and September
under British conditions (Green and Corrall, 1966). This behavior was
described by Spahr and Ormiston (1969) as due to its particular
response to the hot days in midsummer. The effect of different
cutting heights in sorghum.was studied by Mays and Washko (1961) under
Pennsylvania conditions. These authors found a higher dry matter yield
when cut at 2 to 4 inches compared with higher stubble heights. Higher
production of different sorghum varieties was obtained in Illinois,
when cut at 3 inches stubble height than at 6 inches (Burger and
Hittle, 1967). Jung and Reid (1966) observed that with advance in stage
growth, dry matter production per cutting and for the total season
increases. The authors obtained maximum yields harvesting at full bloom,

which corresponded to 61 days between harvest, than a younger stages.

113

Dunavin (1970) obtained higher gains per steer per day and per

hectare when sorghum was seeded early in the Spring due to higher

dry matter production and carrying capacity. Spahr et al. (1967) did
not find any significant difference in animal performance or forage
yield measured by cow-weeks of grazing, with 15 or 21 days regrowth
period. However, the authors noted an important increase in dry matter
production per hectare in July-August-September regardless of a marked
decrease in seasonal yield delaying the seeding from May to late June-
early July .

In summary, the effect of cutting height and frequency on total
pasture production is not completely understood. We tried to analyze
particular effects of these variables on specific species, but it is
rarely correct to assume pure stands of a specie is the method used
under animal production on grazed pastures. Tayler and Rudman (1966)
reviewed the literature available on the effect of height of cutting
on pasture yield and concluded that the effect of this variable is
confounded with the fact that more yield is found with low cutting
heights because more forage is harvested, but not because more growth
is stimulated. Campbell (1966a) proposes the utilization of net
pasture production (new growth minus losses through decay) instead
of forage yield, because it relates more accurately with what animals
consume. The author did not find significant differences in net
pasture production between grazing management, or with high and low
stocking rate which in turn represent 2 degrees of defoliation

intensities (Campbell, 1966a,b,c).

114

3.6 Control of feed intake

 

3.6.1 Introduction

 

Forages are characterized by their nutritive value and their
intake. Within the nutritive value concept, several characteristics
are included: digestibility, percentage of fiber and dry matter,
mineral composition and protein content. Intake is defined as the
amount consumed by animals when forages are provided ad libitum. The
different aspects of measuring intake using the before-and-after—
grazing technique have been previously discussed. Langlands (1975)
presents a review of the different techniques available to estimate
intake of grazing animals.

3.6.2 Factors that affect intake

 

Several factors affect intake of ruminants under grazing
conditions: factors associated with animals, factors associated with
the pastures themselves and factors from the environment around the
animal-plant complex. Weight, physiological condition and level of
production are the most important characteristics associated with the
animals. Among those related to the pasture, chemical composition,
maturity, palatability and species composition are the most significant
factors to consider. Within the last group, level of fertilizer,
temperature, contamination of the forage with feces and urine, grazing
system, time of access to the food and season of the year must be
mentioned (Cordova et al., 1978; Coleman, 1980; Meijs, 1981a; Van
Soest, 1982). Bines (1979) presents a review of the latter group.

Several authors have studied the effect of different animal

characteristics on intake (Corbett, 1960; Corbett et al., 1963;

115

Arnold, 1970). Heaney (1970) studied the ad libitum intake of 3
timothies, 2 alfalfas and 3 grass-legume mixtures with a diverse

group of sheep (lambs, wethers, rams and ewes). He concluded that age,
sex and weight of the animals determine intake, and the values obtained
with one group cannot be used with others. The author also Obtained
different values for intake per unit of metabolic size for sheep and
cattle. Waldo (1970) summarizes the literature on intake expressed in
grams per kilogram of body weight to the 3/4 power. He shows significant
differences between sheep and cattle, and among cattle, with the data
reported by several authors. Calves at liveweight below 70 kg have a
voluntary intake of dry matter that exceeds that of the ruminant.
However, with heavier calves, intake of productive energy is not
higher, regardless of greater intakes of dry matter (Roy and Stobo,
1975). The authors suggested that maximum dry matter intake is
approximately 60 grm per kilogram of body weight to the 0.75 power at
birth, it increases to 62 grm at 125 kg of body weight, declining
thereafter to about 55 grm at 300 kg of liveweight. Bines (1979)
reviews the literature on dairy cattle showing the importance of size
and physiological conditions of animals as final determinants of
intake. Dulphy et al. (1980) summarize the information available on
the influence of physiological state and genetic factors of animals
over intake.

The forage itself affects intake of ruminants. Jarrige and Minson
(1964) established the importance of the cell wall polysacharides upon
the digestibility of the forages. With increasing lignification of the
cell wall, lower digestibility values are obtained and decrease in

intake is observed. Stehr and Kirchgessner (1976) found that herbage

 

116

allowance and digestibility of a grass-legume mixture accounted for
the variation in intake of cows on pasture. Demarquilly and Jarrige
(1964) analyzed 112 different forages in France during a period of 5
years. The authors established the relationship between the quality of
forages and intake. In a more recent report, the authors (1971)
summarize the main results obtained during 10 years of research on
the effect of pastures on intake by ruminants. Thornton and Minson
(1973) reported a 28 Z higher intake of legumes when compared with
grasses of similar digestibilities. That difference was caused by a
shorter retention time (17 Z) and a higher amount of organic matter
(14 Z) in the rumen digesta from legume diets. Reid and Jung (1966)
obtained higher intakes of alfalfa than grasses of similar digestibility.
The authors theorized that the difference could be explained by a
higher content of carbohydrates and a lower cell—wall fraction of
alfalfa. Robles et al. (1981) reported higher intakes of orchardgrass
diets with lower cell wall contents, which in turn supports the theory
of Reid and Jung (1966). Reid et al. (1978) established the importance
of digestibility of grasses as the main factor affecting intake of
grazing lambs. Laredo and Minson (1973) found a 46 Z higher intake of
leaves over stems on 5 grasses, regardless of a slightly lower
digestibility of the leaf fraction. The authors attributed the higher
intake of leaves to a lower retention time of this fraction in the
rumen caused by the large surface initially available for bacterial
attadk. Kartcher and Campbell (1979) make a detailed review of the
literature on the effect of chemical constituents and maturation of

plants over intake of range forages. The importance of protein content

117

in the diet on intake was established by Blaxter and Wilson (1963), and
Minson and Milford (1967). Polan et al. (1976) demonstrated that
maximum intake of complete diets by dairy cows can be obtained with
12.8 Z percent protein. With higher or lower percentages, intake is
reduced.

The interrelationship between voluntary intake, digestibility and
chemical composition is species dependent. Van Soest (1965) showed
that the only consistent relationship between chemical composition and
intake is with cell wall constituents. In those forages with high cell
wall contents (grasses), intake decreases with an increasingly negative
slope with higher proportions of cell wall constituents. However, with
low cell wall forages (legumes) no definite relationship can be
established between digestibility and intake. This has led the author
to conclude that the relationship between digestible dry matter and
voluntary intake depends basically on the digestible energy from cell
wall constituents, and when the latter conforms 50 to 60 Z of the
forage dry matter, the fiber mass starts to play the role of limiting
voluntary intake. The author (1982) grouped grasses in 2 classes
according to the relationship between intake, lignin content and
digestibility. The first group (brome and orchardgrass) shows a
negative and positive association between lignin content and intake,
and digestibility and intake respectively. The second group (fescue
and bluegrass) shows a positive association between lignin and intake.

3.6.3 Mechanisms of control

 

Two mechanisms are involved in intake control: physical capacity
of the gastrointestinal tract and chemostatic or thermostatic

mechanism. Montgomery and Baumgardt (1965) exemplified the importance

118

of these 2 mechanisms in relation to the nutritive value of the forage
ingested (figure 1). With diets of low digestibilities, the capacity

of the reticulorumen plays the decisive role in intake control. When
the energy concentration of the diet increases, the control of intake
is done for chemostatic or thermostatic mechanisms. Bines (1976) and
Coppock (1978) discuss the practical implications of these 2 mechanisms
with forages and more concentrated diets fed to lactating cows in
early and late lactation.

Considerable evidence exists that shows the importance of the
physical factors affecting control of intake. When ruminants are fed
with low quality forages, there is enough evidence that animals eat
to a constant rumen-fill (Campling, 1970). However, when better
quality diets are offered ad libitum, more dry matter is present in
the reticulorumen compared to straw diets (Campling and Balch, 1961;
Montgomery and Baumgardt, 1965). Conrad et al. (1964) observed that
intake of dairy cows on roughage diets with less than 66 Z digestibility
was controlled by physical factors. The authors identified body weight
(reflecting forage capacity), undigested residue per unit body weight
per day (reflecting rate of passage) and dry matter digestibility as
the main factors affecting intake. Campling et al. (1962) found that
with straw diets, the retention time in the reticulorumen plays the
most important role in controlling intake of sheep. Due to these data,
Campling (1970) concluded that with low quality forages physical
factors are important in limiting voluntary intake of forages by
ruminants. These factors exert their influence through limits imposed

by the reticulorumen capacity and the retention time of the ingested

119

 

 

8
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Figure 1: CONTROL OF FEED INTAKE IN RUMINANTS WITH DIETS OF

DIFFERENT QUALITIES (MONTGOMERY AND BAUMCARDT, 1965).

120

material.

With diets of high nutritive value, other factors control intake,
different than physical factors. Baumgardt (1970) summarizes the
literature that supports the basic idea that ruminants can control
energy intake. The author concludes that when physical factors are not
predominant, other factors such as palatability, rumen ph, and
concentration of volatile fatty acids interfere with long-term energy
regulations. Kaufmann (1976) reported that with a more frequent feeding
system, rumen ph is maintained higher, producing a higher cellulolitic
activity which in turn leads to a higher rate of passage and intake.
Montgomery and Baumgardt (1965) found that feed intake of dairy heifers
and lambs is not due to rumen fill with digestibilities of the diet
greater than 60 Z. Jones (1972) proposes a model in whiCh several
factors are responsible for control of intake: concentration of fatty
acids, levels of amino acids and ketone bodies. The liver could
monitor these elements and transfer the signals to the hypothalamus
which in turn could integrate signals from other sources as well to
set up the control system. Egan and Moir (1965) and Egan (1965a,b)
reported an increase in intake by sheep fed low quality forages when
urea and casein were infused per duodenum. Egan (1965c) observed a
higher capacity of sheep to cope with acetate and propionate load
with higher levels of nitrogen in the diet. Journet and Remond (1976)
observed that dairy cows increase their intake during the first part
of lactation in an attempt to adjust the intake of energy to their
needs. The increase in intake is longer with lower digestibility diets.
The authors found that lower intake is observed immediately after

calving which corresponds with high concentrations of plasma free

121

fatty acids from adipose tissue. Forbes (1980) suggests 2 theories that

can explain the effect of fat in intake control:

- there is a maximum rate at which adipose tissue can synthesize
triglycerides. When that limit is reached, receptors sensitive to
the energy level in the animal may start exerting their effects
depressing the intake .

- Lipolysis and lipogenesis occur at the same time. With fatter animals,
lipolysis occurs at a higher rate depressing intake.

The dynamic nature of the adipose tissue was discussed in detail by

Emery (1980).

3.6.4 Effect of grazing conditions on voluntary intake

 

Different pasture characteristics have been related to intake:
yield of herbage, homogeneity of the awards, height of plants and
density of the canopies. Animals select their diets when the herbage
allowance is high, incorporating additional variation to the estimation
of intake. Freer (1981) established that on homogeneous swards, animals
select the diet to consume through the breakdown of the selected
components rather than through any other factor. Hamilton et a1. (1973)
observed that when the yield of green herbage was 550 kg per hectare
or more, sheep select a diet with a higher digestibility than the mean
of green material offered. However, with less than 550 kg per hectare,
the digesta was less digestible than the green herbage on offer because
of the low proportion of that material consumed. Similar results were
reported by Greenhalgh and Reid (1968) with dairy cattle. Baker (1976),
Hodgson (1977) and Ellis (1978) review the literature on award

Characteristics that affect herbage intake under grazing conditions.

122

Total herbage production per unit area and herbage allowance have
been claimed as the most important factors affecting intake by grazing
animals. Allden and Whittaker (1970) have demonstrated that length of
tiller is much more closely related to availability of forage than
yield per acre, and as a consequence with intake of grazing animals.
Arnold and Dudzinski (1967a) reported that about 40 Z of the variation
in dry matter organic intake of legume-grass pastures by sheep was
accounted for by the total available dry matter per unit area.
Langlands and Bennet (1973) have shown that organic matter intake
increases with total herbage available per animal. Gibb and Tracher
(1976) observed an increase in intake with increasing herbage allowance.
The authors concluded that if the herbage present to ground level is
not more than 3 times the daily intake of the animals, intake may be
restricted. With more herbage allowance and without any system of
removing the excess of forage, total intake may decrease significantly
and the dead material accumulated can produce a decrease in quality of
the pasture and in intake as well. However, Greenhalgh et al. (1966,
1967) reported that dairy cows can obtain maximum intake (30 lbs of
dry matter) when the herbage allowance is only 50 Z higher than that
value (45 lbs). Troelsen and Campbell (1969) demonstrated the effect
of maturity and leafiness on the intake by sheep.

The bite size of grazing animals play an important role in intake.
Stobbs (1973a,b) found that award density with low stem content and a
high leaf/plant height ratio are the main factors that affect bite
size, and as a consequence, total intake. Stobbs (1973b) reported that
larger intake with regrowth periods of 4 weeks than with smaller periods,

due to a higher yield and density of the canopy.

123

4. Measurement of animal performance
Characteristics of the Holstein breed as beef producers
Different factors have made possible the utilization of dairy

breeds for meat production in the last few years (Stiles, 1971):

increase in population;

leaner carcasses than the British breeds;

utilization of low quality feeds; and

development of low cost systems of storing feedstuffs.

Kunkle and Cahill (1959) reported that when lbs of palatable lean
meat are of primary interest, dairy breed carcasses will be an
"important economic niche". Guss (1971) and Hallman (1971) make a
detailed review on the management factors to consider in order to
obtain a succesful operation in fattening dairy breed animals.

The first important characteristic to consider is the performance
of Holstein animals when compared to beef breeds. Miles at al. (1961a)
obtained average daily gains of 1.25 lbs for Holstein heifers kept
on irrigated legume-grass pastures. In a later paper, the authors
(1961b) compared the performance of Holstein calves on pastures and on
a diet containing 15 Z protein and found that after the first 28 days,
calves on pastures gained more than their contemporaries in the barn
(2.9 versus 2.8 lbs per day from day 29 to 56, and 2.7 versus 2.3 from
day 57 to 84, respectively). Hibbs et al. (1959) also proved that
dairy calves can be raised economically with a high roughage diet to
feeder age. However, as Griffiths (1980) established, higher daily
energy and protein gain, and higher efficiency of energy and protein

deposition is obtained with higher quality diets, regardless of lower

124

carcass meat deposition. Jacobson et a1. (1970) obtained average gains
per day above 1.32 lbs With yearling dairy cattle on pure stands of
orchardgrass, bromegrass and bluegrass. Kesler et al. (1975) reported
0.91 lbs of gain per day on permanent grass pastures with 4 months old
Holstein steers over 121 days. Stiles et al. (1970) observed higher
gains of Holstein steers grazing alfalfa than those fed alfalfa
greenchop and hay: 2.82, 2.16 and 2.62 lbs per day respectively.
Spahr et al. (1972) reported average daily gains above 1.1 lbs of
Holstein steers on a diet of alfalfa haylage and concentrate. Cole et
al. (1963) reported an average daily gain for Holstein steers of 2.16
lbs, 1.84 lbs for Hereford steers and 1.76 for Angus, from an
experiment that involved 5 years and 154 animals. Garciarde-Siles
et al. (1977) found that Holstein steers grew more efficiently and
faster than Hereford steers, reaching the slaughter weight at a
younger age. However, Garrett (1971) indicated that Hereford steers
are more efficient in converting energy consumed above maintenance to
energy stored as fat and protein. The author stated that the difference
in efficiency seemed to be related to the higher amount of fat gained
by Hereford steers. Hind (1978) observed that Holstein steers had
similar efficiency as Jersey Steers up to 12 weeks of age, but
thereafter the efficiency was higher for Holstein. Martin (1971)
observed that if an extra 0.24 lbs of gain per day equal an extra
carcass grade, there would appear to be little reason to use beef
breeds from the stand point of the total value of the finished animal.
Carcass characteristics have to be considered too. Breed differences

in edible portions have been reported by several authors. Judge and

125

Martin (1965) reported 8 Z more edible portion, 54 Z less excess fat
and 24 Z more bone for Holstein animals when compared with Angus.
Similar results were observed by Cole et al. (1964), Tyler (1970) and
Wellington (1971). Ziegler et a1. (1969) obtained higher cutability
percentage with Holstein steers than with Angus, Hereford and crossbred
animals. However, Branaman et al. (1962) did not find any differences
in percent separable lean or high-priced wholesale cuts between
Holstein, Hereford and Shorthorn. Hedrick (1968) reported that the
major difference between beef and dairy breeds is the way the fat is
distributed in the different fat depots: dairy breeds have a higher
percentage of kidney and pelvic fat and a smaller proportion of
subcutaneous fat. Almquist et al. (1971) found that up to 227 kg

(500 lbs) of body weight, gain of muscle tissue is greater than that
of fat or bone. At heavier weights, fat deposition increases

markedly.

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MATERIALS AND METHODS

Livestock

Two groups of yearling Holstein steers from the same farm were used
for the experiment during both years. Forty seven steers were used in
year one and forty eight in year two. The steers were randomly assigned
to four treatments in both years, resulting in twelve steers per treatment
except in year one when treatment four (Kentucky bluegrass) had only
eleven. The steers were then divided in three replications of four animals
per treatment. The treatments and initial average body weights are shown
in Table 4.

The steers were transported to Lake City Experiment Station in April
of 1981 and in May of 1982. They were fed alfalfa hay for approximately
20 days before the pretreatment period started. Once the pastures were
ready to be grazed, t11e steers were moved to their respective pens for
the pretreatment grazing period. The basic objective of this management
system was to eliminate the effects that the previous feeding program
could have on the performance of the animals on the pastures to be tested
during the initial time. Steers on treatment 1, 3 and 4 grazed their
corresponding pastures. However, the steers on treatment 2 grazed the rye
during both years to be able to seed the sorghum on time. Nineteen and
23 days of pretreatment periods were assigned during year 1 and 2
respectively.

The steers were treated against worms each year before the

initiation of the esperiment. They were also implanted with Ralgro

126

127

Table 4: AVERAGE BODY WEIGHT AND STANDARD ERROR AT THE BEGINNING OF

THE EXPERIMENT IN 1981 and 1982 (in kilograms).

TREATMENT

Alfalfa-Grass
Triple System
Birdsfoot trefoil-Grass

Kentucky bluegrass

Overall Mean

YEAR 1

281.04 : 2.59
290.68 i 0.68
292.95 1 3.91

289.42 t 5.75

288.52

YEAR 2

304.85 1- 1.24
320.92 1" 1.18
311.47 1- 2.54

314.31 t 1.05

312.89

(Zeranol). Pellets were implanted at one inch of the base of the ear,
at the beginning of each experimental period. The de-worming and
implanting of the growth stimulant were done on June 12th for year
one, and on June 16th for year two.

The animals were weighed every time movement to a new pen was
required for the two treatments under rotational grazing (treatments
one and two). On the average, steers were weighed approximately once
every two weeks. In order to minimize weight variations due to gut
fill, animals were fasted for 14 to 16 hours prior to weighing,
according to recommendations of Hughes (1976) and Matches (1981).
Animals were always weighed between 7 and 8.30 A.Mg. Table 5 shows

the weigh schedule for both experimental periods (year 1 and year 2).

128

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Forages
Four different pasture systems were tested during the two seasons:
1981 and 1982.

a.- Treatment 1: Alfalfa (Medicago sativa var Iroquios) - Orchardgrass

 

(Dactylis glomerata var. Potomac). Each replication (pen) of this

 

pasture was divided in three subpens to be grazed rotationally.
Seeding rate: 13.00 kg per ha of alfalfa and 2.60 kg per ha of
orchardgrass.

b.- Treatment 2: This system is a combination of three different mixtures:
b.1.— Alfalfa - Orchardgrass. Similar seeding rates than in treatment 1.

b.2.- Birdsfoot trefoil (Lotus corniculatus var. Viking) - Tall fescue

 

(Festuca arundinacea var. Kentucky 31). Seeding rate: 6.70 and

 

5.80 kg per ha respectively.

- b.3.- Rye (Secale cereale var. Wheeler) — Sorghum sudan hybrid (Sorghum

 

 

 

vulgare x Sorghum sudanense var. Jacques). Seeding rate: 2.1

bu per acre for rye and 26.80 kg per ha for sorghum.
This system provided for three subpens, each one seeded with a dif-
ferent mixture. It was rotationally grazed, with the Rye only being
used for the pretreatment periods during both grazing seasons. Sorghum
provided for only one grazing period in both years: from August 10th
to August 23rd in year one, and from August 3rd to 17th in year two.
Alfalfa-orchardgrass provided for three grazing periods in year one
(June 12th - 22nd, July 24th - August 9th, September 8th - 28th),
and two grazing periods in year two (June 30th - July 19th, August
17th - 30th). Birdsfoot trefoil - grass provided for two grazing
periods in year one (June 29th - July 23rd, August 25th - September
7th), and three grazing periods in year two (June 17th - 29th, July

20th - August 2nd, August Blst - September let).

130

c.- Treatment 3: Birdsfoot trefoil - Orchardgrass - Bromegrass (Bromus
inermis var. Fischer). Seeding rate: 6.70, 1.60 and 1.60 kg per ha
respectively. This system was continuously grazed during both years.

d.- Treatment 4: Kentucky bluegrass (Poa pratensis) under continuous

 

grazing. Seeding rate: 13.20 kg per ha.

Each treatment was randomly replicated in three different pens.
Figure 2 shows the distribution of the different pens in the experimental
area. The area of the different pens is shown in Table 6. Electrified
fences were used to separate pens. The original design provided for one-
strand wire electric fence and one alternator to convert direct to
alternating current. Due to trespassing problems in certain areas, a
second alternator was added at the beginning of year one, and another
strand of wire was also installed in those problematic areas. However,
no problems were encountered the second year, and only one alternator
was used in 1982.

Permanent seedings were made in July 1980. Weeds were supressed
by tillage alone, without the addition of herbicides to any pen. Rye
was seeded in September 1980 and 1981. The ground was disked and seeded
to Sorghum in June 1981 and 1982. Due to the dry summer in 1981 it was
necessary to reseed the Sorghum at the end of June of that year.
Treatments 1, 2 and 3 were fertilized with lime and phosphorus at the
beginning of 1981 according to soil test results, in such a way to
start the experiment with the same levels of those elements in the

soil.

Water supply

 

The experimental area did not provide any natural water streams.
Fifty-gallon water tanks were located in every pen with an automatic

shut-off system to assure constant water supply to the animals. For

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132

TABLE 6: AVERAGE AREA IN ACRES AND HECTARES PER TREATMENT.

Acres Hectares

Treatment Pen 1 2.99 1.2100
Treatment Pen 2 2.92 1.1817
Treatment Pen 3 3.63 1.4690

Average 3.18 1.2869
Treatment Pen 1 2.86 1.1574
Treatment Pen 2 2.90 1.1736
Treatment Pen 3 2.97 1.2019

Average 2.91 1.1776
Treatment Pen 1 3.28 1.3274
Treatment Pen 2 3.36 1.3598
Treatment Pen 3 2.69 1.0886

Average 3.11 1.2586
Treatment Pen 1 4.45 1.8009
Treatment Pen 2 3.12 1.2626
Treatment Pen 3 4.23 1.7119

Average 3.93 1.5918

TOTAL 39.40 15.9448

133

those treatments under rotational grazing systems, the tank was moved
to a new pen every time steers were allocated to fresh pastures. The
water source was the same one used for the other livestock in the

Station.

Trace mineralized salt

 

Mineralized blocks were provided during both years. They were
located near the water tanks allowing the steers free access. Table 7

shows the mineral composition of the blocks in both experimental years.

TABLE 7: MINERAL COMPOSITION OF TRACE MINERALIZED SALT BLOCKS.

Year 1 (MORTON) Year 2 (HARDY)
Salt 98.0 Z 99.5 Z
Salt 95.0 Z 99.0 Z
Zinc 0.35 Z Not specified
Manganese 0.28 Z Not specified
Iron 0.175 Z Not specified
COpper 0.035 Z Not specified
Iodine 0.007 Z 0.011 Z
Cobalt 0.007 Z Not specified

The ingredients specified in the blocks were:

Morton: Sodium chloride, zinc oxide, manganous oxide, ferrous carbonate,
iron oxide, copper oxide, calcium periodate, cobalt carbonate,
calcium chloride.

Hardy: Sodium chloride, calcium iodate, calcium stearate, red iron oxide

color.

134

Pasture management

The initial number of steers was exactly the same (by design) for all
treatments and pens. For the two continuous grazing treatments (three
and four) the relationship between the available dry matter per steer
was higher than for the treatments under rotational grazing (one and
two) at the beginning of the two experimental seasons. This management
system allowed the steers to be more selective under the continuous
grazing systems at the beginning of each season. However, at the end
of both years, this practice produced a shortage in dry matter availa-
ble per steer in both continuous grazing treatments, being more pronoun-
ced for treatment three.

The steers on the two rotational systems were moved to new pastu-
res every twelve to fifteen days. This system was established conside-
ring that alfalfa is better managed when four to six weeks of rest are
assured. When dry matter production declined in both seasons, steers
were taken off the experimental area following the management strategy
explained above .

Clipping was also used as part of the pasture management system
to control quantity and quality of the pasture. Due to a high forage
production early during the second year, it was required to clip the
pens allocated to treatment one, after the first grazing was finished.
This practice was done only once to every subpen of alfalfa - grass
mixture in June and July. The basic reason to clip those areas was to
eliminate the less palatable and digestible forage and decrease the

competition from grasses and to allow alfalfa to grow.

135

Forage sampling

 

Three different pasture samples were obtained from the two rota-
tional systems (treatments 1 and 2) every time steers were moved into
fresh pastures:

a.- two square meters were obtained from the new pastures. This sample
is termed as available forage before animals start grazing.

b.— Two square meters were also collected from the pastures grazed at
themoment steers were moved out. This sample constitutes the forage
left uneaten after a grazing period.

c.- Two square meters from protected areas (forage inside cages not
available for the steers) to measure the growth of the pastures
during the grazing period. To achieve this objective, two metal cages
were placed in the pens before the steers were moved in. The size of
the cages was 1.5 meters long, 1.2 meters wide and 1.7 meters height.

For the two treatments under continuous grazing, a total of six to
eight cages were placed on the pastures. Approximately once every thirty
days two-square-meter samples were taken from outside and inside of the
cages. The outside sample represented the remaining forage for the
preceding grazing period, while the inside sample was utilized to measure
growth. At the same time, the outside sample represented the available
forage for the following grazing period.

The two square meter samples of every treatment were combined in
a composite sample in such a way that for every pen within treatment
three samplesfor each time were obtained: available forage, rejected
forage and forage from inside the cages to measure growth of the pasture
during the specific grazing time. Samples were then sealed in plastic bags,
labeled and stored in a freezer for subsequent analysis.

A square meter made of strong metal was used to collect the samples.

136

It was placed on the ground in representative areas of the pen. The
samples were then cut by hand using a curved knife. All the plants
with the main stem in the square meter were harvested, but those with
the main stem outside were not, independently of the percentage of the
aerial part that remained inside. The samples were cut at a height
similar to the height animals graze: 1 to 2 inches. The sample cuts
were always done by the same person in order to minimize the errors in
forage harvesting.

The sample collection for the two rotational grazing systems
always coincided with the dates animals were weighed. However, for the
two continuous systems, forages were collected in times 1, 3, 5, 6 and

7 during both experimental seasons.

Forage sample preparation

 

Plastic bags were taken from the freezer, thawed and the following
procedures were performed:

a.- weigh the samples using a laboratory scale;

b.- mix the sample and obtain 300 or more grams of subsamples to analyze

them for botanical composition;

c.- obtain an additional 500 grams subsample and chop it to one-two inches

length. Two hundred grams were then separated for dry matter analysis,

100 to 150 grams were utilized for additional analysis for which they

were air dried at ambient temperature, and the rest was placed back

in the freezer;

d.- after the subsamples were air dried, they were ground at 0.5 mm using

a Wiley mill. These ground samples were in turn used for chemical

analysis.

137

Forage analysis

 

a.- Botanical composition:

 

Analysis of the species composition was performed for the different
treatments. For treatments 1, 3 and 4, the analysis was done approxima-
tely every month, but for treatment 2 it was performed every time steers
were moved to a new pen. This was done because of the fact that every
pen was seeded with a different mixture: In order to analyze the trends
in legume percentages in treatments 2 and 3, botanical composition was
studied inside and outside the cages. The composition of the different
pastures at the beginning of the experiment in years 1 and 2 is shown
in Table 8. The basic purpose in analyzing the legume percentage inside
and outside of the cages in both treatments (2 and 3) was to study the
behavior of the legumes when short period rotational practices are
imposed to the system (treatment 2), and under continuous grazing
(treatment 3).

For the species composition analysis, plant speceis were hand
separated and weighed. Results were reported on green matter basis free
of weeds. Weed invasion was only observed in treatment 4, and especially
in pen 2.

b.- Dry matter:

 

Dry matter was determined by drying approximately 200 grams of
samples in a forced air oven at 100 degrees centigrade for forty-eight
hours. Every sample was analyzed in duplicate and the average between the
two was taken as the value for the pen.

c.- In vitro dry matter digestibility

 

In vitro dry matter digestibility analysis were made by a modified

(Goering and Van Soest, 1970) Tilley and Terry method (Tilley and Terry,

138

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139

1963). The rumen liquid was obtained from a fistulated Holstein cow
fed alfalfa hay. The procedure consists of two stages of digestion:
forty-eight hours with rumen inoculum followed by forty eight hours of
digestion with pepsin. The initial values for the different treatments

are shown in Table 9.

TABLE 9: MEANS AND STANDARD ERRORS FOR IN VITRO DRY MATTER DIGESTIBILITY

AT THE BEGINNING OF THE EXPERIMENT IN BOTH YEARS (IN Z).

Year 1 Year 2
Treatment 1 65.36 t 3.60 54.79 i 0.19
Treatment 2 58.34 t 1.74 62.95 i 1.31
Treatment 3 54.34 t 1.23 52.03 t 1.96
Treatment 4 54.17 i 0.27 55.32 i 0.89

d.- Intake

Intake per steer per day was determined using zamethod (method 2)
developed by Lineham et al. (1952). This method provides for a more
accurate measure of intake by animals than the other "difference methods"
proposed, because it considers the growth of the forages during the
grazing period.

The formula used provides for three different forage samples:

available forage, remaining forage left uneaten by the animals and

forage harvested from inside the cages.

140

 

Amount of grass nutrients (LOG D - LOG F)
= (C-F)

consumed by animals (LOG C - LOG F)

where

C is the quantity of grass nutrients present at the beginning og
grazing,

F is the quantity of grass nutrients left uneaten in the grazed
area at the end of the grazing period,

D is the quantity of grass nutrients present in cages at the end
of the grazing period,

LOG are logarithms in base ten.

C, D, F are expressed in kilograms of dry matter when dry matter

intake by the animals is being measured.

For treatments one and two, these three factors can be easily
identified. For treatments three and four, the quantity of grass uneaten
in time t becomes the available grass nutrients at the beginning of the
grazing period in time t + 1. It is also important to adjust the value
of the pasture growth for the different times. Since the cages were
set up on the field at the beginning of the experimental periods, D in
time t is always expressed as the difference between that value and the

value of D at time t - 1, starting from the second sampling period.

141

Statistical analysis

Two different models were used to test animal and forage characte-
ristics, in a split-plot design with repeat measures (Gill, 1978b). For
the liveweight gain data, animals were utilized as the observational
units and pens within treatments as the sampling units. Forages were ana-
lyzed for different traits: dry matter offered, in vitro dry matter di-
gestibility and intake of dry matter. Dry matter offered was expressed
as kilograms per hectare for the different treatments.

The analysis of variance for liveweight gain.was according to the

following model (liveweight gain model) :

yijkl = u + covariate ‘1' A1 + Bj + (AB)ij + C(ij)k '1' D(j)1 ‘1' (AD) (j)11

where
yijkl is the observed value at the l£h_time within year, kph.
pen within treatment, j£h_year and i£h_treatment;
u is the overall mean;

covariate is the average weight of the steers in a pen at the

beginning of both years;

A1 is the fixed effect of the iEQDtreatment, i=1,2,3,4;
33 is the random effect of the j£h_year, j=1,2;

(AB)1j is the interaction of treatment and year;

C(ij)k is the random effect of the k£h_groups of animals or

pen within treatment and year, k=1,2,3;

D(j)1 is the fixed effect of the 15h time within year,
l=1,2,...,9;

(AD)(j)11 is the interaction treatment and time within year.

Three error terms can be identified in this model using the formu-

142

lation of the expected mean squares developed by Gill (1978b):
an. (AD) (1)11 to tESt for D(j)1 ;
b.- C(ij)k to test for Bj and (AB)iJ ; and

c.- (AB)ij to test for A1 .

The analysis of variance for forage characteristics was according

to the following model (forage model):

yijkl I u + A1 + Bj +>(AB)ij + C(i)k + (BC)(i)jk + D(j)l + (AD)(j)11 +

(CD)<1j>k1
where
yijkl is the observed value of the l£h_time within year,
kph pen within treatment, j£h_year and igg treatment;
u is the overall mean;
C(i)k is the random effect of the k£h_pen within treatment;

(BC)(i)jk is the effect of the interaction year-pen within treat-
ment;
(CD)(1j)kl is the effect of the interaction pen within treatment-
time within year; and
A1, Bj, (AB)ij’ D(j)1, and (AD)(j)11 are as previously described.
Three error terms can be identified in this model using the formula-
tion of the expected mean squares (Gill, 1978b):

3,- (CD)(ij)kl to test for (AD)(j)11 , and D(3)1 3

b.- (BC)(i)jk to test for C(i)k , (AB)1j , and 81 ; and

c.- adjusted mean square error to test for treatment effects (A1). The ad-

justed mean square error is defined as the mean square of (AB)1j plus

the mean square of C(i)k minus the mean square of (BC)(i)jk .

RESULTS

1. Botanical composition

Species composition of the available forage was analyzed for
every treatment. Each pen within treatment was analyzed separately,
and the average between the three was taken as the mean for the
treatment. Tables 10 and 11 present means and standard errors for
legume percentages in treatments 1, 2 and 3. For treatments 1 and 2
these values represent the legume percentages of forage samples taken
before grazing started. For treatment 3, the legume percentage repre-
sents the composition of the forage at a point in time since steers
continuously grazed the pasture.

Figures 3 and 4 show the trends in the legume percentage in
treatments 1, 2 and 3 for years one and two. With the exception of
birdsfoot trefoil in treatment 2, the tendencies in both years were
different. In year one, alfalfa from both treatments shows similar
trends and values. The tendencies in both treatments is to decrease
with time, regardless of a not significant (N.S.) increase in
treatment 2. The decline is more pronounced from time three on, for
both treatments. Birdsfoot trefoil also show the same behavior,
regardless of the treatment and of the important differences in value.

In year two, both alfalfas increase in percentage at the beginning,

143

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'_,.—-\ Trt. 2 °----(Birdsfoot)
3s "
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Figure 3: LEGUME COMPOSITION FOR THE DIFFERENT TREATMENTS. YEAR 1.

45

40

35

LEGUME PERCENTAGE

30

25

20

15

10

 

147

 

Trt. 1
Trt. 2 - - - (Alfalfa)
Trt. 2 °°°°° (Birdsfoot)
Trt. 3 ---------
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Figure 4: LEGUME COMPOSITION FOR THE DIFFERENT TREATMENTS. YEAR 2.

148

having a higher percentage in treatment 1 up to time three. After this
time, the alfalfa from the first treatment suffered a sharp decline,
while the one from treatment 2 kept augmenting to readh time five with
a very small difference between them of 1.52 percentage units. However,
the two birdsfoot trefoils had a different trend in time. Up to time
three, the legume in treatment 2 decreased and the legume from treat-
ment 3 inereased, both with a moderate slope. However, treatment 3

had an increase of 126 percent between times three and five, to decline
again by time six. On the other hand, birdsfoot trefoil from treat-
ment 2 increased 0.50 units of percentage from time three to the end

of the experiment.

2. Dry matter offered

Dry matter offered was analyzed by the forage model. Means and
standard errors are presented in Tables 12 and 13 for year one and
two respectively. The following factors showed significance (P<’0.05):
year, treatment, time within year and the interaction treatment-time
within year. Figures 5 and 6 present dry matter offered per treatment
for both years. Treatments 1 and 3 show a decrease in dry matter
offered throughout the season in both years. Treatment 4 presents a
small increase between times one and three during year one, and a
marked decrease thereafter. However, it had an important decrease from
time one and three the second year, and an increase up to time five.
Treatment 2 showed two marked peaks in year one (times two and four)
and a large peak in time six during year two.
Year and treatment effects

Non-orthogonal contrasts were established to test for year and

treatment effects. The only contrasts to test year effect is average

149

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151

Trt. 1

Trt. 2 - - - -

6,500

6,000

5,500 “

5,000 A

4,500

KILOGRAMS PER HECTARE

4,000 4,

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TIME

Figure 5: DRY MATTER OFFERED FOR THE DIFFERENT TREATMENTS. YEAR 1.

152

      

 

 

4,500 4*
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TIME

Figure 6: DRY MATTER OFFERED FOR THE DIFFERENT TREATMENTS. YEAR 2.

153

dry matter offered in year one versus year two. It is possible to
observe that there was an almost 36 percent more dry matter offered

in year one. To test for treatment effects one contrast was performed:
improved rotational grazing system versus continuous system (treat-
ments 1 and 2 versus 3 and 4). The dry matter offered during the

second year was less variable between treatments, and as a consequence,
no significant effects were found (P<f0.05). However, there was a
significant difference between the treatments involved, resulting in

29 percent more dry matter in the two rotational improved systems
(P<:0.05). Table 14 summarizes the means for treatment and year effects

for dry matter offered.

Table 14: DRY MATTER OFFERED FOR THE DIFFERENT TREATMENTS DURING

YEAR ONE AND TWO: KG/HA.

YEAR 1 YEAR 2
TREATMENT 1 3,970‘51 2,7803
TREATMENT 2 3,3783 2,5743
TREATMENT 3 2,980b 2,410‘El
TREATMENT 4 2,700b 1,820a
MEAN PER YEAR 3,260c 2,400d

a,b: Means within columns with different superscripts differ
significantly (P < 0 . 05).

c,d: Means within the same row with different superscripts differ
significantly (P<’0.05).

Contrasts: Year effect: year one versus year two

Treatment effect: Treatments 1 and 2 versus 3 and 4

154

Time withingyear.

Three times were selected to be used in the comparisons: times
one, three and six. Three different contrasts were selected and tested
every year using Scheffe's test:

- time one versus three;
- time one versus six;

time three versus six.

Time effect was only significant (P<?0.10) in year one. There is
a tendency in decreased dry matter offered with time, being almost
93 Z higher in time one than in time six during the first year. Time
three was intermediate between times one and six, but was not signifi-
cantly different from any one of them. In year two there was a
decrease with time between time one and three, but it tended to
increase in time six. Dry matter in time one was 42 and 38 percent
higher than in time three and six respectively, but these differences
were not statitically different (P<:0.10). Table 15 presents the dry

matter offered for year one and two for time one, three and six.

Table 15: MEANS FOR DRY MATTER OFFERED ACROSS TREATMENTS FOR BOTH

YEARS IN TIME ONE, THREE AND SIX: KG/HA.

Time 1 Time 3 Time 6
Year 1 4,7428 3,540ab 2,459b
Year 2 3,6198 2,5578 2,6188

Means within rows with different superscripts differ significantly

(P< 0.10).

155

Treatment-time within year

To analyze the effect of the interaction treatment-time within
year, three times were selected: one, three and six. In this case the
three improved pastures (treatments 1, 2 and 3) were compared with
treatment 4 for every time and year. In year one, treatment effects
were statistically different in time one (P 0.10). In this case,
treatment 1 differed from all other treatments except 2. Treatment 2
differed from treatment 4 but not 3, and finally, treatments 3 and 4
did not show significant differences. In terms of percentages, treat-
ment 1 offered 51 and 108 percent more dry matter than 3 and 4 respec-
tively. At the same time, treatment 2 offered 62 percent more dry
matter than treatment 4. During the second year, treatments did not
differ in times one and six, but they did in time three. In the
latter, treatment 3 offered more kilograms of dry matter per hectare
than the others, followed by treatment 2, 1 and 4. The only significant
differences occured between three and four, and between two and four.
Table 16 shows the summary of the effects of the interaction treat-

ment-time within year.

3. In vitro dry matter digestibigsl

In vitro dry matter digestibility was analyzed by the forage
model. Means and standard errors are presented in Tables 17 and 18
for years one and two respectively. Treatment, the interaction year-
treatment, time within year and the interaction treatment-time
within year were the only factors that showed statistical effects
(P<:0.05). Figures 7 and 8 present the values for in vitro dry matter

digestibility for year one and two respectively. Treatments show a

156

TABLE 16: DRY MATTER OFFERED PER TREATMENT IN YEARS ONE AND TWO
AND IN TIMES ONE, THREE AND SIX: IN KILOGRAMS OF DRY

MATTER PER HECTARE.

YEAR TREATMENT TIME 1 TIME 3 TIME 6
1 1 6,4943 4,431a 2,2578
1 2 5,060ac 3,1648 2,2278
1 3 4,296bc 3,5998 2,8878
1 4 3,120b 3,1818 2,4678
2 1 4,471a 2,642ac 2,0908
2 2 3,8628 3,0238 3,411a
2 3 3,8028 3,0698 2,7188
2 4 2,3428 1,494bc 2,253a

Means within the same column and year with different

differ significantly (P< O. 10)

Contrasts: Treatment 1 versus 4

Treatment 2 versus 4

Treatment 3 versus 4

Every contrast was performed within year and time

superscripts

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IN VITRO DRY MATTER DIGESTIBILITY FOR THE DIFFERENT

TREATMENTS. YEAR 1.

160

 

 

 

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Figure 8: IN VITRO DRY MATTER DIGESTIBILITY FOR THE DIFFERENT

TREATMENTS. YEAR 2.

161

similar trends in both years: digestibility tends to decline with
time. Larger variations were obtained with treatments 1 and 2.

Treatment effects

 

Three non-orthogonal contrasts were established to test for
treatment effects:

- rotational versus continuous grazing systems (treatments 1 and 2
versus 3 and 4);

- improved pastures with rotational grazing systems versus non-
improved forages and continuous grazing (treatments 1 and 2 versus
4);

- the best improved system versus control (treatment 2 versus 4).

The analysis was performed using the mean values per treatment for

both years, and the pooled values across years since the year effect

did not show any significance.

Table 19 presents the comparative analysis for treatment effects.

As a result of the contrasts established, there is a significant

difference (P<:0.05) between the two improved pastures under rotational

grazing systems and the two treatments with continuous grazing. The
material from the rotational grazing plots had a 27 and 21 percent
more digestibility than the latter ones in year one and two respec-
tively, with an average of 24 percent when the data from both years
were pooled.

Time within year

 

Three times were chosen to test for time effect: times one, three
seven. Non—orthogonal contrasts were performed to test time one versus

time seven, time one versus three and three versus seven. Similar

162

Table 19: IN VITRO DRY MATTER DIGESTIBILITY FOR THE FOUR TREAT-

MENTS IN YEAR ONE AND TWO: IN PERCENTAGES.

Treatment Year 1 Year 2 Average
1 56.00a 53.308 54.653
2 55.838 58.668 57.258
3 45.17b 46.03b 45.60b
4 43.13b 46.33b 44.73b

Means within the same row with different superscripts are

significantly different (P< 0.05).

Contrasts analyzed: Treatments 1 and 2 versus 3 and 4
Treatments 1 and 2 versus 4

Treatment 2 versus 4

results were obtained for both years: the only significant difference
was obtained between time one and the other two times (P<:0.05) (Table
20). The digestibility values decreased from time one toward the end
of the experiment in both years: 11 and 15 percent in year one, and
11 and 13 percent in year two, for times three and seven respectively
(Figure 9).
Treatment-time within year

To test for the effect of the interaction treatment-time within
year, times one, three and seven were chosen. Non-orthogonal contrasts
comparing all the possible means were established in order to detect

the differences between all the treatment means. Tuckey's test modified

163

55

DIGESTIBILITY (Z)

53

51 1’

49 7.

47 ..

 

43 «P

 

Figure 9: IN VITRO DRY MATTER DIGESTIBILITY. THE VALUES ARE
AVERAGES ACROSS TREATMENTS FOR EACH SAMPLING TIME

FOR YEARS ONE AND TWO.

164

Table 20: IN VITRO DRY MATTER DIGESTIBILITY OF DRY MATTER ACROSS

TREATMENTS FOR TIMES ONE, THREE AND SEVEN. IN PERCENTAGE.

Time 1 Time 3 Time 7
Year 1 57.30a 50.97b 48.45b
Year 2 56.27C 50.17d 49.15d

Means within the same row with different superscripts differ

significantly (P < O. 05) .

for the degree of unbalance was utilized. The trends for all treat-
ments were the same in both years: digestibility declines with time.
In year one treatment I kept the highest digestibility throughout the
entire period except in time four (Figure 7). Treatment 2 had the next
highest values, while treatments 3 and 4 started with similar values
but the decrease was fastest for the latter. In time one, only
treatment 1 was significantly different than 3 and 4 (P<:0.05), but

in time three treatment 2 showed a significant difference with treat-
ments 3 and 4. In time seven the same situation occurred, but because
of a larger decline in digestibility for treatment 2, there was also

a significant difference between treatments 1 and 2 (Table 21).

During year two, treatment 2 maintained the highest digestibilities
for the entire period followed by treatment 1, 4 and 3 (Figure 8). In
time one, treatment 2 was significantly different than the other three
treatments (P<:0.05). However, in time three due to the lowest value

for treatment 3, treatments 1 and 2 showed a significant difference

165

Table 21: DIGESTIBILITY VALUES FOR THE DIFFERENT TREATMENTS IN

YEAR ONE AND TWO: IN PERCENTAGES.

Year Treatment Year 1 Year 3 Year 7
1 1 62.368 60.168 58.088
1 2 58.348b 56.178 50.25c
1 3 54.34b 46.63b 43.20b
1 4 54.17b 40.92b 42.25b
2 1 54.798 53.348 50.28c
2 2 62.95b 54.468 56.998
2 3 52.038 44.71bc 42.84b
2 p 4 55.328 48.178C 46.49bC

Means within the same column and year with different superscripts

are significantly different (P1<O.05).

with it but not with treatment 4. Finally, in time seven treatment
2 showed a significant difference with the other three treatments,
while treatment 1 showed significance only with treatment 3 (Table

21).

4. Intake
Intake per animal was analyzed with the forage model. Tables 22
and 23 give means and standard errors for intake per steer per day

(in kilograms of dry matter) for year one and two respectively. No

166

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168

significant differences for year or treatment or treatment—year
interaction were found. However, the effect of time within year

and the interaction treatment-time within year were highly signifi-
cant (P<I0.01). Figures 10 and 11 show the intake per treatment
during year one and two respectively. During year one, intakes in
treatments 1, 3 and 4 increased with time, being higher for treatment
1. However, steers in treatment 2 showed a similar pattern up to time
four, then declined to time five. During year two the trends were
different. Steers in treatment 1 increased their intake to time four
and showed a decline by time five and another one in times seven and
eight, after an important increase in time six. Treatments 2 and 3
showed a similar pattern. Steers increased their intake up to time
three to decline thereafter. On the other hand, steers on treatment

4 declined their intake for the first month (times one, two and three),
and then increased to time five where they leveled off.

To analyze the effect of time within year, non-orthogonal
contrasts were performed using only times one, three and six for both
years. The values utilized were means across treatments for the times
especified above. Table 24 gives the summary of the analysis performed.
From the table it is possible to observe that only intakes in times
one and six are significantly different (P<IO.10) in year one. However,
there is not enough confidence to establish any significant difference
between times in year two.

The interaction time within year-treatment was also significant
(P< 0.01). To analyze this effect three contrasts were established:

— improved versus non-improved pastures (treatments 1, 2, 3 vs. 4);

169

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KILOGRAMS PER DAY
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TIME

Figure 10: DAILY INTAKE PER STEER FOR THE DIFFERENT TREATMENTS.

IN DRY MATTER. YEAR ONE.

15

14

12

10

INTAKE: KILOGRAMS PER DAY.

 

170

 

Trt. 2 - - - -
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Figure 11: DAILY INTAKE PER STEER FOR THE DIFFERENT TREATMENTS.

IN DRY MATTER. YEAR TWO.

 

171

Table 24: INTAKES ACROSS TREATMENTS FOR TIMES ONE, THREE, SIX:

KILOGRAMS OF DRY MATTER PER STEER PER DAY.

Time 1 Time 3 Time 6
Year 1 3.958 8.05ab 10.38b
Year 2 7.688 8.798 8.628

Means with different superscripts in the same row are significantly
different (P< 0.10)
Contrasts performed: Time one versus three

Time one versus six

Time three versus six

Times one + three versus six

- rotational versus continuous grazing systems (treatments 1 and 2
versus 3 and 4);

- rotational and improved versus continuous and non-improved pastures
(treatments 1 and 2 versus 4).

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cant difference when compared with 3 and 4 (P<:0.10). In year two,

treatment differences showed significance (P< 0.10) only in time

three. In this case, the three improved pastures did not differ from

each other, but presented a significant difference with the non-improved

system (treatment 4).

Table 25:

172

MEANS FOR INTAKE FOR THE DIFFERENT TREATMENTS IN YEAR

ONE AND TWO, AND TIMES ONE, THREE AND SIX: KILOGRAMS

OF DRY MATTER PER STEER PER DAY.

YEAR

TREATMENT

TIME 1

2.17a
5.12a
3.10a

5.398

9.458
5.228
8.20a

7.84a

TIME 3

10.278
9.628
6.358

5.95a

10.003
10.518
10.90a

3.74b

TIME 6

14.778
12.308
8.30b

6.14b

12.588
6.90
8.163

6.82

Means in the same column each year with a different superscript

differ significantly

(P<0.10).

173

5~Lninele

The animal data were analyzed according to the liveweight gain

model. Year and weightday within year ‘were the only factors that
showed significant effects in the model (P<(0.05). The covariate ef-
fect was highly significant (P<:0.01), which confirms the importance
of adjusting the model for the initial weight of the steers at the

beginning of the experimental periods.

Treatment effects:
Figures 12 and 13 show the average weight gain per treatment
for years one and two respectively. Average gain per treatment is defin-

ed as the product between average daily gain per steer within pen, the
number of steers maintained per pen and the number of days in each

specific time. Three values were obtained per treatment (one value per
pen), and the value reported is an average of the three for each spe-
cific time.

The tendencies for this variable were different between year one
and two. Year one is characterized by large variations between times,
with large differences between maximum and minimum.peaks. Times one,
four and six show maximum.peaks for all treatments, and times two
and five minimum peaks. Treatment one produces the most gain from
time one to two, and from time five to the end of the experiment.
Treatments three has the highest peak in time four with almost 118
kilograms of total gain which represents 18, 44 and 97 percent more

kilograms of liveweight produced than treatment one, two and four

respectively.

174

KILOGRAMS OF LIVEWEIGHT GAIN

 

Trt. 1
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TIME

Figure 12: TOTAL LIVEWEIGHT GAIN PER TREATMENT IN YEAR ONE.

175

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TIME

Figure 13: TOTAL LIVEWEIGHT GAIN PER TREATMENT IN YEAR TWO.

176

The tendencies in year two were different than in year one.
Variations in liveweight gain were not as large in year one for
treatments one and four. Treatments one, three and four had a maxi-

mum peak in time four, and then total gain per treatment started to

decrease until the end of the grazing period. However, treatment 2 showed

a large variation throughout the entire year with higher peaks and
lower valleys than treatments one and four.

No significant differences in total liveweight gain were found bet-
ween treatments (P<C0.10). Analyzing the expected mean squares, the er-
ror term for treatment effects is the interaction between treatment-year
with only three degrees of freedom in an experiment with 734 total de-
grees of freedom. Looking at the upper percentage points of F distri-
bution (Gill, 1978c), it is possible to realize that with an additional
degree of freedom for the error term, treatment effects appeared as
significant (Pxi0.10). Based on this fact, non-orthogonal contrasts
were established to compare the treatment effects using average live-
weight gain per treatment per time. This parameter is defined as the
summation of the average gain per treatment divided by the total number
of days the experiment lasted in years one and two.

Table 26 shows the summary of the comparisons made. Three non-or-
thogonal contrasts were performed to analyze treatment differences:
treatment one versus treatment four, treatment two versus treatment four,
and treatment three versus treatment four. Treatments one and four

marginaly differed (P 0.10) in average liveweight gain per time, dur-

ing both years. The other contrasts did not show any significance.

177

Table 26: AVERAGE LIVEEEIGHT GAIN PER TREATMENT PER TIME IN YEAR

ONE AND TWO: IN KILOGRAMS.

YEAR 1 YEAR 2 INCREMENT (z)
TREATMENT 1 46.958 58.32"”1 25.29
TREATMENT 2 32.00ab 50.658b 58.27
TREATMENT 3 30.328b 37.898‘) 24.97
TREATMENT 4 26.77b 30.07b 12.35
OVERALL MEAN 34.01 44.36 30.22

Means within columns with different superscripts are significantly
different (P < 0. 10).
Contrasts tested: Treatment 1 versus 4

Treatment 2 versus 4

Treatment 3 versus 4

Treatment one produced 57 and 51 percent more kilograms of liveweight
gain per time than treatment four during year one and two respectively.
All treatments produced more liveweight gain during year two.

An additional analysis was performed to test for the effect of
liveweight gain per hectare according to the model for liveweight gain.
Means and standard errors for liveweight gain per hectare per treat-
ment and year are shown in Tables 27 and 28. Treatment, year, treatment-
year interaction and the interaction treatment-time within year

showed significant effects (P<I0.10). Figures 14 and 15 present

178

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Figure 14: ACCUMULATED LIVEWEIGHT GAIN IN YEAR ONE.

181

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ACCUMULATED KILOGRAMS OF BODY GAIN PER HECTARE

60.»

 

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Figure 15: ACCUMULATED LIVEWEIGHT GAIN IN YEAR TWO.

182

the trends of accumulated production per hectare for year one and

two. During year one, treatment one maintained the highest accumulated
production throughout the entire period, except in time four when

it was surpassed by treatment three. Treatment four kept a competi-
tive production per hectare up to time four and from then on the
increments were very small with some negative values included. In
year two, treatment one kept the highest accumulative production per
hectare, and treatment two and three alternate in the second place

up to time five when treatment two kept increasing gains and treatment
three had decreasing increments and finally leveled off. In year

one, treatments one, two and three produced 102.74, 47.55, and 28.98
percent more kilograms of liveweight per hectare than treatment four.
During the second year these values were 118.50, 101.90, and 45.90
percent more respectively. At the same time, treatment one outpro-
duced treatments two and three in 37.40 and 57.20 percent respective-
ly in year one, and 8.20 and 49.80 percent during year two.

Treatment effect for gain per hectare appear significantly dif-
ferent (P<:0.10). Table 29 shows differences between treatments in
gain per hectare. In both years the maximum gain per hectare was ob-
tained with steers on alfalfa - grass (treatment one), followed by
those on the triple system (treatment two). In year one, treatments
one and two are significantly different in terms of liveweight gain
per hectare, but this difference was not observed during the second
year. A similar observation can be mentioned for treatments two and

three, and three and four, but in the latter cases the differences

183

Table 29: LIVEWEIGHT GAIN PER HECTARE FOR THE FOUR TREATMENTS

DURING YEAR ONE AND TWO: IN KILOGRAMS.

YEAR 1 YEAR 2 z INCREASE
TREATMENT 1 321.638 368.218 14.50
TREATMENT 2 234.07c 340.198 45.30
TREATMENT 3 204.61be 245.8o° 20. 10
TREATMENT 4 158.64b 168.51b 6.20
OVERALL MEAN 229.74 280.68 21.60

Means within columns with different superscripts differ significantly

(P< 0.05).

were only important during the second grazing period. All treatments
improved the kilograms of liveweight gain obtained during the second
year over the first year: 14.50, 45.30, 20.10 and 6.20 percent for
treatments one, two, three and four respectively. The highest increase
in treatment two is very important considering that the only change
introduced during the second grazing season was the utilization of

the birdsfoot trefoil-fescue three times and alfalfa-orchardgrass

only two times. During the first grazing season alfalfarorchardgrass
was grazed three times and the mixture birdsfoot trefoil-tall fescue

only two times.

184

Weightdaygwithin year

The effect of weightday within year on liveweight gain
is shown in Figure 16. In year one animal gains varied more than
in year two. In year two treatments show a more constant pattern,
having increasing gains from time two to time four, and then
decresing gains up to time five. Table 30 shows the significant
differences that exist between the different weightdays within
years across treatments. In order to test for the effect of time,
a contrast was established grouping time one to time four and
comparing it with the group times five to eight. The differences
between these two group of means are significant (P< 0.05),
being more significant in year two (P( 0.01). As a result of the
contrast selected, it is possible to mention that the gain is
significantly larger during the first part of the two grazing
seasons. This can be seen in Figure 16.

The effect of time within year in production per hectare is
shown in Table 31. The contrasts established for both years
clearly show a significant higher production per hectare during
the first part of the experiment for both seasons. For year two
the significance was higher (P< 0.001) than for year one (P< 0.05)
which agrees with the time effect on individual weight gains.

The different treatments have different effects on gain per
hectare throughout the experimental periods. Figures 17 and 18

show the effect of treatment on gain per hectare during year one

and two respectively. It is possible to observed a marked peak

LIVEWEIGHT GAIN : KILOGRAMS

90

80

60

4O

20

 

185

1‘

YEAR 1
YEAR 2

Figure 16: EFFECT OF TIME OF WEIGH ON ANIMAL GAIN. VALUES ARE AVERAGES

ACROSS TREATMENTS FOR EACH TIME IN YEAR ONE AND TWO.

186

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187

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188

 

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189

 

Trt. l
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Figure 18: LIVEWEIGHT GAIN PER TREATMENT IN YEAR TWO.

190

in gain per hectare at time four during year one. During year
two, variations were smaller for all treatments, and especially

for treatments one and four. The average gain per hectare per

time for the four treatments are shown in Table 32. Comparisons

were only made in times one, three, five and seven. During the

first year only treatments one and two were significantly different
than four in time seven (P<L0.05). However, treatment three never
showed a significant difference from treatment four. During year
two, treatment two showed significant differences with treatment
four in time three, five and seven. Treatment one has significant
differences at time five and seven (P< 0.05). As occured during the
entire first year, differences between treatment three and control
were not significant at any time.

Average daily gain is another important variable to consider
in the analysis of the animals' data. Means and standard errors for
treatments one, two, three and four are 0.97 i 0.19, 0.66 i 0.12,
0.62 i 0.23, and 0.56 i 0.19 kilograms per animal per day in
year one, and 1.04 i 0.16, 0.90 t 0.22, 0.71 i 0.15 and 0.60 i 0.14
for the second grazing season respectively. Figures 19 and 20
show the average daily gain per treatment for both periods. The
tendencies were similar in both years. However, the highest peak
occured in time four for year one. During the second year, every
treatment peaked at different times: treatments one and two peaked

at time six, while treatments three and four peaked at time four.

Table 32:

YEAR 1

TREATMENT

TREATMENT

TREATMENT

TREATMENT

YEAR 2

TREATMENT

TREATMENT

TREATMENT

TREATMENT

TIME 1

32.028
17.998
28.138

24.408

71.438
62.098
58.688

48.238

191

TIME 3

31.898
39.428
38.498
41.948

45.908
58.35b
29.24ab

27.728

TIME 5

25.29a
25.478
-3.52a

1.168

51.018
57.883
37.738b

20.38

LIVEWEIGHT GAIN PER UNIT AREA FOR THE DIFFERNT TREATMENTS

IN TIMES ONE, THREE AND SEVEN: IN KILOGRAMS PER HECTARE.

TIME 7

34.328
23.748
3.56

-4.90b

39.328
44.318
9.028b

7.67

Means within the same column and year with different superscripts are

significantly different (P< 0.05).

192

Trt. 2 - - - -

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Figure 19: AVERAGE LIVEWEIGHT GAIN PER DAY IN YEAR ONE.

193

Trt. 1
Trt. 2 .....
Trt. 3 0.0000000

Trt. 4 ---°-----

 

KILOGRAMS OF GAIN PER DAY

 

 

Figure 20: AVERAGE LIVEWEIGHT GAIN PER DAY IN YEAR TWO.

DISCUSSION

 

l. Botanical composition

 

Trends in legume percentage in treatments one, two and three are
different for both grazing seasons. During year one, legume percentages
decrease with time with the exception of alfalfa from treatment two,
which increased 1.2 percentage units between times one and three. How-
ever, it decreased 16.3 percentage units between times three and six
(figure 3). During year two, tendencies show an increase in legume
percentage for all treatments and then a decline with time, except
birdsfoot trefoil from treatment two which declined from time one
to three and then leveled off.

The values of legume percentage within treatment for both years
show a marked difference. During year one, alfalfa in treatment one
comprised more than forty percent of the dry matter available at the
beginning of the experiment, While it represented almost twenty-
five percent at the beginning of the second season. An.explanation
for this is that alfalfa was grazed between September and part of
October during the first year which increased winter kill. Smith
and Rohweder (1977) recommend avoiding harvesting alfalfa between
the first week of September and mid October for conditions in Wisconsin.
This allows alfalfa to replenish a high level of carbohydrate reserves
before the first killing frost. Tesar (1978b) presents data for

conditions in Michigan where no harmful effects are produced when

194

195

harvesting a third cutting on a single date with a mower within

the above dates if alfalfa is allowed to flower during the summer

and the glands are annually fertilized. However, grazing (1978b)

for a long period in September is harmful in any state in the

North Central region and is not recommended. Because of the grazing
management imposed, plants did not flower in either of the two grazing
seasons and the plots were fertilized only once very two years. As

a consequence, it is very likely that alfalfa plants entered the winter
after the first grazing season without the required reserves. Under
such conditions the stands were partially killed or at least weakened,
and their contribution at the beginning of the second season was
diminished. The important increment observed during the first

period in year two is due to the fact that after each pen was

grazed, the remaining forage was clipped to a height of approximately
8 to 10 centimeters. This allowed alfalfa to develop more rapidly
and with less competition from orchardgrass. England (1968) observed
that orchardgrass harvested in the vegetative phase has a lower
competitive ability than ryegrass, being dominated by this specie.

At the same time, Templeton et al. (1965) reported a slow start

of orchardgrass when seeded with alfalfa which support the findings

in this situation. However, after the initial period, orchardgrass
has a quick capacity to compete with other species, especially

with legumes. This caused the alfalfa percentage to decrease

rapidly throughout the second grazing season, regardless of the fact

that the rest periods were near optimum for alfalfa persistence.

196

Baxter et al. (1969) also obtained an increase in orchardgrass in an
alfalfa-orchardgrass mixture pastured with dairy cows. However, no
change was observed hithose pens managed in the same way but mechani—
cally harvested.

Orchardgrass is considerably different in spring growth habit
than other cool grasses such as fescue, timothy and bromegrass.
It appears that basal buds are under the control of apical dominance
in timothy, fescue and bromegrass during the period of stem elongation
(Newman and Smith, 1972). As a result of that, there is little if
any growth of the basal buds of these three species prior to anthesis.
However, basal buds of orchardgrass appear to be under less apical
dominance, and as a consequence, they continue to grow throughout
spring. Sheard and Winch (1966) concluded that orchardgrass shoots
are in different stages of development at any given time, which in
turn make this specie more competitive in mixture with legumes than
the other cool season grasses. Smith et al. (1973) reported that
orchardgrass persists well with alfalfa under the three cutting
system imposed in the Great Lakes area, regardless of the height
of cutting. When orchardgrass is cut, leaf growth from shoots with
intact growing points continue, and new leaves develop rapidly. It
is the continuous growth and development of new tillers that produce
the rapid growth of orchardgrass after cutting. Nest of the growth
is leaves when orchardgrass is out near anthesis, (Newman and Smith,

1972).

197

The rotational system for alfalfa persistence is very important.
Seath et al. (1962) observed that when alfalfa-grass mixtures
were rotationally grazed for fourteen days and rested for twenty eight
days, the legume content tended to decrease. Smith (l970a) noted
that the same grazing system did not affect alfalfa persistence
when three wethers per hectare were used. However, when the carrying
capacity was augmented to four wethers per hectare, alfalfa persistence
could only be maintained if it was grazed one week and then rested for
five weeks. Paulson et al. (1977) recommend giving alfalfa based
pastures twenty days rest between the first and second grazing, and
thirty days thereafter between consecutive grazings, for the conditions
in Wisconsin. Hoglund et al. (1974) observed an extensive weed
invasion when alfalfa stands were defoliated at pre-bud stage,
regardless of the rest period established. However, the same practice
did not affect the stands when plants were harvested at first flower
stage, In treatment one, the stocking rate was almost three times
higher than the one reported by Smith (19703), and plants were always
harvested before flowering stage.

Alfalfa from the second treatment showed a very different behavior.
It started the first year being above 37 percent for the first two
grazing times, and declined thereafter more than 16 percentage units.
It finished the first year comprising twenty two percent of the total
mixture. However, it only composed 7.2 percent of the mixture at
the beginning of the second year. As was reported for the mixture

from treatment one, the low level of reserves the plants had at the

198

end of the first grazing season could explain part of the significant
decrease observed between September 1981 and June 1982. The other
reason responsible for this decrease could be the fact that alfalfa
was heavily grazed at the beginning of the first year having only
fifteen days of rest between consecutive grazings. This system is
practically a continuous grazing system considering the high stocking
rates used in the experiment. Fuelleman et al. (1954) and Peart (1968)
showed that continuous grazing of alfalfa with sheep markedly
reduce the stand in a short period and then eliminates it from the
mixture. Smith (1970b) concluded that even under very low stocking
rates (two wethers per hectare), alfalfa plants cannot be retained
in the mixture for a very long time if continuous grazing is practiced.
Birdsfoot trefoil was studied in two treatments under continuous
and rotational grazing. During year one, the birdsfoot trefoil
percentage in both treatments decreased with time, being higher for
treatment two. However, during year two, birdsfoot trefoil percent
increased in treatment three up to time five and then declined,
while in treatment two it decreased. Regardless of the increment,
the rotational system always maintained a higher content of the specie
througout the grazing season. Authors in general agree on the fact
that this specie needs rotational grazing if stands have to be main-
tained (Davis and Bell, 1957; Van Keuren and Davis, 1968; Van Keuren
et al., 1969). Other authors have sustained that birdsfoot trefoil
may be used for continuous grazing (Smith, 1962; Paulson et al., 1977)

as well. Tenpas and Scholl (1970) showed that birdsfoot trefoil is

199

more productive that alfalfa under a more frequent harvesting procedure
(three versus two cuttings) in northern Wisconsin. The suggestion

that alfalfa has to be grazed closely but not frequently and birds—
foot trefoil more frequently but not as closely is based on the re-
covery growth pattern of these two legumes. Alfalfa produces several
growth from the crown, while birdsfoot trefoil derives the first

growth from the crown and additional growths from branches originated
from auxillary buds (Nelson and Smith, 1968; Smith, 1968). Since
alfalfa restores its reserves during a grazing season it can be closely
grazed for short periods providing rest to resynthesize reserves to

be used for additional growth. Birdsfoot trefoil requires some leafy
area to be left to snythesize the material needed for regrowth (Smith,
1962; Nelson and Smith, 1968, 1969). Thus it is very likely that
continuous grazing does not eliminate birdsfoot trefoil unless a

very high stocking rate is utilized. In treatment three, 2.62

and 2.49 steers per hectare were maintained in year one and two respect-
ively. Davis and Bell (1957) Obtained similar results but with 2.94
steer equivalents per hectare over a three year period.

Birdsfoot trefoil was seeded with orchardgrass and bromegrass in
treatment three. The proportion of orchardgrass clearly increased
throughout both grazing seasons to constitute the majority of the
grass in the mixture. Raguse et a1. (1971) showed that orchardgrass
became dominant in a mixture of two legume and two grasses under
continuous grazing. In an additional experiment, Raguse et al. (1975)

using the same mixtures and a rotational grazing system (one week

200

grazing and one week rest) did not obtain any significant difference
in botanical composition. Regardless of the high stocking rates
used (above seven steers per hectare) the pastures were irrigated
on a weekly basis and steers received alfalfa supplementation. These
two factors contributed to alleviate the grazing pressure exerted on
the pasture as it is shown that 70 to 90 percent of the forage in
all pastures kept a 5 to 20 centimeter height.
Several authors have established the importance of height of
cut in persistence of orchardgrass in pastures. Mitchell (1962)
observed that heights of cut less than two inches produce a significane
loss in orchardgrass plants. Colby et al. (1965) noted that cutting
heights of 1.5 inches produce poor recovery of orchardgrass stands,
and Mitchell (1967) observed that with cutting heights of 1 inch
coupled with irrigation and heavy application of nitrogen can eliminate
orchardgrass from the pasture. However, with higher heights orchard-
grass has the abilify to recover more rapidly than bromegrass after
cutting (Carter and Scholl, 1962). Since the stocking pressure in
our experiment was not high enough to make orchardgrass plants to
be harvested at less than the critical values cited above, the rapid
growth of this specie with respect to bromegrass may be the principal
cause to explain the dominance of orchardgrass in treatment three.
Tall fescue shows a similar behavior with timothy and bromegrass
in grow habits. Yeh et al. (1976) observed that in spring and
fall there is accumulation of an endogenous growth regulator (auxin)

in shoots which in tLrn produce rapid tillering. With the high

201

temperatures of summer, the concentration of auxin in stem bases
increases while in shoots it decreases producing inhibition of tiller
elongation. Lopez et al. (1967) observed low growthcflftall fescue

in mid summer regardless of the presence of sites for tiller
production. This low competitive growth ability of fescue in mid
summer could explain why the low decrease in birdsfoot trefoil per-
centage in treatment two during the second grazing season, even
though the stocking pressure was high and the rest period between
consecutive grazings was shorter than the recommended. Berry and
Hoveland (1969) also observed a reduction in yield of tall fescue

Kentucky 31 when harvested in mid summer.

.2 .2189. EPEEX

Leaves and stems within Species differ in their anatomy. Leaves
are composed of an epidermal layer covered with an indigestible
cuticle, a variable proportion of a parenchyma tissue (mesophyll)
formed by cells with walls readily digested and vascular bundles
surrounded by a layer of cells within variable digestibility. Stems
are composed of basically the same components but with less mesophyll,
and the vascular bundles are surrounded by supporting cells with very
low cell wall digestibility (Swakon and Moore, 1980).

There are important differences among species in the anatomical
structure of leaf blades. Akin and Burdick (1975) studied the
percentages of tissue types for four—week-old plants of bromegrass,
fescue, bluegrass and orchardgrass. Kentucky blue grass has the

highest percentage of meSOphyll and the lowest percentage of the less

202

digestible portions: total and lignified vascular tissue and parenchyma
bundle sheath. Bromegrass and orchardgrass are the two species

with the lowest mesophyll and the highest lignified vascular

tissue. Fescue varieties present intermediate values. In general it

is possible to establish the following trend for tissue digestion

(Akin, 1981, 1982b; Akin and Burdick, 1981; Akin and Burton, 1983):

Mesophyll and Epidermis and :> Schlerenchyma j) Lignified
Phloem Parenchyma vascular
sheath

Burdick (1979) established that the relative amounts of the more

rapidly and slowly degraded tissues may play the most important

role in explaining the digestibility of leaf blades. Based on these
facts it is possible to conclude that bluegrass could be more digestible
than orchardgrass and hromegrass,being fescue intermediate between

the two groups during the first part of the growing cycle.

Lignin content has been indicated as the component more related
with digestibility of herbages by many authors (Barton et al., 1976;
Van Soest, 1965, 1968). Barton and Akin (1977) obtained an increase
in the extent of digestion of cell walls of plants chemically deligni-
fied. However, no increase was observed for the digestion of the
vascular bundle, indicating that the amount of lignin is not entirely
responsible for the indigestibility of the vascular tissue. Allinson
(1970) suggested that the nature and distribution of lignin among

different tissues could be more important than tte quantity itself.

203

This could explain why alfalfa is more digestible than grasses
regardless of having a higher content of lignin (Van Soest, 196E).
Akin (1982a) demonstrated that p—coumaric acid, a lignin precursor,
is toxic to certain rumen protozoa and bacteria that normally play
an important role in forage digestion. These findings drove

Deinum (1974) to conclude that the degree and kind of lignification
may be the cause of the deviations observed between the average
relationship between the digestibility and the percentage of lignin
in cell-wall constituents. Akin (1983) explains the differences in
kind and degree of lignification as the determinants of the differences
in the relative ease of tissue digestion for differenct species, and
Akin and Burton (1983) concluded that while degradation of the cell
wall can occur by enzymes of nearby bacterias, some others are
digested only attached microorganisms. This explains the difference
in ease of degradation between species.

Treatments show a significant effect in in vitro digestibility
of dry matter during both years, with treatments one and two having
higher values than the other two treatments. The grazing system and
the species composition of the mixtures compared play the major roles
in those differences. The forages in treatments one and two were
rotationally grazed, allowing a more uniform consumption of the
plants, and as a consequence, a more uniform regrowth of the pasture.
However, the continuous grazing system imposed on treatments three
and four determined that at any point in time there were many more

plants not being consumed and, as a consequence, decreasing in

204

digestiblity as a result of accumulation of more mature material.
More (1980) reports that under conditions of rapid regrowth of the
pasture and low stocking pressure, there is an increase in yield

and availability of forage, but a decrease in quality of the herbage
because of the accumulation of mature stems.

The legume composition in treatments one and two were always
higher than in treatment three. Several authors have established
the advantages of legumes over grasses for quality parameters such
as digestibility and crude protein. Winch et al. (1970) concluded
that alfalfa pure stands and alfalfa—grass mixtures are superior to
pure grass fertilized with nitrogen, which in turn have a higher
digestibility than pure grass stands without nitrogen. In our
experiment treatments one and two showed a superiority over treatment
four and treatment three, the latter with a very small percentage
of trefoil.

All treatments showed a decline in digestibility with time in
both years. In case of treatments three and four, this trend can be
explained by the increase in maturity of the forage. For treatments
one and two, part of the decline in digestibility can be attributed
to increase in maturity, and also to a reduction of tie legume
stands in the mixture. Since both treatments were rotationally grazed
and the maturity was delayed, it is very likely that the main reason
could be attributed to the lower legume composition in the mixture.
Matches et al. (1970) observed a similar behavior Of two alfalfa variet-

ies in four different states in the U.S.

205

The decrease in digestibility showed a different trend in years

one and two for treatment one. During year one, there is a more
marked decline between the end of August and the beginning of
October: approximately 0.4 percentage units per day. However, the
decrease was only approximatley 0.3 units between June and August.
During the second year, there was an increaseixtdigestibility of
the regrowth up to the end of August and, afterwards, the decrease was
approximately 0.14 percentage units per day. Demarquilly and Jarrige
(1971) reported a decline in digestibility for alfalfa of 0.35 to
0.40 percentage units per day for the first cycle of growth and first
regrowth,zuu10.44 units of orchardgrass during the same time.

Treatment two also had a different behavior in both years.
During the first year, alfalfa—grass had a daily decline of 0.05
percentage units between June and the end of July,and.0.04 units
between July and September. However, it increased 9 percentage
units between June and August of the second year, or a daily increase
of 0.20 units. Birdsfoot trefoil showed a daily increase of 1.33
percentage units in 63 days during the first year. During the second
year it decreased 0.26 units per day from June to middle of July,
but it increased 0.06 units per day between July and the end of
August. The participation of birdsfoot trefoil in the mixture decreased
5.57 percentage units during June—July of the second grazing season.
This, in part, could explain the decrease in digestibility values in
that period. Tflnaother possible reason is that there were only 21 days

between two consecutive grazings. This could not be long enough to allow

206

a complete recovery of the pasture, making the steers consume a larger
percentage of mature material left over from the previous grazing period.

Treatments three and four showed different tendencies in years
one and two. During year one treatment three decreased in digesti-
bility until the end of September, which coincides with a decrease
in trefoil percentage in the pasture. The decrease was very similar
throughout the entire season: 0.17 percentage units per day. During
year two, a daily decrease of 0.22 percentage units until the end
of July and 0.12 units from mid August to the end of September was
obtained. However, there was an increase of 2 percentage units of
digestibility between the end of July and mid August which coincides
with a significant increase in trefoil composition in the pasture.
Kentucky bluegrass showed a constant decrease between June and the
end of September of the first year (0.15 units per day). During the
second year the decrease was larger (0.22 units daily), but it in-
creased at the end of August.

Regardless of small increases, the general tendency was to have
lower digestibilities with the regrowths in treatments one and two.
Demarquilly and Jarrige (1971) have concluded that regrowths are
always less digestible than the plants of the first cycle at similar
age because the cell walls are more lignified. Jarrige and Minson
(1964) have shown this tendency on orchardgrass pastures. Van Soest
(1982) established that the aging of forage is characterized by a

decrease in leafiness and an increase in the stem to leaf ratio.

207

Davis (1974) showed that the initial effect of cutting is to reduce
the rate of leaf appearance up to a third to ryegrass stands, and
the same author (1977) also demonstrated that the size of the leaves
become smaller due to frequent cutting. Mbwat et al. (1965)

have shown that in vitro digestibility of stems of orchardgrass

and bromegrass decrease with a higher slope than the digestibility
of the leaves. However, Christian et al. (1970), Kilcher and
Heinrichs (1974) and Thom (1978) observed that digestibility of
alfalfa leaves remain constant throughout the summer months, while
the digestibility of stems decrease rapidly. Hardison et al. (1957)
obtained a daily decrease in digestibility of the bottom portion

of alfalfa plants of 0.6 percent.

3. Animal performance

 

3.1 Stocking rate

 

The evolution of the stocking rate for the four treatments is
shown in tables 33 and 34. In general terms it is possible to
conclude that the stocking rate has been very similar for every
treatment in both years. Treatments one and three kept a 2.77 and
4.8 percent higher stocking rate (steers per hectare) respectively
during the first grazing season. On the other hand, treatments two
and four had a 4.66 and 2.17 percent more steers per hectare in
year two. Treatments one, two and three maintained a two year average
of 24, 23 and 10 percent more steers per hectare than treatment four.

A different program to remove steers when dry matter offered

declined can be observed for both grazing seasons. Four steers per

208

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210

pen were maintained in treatment one until September 22 in year one,
and September 21 in year two. However, three steers could be
maintained in year one but only two in the second season until

the end of the experiment. During the second grazing season,
treatment two maintained for steers per pen until the end of the
experiment, whileix1year one one steer per pen was removed at the
beginning of September and another steer during the last six days
of the trail. The basic reason behind this system was that the
birdsfoot trefoil—fescue was rotated three times during the second
year and alfalfa—grass only two, allowing the animals to make a more
efficient utilization of the additional forage produced by the
trefoil-fescue mixture. During the first year, the system allowed
alfalfa-grass to be grazed three times and trefoil-grass only two.
The convenience of grazing trefoil—grass three times relies on the
fact that this mixture can produce more forage at the end of the
season when alfalfa grows at a slower rate due to the lower
temperatures and shorter days. For treatment three, three steers
were maintained until September 22 in year one, while only two in
year two. During both years the limiting pen, in terms of carrying
capacity of the pasture, was pen three. The smaller size (19 percent
smaller than the average size of the other two replications) could
explain the fact that it was the pen that showed more limitations
maintaining a high stocking rate at the end of the two grazing seasons.
In case of treatment four, it was not required to move out any steer

during year one. However, two steers were removed on September 22 of

211

the second season. Pen two was at this time the limiting pen with
an average daily gain per steer 73 percent lower than the average

of the other two replications.

3.2 Gain per animal and per hectare

 

No significant differences between treatments were found in
average gain per day and total production per animal in either one
of the two years, except for a marginal difference between treatments
one and four. This lack of significance in daily gains suggests
that the steers consumed similar amounts of nutrients. The analogy
in animal performance indicates that within the range of stocking
pressure utilized in the experiment, gain per animal is independent
of the animals maintained per unit area. Various researchers have
proposed different mathematical relationships between stocking
rate and liveweight gain per animal (Mott, 1960; Petersen et al., 1965;
Conniffe et al., 1970; Hart, 1972, 1978; Jones and Sandland, 1974;
Sandland and Jones, 1975; Connolly, 1976). Figure 21 shows the
different curves proposed for the different authors and summarized
by Hart (1978, 1980). Different factors affect the performance of
animals under grazing conditions, with the available forage per
unit area an important factor. Willoughby (1958) determined that the
maximum response per animal occurs at 1,570 kilograms of dry matter

per hectare when 3.95 steer equivalents are used per hectare. Since

the stocking pressure in our experiment was lower and the dry matter

212

 

 

1(6)

Gain/head

 

 

 

Head/area

(1) Mott, 1960.

(2) Petersen et al., 1965.

(3) Conway, 1974.

(4) Hart, 1972; Jones and Sandland, 1974.
(5) Conniffe et al., 1970.

(6) Connolly, 1976.

Figure 21: PROPOSED RELATIONSHIP BETWEEN STOCKING RATE AND GAIN

PER ANIMAL (HART, 1978, 1980).

213

available always higher, we can assume that other factors are
responsible for the differences between treatments.

Figures 19 and 20 show important fluctuations in average daily
gain throughout the experimental periods, being more accentuated
during year one. The variations in treatment two could be explained
by the fact that the steers were moved to different mixtures every
time. Since the diet was of different species, with different
palatabilities and nutritive values, that lack of uniformity in
gains per animal can be expected. However, no rational explanation
can be derived for the other treatments, at least during the first
part of the experiment. Additional research is required to explain
this point. During year one, the steers on treatments one, two
and three had an increase in liveweight gain per day at the end
of the grazing season, which in turn coincides with a lower
stocking pressure. This supports the idea of a possible limitation
on intake per animal and less selectivity of the pasture for excessive
stocking pressure. Analyzing the intake per animal it is possible
to observe that steers on treatments two and three increased their
consumption, but this did not occur in treatment one. As a result
of this, the more likely reason to explain this increment in gain
per animal would be a combination of higher intake and more selectivity
of the pasture, the latter being more important in treatment one and
the former in treatments two and three. Bryant et al. (1970)
analyzed the relationship between grazing pressure and animal and plant

responses. When the stocking pressure is high, animals tend to

214

consume less quality forage resulting in lower digestibility and
nutrient content of the harvested diet.

Different reports have established the benefits of including
legumes in mixtures for grazing livestock. Matches et al. (1975)
concluded that even with as little as 20 to 25 percent legumes in
the mixture, cattle gain per day can be expected to be approximately
0.11 kilograms higher than where cattle graze pure stand of grasses.
Campbell (1967) summarizes different sources of information where
cattle and sheep grazing alfalfa produce higher liveweight gains
than grasses alone and legume-grass combinations. This concept
was analyzed by Thompson (1979) who concluded that the feeding
value of legumes is superior to that of grasses. Joyce and
Newth (1967), and Ulyatt (1971) also confirmed this concept and
showed that the energy from legumes is utilized more efficiently
for growth and fattening than that of grasses. Corbett et al. (1976)
showed that the energetic efficiency of ruminal fermentation is greater
for alfalfa than for phalaris, and this could explain the higher
liveweight gain of lambs grazing alfalfa. Ulyatt (1973, 1981)
presents some data comparing the feeding value of some legumes and
grasses. Alfalfa has 70 percent and trefoil 43 percent higher relative
feeding value than perennial ryegrass. Steers on Kentucky bluegrass
also showed an increase in liveweight gain at the end of the grazing
period in year one. In this particular case, higher intakes cannot
explain the higher gains since the increase in intakes have been

very small during the entire period. A possible explanation could

215

be the increase in digestibility of the pasture at the end of the
period, which in turn allows the steers to utilize the forage

in a more efficient way. The lower productivity of Kentucky bluegrass
during summer months was reported by Seath et al. (1956).

During year two, the maximum average daily gains have occured at
time four for treatments one, three and four, and at time six for
treatments one and two. For treatment one it is possible to conclude
that maximum gain in time six can be explained by a maximum intake
during that time too. The largest peak in liveweight gain for
steers in treatment one occured at time four and is also accompanied
for the second largest peak in intake. In treatment two, the highest
liveweight gain in time six coincides with a high peak in dry
matter offered but not with increase in intake. This would suggest
that the steers had more forage to select from, and the higher gain
was basically due to a more selection of the available pasture but
not from a higher intake.

When comparing animal performance at the end of the two grazing
seasons in treatment two, it is possible to observe a higher gain in
year two in spite of a higher stocking rate. During year one,
steers grazed alfalfa-orchardgrass, and during the second year
trefoil-fescue. Alfalfa may be harvested in September in Michigan if
the previous cutting schedule allows plants to replenish their
reserves (Tesar, 1978b). According to the grazing schedule performed
during year one, that was not possible and less production was obtained

during the last grazing of the alfalfa—grass mixture. Another reason

216

is that fescue produces a higher quantity and forage then orchard-
grass early in spring and at the end of summer-beginning of fall,
which in turn means higher animal performances (Hobbs et al., 1965;
Fuller et al., 1971; Burns et al., 1973; Matches and Mbtt, 1975;
Matches et al., 1975; Smith and Rohweder, 1977). Finally, if trefoil
is utilized first in the rotational season as occured during year
two, it is possible to use more efficiently the early yield from

this legume. In studies done in Iowa, Wedin et al. (1967) found

that birdsfoot trefoil pastures produce thirty five percent of their
total season's growth by June 30th.

For treatments three and four, maximum gain per animal occured
at time four. In treatment three, dry matter offered and intake
per animal were decreasing but with a small slope. On the other
hand, in treatment four these two variables were increasing from
time three on.

Treatment two shows a particular behavior when steers grazed
sorghum. During the first grazing season the maximum gain per animal
per day occured when steers grazed sorghum. However, in year two,
the average daily gain from sorghum was the second smallest gain.
Kilograms of dry matter consumed per steer per day was 44.41 percent
higher in year one and dry matter offered was 107.13 percent higher
during the same year, in spite of a 5.21 percent higher digestibility
during the second year. A possible explanation for these differences
in animal performance on sorghum could be that because of the larger

dry matter offered during the first grazing season, steers could select

217

and consume more, regardless of a lower digestibility. Pratt et al.
(1966) concluded that sorghum does not have any special merit,
and should only be included in grazing systems when alfalfa-grass
mixtures are lost or badly reduced because of winter—killing.
Production per hectare was significantly different between
the four treatments. The dry matter offered per treatment was
significantly different for year one only. This indicates that dry
matter offered only explains part of the different responses in
liveweight gain per unit area. The other part may be explained for the
superior efficiency of the energy consumed from legumes (Thomson, 1977).
The superiority of the legumes is based on the fact that metabolizable
energy of the regrowth of these species are utlized with similar
efficiency as the primary growth (Smith et al., 1976), while the
first cut of grasses is used with higher efficiency than posterior
regrowths (Blaxter et al., 1971).
Marten and Jordan (1979) obtained higher animal performance on
a per day and per hectare basis when two thirds of the area was
seeded to birdsfoot trefoil pure stands and one third to alfalfa-grass,
compared with a mixture of alfalfa-grass. The basic reason behind
the better performance of lambs on trefoil and alfalfa-grass system
could be attributed to a higher legume percentage on the overall
treatment, which in turn produced higher intakes. Higher animal
days per hectare were obtained from the alfalfa—grass mixture by these
authors, and this reflects a higher dry matter production from alfalfa

than from birdsfoot trefoil. The possible reason why we did not obtain

218

better animal results from treatment two over one is because we
seeded trefoil with fescue. The birdsfoot trefoil percentage was

not higher than 30 percent in either of the two years, while in the
experiment reported by Marten and Jordan (1979) it was seeded in

pure stands. This in turn produced important differences in chemical
composition of the pastures between their results and ours.

Several experiments are reported on animal performances on alfalfa—
grass mixtures, but all of them use irrigation to increase yield of
forage per unit area (Heinemann, 1969, 1970; Accord, 1970; Reid et al.,
1973; Matches et al., 1975; Hayes et al., 1980). In general, the
average daily gain obtained by us is higher than the values reported
by others. However, due to a much lower stocking rate in our
experiment, the other researchers report much higher production
per hectare. The additional number of steers per hectare maintained
in other experiments is a direct consequence of the utilization of
irrigation. Reed et al. (1972) reported satisfactory gains on
young sheep on alfalfa dominant pastures (87 percent) without irrigation
carrying 16.5 sheep per hectare (3.3 steer equivalents), even during
exceptional dry years. The basic reason for such a high pressure
is that sheep were Supplemented resulting in an effective lower
pressure exerted on the pasture. Merley and Axelsen (1965) obtained
a uniform performance of lambs at a stocking rate of 24 weaners
per hectare (4.9 steer equivalents) on non irrigated alfalfa pastures

on low rainfall environments.

219

Treatment one provided for 3 subpens per replication. With the
management system imposed in our experiment, the rest period was
fixed in approximately 4 weeks, and the stocking rate was adjusted
to achieve that spelling time. McKinney (1974) concluded that maximum
lifeweight gain was obtained with plots spelled 5.5 weeks in summer.
Providing that the maximum profitability is obtained with only
three pens (McKinney, 1974), the optimum stocking rate to achieve
a 5.5 weeks of rest in lower than the one we had. With the stocking
rate maintained in our experiment, more days of grazing per pen had
to be obtained for the 5.5 weeks rest, which in turn means a higher
proportion of the alfalfa stems had to be consumed with no beneficial
effects for the pasture (Hayes et al., 1980) or animals (McKinney
et al., 1970).

Wedin et al., (1967), Van Keuren et a1. (1969) and Matches et a1.
(1975) report animal performances on birdsfoot trefoil—grass mixtures.
Our results in average daily gain are intermediate between the ones
reported by these authors: 35.71 percent higher than the results
reported by Van Keuren et al. (1969), and 14.29 and 35.33 percent
lower than the performance obtained by Wedin et a1. (1967) and
Matches et al. (1975) respectively. Similar conclusions can be drawn
when production per unit area is analyzed.

Only one grazing was obtained from the sorghum each season.
Dunavin (1970) reports average daily gains of 0.40 and 0.31 kilograms
of liveweight gain per day for early and late planting sorghum

respectively, while 0.60 kilograms per day was obtained in our

220

experiment as average of the two years. It is possible that the
values obtained by us do not reflect exactly the potentiality of
the sorghum alone since this pasture was rotated with two other
legume—grass mixtures. However it is important to consider it since
sorghum was basically included in the system to provide good
quality forage in mid—summer, when other mixtures decrease in
yield as a consequence of dry weather and high temperatures.

Treatments one and four had a longer grazing season than two
and three in both years. During year one the difference was 13
days while in year two was 15 days. The basic reasons to stop
treatments two and three was the poor conditions of the pasture,
being more limiting in treatnent three.

.The number of grazing days obtained from the different pastures
is a function of different factors, being stocking pressure one
important variable. In case of treatment two, the high stocking
pressure and the fact that sorghum could be grazed only once in
each year produced a high pressure on the other two mixtures.
This in turn shortened the rest period of the alfalfa-grass and
the birdsfoot trefoil-grass and the grazing period. For treatment
three, the continuous grazing system with the stocking pressure
used were responsible for the decrease in the birdsfoot trefoil
population in the mixture, which in turn caused a shorter grazing

utilization.

221

4. Forage growth: a model

Tables 35 and 36 show the response of the different factors
included in the model for the alfalfa-orchardgrass mixture and the
pooled data from the four treatments. The factors analyzed were growth
period (in days), evaporation (in hundreths of inches), forage present
at the beginning of the growing period (in kgs of dry matter per
hectare), precipitation (in inches), maximum temperature and minimum
temperature (in degrees Farenheit). Precipitation and evaporation
represent the total amount registered during the growing period, while
maximum and minimum temperatures represent averages throughout the
same time period.

Only linear models were considered to establish the relationship
between forage growth and the factors involved. The model utilized for

the analysis was a first order model of the following type:
Y1 = b0 + b1811 + b2812 + 1)3813 + b4814 + bsxis + b5Xi6

where

Y1 represents the experimental unit total dry matter yield
per hectare;

x11 represents the effect of the growth period;

x12 represents the effect of the evaporation;

x13 represents the effect of the forage available at the
initiation of the growing period;

x14 represents the effect of total precipitation;

x15 represents the effect of maximum temperature; and

x16 represents the effect of minimum temperature.

222

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224

The analysis was performed using Genstat (Alvey et al., 1977) with the
regression option. The first step was to develop the linear univariate
models with the parameters explained, and the second step was to
include sucessive variables to establish the model that explains the
maximum of the total variation. Two different data files were used:
data from the alfalfa—orchardgrass mixture (treatment one) and the pooled
data for the four treatments, with the information from both experi-
mental periods.

Table 35 shows the models for the alfalfa-orchardgrass mixture.
The variable that explains the largest component of the total variation
is growth period, then evaporation and kilograms of dry matter present
at the beginning of the growing period. Precipitation and temperature
show a less important participation in the univariate models. When
several variables were included, it is possible to observe an increase
in the total variance accounted for by the model, over the effect of
the growing period alone. The most complete model for alfalfa-grass
includes growth period, kilograms of dry matter present at the initia-
tion of the growing period, evaporation and precipitation, which in
turn accounts for almost 66 Z of the total variation.

In Table 36 the different models for the pooled data are presented.
In general, the univariate models explain significantly lower percent-
ages of the total variation compared with the model for alfalfa-grass.
In case of the pooled data, kilograms of dry matter present at the
initiation of the growing period is the most important variable,
followed by growth period, precipitation and evaporation. Maximum.and

minimum temperatures play a very minor role in determining the total

225

dry matter produced. Growing period and dry matter present at the
beginning of the growing period explain 50.2 Z of the total variation,
and the addition of precipitation and evaporation only increases the
coefficient of determination to 54 2.

Amount of forage present on the field at the initiation of the
growing period explains 57.1 and 38.2 2 of the total variation for the
alfalfa-orchardgrass and the pooled data respectively. The range goes
from 928 to 5700 kgs of dry matter per hectare with a mean equal to
2670.81 for the alfalfa—grass treatment. For the pooled data, the
values obtained were 926, 5857 and 2945.96 kgs of dry matter per
hectare respectively. Brougham (1961) reported an increase of 377 Z
in lbs of dry matter per acre produced by orchardgrass (from 265 to
1,000 lbs), when the pasture was defoliated to 3 inches instead of 1
inch. The higher stubble height in this case represents a greater
amount of dry matter left per unit area, and a more advantageous leaf
area index to reinitiate growth. However, Knievel et a1. (1971) obtained
a higher dry matter production per hectare from bromegrass stands when
cut at 4 centimeters than at 10 centimeters, over a two year period.
Regardless of a greater regrowth obtained at 10 centimeters, the total
production throughout both growing seasons was higher using 4
centimeters height. No data relating height of defoliation and yield
of tall fescue are available (Beaty et al., 1978a). The importance of
the forage left to initiate regrowth is based on the minimum leaf area
present required for photosynthesis. Pearce et al. (1965) obtained an
optimum value of leaf area index for orchardgrass of 5.5. Under these

conditions, the authors reported a 95 Z of the light intercepted by

226

the pasture after 15 days of regrowth, and the regrowth shows a
linear shape between days 8 and 30 after cutting,

The growing period is another variable that plays a major role
in both models. The mdnimum, maximum. and average values were 17, 48
and 28 days for alfalfa—orchardgrass, and 17, 63 and 33 days for the
pooled data. In case of the alfalfa—grass model, the growing period
represents the time between two consecutive grazings for the different
pens. In case of the treatments under continuous grazing, the growing
period was determined as the number of days between two consecutive
sampling times. Bartholomew and Chestnutt (1977) observed an increase
in dry matter production of ryegrass pastures when the growing period
was increased from 3 to 6 weeks. However, Bartholomew et al. (1981)
obtained erratic results when 20 and 35 day intervals between grazings
were used over a 3 year period.

Evaporation plays an important role in alfalfa-orchardgrass
pastures, but less significant in the model with pooled data. Several
authors have used evapotranspiration as the independent variable
related to forage yield. This concept considers not only the evaporation
from the soil, but the transpiration of the plants on the field as
well. Bauder et a1. (1978) explained 96.6 % of the total variation ha
alfalfa yield (in pure stands) using evapotranspiration as the unique
independent variable. Sammis (1981) obtained different coefficients
of determination for different years on alfalfa pure stands: 57 to
97 Z. The author also presents different linear regression equations
for the different cuttings of alfalfa pure stands, relating yield of

forage per hectare and evapotranspiration.

227

Precipitation shows a higher relationship with alfalfaégrass
than with the pooled data. One possible explanation for this behavior
could be the fact that part.of the precipitation drains down to deeper
layers of soil without being reached by the root system of the grasses
utilized in the experiment. On the other hand, alfalfa can utilize
the available water at deeper soil stratum (Dennis et al., 1959).
Hobbs (1953) reported that alfalfa can use water down to 18 feet, but
the soil water in the top 6-12 inches is more rapidly removed (Lucey
and Tesar, 1965). Due to the deeper root system alfalfa has, the
general impression is that alfalfa uses water wastefully because it
continues growing when other plants remain dormant due to water stress
(Christian, 1977). Bauder et al. (1978) established linear regression
equations for alfalfa growth considering not only the water from
precipitation and irrigation, but a drainage function to consider the
water not available in the top layers of soil. Considering these three
variables the authors could explain 95.7 2 of the total variation in
alfalfa yield. Other authors have obtained a more definite relation
between precipitation and forage yield. Occumpaugh and Matches (1977)
found a correlation of 0.93 and 0.98 between accumulated precipitation
and tall fescue production in fall during 2 years. However, the yield
of dry matter per hectare per centimeter of accumulated precipitation
was 62 and 164 for the 2 years, basically due to the uneven distribution
of the rainfall between years.

Maximum and minimum temperatures play a small role in both sets
of data. These 2 variables explain a minor percentage of the total

variation when considered in a univariate model. At the same time,

228

when they were included in the multivariate models no additional
improvement was obtained over the other 4 variables. Morley (1968)
concluded that for the model he developed, temperatures are not
significantly important for Australian conditions. In spring, although
soil and ambient temperatures may be suboptimal for growth, the light
energy received on the soil may set the upper limit for maximum growth.'
In fall, on the other hand, temperatures may be near optimum, but the
low light energy and short days may become the limiting factors for
forage production.

The climatic effects are diverse and may involve the interaction
with other factors such as soil type, drainage, nutrient supply, pests,
diseases and management. It is very difficult to identify the exact
effects of the different variables included in the climate over the
other causative agents that affect crop production and quality
(Copemen, 1979). Authors, in general, study the effects of the climate
on a specific specie, for a short period of time and under very well
controlled environments in greenhouses and growth chambers (Bowman
and Law, 1964; Baker and Jung, 1970; Smith, 1969, 1970; Marten, 1970a;
Allinson, 1971; Vough and Marten, 1971; Wolf and Blaser, 1972;

McKinion et al., 1974). In the experiments we worked with mixtures of
grass and legumes, under field conditions and over a long period of

time. At the same time, grazing animals introduce another factor that
affects the herbage growth response. The defoliation is not as

uniform as it is under laboratory conditions, and some losses such

those due to senescence, decay and decomposition can not accuratelytua
quantified and exert an important bias in the forage growth determination

(Wade, 1976; Bircham and Hodgson, 1983).

10-

CONCLUSIONS

Legume percentage in treatments 1, 2 and 3 decreased with time
in year one. In year two all treatments showed an increase hi
legume percentage during the first part of the experimental
period, to decrease thereafter.

Legume percentages at the beginning of the second year were much
lower than in the same period in year one. The type of grazing
program used during the first year could explain the low values

obtained in treatments 2 and 3. For treatment 1, the long grazing

period may be responsible for such condition.

Dry matter offered per treatment was much higher in year one than

in year two. Differences between treatments were only significant

in year one, being higher for treatments 1 and 2 than for treatments
3 and 4. During year two, no significant differences were observed
between treatments.

During both years the dry matter offered was higher during the

first part of the experiment. Treatment 1 maintained the highest
forage available up to the end of August during the first year,

and to mdd August in the second grazing season.

In vitro dry matter digestibility across treatments decreased

with time in both years, and the average values for the different

229

100-

11.-

230

treatments were very similar for both grazing seasons.
Digestibility was higher in treatments 1 and 2 with respect to 3
and 4. The differences increase at the end of both grazing periods.
Part of the differences could be explained by the grazing system,
since rotation allows for a more uniform consumption of the
forage and its posterior regrowth.

Steers on treatment 1 had a higher intake during both years with
respect to the steers in the other three treatments. However, no
significant differences were obtained between treatments across
time.

The digestibility values across treatments are lower than 65 %,
indicating a possible physical control of forage intake. However,
it is very likely that the steers in treatments 1 and 2 could
select a higher quality diet than the average taken from hand-
harvested material. This is supported by the sharp decreases
observed in legume percentages at the end of every grazing time.
Treatment 1 showed the highest gain per treatment per time in
both grazing years. However, only treatments 1 and 4 showed
significant differences in both experimental periods.

Gain per treatment and per day was higher in year two for all
treatments. Treatment 2 produced the highest increase (58.27 %)
in the second year.

When kilograms of liveweight per hectare is considered,
treatment 1 outproduced the other three treatments in year one.
Treatments 3 and 4 obtained the lowest production per hectare,

but no significant differences were observed between them in

12.-

13.-

14.-

150-

16.-

17.-

231

year one. Treatment 2 produced intermediate gains per hectare,
significantly higher than treatment 4 and lower than treatment
1.

During year two, the ranking of the treatments was similar to
year one, but the differences between treatments 1 and 2 were
not significant. However, a significant difference was obtained
between treatments 2 and 3, and between treatments 3 and 4.

An important increase in gain per hectare in year two with
respect to year one was observed, and the most marked increment
occured with steers in treatment 2 (45.34 Z). In all treatments,
the gain per animal was higher than the gain per unit area,
which indicates that we still can increase the stocking rate in
all treatments if the main objective is maximization of gain

per unit area.

Total gain per treatment and per hectare were larger during the
first two months of the experimental seasons. The peak observed
in average daily gain at the end of the first year was basically
attributed to a lower stocking rate across treatments, which in
turn allowed the steers a higher degree of forage selection.
Steers per hectare were higher for treatments 1 and 2 during
both years.

Treatments 1 and 4 produced a longer grazing period than treatments
2 and 3.

Treatment 2 had the highest increment in all parameters considered
from the first to the second year. This shows the importance of

rotating the birdsfoot trefoil-grass mixture three times during

232

the grazing cycle. The advantage of this system is to utilize
this mixture early and late in the season, in order to harvest
the fescue at its optimum quality. At the same time, a longer

rest period for the alfalfa-grass mixture is allowed.

RECOMMENDATIONS FOR FUTURE RESEARCH

Different possible areas of research can be identified: animal

production, forage production and quality, and plant-animal

relationship.

l.- Animal production:

1. 10-

1020-

1.3.-

1.4.-

To continue with this experiment for the remaining useful
life of the pastures. However, two modifications can be
introduced to the design: introduction of a third mixture
instead of sorghum, since this species did not show any
specific advantage during both experimental seasons. The
second modification is to increase the stocking rate in
treatments 1 and 2 to evaluate the responses per animal
and per unit area.

To determine the mathematical relationship between production
per animal and per unit area with different stocking rates.
Since this is dependent on the quantity and quality of the
pasture, I propose to use the alfalfa-grass mixture until
maximum potential is determined for treatment 2.

To study the influence of the pasture stage on the
final performance of the steers on feedlot.

To study the mathematical relationship between intake and

forage related characteristics. There is some encouraging

233

234

information to use dry matter available and digestibility
when legume-grasses are used.
2.- Forage production:

2.1.- To study the growth pattern of the alfalfa grass mixture
in relation with the variables used in our model. It may
be necessary to include evapotranspiration instead of
evaporation as one independent variable. At the same time,
it may be advisable to use daylength as well, according to
some previous reports published recently. Not enough
information regarding forage growth under grazing conditions
and on pasture mixtures is available.

2.2.— To determine quality parameters of the pasture: fiber,
digestibility, lignin, silica. Once mathematical relations
were established for each specie or mixture of species,
lignin and silica components have to be identified. The
following step in the sequence is to study the anatomy of
the pastures and identify the differences in deposition
that exist between the different species. This seems to be
the most important factor to explain species differences
in digestibility and intake.

3.- Plant-animal relationship:

3.1.- To study pasture selection by animals relating dry matter
availability, stocking pressure and quality parameters
within species or mixture of species.

3.2.- To determine the relationship between hand-harvested forage

digestibility and digestibility of the selected forages by

3.3.-

3040-

235

the animals themselves, with various amounts of dry matter
available per animal.

To establish economic evaluations of all pature systems

in order to determine the systems with more comparative
advantages to be applicable under field conditions.

Since this is a five year project, it is suggested to
complete the economic analysis at the end of the period.
Partial budgeting is the easiest procedure for such a
purpose. The variables to consider can be summarized as

follows:

a description of the grazing systems;

- stocking pressures and weight gains per animal and
per hectare;

- investments attributable to each specific grazing
system such as fertilizer, fencing, water facilities,
labor costs, use of equipment and management skills
involved;

- major receipt changes due to variation in animal

wights, livestock quality and prices; and

- total costs common to all grazing systems.

BIBLIOGRAPHY

Acord, C. R. 1970. Beef production on irrigated alfalfa pastures.
J.A.V.M.A. 157: 1564.

Ahlgren, H. L. A. 1947. A comparison of methods used in evaluating
the results of pasture research. J. Amer. Soc. Agron. 39:240.

Akin, D. E. 1981. Microbial breakdown of feed in the digestive tract.
Proc. of Int. Symp., Nutritional limits to animal production
from pastures, Sta. Lucia, Australia, p. 201.

Akin, D. E. 1982a. Forage cell wall degradation and proumaric,
Ferulic, and Sinapic acids. Agron. J. 74:424.

Akin, D. E. 1982b. Section to slide technique for study of forage
anatomy and digestion. Crop Sci. 22:444.

Akin, D. E. 1983. Structural characteristics limiting digestion of
forage fiber. Proc. XIV Int. Grassld. Conf. 14:511.

Akin, D. E., D. Burdick. 1975. Percentage of tissue types in tropical
and temperate grass leaf blades and degradation of tissues by
rumen microorganisms. Crop Sci. 15:661.

Akin, D. E., D. Burdick. 1981. Relationships of different hystodhemical
types of lignified cell walls to forage digestibility. Crop
Sci. 21:577.

Akin, D. E., F. E. Barton II. 1983. Rumen microbial attachment and
degradation of plant cell walls. Fed. Proc. 42:114.

Alder, F. E. 1969. Comparative studies of perennial ryegrass, timothy
and meadow fescue. 1.- Herbage consumption and performance of
calves fed on cut grass. J. Br. Grassl. Soc. 24:308.

Alder, F. E. 1970. Comparative studies of perennial ryegrass, timothy

and meadow fescue. 2.~ Results obtained with grazing experiments.
J. Br; Grassl. Soc. 25:53.

236

237

Alder, F. E., D. J. Minson. 1963. The herbage intake of cattle
, grazing lucerne and cocksfoot pastures. J. agric. Sci. 60:359.

Allden, W. G., I. A. M. Whittaker. 1970. The determinants of herbage
intake by grazing sheep: the interrelationship of factors
influencing herbage intake and availability. Aust. J. Agric.
Res. 21:755.

Allinson, D. W. 1970. Forage lignins and their relationship to
nutritive value. Proc. of the Natl. Conf. on forage quality
evaluation and utilization, Paper S, University of Nebraska.

Allinson, D. W. 1971. Influence of photoperiod and thermoperiod on
the IVDMD and cell wall components of tall fescue. Crop Sci.
11:456.

Almquist, C. N., V. H. Brungardt, W. J. Tyler, R. C. Waldman. 1971.
Growth and efficiency of Holstein steers as influenced by
live weight and energy intake. J. Dairy Sci. 54:681.

Alvey, N. G., members of the Rothamsted Experiment Station. 1977.
Genstat: a general statistical program. Rothamsted Expt.
Station, volumes 1 and 2.

Anonymous. 1952. Pasture and range research techniques. Joint
Committee Am. Soc. of Agron., Agron. J. 44:39.

Anonymous. 1961. Research techniques in use at the Grassland
Research Institute, Hurley. Bull. 45. Commonwealth Bureau
of Pastures and Field Crops, Berkshyre, England, 167 pages.

Anonymous. 1974. Census of Agriculture, volume 1 part 22. Michigan
Bureau of the Census. U. S. Department of Commerce.

Anthony, W. B., R. R. Harris. 1976. Effects of legumes on performance
of grazing animals. Biological nitrogen fixation in forage-
livestock systems, Special publ. 28, Am. Soc. of Agron.,

Crop Sci. Soc. of America, Soil Sci. Soc. of America, page 73.

Archibald, K. A. E., R. C. Campling, W. Holmes. 1975. Mfllk production
and herbage intake of dairy cows kept on a leader and follower
grazing system. Anim. Prod. 21:147.

Arizona Interagency Range Committee. 1973. Grazing systems for
Arizona Ranges. Mimeographed.

Arnold, G. W. 1960. Selective grazing by sheep of two forage species
at different stages of growth. Aust. J. Agric. Res. 11:1026.

238

Arnold, G. W. 1962. The influence of several factors in determining
the grazing behavior of Border Leicester x Merino sheep.
J. Br. Grassl. Soc. 17:41.

Arnold, G. W. 1963. PhD thesis. Australia. Cited by Arnold, 1964.

Arnold, G. W. 1964. Some principles in the investigation of selective
grazing. Proc., Aust. Soc. Anim. Prod. 5:258.

Arnold, G. W. 1966a. The special senses in grazing animals. 1.— Smell,
taste and touch and dietary habits in sheep. Aust. J. Agric.
Res. 17:521.

Arnold, G. W. 1966b. The special senses in grazing animals. 2.— Sight
and dietary habits in sheep. Aust. J. Agric. Res. 17:531.

Arnold, G. W. 1970. Regulation of food intake in grazing ruminants.

Proc. 3rd. Int. Symp., Physiology of digestion and metabolism
in the ruminant, page 264. Oriel Press,

Arnold, G. W. 1981. Grazing behavior. Grazing animals, volume B-l,
chapter 5, page 79, Elsevier Publication.

Arnold, G. W., M. L. Dudzinski. 1967a. Study on the diet of the
grazing animals. 2.- The effect of physiological status in
ewes and pasture availability on herbage intake. Aust. J.
Agric. Res. 18:349.

Arnold, G. W., M. L. Dudzinski. 1967b. Studies on the diet of the
grazing animals. 3.- The effect of pasture species and pasture
structure on the herbage intake of sheep. Aust. J. Agric.

Res. 18:657.

Arnold, G. W., J. L. Hill. 1972. Chemical factors affecting selection
of food plants by ruminants. Phytochemical ecology, page 71,
Academic Press.

Arnold, G. W., M. L. Dudzinski. 1978. The ethology of freeeranging
domestic animals. Elsevier Publication, 198 pages.

Axelson, A., F. Morley. 1968. Evaluation of eight pastures by animal
production. Proc., Aust. Soc. Animn Prod. 7:92.

Bailey, P. J., A. H. Bishop, C. T. Boord. 1974. Grazing behavior of
steers. Proc., Aust. Soc. Anim. Prod. 10L303.

Baker, B. S., G. A. Jung. 1970. Response of four perennial grasses
to high temperature stress. Proc. XI Int. Grassl. Cong.
11:499.

Baker, B. S., R. E. Blaser, D. A. Dinius, D. Fox, R. R. Hill, Jr.,

239

P. E. Nesselroad, J. B. Washko. L. L- Wilson. 1974, Forageebeef cowv
calf workshop. Second task group. University of Pennsylvania.

Baker, R. D. 1976. Effect of award characteristics on herbage intake
under grazing: nutritive quality, species and amount. Occasional
Symposium, British Grassland Society, page 87.

Balasko, J., J. Baylor, C. Boyles, P. Comerford, V. Crowley, R. Hammes
Jr., R. Lucey, W. Pardee, J. Peters. 1974. Forageébeef cow-
calf workshop. First task group. University of Pennsylvania.

Barnes, R. F. 1981. The role of forage in the United States. Proc.,
Forage evaluation: concepts and techniques, page 1.Armidale,
Australia. CSIRO.

Bartholomew, P. W., D. M. B. Chestnutt. 1977. The effect of a wide
range of fertilizer nitrogen appltation rates and defoliation
intervals on the dry matter production, seasonal response to
nitrogen, persistence and aspects of chemical composition of
perrennial ryegrass. J. Agric Sci. 88:711.

Bartholomew, P. W., W. McLauchlan, D.M. B. Chestnutt. 1981. An
assessment of the influence on net herbage accumulation, herbage
consumption and individual animal performance of two length of
grazing rotation and three herbage allownaces for grazing beef
cattle. J. Agric. Sci. 96:363.

Barton, F. E. II, H. E. Amos, D. Burdick, R. L. Wilson. 1976.
Relationship of chemical analysis to in vitro digestibility
for selected tropical and temperate grasses. J. Anim. Sci.
43:504.

Barton, F. E., D. E. Akin. 1977. Digestibility of delignified forage
cell walls. J. Agr. Food Chem. 25:1299.

Bauder, J. W., A. Bauer, J. M. Ramirez, D. K. Cassel. 1978. Alfalfa
water use and production on dryland and irrigated sandy loam.
Agron. J. 70:95.

Baxter, H. D., J. R. Owen, M. J. Montgomery, D. R. Waldo, J. T. Miles.
1969. Pasturing versus harvesting of a grass—legume mixture.
Tennessee Experimental Station, Research Bulletin 454.

Beardsley, A. E., S. R. Anderson. 1960. The effect of height and
frequency of cutting various strains of birdsfoot trefoil—
timothy associations as compared to a Ranger alfalfaptimothy
association. Am. Soc. Agron. Abstracts Pp. 62.

Beaty, E. R., J. W. Dobson, A. E. Smith. 1978a. Tall fescue tiller
weights, green forage present and forage IVDMD. Agron. J.
70:223.

240

Beaty, E. R., 0. L. Brooks, D. D. Hayes, N. D. McRainey, P. Gardner.
1978b. Alfalfa for Georgia. ResearCh Bulletin 211, university
of Georgia.

Beaty, E. R., J. L. Engel. 1980. Forage quality measurements and
forage research. A review, critique and interpretation.
J. Range Mgmt. 33:49.

Beevers, H. 1969. Metabolic sinks. Proc. of Symp., Physiological
aspects of crop yield, chapter 8, page 169. Published by
ASA, CSSA, University of Nebraska.

Bell, F. R. 1961. Some observations on the physiology of rumination.
Proc., Digetsive physiology and nutrition of the ruminant,
page 59, Butterworths.

Beranger, C., M. Negrin, C. Malterre. 1970. Cited by Beranger, 1977.

Beranger, C. 1977. Grazing management for beef production. Proc.,
Int. Meeting on Animal Production from Temperate Grassland,
page 126, Dublin, An Foras Taluntais.

Berry, J. A. 1975. Adaptation of the photosynthetic process to stress.
Science 188:644.

Berry, R. F., C. S. Hoveland. 1969. Summer defoliation and autumn-
winter production of phalaris sps and tall fescue varieties.
Agron. J. 61:493.

Bines, J. A. 1976. Regulation of food intake in dairy cows in relation
to milk production. Livestock Prod. Sci. 3:115.

Bines, J. A. 1979. Voluntary food intake. Feeding strategy for high
yielding dairy cows, chapter 3, page 23. Granada Publishing,
E.A.A.P. Publication 25.

Bircham, J. S., J. Hodgson. 1983. Dynamics of herbage growth and
senescence in a mixed species temperate award continuously
grazed by sheep. Proc. XIV Int. Grassl. Cong., 14:601.

Blaser, R. E., W. H. Skrdla, T. Taylor. 1952. Advantages and disadvantages
of simple and complex mixtures. Proc. VI Int. Grassl. Cong.,
6:349, section B-l.

Blaser, R. E., R. C. Hammes Jr., H. T. Bryant, C. M. Kincaid, W. H.
Skrdla, T. H. Taylor, W. L. Griffith. 1956. The value of
forage species and mixtures for fattening steers. Agron. J.
48:508.

Blaser, R. E., H. T. Bryant, C. Y. Ward, R. C. Hammes Jr., R. C.
Carter, N. H. Macleod. 1959. Symposium on animal evaluation.

241

VII. Animal performance and yields with methods of utilizing pasturage.
Agron. J. 51:238.

Blaser, R. E., R. C. Hammes Jr., H. '1‘. Bryant, W. A. Hardison, J. P.
Fontenot, R. W. Engel. 1960. The effect of selective grazing
on animal output. Proc. VIII Int. Grassl. Cong., 8:601.

Blaser, R. E., J. R. Harlan, R. ML Love. 1962. Grazing management.
Pasture and range research tecniques, chapter 4, page 11.
Prepared by ASA, ADSA, ASAP, ASRM, Cornell University Press.

Blaser, R. E., H. T. Bryant, R. C. Hammes Jr., R. L. Boman, J. P.
Fontenot, C. E. Polan, C. Y. Kramer. 1969. Managing forages
for animal production. Research Bulletin 45, Virginia Pol.
Inst. and State University.

Blaser, R. E., W. C. Stringer, E. B. Rayburn, J. P. Fontenot, R. C.
Hammes Jr., H. T. Bryant. 1875. Increasing digestibility and
intake through management of grazing systems. Southern
Regional Forage—fed Beef Research Workshop, New Orleans.

Blaxter, K. L., R. S. Wilson. 1963. The assessment of a crop husbandry
technique in terms of animal production. Anim. Prod. 5:27.

Blaxter, K. L., F. W. Wainman, P. J. S. Dewey, J. Davidson, H. Denerle,
J. B. Gunn. 1971. The effect of nitrogenous fertilizer on the
nutritive value of artificially dried grass. J. Agric. Sci.
76:307.

Blue, W. G. 1980. Long term fertility studies as related to pastures
and small plots: how precise are small-plot data for predicting
pasture needs?. Proc. 37th Southern Pasture and Crop Improvement
Conference, page 64.

Bone, J. S., R. S. Tayler. 1963. The effect of irrigation and stocking
rate on the output from a sward. II. Dairy cow production.
J. Brit. Grassl. Soc. 18:295.

Booysen, P. de V. 1966. A physiological approach to research in pasture
utilization. Proc. Grassl. Soc. Sth. Afr. 1:77.

Bosch, S. 1956. The determination of pasture yield. Neth. J. Agric.
Sci. 4:305.

Boyd, D. A. 1949. Experiments with leys and permanent grass. J. Brit.
Grassl. Soc. 4: 1.

Brady, C. J. 1976. Plant proteins, their occurrence, quality and
distribution. Proc., Symp. From plant to animal protein, Reviews
in Rural Sci., number II, page 13.

242

Branaman, G. A., A. M. Pearson, W. T. Magee, R. M. Griswold, G. A.
Brown. 1962. Comparison of the cutability and eatibility of
beef and dairy-type cattle. J. Anim. Sci. 21:321.

Bransby, D. I., A. G. MatChes, G. F. Krause. 1977. Disk meter for
rapid estimation of herbage yield in grazing trials. Agron.
J. 69:393.

Branson, F. A. 1962. Botanical analysis and sampling: natural pastures
and range. Pasture and range research techniques, chapter 21,
page 134, ASA, ADSA, ASAP, ASRM, Cornell Univ. Press.

Breese, E. L. 1979. The importance of genotype in sward change. Proc.
Occ. Symp. number 10, Brit. Grassl. Soc., page 141.

Brougham, R. W. 1956. Effect of intensity of defoliation on regrowth
of pasture. Aust. J. Agric. Res. 7:377.

Brougham, R. W. 1958. Interception of light by the foliage of pure
and mixed stands of pasture plants. Aust. J. Agric. Res. 9:39.

Brougham, R. W. 1961. Factors limiting pasture production. Proc. N.
Z. Soc. Anim. Prod. 21:33.

Brown, D. 1954. Methods for surveying and measuring vegetation.
Commonwealth Bureaux of Pasture Field Crops, Bull. 42, 233
pages, England.

Brown, K. R. 1968. The influence of herbage height at treading and
treading intensity on the yields and botanical composition of

a perennial ryegrassawhite clover pasture. N. Z. J. Agric.
Res. 11:131.

Brown, K. R., P. S. Evans. 1973. Animal treading. A review of the
work of the late D. B. Edmond. N. Z. J. Exp. Agric. 1:217.

Brown, R. E., R. E. Blaser. 1968. Leaf area index in pasture growth.
Herb. Abstr. 38:1.

Brumby, P. J. 1959. The grazing behavior of dairy cattle in relation
to milk production, liveweight and pasture intake. N. Z. J.
Agric. Res. 2:797.

Brundage, A. L., W. E. Petersen. 1952. A comparison between daily
rotational grazing and continuous grazing. J. Dairy Sci. 35:623.

Brundage, A. L., W. J. Sweetman. 1956. The utilization of Smooth
bromegrass (Bromus inermis) under rotational and strip grazing
systems of pasture management. III. Animal behavior. J. Dairy
Sci. 39:297.

243

Bryann, W. W., N. H. Shaw, L. A. Edye, R. J. Jones, L. 't Mannetje,
J. J. Yates. 1964. The development and assessment of pastures.
Commonwealth Bureaux of Pasture Field Crops, Bull. 47, page
12 3, England.

Bryant, H. T., R. E. Blaser, R. C. Hammes Jr., W. A. Hardison. 1961a.
Method for increased milk production with rotational grazing.
J. Dairy Sci. 44 H733.

Bryant, H. T., R. E. Blaser, R. C. Hammes Jr., W. A. Hardison. 1961b.
Comparison of continuous and rotational grazing of three
forage mixtures by dairy cows. J. Dairy Sci. 44:1742.

Bryant, H. T., R. E. Blaser. 1961. Yields and stands of orchardgrass
compared under clipping and grazing intensities. Agron. J.
53:9.

Bryant, H. T., R. E. Blaser. 1963. Effect of defoliation of four
alfalfa and one birdsfoot trefoil variety on yield of tops
and roots. Virginia Agr. Exp. Stat. and State Univ., Bull. 548.

Bryant, H. T., R. E. Blaser. 1964. Yield and persistency of an
alfalfa-orchardgrass mixture as affected by cutting treatment.
Virginia Agr. Exp. Stat. and State Univ., Bull. 555.

Bryant, H. T., R. C. Hammes Jr., R. E. Blaser, J. P. Fontenot. 1965.
Effect of stocking pressure on animal and acre output. Agron.
J. 57:273.

Bryant, H. T., R. E. Blaser, R. C. Hammes Jr., J. P. Fontenot. 1970.
Symposium on pasture methods for maximum production in beef
cattle: effect of grazing management on animal and area
output. J. Anim. Sci. 30:153.

Buckner, R. C. 1960. Performance of inbred lines, polycross progenies,
and synthetics of tall fescue selected for improved palatability.
Agron. J. 52:177.

Bull, T. A. 1969. Photosynthetic efficiencies and photorespiration
in Calvin Cycle and C4-Dicarboxylic acid plants. Crop Sci.
9:726.

Burdick, D. 1980. Composition and microbial degradation of forage cell
walls. King visiting scholar lectures, Special reports 77,
page 15, Univ. of Arkansas.

Burger, A. W., J. A. Jackobs, C. N. Hittle. 1958. The effect of height
and frequency of cutting on the yield and botanical composition
of tall fescue and smooth bromegrass mixtures. Agron. J. 50:629.

244

Burger, A. W., C. N. Hittle. 1967. Yield, protein, nitrate, and
prussic acid content of sudangrass, sudangrass hybrids and
pearl millets harvested at two cutting frequencies and two
stubble heights. Agron. J. 59:259.

Burns, J. C. 1978. Symposium: Forage quality and animal performance.
Antiquality factors as related to forage quality. J. Dairy
Sci. 61:1809.

Burns, J. C., H. D. Gross, W. B. Gilbert, R. W. Harvey, M. W. Wise,
D. F. Tugman, J. W. Bentley. 1970a. Pastures and grazing
systems in the mountains of North Carolina. North Carolina
State Univ., Agric. Exp. Sta., Bull. 437.

Burns, J. C., R. D. Mochrie, H. D. Gross, H. L. Lucas, R. Teichman.
1970b. Comparison of set-stocked and put-and-take systems
with growing heifers grazing coastal bermudagrass (Cynodon
dactylon L. Pers.). Proc. XI Int. Grassl. Cong. 11:904.

Burns, J. C., L. Goode, H. D. Gross, A. C. Linnerud. 1973. Cow and
calf gains on ladino clover-tall fescue and tall fescue,
grazed alone and with coastal bermudagrass. Agron. J. 65:877.

Burns, J. C., R. D. Mochrie. 1980. Methods to determine or estimate
voluntary intake in grazing livestock. Proc. 37th. Southern
Pasture and Forage Crop Improvement Conf., page 127.

Burton, G. W. 1976. Legume nitrogen versus fertilizer nitrogen for
warm season grasses. Proc., Symp. Biological nitrogen fixation
in forage-livestock systems, ASA Special Publ. number 28,
page 55.

Burton, G. W. 1981. The philosophy of the genetic improvement of
forage grasses. King visiting scholar lectures, Special
report 63, page 21, Univ. of Arkansas.

Calder, J. W. 1952. The important role of legumes in grazed pastures
with special reference to improved productivity of farms in
Canterbury, New Zealand. Proc. VI Int. Grassl. Cong. 6:462.

Clader, F. W., J. W. G. Nicholson, R. B. Carson. 1970. Effect of
actual versus simulated grazing on pasture productivity and
chemical composition of forage. Can. J. Anim. Sci. 50:475.

Campbell, A. G. 1961. A theoretical basis for grazing management.
Proc. N. 2. 80¢. Anim. Prod. 21:18.

245

Campbell, A. G.1966a. Grazed pasture parameters. I. Pasture dry matter
production and availability in a stocking rate and grazing
management experiment with dairy cows. J. Agric. Sci. 67:199.

Campbell, A. G. 1966b. Grazed pasture parameters. II. Pasture dry
matter use in a stocking rate and grazing management experiments
,with dairy cows. J. Agric. Sci. 67:211.

Campbell, A. G. 1966c. Grazed pasture parameters. III. Relationships
of pasture and animal parameters, and general discussion of a
stocking rate and grazing management experiment with dairy cows.
J. Agric. Sci. 67:217.

Campbell, A. G. 1967. Liveweight gains from lucerne. The lucerne crop,
page 261, Australia.

Campbell, J. B. 1963. Grass-alfalfa versus grass alone pastures grazed
in a repeated-seasonal pattern. J. Range Mgmt. 16:78.

Campbell, J. B. 1969. Pasture activities of cattle and sheep.
Experimental methods for evaluating herbage, Publ. 1315, Canada
Dept. of Agric., page 105.

Campling, R. C. 1970. Physical regulation of voluntary intake. Symp.,
Physiology of digestion and metabolism in the ruminant, page 226,
Oriel Press. ‘

Campling, R. C. 1976. Systems of grazing management for dairy cattle.
Proc, Occ. Symp. number 8, page 113, Brit. Grassl. Soc.

Campling, R. C., C. C. Balch. 1961. Cited by Campling et al., 1962.

Campling, R. C., M. Freer, C. C. Balch. 1962. Factors affecting voluntary
intake of food by cows. III. The effect of urea on the voluntary
intake of oat straw. Br. J. Nutr. 16:115.

Carr, A. J. 1979. Causes of award changes: diseases. Proc., Occ. Symp.
number 10, Brit. Grassl. Soc., page 161.

Carter, E. D., T. Sivalingam. 1977. Some effects of treading by sheep
on pastures of the mediterranean climate zone of Sputh Australia.
Proc. XIII Int. Grassl. Cong. 13:641.

Carter, J. F. 1962. Herbage sampling for yield: tame pastures. Pasture
and range research techniques, ASA, ADSA, ASAP, ASRM, page 90,
Cornell Univ. Press.

Carter, J. F., A. G. Law. 1948. The effect of clipping upon the
vegetative development of some perennial grasses. J. Amer. Soc.
Agron. 40:1084.

246

Carter, J. F., H. L. Ahlgren. 1951. Forage yield and disease
development of two varieties of smooth bromegrass, Bromus
inermis Leyss., grown under various conditions in the field.
Agron. J. 43:166.

Carter, J. F., D. W. Bolin, D. Erickson. 1960. The evaluation of
forages by the agronomic "difference" method and the chromogen-
chromic oxide "indicator" technique. North Dakota Agric.
College, Agr. Exp. Sta., Tech. bull. 426.

Carter, L. P., J. M. Scholl. 1962. Effectiveness of inorganic nitrogen
as a replacement for legumes grown in association with forage
grasses. I. Dry matter production and botanical composition.
Agron. J. 54:161.

Castle, M. E., E. MacDaid, J. N. Watson. 1972. Some factors affecting
milk production from grassland at the Hannah Research Institute,
1951-1970. J. Brit. Grassl. Soc. 27:87.

Castle, M. E., J. N. Watson. 1978. Further comparisons between a rigid
rotational "Wye College" system and other systems of grazing .
for milk production. J. Brit. Grassl. Soc. 30:1.

Charcon, E., T. H. Stobbs. 1976. Influence of progressive defoliation
of a grass award on the eating behavior of cattle. Aust. J.
Agric. Res. 27:709.

Charles, A. H. 1979. Treading as a factor in sward deterioration.
Proc., Occ. Symp. number 10, page 137, Brit. Grassl. Soc.

Chase, L. E., P. J. Wangsness, B. R. Baumgard. 1976. Feeding behavior
of steers fed a complete mixed ration. J. Dairy Sci. 59:1923.

Christian, K. R. 1977. Effects of the environment on the growth of
alfalfa. Adv. in Agronomy 29:183.

Christian, K. R., D. B. Jones, M. Freer. 1970. Digestibility and
chemical composition of fractions of lucerne during spring
and summer. J. Agric. Sci. 75:213.

Colby, W. G., Mack Drake, D. L. Field, G. Kreowski. 1965. Seasonal
pattern of fructosan in orchardgrass stubble as influenced by
nitrogen and harvest management. Agron. J. 57:169.

Cole, J. W., C. B. Ramsey, C. S. Hobbs, R. S. Temple. 1963. Effect
of type and breed of British, Zebu and dairy cattle on production,
palatability and composition. I. Rate of gain, feed efficiency
and factors affecting market value. J. Anim. Sci. 22:702.

247

Cole, J. W., C. B. Ramsey, C. S. Hobbs, R. 8. Temple. 1964. Effect of
type of breed of British, Zebu and dairy cattle on production,
palatability and composition. III. Percentage wholesale cuts
and yield of edible portion as determined by physical and
chemical analysis. J. Anim. Sci. 23:71.

Coleman, S. W. 1980. A review of three methods to estimate voluntary
intake of grazing cattle. Proc. 37th Southern Pasture and
Forage Crop Improvement Conf., page 106, U.S.D.A.

Coleman, S. W.,‘K. M. Barth, J. B. McLaren, T. W. High, H. C. Wrang,
C. S. Hobbs. 1971. Composition of diets selected by grazing
beef cattle determined after adjusting for esophageal-fistula
effects. Univ. of Tennessee, Agr. Exp. Sta., Bull. 483.

Coleman, S. W., K. M. Barth. 1973. Quality of diets by grazing animals
and its relation to quality of available forage and species
composition of pastures. J. Anim. Sci. 36:754.

Conniffe, D., D. Brown, M. J. Walshe. 1970. Experimental design for
grazing trials. J. Agric. Sci. 74:339.

Conniffe, D., D. Brown, M. J. Walshe. 1972. An example of a method
of statistical analysis of a grazing experiment. Short notes.
J. Agric. Sci. 79:165.

Connolly, J. 1976. Some comments on the shape of the gain-stocking
rate curve. J. Agric. Sci. 86:103.

Conrad, H. R., A. D. Pratt, J. W. Hibbs. 1964. Regulation of feed
intake in dairy cows. I. Change in importance of physical and
physiological factors with increasing digestibility. J. Dairy
Sci. 47:54.

Conway, A. 1963a. Effect of grazing management on beef production.
I. Comparison of three systems of grazing. Irish J. of Agric.
Res. 2:87.

Conway, A. 1963b. II. Comparison of three stocking rates under two
systems of grazing. Irish J. of Agric. Res. 2:243.

Conway, A. 1968. IV. Effect of seasonal variation in the stocking

rate of beef cattle on animal production and on award composition.
Irish J. of Agric. Res. 7:93.

Conway, A. 1974. A production function for grazing cattle. III. An
estimated relationship between rate of liveweight gain and
stocking rate for grazing steers. Irish J. of Agric. Econ.
and Rural Sociol. 5:43.

248

Cook, C. W. 1973. Forage utilization, daily intake and nutrient value
of desert range. Proc., Third workshop of the U.S.A. and
Australian Rangelands Panel, page 47, Arizona.

Cook, C. W., L. E. Harris, L. A. Stoddart. 1948. Measuring the nutritive
content of a foraging sheep's diet under range conditions.
J. Anim. Sci. 7:170.

Cook, C. W., L. E. Harris. 1950. The nutritive content of the grazing
sheep's diet on summer and winter ranges of Utah. Utah Agr.

Cook, C. W., J. T. Blake, C. W. Call. 1963. Use of esophageal-fistula
cannulae for collecting forage samples from.both sheep and
cattle grazing in common. J. Anim. Sci. 22:579.

Cook, C. W., L. E. Harris. 1968a. Nutritive value of seasonal ranges.

Cook, C. W., L. E. Harris. 1968b. Effect of supplementation on
intake and digestibility of range forage. Utah Agr. Exp. Sta.,
Bull. 475.

Cook, R. 1980. Advanced ruminant biochemistry. Mimeographed, Michigan
State University.

Cooke, D. A. 1969. Estimating herbage yield from simulated grazing
trials. Experimental methods for evaluating herbage, Publ.
1315, page 80, Canada Dept. of Agric.

Cooper, C. S. 1966. Response of birdsfoot trefoil and alfalfa to
various levels of shade. Crop Sci. 6:63.

Cooper, C. S., C. A. Watson. 1968. Total available carbohydrates in
roots of sainfoin (Onobrychis viciaefolia Scop.) and alfalfa
(Medicago sative L.) when grown under several management
regimes. Crop Sci. 8:83.

Copeman, G. J. F. 1979. Causes of sward changes: climate. Proc.,
Occ. Symp. number 10, page 151, Brit. Grassl. Soc.

Coppock, C. E. 1978. Feeding energy to dairy cattle. Proc. Symp.
Large dairy herd management, page 266, Univ. of Florida.

Cordova, F. J., J. D. Wallace, R. D. Pieper. 1978. Forage intake by
grazing livestock. A review. J. Range Mgmt. 31:430.

Corbett, J. L. 1960. Fecal-index techniques for estimating herbage
consumption by grazing animals. Proc. VIII Int. Grassl. Cong.
8:438.

Corbett, J. L. 1978. Measuring animal performance. Commonwealth
Agricultural Bureaux, chapter 7, page 163, Bulletin 52,
Great Britain.

249

Corbett, J. L. 1981. Determination of retention of energy and nutrients
by confined animals. Proc., Forage evaluation: concepts and
techniques, page 191, CSIRO, Australia.

Corbett,J. L., J. P. Langlands, G. W. Reid. 1963. Effects of season
of growth and digestibility of herbage on intake by grazing
dairy cattle. Anim. Prod. 5:119.

Corbett, J. L., E. P. Furnival, M. W. Inskip, C. J. Perez, F. 8.
Pickering. 1976. Nutrition and growth of lambs grazing lucerne
or phalaris. Proc. Aust. Soc. Anim. Prod. 11:329.

Cowlishaw, S. J. 1951. The effect of sampling cages on the yield of
herbage. J. Brit. Grassl. Soc. 6:179.

Cowlishaw, S. J. 1969. Carrying capacity of pastures. J. Brit. Grassl.
Soc. 24:207.

Cowlishaw, S. J., F. E. Alder. 1960. The grazing preferences of cattle
and sheep. J. Agric. Sci. 54:257.

Cowan, R. T. 1975. Grazing time and pattern of grazing of Friesian
cows on a tropical grass-legume pasture. Aust. J. of Exp.
Agric. and Anim. Husb. 15:32.

Cuykendall, C. H., G. C. Marten. 1968. Defoliation by sheep-grazing
versus mower-clipping for evaluation of forages. Agron. J.
60:404.

Davidson, J. L., F. L. Milthorpe. 1965. Carbohydrate reserves in
regrowth of cocksfoot (Dactylis glomerata L.). J. Brit.
Grassl. Soc. 20:15.

Davidson, R. L. 1976. Root systems: the forgotten component of
pastures. Proc., Symp. Plant relations in pastures, page 86,
CSIRO, Australia.

Davies, W. 1952. Maintaining legumes in the award. Proc. VI Int.
Grassl. Cong. 6:456.

Davies, W. Ellis, R. 0. Davies. The yield and composition of lucerne,
grass and clover under different systems of management. J. Brit.
Grassl. Soc. 11:127. 1956.

Davies, W. Ellis, R. 0. Davies, A. Harvard. 1960. The yield and
composition of lucerne, grass and clover under different
systems of management. III. The effect of nitrogen and
frequency of cutting. J. Brit. Grassl. Soc. 15:106.

250

Davies, W. Ellis, B. F. Tyler. 1962. The yield and composition of
lucerne, grass and clover under different systems of management.
IV. Further studies on the effect of frequency of cutting
lucerne and lucerne grown with grasses. J. Brit. Grassl. Soc.
17:306.

Davies,A. 1974. Leaf tissue remaining after cutting and regrowth in
perennial ryegrass. J. Agric. Sci. 82:165.

Davies, A. 1977. Structure of the grass sward. Proc. Int. Meeting on
Anim. Prod. from Temperate Grasslands, page 36, An Foras
Taluntais.

Davis, R. 0., T. B. Morgan, W. E. Davies. 1953. The yield and
composition of lucerne, grass and clover under different
systems of management. Part I. J. Brit. Grassl. Soc. 8:149.

Davis, R. R., A. D. Pratt. 1956. Rotation versus continuous grazing
with dairy cows. Ohio Exp. Sta., Res. Bull. 778.

Davis, R. R., D. S. Bell. 1957. A comparison of birdsfoot trefoil-
bluegrass and ladino clover-bluegrass for pasture. I. Response
of lambs. Agron. J. 49:436.

Davis, R. R., E. W. Klosterman. 1959. Response of beef cattle to
pasture improvement with birdsfoot trefoil. Ohio Agr. Exp.
Sta. Res. Circ. 75.

Deinum, B. 1974. Structural inhibitors of quality in forages. Proc.
5th General Meeting, European Grassland Federation, page 42.

Demarquilly, C., R. Jarrige. 1964. Valeur alimentaire de 1'herbe des
prairies temporaires aux stades d'explitation pour le paturage.
I. Composition chemique et digestibilite. ANN. Zootech.
13:301.

Demarquilly, C., R. Jarrige. 1971. The digestibility and intake of
forages from artificial and natural grasslands. Proc. 4th
General Meeting, European Grassland Federation, page 91.

Denmead, O. T. 1972. The microclimate of grass communities. The
biology and utilization of grasses, chapter 12, page 155,
Academic Press.

Dennis, R. E., C. M. Harrison, A. E. Erickson. 1959. Growth response
of alfalfa and sudangrass to cutting practices and soil
moisture. Agron. J. 51:617.

Dent, J. W. 1955. Seasonal yield and composition of lucerne in
relation to time of spring cutting. J. Brit. Grassl. Soc.
10:330.

251

Donnelly, E. D. 1954. Some factors that affect palatability in
Sericea lespedeza, L. cuneata. Agron. J. 46:96.

Dulphy, J. P., B. Remond, M. Theriez. 1980. Ingestive behavior and
related activities in ruminants. Symp., Digestive Physiology
and metabolism in ruminants, page 103.

Dunavin, L. S. 1970. Gahi-l pearl millet and two sorghum;x sudangrass
hybrids as pasture for yearling beef cattle. Agron. J. 62:375.

Duncan, W. G. 1969. Cultural manipulation for higher yields. Symp.,
Physiological aspects of crop yield, page 327, ASA, CSSA.

Edmond, D. B. 1958. The influence of treading on pasture: a
preliminary study. N. Z. J. Agric. Res. 1:319.

Edmond, D. B. 1962. Effects of treading pasture in summer under
different soil moisture levels. N. Z. J. Agric. Res. 5:389.

Edmond, D. B. 1963. Cited by Edmond, 1970.

Edmond, D. B. 1964. Some effect of sheep treading on the growth of
ten different pasture species. N. Z. J. Agric. Res. 7:1.

Edmond, D. B. 1966. Influence of animal treading on pasture growth.
Proc. X Int. Grassl. Cong. 10:453.

Edmond, D. B. 1970. Effects of treading on pastures using different
animals and soils. Proc. XI Int. Grassl. Cong. 11:604.

Egan, A. R., R. J. Moir. 1965. Nutritional status and intake
regulation in sheep. I. Effects of duodenally infused single
doses of casein, urea and propionate upon voluntary intake
of a low protein roughage by sheep. Aust. J. Agric. Res.
16:437.

Egan, A. R. 1965a. II. The influence of sustained duodenal infusions
of casein or urea upon the voluntary intake of low protein
roughages by sheep. Aust. J. Agric. Res. 16:451.

Egan, A. R. 1965b. III. The relationship between improvement of
nitrogen status and increase in voluntary intake of low
protein roughages by sheep. Aust. J. Agric. Res. 16:464.

Egan, A. R. 1965c. IV. The influence of protein supplements upon
acetate and propionate tolerance of sheep fed on low
quality chaffed oaten hay. Aust. J. Agric. Res. 16:473.

Ellis, W. C. 1978. Determinants of grazed forage intake and
digestibility. J. Dairy Sci. 61:1828.

252

El-Sharkway, M. A., J. D. Hesketh. 1964. Effect of temperature and
water deficit on leaf photosynthetic rates of different species.
Crop Sci. 4:514.

Emery, R. S. 1980. Mobilization, turnover and disposition of adipose
tissue lipids. Proc. Digestive physiology and metabolism in
ruminants, page 541.

England, F. 1968. Competition in mixtures of herbage grasses. J. of
Applied Ecol. 5:227.

Escuder, J. 1976. Experiment com animais em pastejo. Epamig, Brazil.

Evans, G. C. 1972. The quantitative analysis of plant growth.
Blackwell Scientific Publ., Oxford, 734 pages.

Evans, L. T. 1980. The physiological basis of crop yield. Crop
Physiology, some case histories, chapter 11, page 327,
Cambridge Univ. Press.

Federer, C. A., G. H. Tenpas, D. R. Schmidt, C. B. Tanner. 1961.
Pasture compaction by animal traffic. Agron. J. 53:53.

Ferris, J. N., K. T. Wright. 1976. The status of Michigan agriculture
in 1976. Agric. Economics Report 299, Michigan State University.

Folkins, L. P., J. E. R. Greenshields, F. S. Nowosad. 1961. Effect
of date and frequency of defoliation on yield and quality of
alfalfa. Can. J. Plant Sci. 41:188.

Fontenot, J. P., R. E. Blaser. 1965. Symposium on factors influencing
the voluntary intake of herbage by ruminants: selection and
intake by grazing animals. J. Anim. Sci. 24:1202.

Food and Agriculture Organization: F.A.O. 1978. Cited by Meijs,
1981a.

Forbes, J. M. 1980. Hormones and metabolites in the control of food
intake. Proc. Digestive physiology and metabolism in
ruminants, page 145.

Frame, J. 1976. A comparison of herbage production under cutting and
grazing (including comments on deleterious factors sudh as
treading). Proc. Occ. Symp. number 8, page 39, Brit. Grassl.
Soc.

Frame, J., I. V. Hunt. 1971. The effects of cutting and grazing
systems on herbage production from grass awards. J. Brit.
Grassl. Soc. 26:163.

Freer, M. 1981. The control of food intake by grazing animals.
Grazing animals, B-1:105, Elsevier.

253

Fuelleman, R. F., W. L. Burlison, W. G. Kammlade. 1944. A comparison
of bromegrass and orchardgrass pastures. J. Amer. Soc. Agron.
36:849.

Fulkerson, R. S. 1970. Location and fall harvest effects in Ontario
on food reserve storage in alfalfa. Proc. XI Int. Grassl.
Cong. 11:555.

Fuller, W.W., W. C. Elder, B. B. Tucker, W. E. MeMurphy. 1971. The
fescue in Oklahoma. Oklahoma State Univ. Agric Exp. Sta.
Prog. Report P-650.

Garcia—de-Siles, J. L., J. H. Ziegler, L. L. Wilson, J. D. Sink.
1977. Growth, carcass and muscle characters of Hereford and
Holstein steers. J. Anim. Sci. 44:973.

Garner, F. H. 1963. The palatability of herbage plants. J. Brit.
Grassl. Soc. 18:79.

Garrett, W. N. 1971. Energetic efficiency of beef and dairy steers.
J. Anim.. Sci. 32:451.

Garstang, J. R., C. H. Mudd. 1971. The rejection of contaminated
herbage by dairy cows. J. Brit. Grassl. Soc. 26:194 (Abstr.).

Gibb, M. J., T. T. Treacher. 1976. The effect of herbage allowance
on herbage intake and performance of lambs grazing perennial
ryegrass and red clover awards. J. Agric. Sci. 86:355.

Gill, J. L. 1978a.Design and analysis of experiments in the animal
and medical sciences. Volume 1, 409 pages, Iowa State Univ.
Press.

Gill, J. L. 1978b. Volume 2, 301 pages, Iowa State Univ. Press.

Gill, J. L. 1978c. Volume 3, Appendices, 173 pages, Iowa State
Univ. Press.

Goatdher, W. D., D. C. Churdh. 1970a. Taste responses in ruminants.
I. Reactions of sheep to sugars, sacharin, ethanol and salts.
J. Anim. Sci. 30:777.

Goatcher, W. D., D. C. Church. 1970b. II. Reactions of sheep to acids,
quinine, urea, and sodium hydroxide. J. Anim. Sci. 30:784.

Goatcher, W. D., D. C. Church. 1970c. III. Reactions of pigmy goats,

normal goats, sheep and cattle to sucrose and sodium chloride.
J. Anim. Sci. 31:364.

Goatcher, W. D., D. C. Church. 1970d. IV. Reactions of pigmy goats,
normal goats, sheep and cattle to acetic acid and quinine
hydrochloride. J. Anim. Sci. 31:373.

254

Goatcher, W. D., D. C. Church. 1970e. Review of some nutritional
aspects of the sense of taste. J. Anim. Sci. 31:973.

Goering, H. K., P. J. Van.Soest. 1970. Forage fiber analysis.
Agriculture Handbook, number 379, U.S.D.A.

Gordon, F. J. 1973. The effect of high nitrogen levels and stocking
rates on milk output from pastures. J. Brit. Grassl. Soc.
28:193.

Gradwell, M. V. 1960. Changes in the pore-space of a pasture topsoil
under animal treading. N. Z. J. Agric. Res. 3:663.

Gradwell, M. V. 1968. Cited by Charles, 1979.

Green, J. O. 1949. Herbage sampling errors and grazing trials.
J. Brit. Grassl. Soc. 4:11.

Green, J. O. 1952. Unpublished thesis. Cited by Green et al., 1952.

Green, J. 0., H. J. Langer, T. E. Williams. 1952. Sources and magnitudes
of experimental errors in grazing trials. Proc. VI Int. Grassl.
Cong. 6:1374.

Green, J. 0., A. J. Corrall. 1966. Forage sorghum trials at Hurley.
Technical Report number 5, Grassland Research Institute, Hurley.

Greenhalgh, J. F. D., G. W. Reid, J. N. Aitken, E. Florence. 1966.
The effects of grazing intensity on herbage consumption and
animal production. I. Short-term.effects in strip grazed
dairy cows. J. Agric. Sci. 67:13.

Greenhalgh, J. F. D., G. W. Reid, J. N. Aitken. 1967. II. Longer-term
effects in strip grazed dairy cows. J. Agric. Sci. 69:217.

Greenhalgh, J. F. D., G. W. Reid. 1969. III. Dairy cows grazed at two
intensities on clean or contaminated pastures. J. Agric. Sci.
72:223.

Greenhalgh, J. F. D., J. N. Aitken, G. W. Reid. 1972. A note on the
zero-grazing of beef cattle. J. Brit. Grassl. Soc. 27:173.

Greenwood, E. A. N., G. W. Arnold. 1968. The quantity and frequency
of removal of herbage from an emerging annual grass award by
sheep in a set-stocked system of grazing. J. Brit. Grassl.
Soc. 23:144.

Graig-Smith, P. 1964. Quantitative plant ecology. Butterworths
Scientific Publ.

Griffith, W. K., M. R. Teel. 1965. Effect of nitrogen and potassium
fertilization, stubble height and clipping frequency on yield
and persistence of ordhardgrass. Agron. J. 57:147.

255

Griffiths Davies, J. 1952. The establishment and maintenance of
legumes in the award. Proc. VI Int. Grassl. Cong. 6:433.

Griffiths, T. W. 1980. The relative efficiency of food utilization
of British Friesian entire male and castrate male cattle at
two levels of feeding. Anim. Prod. 30:53.

Grime, J. P. 1973. Cited by Hutchings and Budd, 1981.

Guss, S. B. 1971. Management of disease prevention in dairy beef
enterprises. J. Anim. Sci. 32:438.

Hall, R. L. 1978. The analysis and significance of competitive and
non competitive interference between species. Proc., Symp.
Plant relations in pastures, page 163, CSIRO, Australia.

Hallman Jr, L. C. 1971. Raising dairy calves for beef purposes.
J. Anim. Sci. 32:442.

Hamilton, B. A., K. J. Hutchinson, P. C. Annis, J. B. Donnelly.
1973. Relationships between the diet selected by grazing
sheep and the herbage on offer. Aust. J. Agric. Res. 24:271.

Hamilton, R. I., J. M. Scholl, A. L. Pope. 1969. Performance of three
grass species grown alone and with alfalfa under intensive

pasture management: animal and plant response. Agron. J.
61:357.

Hancock, J. 1952. Grazing behavior of identical twins in relation to
pasture type, intake and production of dairy cattle. Proc. VI
Int. Grassl. Cong. 6:1399.

Hancock, J. 1953. Grazing behavior of cattle. Anim. Breed. Abstr.
21:1.

Hancock, J. 1954. Studies of grazing behavior in relation to grassland
management. I. Variations in grazing habits of dairy cattle.
The J. of Agric. Sci. 44:420.

Hardison, W. A., J. T. Reid, C. M. Martin, P. G. Woolfolk. 1954.
Degree of herbage selection by grazing cattle. J. Dairy Sci.
37:89.

Harker, K. W., D. H. L. Rollinson, J. I. Taylor, R. N. Gourlay, W. R.
Nunn. 1961. Studies on the habits of Zebu cattle. VI. The
results on different pastures. J. Agric. Sci. 56:137.

Harper, J. L. 1978. Plant relations in pastures. Proc., Symp. Plant
relations in pastures, page 3, CSIRO, Australia.

Harris, L. E. 1962. Measurement of the energy value of pastures and
range forage. Pasture and range research techniques, page 75,
ASA, ADSA, ASAP, ASRM, Cornell Univ. Press.

256

Harris, L. E., G. P. Lofgreen, C. J. Kercher, 1% J. Raleigh, V. R.
Bohman. 1977. Techniques of research in range livestock
nutrition. Utah Sta. Univ. Bull. 471.

Harris, R. R., E. M. Evans, J. K. Boseck, W. B. Webster. 1972.
Fescue, orchardgrass and coastal bermudagrass grazing for
yearling beef steers. Alabama Agric. Exp. Sta. and Auburn
Univ. Bull 432.

Harris, W. 1978. Defoliation as a determinant of the growth,
persistence and composition of pastures. Proc., Symp. Plant
relations in pastures, page 67, CSIRO, Australia.

Hart, R. H. 1972. Forage yield, stocking rate and beef gains on
pasture. Herb. Abstr. 42:345.

Hart, R. H. 1978. Stocking rate theory and its application to
grazing on rangelands. Proc. lst. Int. Rangeland Cong.
page 547, Soc. for Range Management,) Olorado.

Hart, R. H. 1980. Determining a proper stocking rate for a grazing
systems. Proc., Symp. Grazing Mgmt. Systs. for S.W. Rangelands,
page 49, New Mexico.

Hart, R. H., G. E. Carlson, D. E. McCloud. 1971. Cummulative effects
of cutting management on forage yields and tiller densities
of tall fescue and orchardgrass. Agron. J. 63:895.

Harrison, C. M., C. L. Cole, H. C. Rather. 1941. Continuous and
rotation grazing of alfalfarbromegrass pastured with ewes
and lambs. Soil Sci. Soc. of America 6:303.

Hayes, D., L. Corah, G. E. Bartley. 1980. Grazing cattle on alfalfa.
KSU Cattleman's day, Report on Progress, 5 pages.

Hayman, J. M., D. J. Saville. 1981. Comparison of rotational grazing
with set stocking of ewes and lambs in spring on irrigated
pasture in Canterbury. N. Z. J. Exp. Agric. 9:11.

Heady, H. F. 1964. Palatability of herbage and animal preference.
J. Range Mgmt. 17:76.

Heady, H. F. 1970. Grazing systems: terms and definitions. J. Range
Mgmt. 23:59.

Heany, D. P. 1970. Voluntary intake as a component of an index to
forage quality. Proc., Nat. Conf. Forage quality, evaluation
and utilization, paper C, Univ. Nebraska.

Hedin, L., J. Rebischung. 1952. Maintien des legumineuses dans les
prairies. Proc. VI Int. Grassl. Cong. 6:450.

257

Hedrick, H. B. 1968. Bovine growth and composition. Univ. Missouri,
Res 0 Bull. 928.

Heinemann, W. W. 1969. Productivity of irrigated pastures under
combination and single species grazing. Washington Agr. Exp.
Sta. Bull. 717.

Heinemann, W. W. 1970. Continuous and rotation grazing by steers
on irrigated pastures. Washington Agr. Exp. Sta. Bull. 724.

Heinemann, W. W., R. W. Van Keuren. 1960. Grass-legume mixtures
versus grass and nitrogen for beef steers. Proc. VIII Int.
Grassl. Cong. 8:583.

Helsel, Z. R., H. Ritchie, J. R. Black, G. D. Schwab. 1978. Crown
forages and crop residues in the extension production of
feeder calves. Project outline, Michigan State University.

Herriot, J. B. D., D. A. Wells. 1963. The grazing animal and award
productivity. J. Agric. Sci. 61:89.

Hesketh, J. D. 1963. Limitations to photosynthesis responsible for
differences among species. Crop Sci. 3:493.

Hibbs, J. W., E. W. Klosterman, H. R. Conrad, L. E. Kunkle, V. R.
Cahill. 1959. Dairy beef production. Part 1. Ohio Agr. Exp.
Sta. Bull. 833.

High Jr, J. W., L. M. Safley, O. H. Long, H. R. Duncan, T. W. High
Jr. 1965. Combinations of orchardgrass, fescue and ladino

clover pastures for producing yearling steers. Tennessee
Agr. Exp. Sta. Bull. 388.

High, T. W., C. S. Hobbs. 1966. A study of dietary selectivity by
esophageal fistulated steers. J. Anim. Sci. 25:249 (Abstr.).

Hildebrand, S. 1938. The effect of height and frequency of cutting
alfalfa upon its growth and root development. M. S. Thesis,
Michigan State University.

Hildreth, R. J., M. E. Riewe. 1963. Grazing production curves.
I. Determining the economic optimum stocking rate. Agron. J.
55:370.

Hind, E. 1978. Efficiency of lean meat production by British Friesian
and Jersey steers. Anim. Prod. 27:181.

Hobbs, C. S., T. W. High Jr., I. Dyer Jr. 1965. Orchardgrass and tall
fescue for producing yearling slaughter steers. Tennessee
Agr. Exp. Sta. Bull. 386.

258

Hodgkinson, K. C. 1970. Physiological aspects of the regeneration of
lucerne. Proc. XI Int. Grassl. Cong. 11:559.

Hodgson, J. 1966. The frequency of defoliation of individual tillers
in a set-stocked sward. J. Brit. Grassl. Soc. 21:258.

Hodgson, J. 1977. Factors limiting herbage intake by the grazing
animal. Proc. Int. Meeting on Anim. Prod. from Temperate
Grasslands, page 70, An Foras Taluntais.

Hodgson, J., J. M. Wilkinson. 1967. The relationship between liveweight
and herbage intake in grazing cattle. Anim. Prod. 9:365.

Hodgson, J., J. H. Ollerenshaw. 1969. The frequency and severity of
defoliation of individual tillers in set-stocked swards.
J. Brit. Grassl. Soc. 24:226.

Hodgson, R. E. 1952. Importance of legumes in dairy pastures. USDA,
BID-Inf-138, ADSA Meeting, Bloat symposium

Hogan, J. P., J. A. Hemsley. 1976. Protein digestion in the rumen.
Proc., Symp. From plant to animal protein, Reviews in Rural
Science number 2, page 73, Australia.

Hoglund, J. H., C. T. Dougherty, R. H. M. Langer. 1974. Response of
irrigated lucerne to defoliation and nitrogen fertilizer.
N. Z. J. of Exp. Agric. 2:7.

Holder, J. M. 1960. Observations on the grazing behavior of lactating
dairy cattle in a subtropical environment. J. Agric. Sci.
55:261.

Holder, J. M. 1962. Supplementary feeding of grazing sheep: its effects
on pasture intake. Proc. Aust. Soc. Anim. Prod. 4:154.

Holloway, J. W. 1980. New research and researchers in the area of
pasture forage utilization in Kentucky, North Carolina, Virginia,
South Carolina, Georgia and Tennessee. Proc., 37th. Southern
Pasture and Forage Crop Improvement Conf., page 111, USDA.

Holloway, J. W., R. E. Estell II, W. T. Butts Jr. 1980. Fecal indices
for prediction of green forage digestibility and consumption.
Proc., 37th. Southern Pasture and Forage Crop Improvement Conf.,
page 113, USDA.

‘Holmes, W. 1962. Grazing management for dairy cattle. J. Brit. Grassl.
Soc. 17:30.

Holmes, W. 1980. Grazing management. Grass, its production and
utilization, page 125, Brit. Grassl. Soc.

259

Holmes, W., R. C. Campling, N. D. Joshi. 1972. A comparison between
a rigid rotational grazing system for dairy cows and a system
in which grazing alterned with cutting. Anim. Prod. 14:283.

Holt, D. A., A. R. Hilst. 1969. Daily variation in carbohydrate
content of selected forage crops. Agron. J. 61:239.

Hoveland, C. S. 1975. Potential for grass-fed beef in the Southeast.
Feed Mgmt. 26:8.

Hoveland, C. S., R. F. McCormick, E. L. Carden, R. Rodriguez-Cabana,
J. T. Shelton. 1978. Maintaining tall fescue stands in
association with bahiagrass. Agron. J. 70:649.

Hrabe, F. 1977. Some results of studies on correlation between the
size of the assimilating area and the biomas production in
Medicago sativa L. and Trifolium pratense L. Proc. XIII Int.
Grassl. Cong. 13:181.

Huffman, C. F. 1959. Summer feeding of dairy cattle: a review.
J. Dairy Sci. 42:1495.

Hughes, J. G. 1976. Short-term variation in animal liveweight and
2 reduction of its effect on weighing. Anim. Breed. Abstr.
44:111.

Hull, J. L., J. H. Meyer, C. A. Raguse. 1967. Rotation and continuous
grazing on irrigated pasture using beef steers. J. Anim. Sci.
26:1160.

Hunt, R. 1978. Plant growth analysis. The Institute of Biology,
Studies in Biology number 96, 67 pages, Edward Arnold Ltd.

Hutchings, M. J., C. S. J. Budd. 1981. Plant competition and its
course through time. BioScience 31:640.

Hutchinson, H. G., R. Woof, R. M. Mabon, I. Salehe, J. M. Robb.
1962. A study of the habits of Zebu cattle in Tanganyika.
J. Agric. Sci. 59:301.

HutChinson, K. J., R. W. MacLean, B. A. Hamilton. 1972. The visual
estimation of pasture availability using standard pasture
cores. J. Brit. Grassl. Soc. 27:29.

Hutchinson, K. J., K. L. King. 1980. Management impacts on structure
and function of sown grasslands. Grasslands, systems analysis
and man, page 823, Cambridge Univ. Press.

Hutton, J. B., O. F. Parker. 1973. The significance of differences in
levels of feeding, before and after calving, on milk yield
under intensive grazing. N. Z. J. Agric. Res. 16:95.

260

Hyder, D. N. 1972. Defoliation in relation to vegetative growth. The
biology and utilization of grasses, page 305, Academic Press.

Inchausty, D., E. C. Tagle. 1980. Bovinotecnia. 800 pages, El Ateneo.

Ittner, N. R., G. P. Lofgreen, J. H. Meyer. 1954. A study of pasturing
and soiling alfalfa with beef steers. J. Anim. Sci. 13:37.

Ivins, J. D. 1952. The relative palatability of herbage plants.
J. Brit. Grassl. Soc. 7:43.

Ivins, J. D. 1955. The palatability of herbage. Herb. Abstr. 25:75.

Ivins, J. D. 1959. The interpretation of animal production data in
grassland evaluation. The measurement of grassland productivity,
page 148, Academic Press.

Jackobs, J. A., D. I. Oldemeyer. 1955. The response of four varieties
of alfalfa to spring clipping, interval between clippings, and
fall clipping in the Yakima Valley. Agron. J. 47:169.

Jacobson, D. R., S. B. Carr, R. H. Hatton, R. C. Buckner, A. P. Graden,
D. R. Dowden, W. M. Miller. 1970. Growth, physiological response
and evidence of toxicity in yearling dairy cattle grazing
different grasses. J. Dairy Sci. 53:575.

Jarrige, R., D. J. Minson. 1964. Digestibilite des constituants du
ray-grass anglais 324 et du dactyle S37, plus specailment des
constituants glucidiques. Ann. Zoot. 13:117.

Jensen, E. H., M. A. Massengale, D. O. Chilcote. 1967. Environmental
effects on growth and quality of alfalfa. Univ. of Nevada,
Bull. T 9.

Johnson, A. D. 1978. Sample preparation and chemical analysis of
vegetation. Commonwealth Agricultural Bureaux, Bull. 52,
page 96, England.

Johnson, J. R., J. T. Nichols. 1969. Crude protein content of eleven
grasses as affected by yearly variation, legume association
and fertilization. Agron. J. 61:65.

Jones, C. M. 1972. Chemical factors and their relation to feed intake
regulation in ruminants: a review. Can. J. Anim. Sci. 52:207.

Jones, Ll. I. 1952. Measurement of palatability. Proc. VI Int. Grassl.
Soc. 6:1348.

Jones, R. J. 1974. The relation of animal and pasture production to
stocking rate on legume based and nitrogen fertilized subtropical
pastures. Proc. Aust. Soc. Anim. Prod. 10:340.

261

Jones, R. J. 1981. Interpreting fixed stocking rate experiments.
Proc. Forage evaluation: concepts and techniques, page 419,
CSIRO, Australia.

Jones, R. J., R. L. Sandland. 1974. The relation between animal
gain and stocking rate. Derivation of the relation from the
results of grazing trials. J. Agric. Sci. 83:335.

Journet, M., B. Remond. 1976. Physiological factors affecting
voluntary intake of feed by cows. A review. Livest. Prod.
Sci. 3:129.

Journet, M., C. Demarquilly. 1979. Grazing. Feeding strategy for
high yielding dairy cows, page 295, Granada Publishing Co.

Joyce, J. P., R. P. Newth. 1967. Use of the comparative slaughter
technique to estimate the nutritive value of pasture for
hoggets. Proc. N. Z. Soc. Anim. Prod. 27:166.

Jung, G. A. 1975. Improved energy levels in the forage of cool-
season grasses. Proc. Joint Session, west Va. Chapter
SCSA and west Va. Grassl. Counc., page 35.

Jung, G. A., R. L. Reid. 1966. Sudangrass: studies on its yield
management, chemical composition and nutritive value. West
Va. Agr. Exp. Sta. Bull. 524T.

Jung, C. A., R. L. Reid, J. A. Balasko. 1969. Studies on yield,
management, persistence and nutritive value of alfalfa in
west Virginia. West Va. Agr. Exp. Sta. Bull. 581T.

Jung, G. A., R. E. Kocher, C. F. Gross, C. C. Berg, 0. L. Bennett.
1974. Seasonal fluctuations of nonstructural carbohydrate
concentration in the forage of cool-season grasses. Proc.
XII Int. Grassl. Cong. 12:285.

Kaiser, C. J., G. F. Cmarik. 1976. Finishing slaughter cattle on
pasture. Proc., Symp. Biological nitrogen fixation in forage-
livestock systems, ASA Special publ. number 28, page 85.

Kalmbacher, R. S. 1980. Forage management: a lock to the future.
Proc. 37th Southern Pasture and Forage Crop Improvement Conf.,
page 37, USDA.

Kare, M. R., M. S. Ficken. 1963. Comparative studies on the sense of
taste. Olfactation and Taste, page 285, The MacMillan Co.

Kartchner, R. J., C. M. Campbell. 1979. Intake and digestibility of
range forage consumed by livestock. Montana State Univ.
Bull. 718.

262

Kaufmann, W. 1976. Influence of the composition of the ration and the
feeding frequency on ph-regulation in the rumen and on feed
intake in ruminants. Livest. Prod. Sci. 3:103.

Kehr, w. R., E. c. Conrad, M. A. Alexander, F. C. Owen. 1963.
Performance of alfalfa under five management systems. Nebraska
Agr. Exp. Sta., Res. Bull. 211.

Kennedy, R. K. 1972. The sickledrat: a circular quadrat modification
useful in grassland studies. J. Range Mgmt. 25:312.

Kennedy, W. K., J. T. Reid, M. J. Anderson, J. C. Wilcox, D. G.
Davenport. 1960. Influence of the system of grazing on animal
and plant performance. Proc. VIII Int. Grassl. Cong. 8:640.

Keoghan, J. M. 2967. Effect of cutting frequency and height on top-
growth of pure lucerne stands. The Lucerne Crop, page 117,
Australia.

Kesler, E. M., J. H. Ziegler, J. M. Wilson, J. L. Watkins, J. M.
Buckalew. 1975. Studies on dairy beef production using male
Holstein. Pennsylvania State University, Bull. 802.

Kilcher, M. R., D. H. Heinrichs. 1974. Contribution of stems and
leaves to the yield and nutrient level of irrigated alfalfa
at different stages of development. Can. J. Plant Sci. 54:739.

King, R. W., L. T. Evans. 1967. Photosynthesis in artificial
communities of wheat, lucerne and subterranean clover plants.
Aust. J. Biol. Sci. 20:623. “

King, W. A. 1962. Animal behavior. Pasture and range research
techniques, page 31, ASA, ADSA, ASAP, ASRM, Cornell Univ. Press.

Klingman, D. L., S. R. Miles, G. O. Mott. 1943. The cage method for
further determining consumption and yield of pasture herbage.
J. Amer. Soc. of Agron. 35:739.

Knievel, D. P., A. V. A. Jacques, D. Smith. 1971. Influence of growth
stage and stubble height on herbage yields and persistence of
smooth bromegrass and timothy. Agron. J. 63:430.

Kothmann, M. M. 1974. A glossary of terms used in range management.
Soc. for Range Management, 2nd edition, Colorado.

Kothmann, M. M. 1980a. Nutrition of livestock grazing on range and
pasture lands. Digestive physiology and nutrition of ruminnats,,
page 56, volume 3, 0 & K Books.

Kothmann, M. M. 1980b. Integrating livestock needs to the grazing
system. Proc., Symp. Grazing Mgmt. Systems for Southwest
Rangelands, page 65, New Mexico.

263

Koter, Z. 1977. Relationship between some growth indices and dry
matter formation in alfalfa and three grass spesies. Proc.
XIII Int. Grassl. Cong. 13:225.

Kunkle, L. E., V. R. Cahill. 1959. Dairy beef production. Part 2.
Ohio Agr. Exp. Sta. Bull. 833.

Kust, C. A., D. Smith. 1961. Influence of harvest management on the
level of carbohydrate reserves, longevity of stands, and yields
of hay and protein from Vernal alfalfa. Crop Sci. 1:267.

Langlands, J. P. 1975. Techniques for estimating nutrient intake and
its utilization by the grazing ruminant. Symp. Digestion and
metabolism in ruminants, page 320.

Langlands, J. P., I. L. Bennett. 1973. Stocking intensity and
pastoral production. J. Agric. Sci. 81:193.

Laredo, M. A., D. J. Minson. 1973. The voluntary intake, digestibility
and retention time by sheep of leaf and stem fractions of
five grasses. Aust. J. Agric. Res. 24:875.

Laude, H. M. 1972. External factors affecting tiller development.
The biology and utilization of grasses, page 146, Academic
Press.

Lazenby, A., F. G. Swain. 1972. Pasture species. Intensive pasture
production, page 67, Halstead Press.

Leach, G. J. 1967. Growth and development of lucerne. The lucerne
crop, page 15, Australia.

Leach, G. J. 1968. The growth of the lucerne plant after cutting:
the effects of cutting at different stages of maturity and
at different intensities. Aust. J. Agric. Res. 19:517.

Leach, G. J. 1970. Growth of the lucerne plant after defoliation.
Proc. XI Int. Grassl. Cong. 11:562.

Leach, G. J., R. M. Jones, R. J. Jones. 1976. The agronomy and
ecology of improved pastures. Commonwealth Agricultural
Bureaux, Bull. 51, page 277, England.

Leaver, J. D. 1970. A comparison of grazing systems for dairy herd
replacement. J. Agric. Sci. 75:265.

Leaver, J. D. 1974. Rearing of dairy cattle. V. The effect of
stocking rate on animal and herbage production in a grazing
system for calves and heifers. Anim. Prod. 18:273.

Lee, J. W. 1976. The biology of cereal and legume storage proteins.
Proc., Symp From plat to animal protein, Reviews in Rural
Science number 2, page 17, Australia.

264

Lineham, P. A. 1952. Use of cage and mower strip methods for measuring
the forage consumed by grazing animals. Proc. VI Int. Grassl.
Cong. 6:1328.

Lineham, P. A., J. Lowe, R. H. Stewart. 1952. The output of pasture
and its measurement. Part III. J. Brit. Grassl. Soc. 7:73.

Logan, V. 8., W. J. Pigden, V. J. Miles, G. J. Brisson, A. I. Magee,
K. Rasmussen. 1960. Mechanical grazing versus daily or strip
grazing for lactating cows. Proc. VIII Int. Grassl. Cong.
8:652.

Loomis, R. S., W. A. Williams.'1969. Productivity and the morphology
of crop stands: patterns with leaves. Symp. Physiological
aspects of crop yield, page 27, ASA, CSSA, Univ. of Nebraska.

Loomis, R. S., W. A. Williams, A. E. Hall. 1971. Agricultural
productivity. Ann. Rev. Plant Physiol. 22:431.

Lopez, R. R., A. G. Matches, J. D. Baldridge. 1967. Vegetative
development and organic reserves of tall fescue under
conditions of accumulated growth. Crop Sci. 7:409.

Lotero, J., W. W. Woodhouse, R. F. Petersen. 1965. Distribution and
loss rate of nitrogen and potassium applied to the soil by
grazing animals. Proc. IX Int. Grassl. Cong. 9:1687.

Lucas, M. A. M., C. P. McMeekan. 1959. The effect of stocking rate
upon a comparison of break and rotational paddodk grazing
for dairy cows. N. Z. J. Agric. Res. 2:707.

Lucey, R. F., M. B. Tesar. 1965. Frequency and rate of irrigation as
factors in forage growth under water absorption. Agron. J.
57:519.

Ludlow, M. M. 1976. Physiology of growth and chemical composition.
Commonwealth Agricultural Bureaux, Bull. 51, page 251,
England.

Ludlow, M. M. 1978. Light relations of pasture plants. Proc., Symp.
Plant relations in pastures, page 35, CSIRO, Australia.

Lyttleton, J. W. 1973. Proteins and nucleic acids. Chemistry and
Biochemistry of forages, 1:63, Academic Press.

Mac Diarmid, B. N., B. R. Watkin. 1971. The cattle dung patch.
I. Effect of dung patches on yield and botanical composition
of surrounding and underlying pasture. J. Brit. Grassl. Soc.

26:239.

265

Mac Diarmid, B. N., B. R. Watkin. 1972a. II. Effect of a dung patdh
on the Chemical status of the soil, and ammonia nitrogen
losses from the patch. J. Brit. Grassl. Soc. 27:43.

Mac Diarmid, B. N., B. R. Watkin. 1972b. III. Distribution and rate
of decay of dung patches and their influence on grazing
behavior. J. Brit. Grassl. Soc. 27:48.

Macleod, J. 1976. Systems of grazing management for lowland sheep.
Proc. Occ. Symp. number 8, page 129, Brit. Grassl. Soc.

Maclusky, D. S. 1959. Studies of herbage production and consumption,
and the production of dairy cows in various grazing conditions.
The measurement of grassland productivity, page 129, Academic
Press.

Maclusky, D. S. 1960. Some estimates of the areas of pasture fouled
by the excreta of dairy cows. J. Brit. Grassl. Soc. 15:181.

't Mannetje, L. 1974. Relations between pasture attributes and
liveweight gain on a subtropical pasture. Proc. XII Int.
Grassl. Cong. 12:386.

't Mannetje, L. 1978a. An introduction to grassland vegetation and
its measurements. Commonwealth Agricultural Bureaux, Bull. 52,
page 1, England.

't Mannetje, L. 1978b. Measuring quantity of grassland vegetation.
Commonwealth Agricultural Bureaux, Bull. 52, page 63, England.

't Mannetje, L., R. J. Jones, T. H. Stobbs. 1976. Pasture evaluation
by grazing experiments. Commonwealth Agricultural Bureaux,
Bull. 51, page 194, England.

Marsh, R. 1976. Systems of grazing management for beef cattle. Proc.
Occ. Symp. number 8, page 119, Brit. Grassl. Soc.

Marsh, R., R. C. Campling. 1970. Fouling of pastures by dung.
Herb. Abstr. 40:123.

Marten, G. C. 1970a. Temperature as a determinant of quality of
alfalfa harvested by bloom stage or age criteria. Proc. XI
Int. Grassl. Cong. 11:506.

Marten, G. C. 1970b. Measurement and significance of forage
palatability. Proc. Nat. COnf. Forage quality evaluation
and utilization, Univ. Of Nebraska, paper D.

Marten, G. C. 1973. Alkaloids in reed canarygrass. Antiquality
components of forages, CSSA, Special publ. number 4, Wisconsin.

Marten, G. C. 1978. The animal-plant complex in forage palatability
phenomena. J. Anim. Sci. 46:1470.

266

Marten, G. C. 1981. Effect of deleterious compounds on animal
preference for forage and on animal performance. Proc.
Forage evaluation: concepts and techniques, page 225, CSIRO,
Australia.

Marten, G. C., J. D. Donker. 1964a. Selective grazing induced by
animal excreta. I. Evidence of occurrence and superficial
remedy. J. Dairy Sci. 47:773.

Marten, G. C., J. D. Donker. 1964b. II. Investigation of a casual
theory. J. Dairy Sci. 47:871.

Marten, G. C., J. D. Donker. 1966. Animal excrement as a factor
influencing acceptability of grazed forage. Proc. X Int.
Grassl. Cong. 10:359.

Marten, G. C., R. F. Barnes, A. B. Simona, F. J. Wooding. 1973.
Alkaloids and palatability of Phalaris arundinacea L. grown
in diverse environment. Agron. J. 65:199.

Marten, G. C., R. M. Jordan. 1974. Significance of palatability
differences among Phalaris arundinacea L., Bromus inermis Leyss,
and Dactylis glomerata L. grazed by sheep. Proc. XII Int.
Grassl. Cong. 12:305.

Marten, G. C., R. M. Jordan. 1979. Substitution value of birdsfoot

trefoil for alfalfa-grass in pasture systems. Agron. J.
71:55.

Martin, T. G. 1971. Genetic aspects of dairy beef production. J.
Anim. Sci. 32:433.

Martin, T. G., R. T. Starkenburg. 1965. Genetic correlations between
beef and dairy traits in dual purpose cattle. World Rev.
Anim. Prod. 1965:45.

Matches, A. G. 1969. Influence of cutting height in darkness on
measurement of energy reserves of tall fescue. Agron. J.
61:896.

Matches, A. G. 1979. Management, tall fescue. Agronomy number 20,
ASA, CSSA, SSSA, page 171.

Matches, A. G. 1981. Full versus shrunk weights to estimate gain of
cattle. Proc. Forage evaluation: concepts and techniques,
page 357, CSIRO, Australia.

Matches, A. G., W. F. Wedin, G. C. Marten, D. Smith, B. R. Baumgardt.
1970. Forage quality of Vernal and Du Puits alfalfa harvested
by calendar date and plant maturity schedules in Missouri, Iowa,
Wisconsin and Minnesota. Univ. of Wisconsin, Res. Rpt. 73.

267

Matches, A. G., G. O. Mott. 1975. Estimating the parameters associated
with grazing systems. Proc. III World Conf Anim. Prod., page
203.

Matches, A. G., G. B. Thompson, F. A. Martz. 1975. Post establishment
harvesting and management systems of forages. Proc. No-tillage
forage symposium, Ohio State Univ., page 111.

Matheson, E. M. 1972. Intensification of production through crop
plants. Intensive pasture production, page 145, Halstead Press.

Matthews, L. R., R. Kilgour. 1980. Learning and associated factors in
ruminant feeding behavior. Symp. Digestive physiology and
metabolism in ruminants, page 123.

Mays, D. A., J. B. Washko. 1961. Cutting and grazing management for
sudangrass and pearl millet. Pennsylvania Agr. Exp. Sta. Bull.
682.

McCartor, M. M., F. M. Rouquette Jr. 1977. Grazing pressures and
animal performance from pearl millet. Agron. J. 69:983.

McCullough, M. E. 1953. The use of indicator methods in measuring the
contribution of two forages to the total ration of the dairy
cow. J. Dairy Sci. 36:445.

McIntyre, G. A. 1978. Statistical aspects of vegetation sampling.
Commonwealth Agricultural Bureaux, Bull. 52, page 8, England.

McKee, G. W. 1961. Some effects of liming, fertilization and soil
moisture on seedling growth and nodulation in birdsfoot
trefoil. Agron. J. 53:237.

McKee, G. W. 1962. Some effects of daylength on seedling growth and
nodulation in birdsfoot trefoil. Crop Sci. 2:315.

McKinion, J. M., J. D. Hesketh, D. N. Baker. 1974. Analysis of the
experimental growth equation. Crop Sci. 14:549.

McKinney, G. T. 1974. Management of lucerne for sheep grazing on the
Southern Tablelands of New South Wales. Aust. J. Exp. Agric.
Anim. Husb. 14:726.

McKinney, G. T., A. Axelsen, F. H. W. Morley. 1970. The consumption
of lucerne by sheep at pasture. Proc. Aust. Soc. Anim. Prod.
8:466.

MCMeekan, C. P. 1956. Grazing management and animal production. Proc.
VII Int. Grassl. Cong. 7:146.

McMeekan, C. P. 1961. Grazing management. Proc. N. Z. Soc. Anim.
Prod. 21:47.

268

McMeekan, C. P., M. J. Walshe. 1963. The interrelationships of grazing
method and stocking rate in the efficiency of pasture utilization
by dairy cattle. J. Agric. Sci. 61:147.

McWilliam, J. R. 1978. Response of pasture plant to temperature. Proc.
Symp. Plant relations in pasture, page 17, CSIRO, Australia.

Meijs, J. A. C. 1981a. Herbage intake by grazing dairy cattle. Center
for Agricultural Publishing and Documentation, Wageningen.

Meijs, J. A. C. 1981b. The effect of herbage mass and allowance upon
herbage intake by grazing dairy cows. Proc. XIV Int. Grassl.
Cong. 14:667.

Merrill, L. B. 1954. A variation of deferred rotation grazing for use
under Southwest range conditions. J. Range Mgmt. 7:152.

Merrill, L. B. 1973a.Intensive deferred rotation grazing. Beef Cattle
Science Handbook 10:371

Merrill, L. B. 1973b. Non intensive rotation grazing. Beef Cattle
Science Handbook 10:377.

Meyer, J. H., G. P. Lofgreen, N. R. Ittner. 1956. Further studies on
the utilization of alfalfa by beef steers. J. Anim. Sci. 15:64.

Miles, V., V. 8. Logan, W. J. Pigden. 1961a. Pasture for young dairy
stock. I. Effect of previous nutritional level and age on
growth of Ayrshire and Holstein heifer calves and yearlings
on pasture. Can. J. Anim. Sci. 41:55.

Miles, V.,V. S. Logan,W. J. Pigden. 1961b. II. Effect of previous
nutritional level and age on growth of Holstein calves on
pasture. Can. J. Anim. Sci. 41:63.

Minson, D. J. 1967. The voluntary intake and digestibility, in sheep,
of chopped and pelleted Digitaria decumbens (Pangola grass)
following a late application of fertilizer nitrogen. Br. J.
Nutr. 21:587.

Minson, D. J. 1976. Nutritional significance of protein in temperate
and tropical grasses. Proc., Symp. From plant to animal protein,
page 27, Reviews in Rural Science number 2, Australia.

Minson, D. J., R. Milford. 1967. The voluntary intake and digestibility
of diets containing different proportions of legume and mature
Pangola grass (Digitaria decumbens). Aust. J. Exp. Agric.

Anim. Husb. 7:546.

Minson, D. J., T. H. Stobbs, M. P. Hegarty, M. J. Playne. 1976.
Measuring the nutritive value of pasture plants. Commonwealth
Agricultural Bureaux, Bull. 51, page 308, England.

269

Mitdhell, K. J. 1960. The structure of pasture in relation to
production potential. Proc. N. Z. Soc. Anim. Prod. 20:82.

Mitchell, R. L. 1970. Crop growth and culture. Iowa Univ. Press,
341 pages.

Mitchell, W. H. 1962. Influence of nitrogen and irrigation on the
root and top growth of forage crops. Univ. of Delaware,
Bull. 341.

Mitchell, W. H. 1967. Influence of cutting height, irrigation and
nitrogen on the growth and persistency of orchardgrass.
Delaware Agr. Exp. Sta. Bull. 364.

Mochrie, R. D. 1981. Survey of techniques used in grazing trials in
the U.S. from 1975 to 1980. Proc. Forage evaluation: concepts
and techniques, page 449, CSIRO, Australia.

Mochrie, R. D., J. C. Burns, D. H. Timothy. 1981. Recommended
protocols for evaluating new forages for ruminants. Proc.
Forage evaluation: concepts and techniques, page 553, CSIRO,
Australia.

Moldenhauer, W. C., G. V. Holmberg, J. T. Pesek, L. C. Dumenil, J.
J. Hanway. 1965. The influence of nitrogen and phosphorus
fertilizers on nutrient status and profitability of bromegrass
on Ida soils. Iowa.Agr. Home Econ. Exp. Sta. Res. Bull. 532.

Monteith, J. L. 1965. Light distribution and photosynthesis in field
crops. Ann. Bot. 29:17.

Monteith, J. L. 1969. Light interception and radiative exchange in
crop stands. Proc. Symp. Physiological aspects of crop yield,
page 89, ASA, CSSA, Univ. of Nebraska.

Montgomery, M. J., B. R. Baumgardt. 1965. Regulation of food intake
in ruminants. I. Pelleted rations varying in energy concentration.
J. Dairy Sci. 59:1625.

Moore, J. E. 1980. Forage crops. Crop quality, storage and utilization,
ASA, CSSA, page 61.

Moore, J. E. 1981. Principles of forage quality evaluation. King
Visiting Scholar Lectures, Special Rpt 93, page 66, Arkansa

Agr. Exp. Sta.

Moore, R. M. 1970. Australian grasslands. lst. edition, Australian
Nat. Univ. Press.

Morley, F. H. W. 1968. Pasture growth curves and grazing management.
Aust. J. Exp. Agric. Anim. Husb. 8:40.

270

Morley, F. H. W. 1978. Animal production studies on grasslands.
Commonwealth Agricultural Bureaux, Bull. 52, page 103,
England.

Morley, F. H. W. 1981. Management of grazing systems. Grazing animals,
vol. B-1:379, Elsevier.

Morley, F. H. W., A. Axelsen. 1965. The role of lucerne for summer
grazing. Field Sta. Record 4:13.

Morley, F. H. W., C. R. W. Spedding. 1968. Agricultural systems and
grazing experiments. Herb. Abstr. 38:279.

Morris, R. M. 1969. Pattern of grazing in "continuously" grazed
awards. 1969. J. Brit. Grassl. Soc. 24:65.

Mott, G. O. 1959. Intersociety forage evaluation symposium.
IV. Animal variation and measurement of forage quality.
Agron. J. 51:223.

Mott, G. O. 1960. Grazing pressure and the measurement of pasture
production. Proc. VIII Int. Grassl. Cong. 8:606.

Mott, G. O. 1974. Nutrient recycling in pastures. Forage fertilization,
page 323, ASA.

Mott, G. O. 1980. Measuring forage quality and quantity in grazing
trials. Proc. 37th Southern Pasture and Forage Crop Improvement
Conf., page 3, USDA.

Mott, G. 0., H. L. Lucas. 1952. The design, conduct and interpretation
of grazing trials on cultivated and improved pastures. Proc.
VI Int. Grassl. Cong. 6:1380.

Mott, G. 0., W. M. McVey, R. E. Smith, W. M. Beeson. 1953. Grazing
trials with beef cattle. Purdue Univ., Agr. Exp. Sta. Bull.
581.

Mott, G. 0., J. E. Moore. 1970. Forage evaluation techniques in
perspective. Proc. Nat. Conf. Forage quality evaluation and
utilization, paper L, Univ. of Nebraska.

Mott, G. 0., J. E. Moore. 1975. Existing and potential systems of
finishing cattle on forage or limited grain rations in the
tropical region of the south. Forage fed beef, Southern Coop.
Series, Bull. 220, page 419.

Mowat, D. N., R. S. Fulkerson, W. E. Tossell, J. E. Winch. 1965. The
in vitro digestibility and protein content of leaf and stem
portions of forage. Can. J. Plant Sci. 45:321.

 

 

 

271

Mulder, E. G. 1952. Fertilizer versus legume nitrogen for grasslands.
Proc. VI Int. GRassl. Cong. 6:740.

Mullen, G. J., R. M. Jelley, D. M. McAleese. 1974. Effect of animal
treading on soil properties and pasture production. Irish J.
Agric. Res. 13:171.

Mullen, G. J., R. M. Jelley, D. M. McAleese. 1977. Effects of cattle
treading on soil properties and total and seasonal pasture
production. Proc. Int. Meeting on Anim. Prod. from Temperate
Grasslands, page 152, An Foras Taluntais, Abstract.’

Mundy, E. J. 1961. The effect of urine and its components on the
botanical composition and production of a grass/clover sward.
J. Brit. Grassl. Soc. 16:100.

Murphy, W. E. 1977. Management factors affecting seasonal growth
pattern in grassland production. Proc. Int. Meeting on Anim.
Prod. from Temperate Grasslands, page 116, An Foras Taluntais.

Myers, L. F., J. V. Lovett, M. H. Walker. 1974. Screening of pasture

plants: a proposal for standardizing procedure. J. Aust. Inst.
Agric. Sci. 40:283.

Neal, D. L., J. L. Neal. 1973. Uses and capabilities of electronic
‘ capacitance instruments for estimating standing herbage.
I. History and development. J. Brit. Grassl. Soc. 28:81.

NelsOn, C. J., D. Smith. 1968. Growth of birdsfoot trefoil and
alfalfa. Crop Sci. 8:21.

Nelson, C. J., D. Smith. 1969. Growth of birdsfoot trefoil and
alfalfa. Carbohydrate reserve levels and growth analysis
under two temperature regimes. Crop Sci. 9:589.

Newman, R. C., D. Smith. 1972. Influence of two seeding patterns,
nitrogen fertilization and three alfalfa varieties on dry
matter and protein yields and persistence of alfalfaegrass
mixtures. Wisconsin Agr. Exp. Sta. Res. Rpt. 2377.

Norman, M. J. T. 1970. Relationships between liveweight gain of
grazing beef steers and availability of Townsville lucerne.
Proc. XI Int. Grassl. Cong. 11:829.

Norman, M. J. T., J. 0. Green. 1958. The local influence of cattle
dung and urine upon the yield and botanical composition of
permanent pastures. J. Brit. Grassl. Soc. 13:39.

0cokoljic, S., G. Velockovic. 1970. Composition and productivity of
high quality pasture and its potential for milk production
in the lowland region of Yugoslavia. Proc. XI Int. Grassl.
Cong. 11:723.

272

Ocumpaugh, W. R., A. G. Matches. 1977. Autumn-winter yield and
quality of tall fescue. Agron. J. 69:639.

O'Donovan, P. B., R. F. Barnes, M. L. Plumlee, G. O. Mett, L. V.
Packett. 1967. Ad libitum intake and digestibility of selected
reed canarygrass (Phalarys arundinacea L.) clones as measured
by the fecal index method. J. Anim. Sci. 26:1144.

Okajima, H., D. Smith. 1964. Available carbohydrate fractions in the
stem bases and seed of timothy, smooth bromegrass and several
other northern grasses. Crop Sci. 4:317.

Orskov, E. R. 1976. Manipulation of protein nutrition for production
in young animals. Proc., Symp. From plant to animal protein,
Reviews in Rural Science number 2, page 123, Australia.

Owen, F. G., R. G. Hinders. 1962. Orchardgrass-alfalfa versus alfalfar
bromegrass for lactating cows. ADSA Annual Meeting, paper P111.

Owen, J. B., W. J. Ridgman. 1968. The design and interpretation of

experiments to study animal production from grazed pastures.
J. Agric. Sci. 71:327.

Parsons, J. L. 1958. Nitrogen fertilization for alfalfa-grass mixture.
Agron. J. 50:593.

Paulsen, G. M., D. Smith. 1968. Influence of several management
practices on growth characteristics and available carbohydrate
content of smooth bromegrass. Agron. J. 60:375.

Paulsen, G. M., D. Smith. 1969. Organic reserves, axillary bud
activity, and herbage yields of smooth bromegrass as influenced
by time of cutting, nitrogen fertilization and shading.

Crop Sci. 9:529.

Paulson, W. H., J. M. Scholl, H. W. Ream, R. J. Vatthauer, A. W.
Young. 1977. More beef from improved pastures of the driftless

area of Upper Mississippi Valley. Univ. of Wisconsin, Res.
Rpt. R2893.

Payne, W. J. A., W. I. Laing, E. N. Raikova. 1951. Grazing behavior
of dairy cattle in the tropics. Nature 167:610.

Pearce, R. B., R. H. Brown, R. E. Blaser. 1965. Relationship between
leaf area index, light interception and net photosynthesis in
orchardgrass. Crop Sci. 5:553.

Pearce, R. B., G. Fissel, G. E. Carlson. 1969. Carbon uptake and
distribution before and after defoliation of alfalfa. Crop
Sci. 9:756.

Peart, G. R. 1968. A comparison of rotational grazing and set stocking
of dryland lucerne. Proc. Aust. Soc. Anim. Prod. 7:110.

273

Penning, P. D., M. J. Gibb. 1979. The effect of milk intake on the
intake of cut and grazed herbage by lambs. Anim. Prod. 29:53.

Petersen, R. G., H. L. Lucas, W. W. Woodhouse Jr. 1956a. The
distribution of excreta by freely grazing cattle and its
effect on pasture faertility. I. Excreta distribution.
Agron. J. 48:440.

Petersen, R. G., W. W. Woodhouse Jr, H. L. Lucas. 1956b. II. Effect
of returned excreta on the residual concentration of some
fertilizer element. Agron. J. 48:444.

Petersen, R. G., H. L. Lucas, G. O. Mott. 1965. Relationship between
rate of stocking rate and per animal and per acre performance.
Agron. J. 57:27.

Peterson, M. L., W. E. Loomis. 1948. Effect of photoperiod and
temperature on growth and flowering of Kentucky bluegrass.
Plant Physiol. 24:31.

Peterson, M. L., G. P. Lofgreen, J. H. Meyer. 1956. A comparison of
the chromogen and clipping methods for determining the
consumption of dry matter and TDN by beef steers on alfalfa
pastures. Agron. J. 48:560.

Peterson, M. L., L. E. Bendixen. 1960. Nitrogen fertilization of
irrigated pastures to improve forage productive capacity.
California Agric., page 7.

Phillips, T. G., J. T. Sullivan, M. E. Laughlin, V. G. Sprague.
1954. Chemical composition of some forage grasses. I. Changes
with plant maturity. Agron. J. 46:361.

Pieper, R., C. W. Cook, L. E. Harris. 1959. Effect of intensity of
grazing upon nutritive content of the diet. J. Anim. Sci.
18:1031.

Pigden, W. J., D. J. Minson. 1969. Measuring the herbage consumption
of grazing animals. Experimental methods for evaluating
herbage, Publ. 1315, page 152, Dpt. of Agric., Canada.

Plice, M. J. 1951. Sugar versus the intuitive choice of foods by
livestock. Agron. J. 43:341.

Plice, M. J. 1952. Sugar versus the intuitive choice of foods by
livestock. J. Range Mgmt. 5:69.

Polan, C. E., C. N. Miller, M. L. McGilliard. 1976. Variable
dietary protein and urea for intake and production in Holstein
cows. J. Dairy Sci. 59:1910.

Pratt, A. D., R. R. Davis, R. W. Van Keuren. 1966. Sudangrass versus
alfalfa-grass for dairy pasture and silage in Northeastern
Ohio. Ohio Agr. Res. Dev. Center Res. Bull. 990.

274

Putnam, P. A., R. E. Davis. 1963. Ration effects on drylot steer
feeding program. J. Anim. Sci. 22:437.

Putnam, P. A., R. Lehmann, R. E. Davis. 1967. Ration selection
and feeding patterns of steers fed in drylot. J. Anim. Sci.
26:647.

Putnam, P. A., R. Lehmann, W. Luber. 1968. Diurnal rates of feed
intake by steers in drylot. J. Anim. Sci. 27:1494.

Quinn, J. A., D. F. Hervey. 1970. Trampling losses and travel by
cattle on sandhills range. J. Range Mgmt. 23:50.

Raguse, C. A., D. W. Henderson, J. L. Hull. 1971. Perennial irrigated
pastures. I. Plant, soil water, and animal responses under
rotational and continuous grazing. Agron. J. 63:306.

Raguse, C. A., J. L. Hull, D. W. Henderson, A. Osman. 1975. II. Average
daily gain and carcass characteristics of yearling beef steers
on irrigated pasture supplemented by alfalfa cubes. Agron.

J. 67:580.

Raleigh, R. J., R. J. Kartchner, L. R. Rittenhouse. Chromic oxide in
range nutrition studies. Oregon Agr. Exp. Sta. Bull 641.

Raymond, W. F. 1969. The nutritive value of forage crops. Adv. in
Agronomy 21:1.

Reed, K. F. M. 1972. The performance of sheep grazing different pasture
types. Plants for sheep in Australia, page 193, Halstead Press.

Reed, K. F. M. 1981. A review of legume-based versus nitrogen-
fertilized pasture systems for sheep and beef cattle. Some
limitations of the experimental techniques. Proc. Forage
evaluation: concepts and techniques, page 401, CSIRO, Australia.

Reed, K. F. M., R. W. Snaydon, A. Axelsen. 1972. The performance of
young sheep grazing pastures sown to combinations of legumes or
subterranean clover with ryegrass or phalaris. Aust. J. Exp.
Agric. Anim. Husb. 12:240.

Reid, D. J., G. A. Greathouse, D. R. Hawkins, T. R. Greathouse. 1973.
Evaluating animal production and productivity of seven forage
mixtures. Michigan State Univ, Res. Rpt. 226, page 24.

Reid, G. W., J. F. D. Greenhalgh, J. N. Aitken. 1972. The effects
of grazing intensity on herbage consumption and animal production.
IV. An evaluation of two methods for avoiding the rejection of
fouled herbage by dairy cows. J. Agric. Sci. 78:491.

Reid, J. T., W. K. Kennedy, K. L. Turk, J. T. Slack, G. W. Trimberger,
R. P. Murphy. 1959. Effect of growth stage, chemical composition,
and physical properties upon the nutritive value of forages.

J. Dairy Sci. 42:567.

275

Reid, R. L., G. A. Jung. 1966. Factors affecting intake and palatability
of forages by sheep. Proc. IX Int. Grassl. Soc. 9:863.

Reynolds, J. H. 1971. Carbohydrate trends in alfalfa (Medicago sativa
L.) roots under several forage harvest schedules. Crop Sci.
11:103.

Reynolds, J. H., D. Smith. 1962. Trend in carbohydrate reserves in
alfalfa, smooth bromegrass and timothy grown under various
cutting schedules. Crop Sci. 2:333.

Rhodes, I., W. R. Stern. 1978. Competition for light. Proc., Symp.
Plant relations in pasture, page 175, CSIRO, Australia.

Richards, I. R. 1973. Grazing and nitrogen circulation in pure grass
swards. PhD Thesis, cited by Wolton, 1979.

Ridgman, W. J. 1960. The effect of height of cutting on the subsequent
growth and yield of lucerne. J. Brit. Grassl. Soc. 15:291.

Riewe, M. E. 1961. Use of the relationship of stocking rate to gain
of cattle in an experimental design for grazing trials.
Agron. J. 53:309.

Riewe, M. E. 1976. Principles of grazing management. Grasses and
legumes in Texas, Development, principles and utilization.
Chapter 5C, RM96, Texas A & M Univ.

Riewe, M. E. 1980. Designing rational experiments at the plant-
animal interface: adapted from Dr. H. L. Lucas. Proc. 37th
Southern Pasture and Forage Crop Improvement Conf., page 10,
USDA.

Riewe, M. E. 1981. Expected animal response to certain grazing
strategies. Proc. Forage evaluation: concepts and techniques,
page 341, CSIRO, Australia.

Riewe, M. E., J. C. Smith, E. C. Holt, J. H. Jones. 1959. Systems of
grazing dallisgrass-white clover pastures. Texas Agr. Exp. Sta.

Riewe, M. E., J. c. Smith, J. H. Jones, E. c. Holt. 1963. Grazing
production curves. I. Comparison of steer gains on Gulf
ryegrass and tall fescue. Agron. J. 55:367.

Robards, G. E. 1981. Techniques used in practice in forage evaluation
in Australia. Proc. Forage evaluation: concepts and techniques,
page 461, CSIRO, Australia.

Roberts, C. R. 1980. Effect of stocking rate on tropical pastures.
Cited by Jones, 1981.

276

Robinson, G. G., I. H. Simpson. 1975. The effect of stocking rate on
animal production from continuous and rotational grazing
systems. J. Brit. Grassl. Soc. 30:327.

Robles, A. Y., R. L. Belyea, F. A. Martz, M. F. Weiss, R. W. Maus.
1981. Intake, digestibility, ruminal characteristics and rate
of passage of orchardgrass diets fed to sheep. J. Anim. Sci.
53:489.

Rossiter, R. C. 1966. Ecology of the mediterranean annual-type
pasture. Adv. in Agronomy 18:1.

Rowland, J. W., E. D. Bumpus. 1952. The place of legumes in the
award. Proc. VI Int. Grassl. Cong. 6:468.

Roy, J. H. B., I. J. F. Stobo. 1975. Nutrition of the pre-ruminant
calf. Proc. Symp. Digestion and metabolism in the ruminant,
page 30.

Ruane, J. B., T. F. Raftery. 1964. An investigation into the merits
of intensive rotational grazing. J. Brit. Grassl. Soc. 19:376.

Sammis, T. W. 1981. Yield of alfalfa and cotton as influenced by
irrigation. Agron. J. 73:323.

Sandland, R. L., R. J. Jones. 1975. The relationship between animal
gain and stocking rate in grazing trials: an examination of
published theoretical models. J. Agric. Sci. 85:123.

Schmidt, D. R., G. H. Tenpas. 1965. Seasonal response of grasses
fertilized with nitrogen compared to a legume-grass mixture.
Agron. J. 57:428.

Scholl, J. M., W. H. Paulson, J. H. Brungardt, H. W. Rean. 1974. A
comparison of production from nitrogen fertilized and legume-
grass pastures for beef cattle in SW Wisconsin. Univ. of
Wisconsin, Bull. R2680 .

Schultz, E. F. Jr., W. R. Langford, E. M. Evans, R. M. Patterson,
W. B. Anthony. 1959. Relationship of beef gains to forage
yields. Agron. J. 51:207.

Sears, P. D. 1951. The technique of pasture measurement. N. Z. J.
Sci. Technol. 33A:1.

Seath, D. M., G. D. Miller. 1946. Effect of warm weather on grazing
performance of milking cows. J, Dairy Sci. 29:199.

Seath, D. M., C. A. Lassiter, J. W. Rust, M. Cole, G. M. Bastin.
1956. Comparative value of Kentucky bluegrass, Kentucky 31

fescue, orchardgrass and bromegrass as pastures for milk cows.
J. Dairy Sci. 39:574.

277

Seath, D. M., W. C. Templeton Jr., D. R. Jacobson, W. M. Miller, T.
H. Taylor. 1962. Grazing comparisons of two alfalfa-grass-
ladino clover mixtures. Kentucky Agr. Exp. Sta. Bull. 676.

Semple, A. T., H. N. Vinall, C. R. Enslow, T. E. Woodward. 1942.
A pasture handbook. USDA.Misc. Publ. 194.

Sharrow, S. H., W. C. Krueger. 1979. Performance of sheep under
rotational and continuous grazing on hill pastures. J. Anim.
Sci. 49:893.

Shaw, N. H., R. M. Jones, L. A. Edye, W. W. Bryan. 1976a. Developing
and testing new pastures. Commonwealth Agricultural Bureaux,
Bull. 51, page 175, England.

Shaw, N. H., L. 't Mannetje, R. M. Jones, R. J. Jones. 1976b. Pasture
measurement. Commonwealth Agricultural Bureaux, Bull. 51,
page 235, England.

Sheard, R. W. 1973. Organic reserves and plant regrowth. Chemical
and Biochemical of herbage, 2:353, Academic Press.

Sheard, R. W., J. E. Winch. 1966. The use of light interception,
grass morphology and time as criteria for the harvesting of

timothy, smooth bromegrass and cocksfoot. J. Brit. Grassl.
Soc. 21:231.

Shepherd, W. O. 1962. Herbage sampling for yield: natural pastures
and range. Pasture and range research techniques, page 102,
ASA, ADSA, ASAP, ASRM, Cornell Univ. Press.

Sheppard, A. J., R. E. Blaser, C. M. Kincaid. 1957. The grazing habits
of beef cattle on pasture. J. Anim. Sci. 16:681.

Shiflet, T. N., H. F. Heady. 1971. Specialized grazing systems: their
place in range management. USDA, SCS TP-152.

Sibma, L., W. Louwerse. 1977. The effect of changes in crop structure
on photosynthesis, dry matter production, and chemical
composition of Lolium perenne. Proc. XIII Int. Grassl. Cong.

13:171.

Simpson, J. R., T. H. Stobbs. 1981. Nitrogen supply and animal
production from pastures. Grazing animals, vol. B-1:261,
Elsevier.

Smith, D. 1962. Carbohydrate root reserves in alfalfa, red clover,
and birdsfoot terfoil under several management schedules.
Crop Sci. 2:75.

Smith, D. 1965. Forage production of red clover and alfalfa under
differential cutting. Agron. J. 57:463.

Smith,

Smith,

Smith,

Smith,

Smith,

Smith,

Smith,

Smith,

Smith,

Smith,

Smith,

278

D. 1967. Carbohydrates in grasses. II. Sugar and fructosan
composition of the stem bases of bromegrass and timothy at
several growth stages and in different plant parts at anthesis.
Crop Sci. 7:62. '

D. 1968. Classification of several native North American grasses
as starch or fructosan accumulators in relation to taxonomy.
J. Brit. Grassl. Soc. 23:306.

D. 1969. Influence of temperature on the yield and chemical
composition of "Vernal" alfalfa at first flower. Agron. J.
61:470.

D. 1970. Yield and chemical composition of leaves and stems
of alfalfa at intervals up to the shoot. J. Agric. Food Chem.
18:652.

D. 1972. Carbohydrate reserves of grasses. The biology and
utilization of grasses, page 318, Academic Press.

D. 1975. Forage management in the north, Kendall Hunt Publ.
Co., Iowa.

D., R. D. Grotelueschen. 1966. Carbohydrates in grasses.

II. Sugar and fructosan composition of the stem.base of
several northern-adapted grasses at seed maturity. Crop Sci.
6:263.

D., C. J. Nelson. 1967. Growth of birdsfoot trefoil and alfalfa.
I. Responses to height and frequency of cutting. Crop Sci.
7:130.

D., G. C. Marten, A. G. Matches, W. F. Wedin. 1968. Dry matter
yields of Vernal and Du Puits alfalfa harvested by calendar
date and plant maturity schedules in Missouri, Iowa, Wisconsin
and Minnesota. Univ. of Wisconsin Res. Rpt. 37.

D., A. V. A. Jacques, J. A. Balasko. 1973. Persistence of

several temperate grasses grown with alfalfa and harvested
two, three, or four times annually at two stubble heights.
Crop Sci. 13:553.

D., D. A. Rohweder. 1977. Establishing and managing alfalfa.
Univ. of Wisconsin Res. Rpt. R1741.

J. S., F. W. Wainman, P. J. S. Dewey. 1976. The energy value
for sheep of three successive harvests of lucerne when
artificially dried and fed in the chopped and pelleted forms.
Proc. Nutr. Soc. 35:97A.

279

Smith, M. V. 1970a. The effect of stocking rate and grazing
management on the liveweight and wool production of wethers
grazing dryland lucerne. Proc. Aust. Soc. Anim. Prod. 8:461.

Smith, M. V. 1970b. Effect of stocking rate and grazing management
on the persistency and production of dryland lucerne on deep
stands. Proc. IX.Int. Grassl. Cong. 9:624

Snaydon, R. W. 1981. The ecology of grazed pastures. Grazing animals,
vol. B-1:13, Elsevier.

Spahr, S. L., E. E. Ormiston, R. G. Peterson. 1967. Sorghum-sudan
hybrid 5X-11, Piper sudan grass and alfalfaeorchardgrass for
dairy cows. J. Dairy Sci. 50:1925.

Spahr, S. L., E. E. Ormiston. 1969. The promise and problems of
sorghum-sudan hybrids. Illinois Res., page 3.

Spahr, S. L., J. R. Romans, K. L. Siewert, D. H. Steyerc, J. E.
McClendon. 1972. Genetic relationships between body measurements
and carcass traits in dairy steers. Amer. Soc. Anim. Sci.,
Annual Meeting, Virginia Pol. Inst. and State Univ.

Spedding, C. R. W. 1965. The physiological basis of grazing management.
J. Brit. Grassl. Soc. 20:7.

Spooner, A. E., M. L. Ray. 1969. Pasture fertilization and grazing
management studies in Southwest Arkansas. Arkansas Agr. Exp.
Sta. Bull. 741.

Spooner, A. E., M. L. Ray. 1972. Finishing yearling steers on pasture
with grain. Arkansas Agr. Exp. Sta. Bull. 772.

Sprague, M. A., E. R. Cowett, M. V. Adams. 1964. Early and deferred
cutting management of alfalfa, ladino clover, bromegrass and
orchardgrass. Crop Sci. 4:35.

Sprague, V. G. 1952. Maintaining legumes in the sward. Proc. VI Int.
Grassl. Cong. 6:443.

Sprague, V. G., J. T. Sullivan. 1950. Reserve carbohydrates in
orchardgrass clipped periodically. Plant Physiol. 25:92.

Stehr, W., M. Kirchgessner. 1976. The relationship between the
intake of herbage grazed by dairy cows and its digestibility.
Anim. Feed Sci. Technol. 1:53.

Stiles, D. A., E. E. Bartley, A. D. Dayton, H. B. Perry, G. L. Kilgore,
F. W. Boren. 1970. Growth of Holstein calves fed alfalfa
pasture, alfalfa greenchop or alfalfa hay. J. Dairy Sci.

53:489.

280

Stiles, J. W. 1971. The potential for dairy beef. J. Anim. Sci.
32:431.

Stobbs, T. H. 1973a. The effect of plant structure on the intake of
tropical pastures. I. Variation in the bite size of grazing
cattle. Aust. J. Agric. Res. 24:809.

Stobbs, T. H. 1973b. II. Differences in sward structure, nutritive

value and bite size of animals grazing. Aust. J. Agric. Res.
24:821.

Stoddart, L. A., A. D. Smith, T. W. Box. Range management. 532 pages,
McGraw Hill Book Co, 2nd edition, 1975.

Stoy, V. 1969. Interrelationships among photosvnthesis. respiration
and movement of carbon in developing crops. Proc. Symp.
Physiological aspects of crop yield, page 185, ASA, CSSA,
Univ. of Nebraska.

Swakon, D. H. D., J. E. Moore. 1980. Relationship between structural
characteristics of forages and in vivo quality in warm season
grasses. Forage and Grassland Conf, page 65, Univ. of KentuCky.

Tansley, A. D. 1935. Cited by Stoddart et al., 1975.

Tayler, J. C., J. E. Rudman. 1966. The distribution of herbage at
different heights in "grazed" and "dung patch" areas of a
sward under two methods of grazing management. J. Agric.
Sci. 66:29.

Teel, M. R. 1962. Developmental physiology as a factor in evaluating
forage grasses. American Soc. of Agronomy, Annual Meeting.

Templeton Jr., W. C. 1976. Legume nitrogen versus fertilizer nitrogen
for cool season grasses. Proc. Symp. Biological nitrogen
fixation in forage-livestock systems, ASA Special Publ. 8,
page 35 .

Templeton Jr., W. C., T. H. Taylor, J. R. Todd. 1965. Comparative
ecological and agronomic behavior of orchardgrass and tall
fescue. Kentucky Agr. Exp. Sta. Bull. 699.

Templeton Jr., W. C., T. H. Taylor. 1966. Yield response of a tall
fescuedwhite clover award to fertilization with nitrogen,
phosphorus and potassium. Agron. J. 58:319.

Tenpas, G. H., J. M. Scholl. 1970. Performance of birdsfoot trefoil
in the northern Wisconsin. Univ. of Wisconsin Res. Rpt. 64.

Tesar, M. B. 1974. Nitrogen on grasses compared to alfalfa-grass
mixtures in northern Michigan. Michigan State Univ. Res.
Rpt. 256, page 101.

281

Tesar, M. B. 1978a. Productivity of three grasses fertilized with
ammonium nitrate or urea. Michigan State Univ. Res. Rpt.
353, page 13.

Tesar, M. B. 1978b. Forage management. Michigan State Univ., 134
pages.

Tesar, M. B., T. R. Greathouse, C. M. Hansen. 1973. Nitrogen
fertilization of pastures with anhydrous ammonia and ammonium
nitrate. Michigan State Univ. Res. Rpt. 226, page 113.

Theurer, C. B. 1970. Determination of botanical and chemical
composition of the grazing animal's diet. Proc. Nat. Conf.
Forage quality evaluation and utilization, paper J, Univ.
of Nebraska.

Theurer, C. B., A. L. Lesperance, J. D. Wallace. 1976. Botanical
composition of the diet of livestock grazing native ranges.
Arizona Agr. Exp. Sta. Tech. Bull. 233.

Thom, E. R. 1978. Effect of stage of growth and season on yield
of lucerne (Medicago sativa L.) and on in vitro digestibility
of the whole plant and its component parts. Proc. Agron.
Soc. New Zealand 8:43.

Thomson, D. J. 1977. The role of legumes in improving the quality of
forage diets. Proc. Int. Meeting Anim. Prod. from Temperate
Grasslands, page 131, An Foras Taluntais.

Thomson, D. J. 1979. Effect of the proportion of legumes in the award
on animal output. Proc. Occ. Symp. number 10, page 101, Brit.
Grassl. Soc.

Thornton, R. F., D. J. Minson. 1973. The relationship between
apparent retention time in the rumen, volunatry intake and
apparent digestibility of legume and grass diets in sheep.
Aust. J. Agric. Res. 24:889.

Till, A. R. 1981. Cycling of plant nutrients in pastures. Grazing
animals, vol. B-1:33, Elsevier.

Tilley, J. M. A., R. A. Terry. 1963. A two-stage technique for the

in vitro digestion of forage crops. J. Brit. Grassl. Soc.
18:104.

Tothill, J. C. 1975. Measuring botanical composition of grasslands.
Commonwealth Agricultural Bureaux, Bull. 52, page 22, England.

Tothill, J. C., M. L. Peterson. 1962. Botanical analysis and sampling:
tame pastures. Pasture and range research techniques, page 109,
ASA, ADSA, ASAP, ASRM, Cornell Univ. Press.

282

Troelsen, J. E., J. B. Campbell. 1969. The effect of maturity and
leafiness on the intake and digestibility of alfalfa and
grasses fed to sheep. J. Agric. Sci. 73:145.

Tyler, W. J. 1970. Relationship between growth traits and production
of meat and milk. J. Dairy Sci. 53:830.

Ulyatt, M. J. 1971. Studies on the causes of the differences in
pasture quality between perennial ryegrass, short-rotation
ryegrass and white clover. N. Z. J. Agric. Res. 14:352.

Ulyatt, M. J. 1973. The feeding value of herbage. Chemistry and
Biochemistry of herbage, 3:131, Academic Press.

Ulyatt, M. J. 1981. The feeding value of temperate pastures.
Grazing animals, vol B—1:125, Elsevier.

Van Dyne, G. M, W. G. Vogel, H. G. Fisser. 1963. Influence of small
plot size and shape on range herbage production estimates.
Ecology 44:746.

Van Keuren, R. W., R. R. Davis. Persistence of birdsfoot trefoil,
Lotus corniculatus L., as influenced by plant growth habit
and grazing management. Agron. J. 60:92.

Van Keuren, R. W., R. R. Davis, D. S. Bell, E. W. Klosterman. 1969.
Effect of grazing management on the animal production from
birdsfoot trefoil pastures. Agron. J. 61:422.

Vartha, E. W., A. G. Matches, G. B. Thompson. 1977. Yield and quality
trends of tall fescue grazed with different subdivisions of
pasture. Agron. J. 69:1027.

Van Soest, P. J. 1965. Symposium of factors influencing the voluntary
intake of herbage by ruminants: voluntary intake in relation
to chemical composition and digestibility. J. Anim. Sci.
24:834.

Van Soest, P. J. 1982. Nutritional ecology of the ruminant. O & B
Books, Inc., 374 pages.

Vickery, P. J. 1981. Pasture growth under grazing. Grazing animals,
vol. B—1:55, Elsevier.

Voigtlander, G., N. Voss. 1977. Factors maximizing pasture growth.
Proc. Int. Meeting Anim. Prod. from.Temperate Grasslands,
page 96, An Foras Taluntais.

Vough, L. R., G. C. Marten. 1971. Influence of soil moisture and
ambient temperature on yield and quality of alfalfa forage.
Agron. J. 63:40.

283

Wade, M. H. 1976. The growth and losses of herbage in grazed swards.
Proc. Occ. Symp. number 8, page 61, Brit. Grassl. Soc.

Wagner, R. E. 1954. Influence of legume and fertilizer nitrogen on
forage production and botanical composition. Agron. J. 46:167.

Waldo, D. R. 1970. Factors influencing the voluntary inatke of forages.
Proc. Nat. Con. Forage quality evaluation and utilization, paper
E, Univ. of Nebraska.

Walters, R. J. K., M. Evans. 1979. Evaluation of award sampling
technique for estimating herbage intake by grazing sheep.
Grass and Forage Sci. 34:37.

Ward, A. L. 1970. Stomach content and fecal analysis: methods of
forage identification. Range and wildlife habitat evaluation,
a research symposium, USDA Forest Service, Misc. Publ. 1147.

Warren Wilson, J. 1965. Stand structure and light penetration.
I. Analysis by point quadrats. J. Appl. Ecol. 2:383.

Warren Wilson, J. 1967. III. Sunlit foliage area. J. Appl. Ecol.
4:159.

Washko, J. B., G. A. Jung, A. M. Decker, R. C. Wakefield, D. D. Wolf,
M. J. Wright. 1967. Management and productivity of perennial
grasses in the Northeast. III. Orchardgrass. West Virginia
Univ. Agr. Exp. Sta. Bull. 557 T.

Washko, J. B., J. W. Price. 1970. Intensive management of alfalfa
for forage production. Proc. XI Int. Grassl. Cong. 11:628.

Watkin, B. R., R. J. Clements. 1978. The effect of grazing animals
on pastures. Proc. Symp. Plant relations in pastures, page
273, CSIRO, Australia.

Watson Jr., C. E. 1978. Breeding grasses and legumes for use in
mixtures. Proc. 35th Southern Pasture and Forage Crop
Improvement Conf., page 104, USDA.

Watson, D. J. 1947. Comparative physiological studies on the growth
of field crops. I. Variation in net assimilation rate and
leaf area between species. Ann. Bot. 11:41.

Watson, D. J. 1956. Leaf growth in relation to crop yield. The growth
of leaves, Butterworths Scientific Publ., London.

Watson, D. J. 1958. The dependence of net assimilation rate on leaf
area index. Ann. Bot. 22:37.

Wedin, W. F., R. L. Vetter, J. M. Scholl, W. R. Woods. 1967. An
evaluation of birdsfoot trefoil (Lotus corniculatus) in
pasture improvement. Agron. J. 59:525.

284

Weinmann, H. 1952. Carbohydrate reserves in grasses. Proc. VI Int.
Grassl. Cong. 6:655.

Weir, W. C., D. T. Torrell. 1959. Selective grazing by sheep as
shown by a comparison of the chemical composition of range
and pasture forage obtained by hand clipping and that collected
by esophageal-fistulated sheep. J. Anim. Sci. 18:641.

Weir, W. C., L. G. Jones, J. L. Meyer. 1960. Effect of cutting interval
and stage of maturity on the digestibility and yield of alfalfa.
J. Anim. Sci. 19:5.

Wellington, G. H. 1971. Dairy-beef. J. Anim. Sci. 32:424.

Wheeler, J. L. 1958. The effect of sheep excreta and nitrogenous
fertilizer on the botanical composition of a ley. J. Brit.
Grassl. Soc. 13:196.

Wheeler, J. L. 1962. Experimentation in grazing management. Herb.
Abstr. 32:1.

Wheeler, J. L. 1981a. The role of forages in animal production in
Australia. Proc. Forage evaluation: concepts and techniques,
page 21, CSIRO, Australia.

Wheeler, J. L. 1981b. Forage evaluation in developing countries.
Proc. Forage evaluation: concepts and techniques, page 561,
CSIRO, Australia.

Wheeler, J. L., J. C. Burns, R. D. Mochrie, H. R. Gross. 1973. The
choice of fixed or variable stocking rates in grazing
experiments. Exp. Agr. 9:289.

White, L. M. 1973. Carbohydrate reserves of grasses: a review. J.
Range Mgmt. 26:13.

Whitney, A. S. 1974. Measurement of foliage height and its
relationships to yield of two tropical forage grasses.
Agron. J. 66:334.

Williams, A. W. 1966. Range improvement as related to net productivity,
energy flow and foliage configuration. J. Range Mgmt. 19:29.

Williams, 0. B. 1976. Protein of grazed plants in semiarid and arid
rangelands: availability and significance. Proc. Symp. From
plant to animal protein, Reviews in Rural Science number II,
page 21, Australia.

Williams, R. J., R. L. Burt, R. W. Strickland. 1976. Plant introduction.
‘ Commonwealth Agricultural Bureaux, Bull. 51, page 77, England.

285

Williams, T. E. 1980. Herbage production: grasses and leguminous
forage crops. Grass, its production and utilization, page 6,
Brit. Grassl. Soc.

Williams, W. 1970. White clover in British agriculture. Proc. Occ.
Symp. number 6, Brit. Grassl. Soc.

Williams, W. A., R. J. Loomis, C. R. Lepley. 1965. Vegetative growth
of corn as affected by population density. II. Components of

growth, net assimilation rate and leaf area index. Crop Sci.
5:215.

Willoughby, W. M. 1958. The relationship of pasture availability
and animal production. Proc. Aust. Soc. Anim. Prod. 2nd.
Biennial Conf., page 42.

Willoughby, W. M. 1970. Feeding value and utilization of pasture.
Proc. Aust. Soc. Anim. Prod. 8:415.

Wilman, D. 1977. The effect of grazing compared with cutting, at
different frequencies, on a lucerne-cocksfoot ley. J. Agric.
Sci. 88:483.

Wilson, D. 1973. Physiology of light utilization by swards.
Chemistry and biochemistry of herbage 2:57, Academic Press.

Wilson, D. B. 1966. Variability in herbage yields from caged areas
in a pasture experiment. Can. J. Plant Sci. 46:249.

Wilson, D. B. 1969. Replicated animal and paddock experiments.
Experimental methods for evaluating herbage, Publ. 1315,
page 96, Canada Dept. of Agric.

Winch, J. E., R. W. Sheard, D. N. Mewat. 1970. Determining cutting
schedules for maximum yields and quality of bromegrass,

timothy, lucerne and lucerne—grass mixtures. J. Brit. Grassl.
Soc. 25:44.

Wittwer, S. H. 1974. Maximum production capacity of food crops.
BioScience 24:216.

Wolf, D. D., R. E. Blaser. 1972. Growth rate and physiology of alfalfa
as influenced by canopy and light. Crop Sci. 12:23.

Wolfe, E. C. 1972. Pasture management and its effects on the botanical
composition and productivity of pasture. Intensive pasture
production, page 199, Halstead Press, Australia.

Wolton, K. M. 1963. An investigation into the simulation of nutrient
returns by the grazing animal in grassland experimentation.
J. Brit. Grassl. Soc. 18:213.

286

Wolton, K. M. 1979. Dung and urine as agents of award change: a
review. Proc. Occ. Symp. number 10, page 131, Brit. Grassl.
Soc.

Woodward, T. E., J. B. Shepherd, M. A. Hein. 1938. The Hohenheim
system in the management of permanent pastures for dairy
pastures for dairy cattle. USDA Tech. Bull. 660.

Woolfolk, P. G. 1962. Measuring yield by animal performance.
Pasture and range research techniques, page 73, ASA, ADSA,
ASAP, ASRM, Cornell Univ. Press.

Wright, M. J., G. A. Jung, C. S. Brown, A. M. Decker, K. E. Varney,
R. C. Wakefield. 1967. Management and productivity of
perennial grasses in the northeast. II. Smooth bromegrass.
West Virginia Univ. Agr. Exp. Sta. Bull. 554 T.

Yeh, R. Y., A. G. Matches, R. L. Larson. 1976. Endogenous growth
regulators and summer tillering of tall fescue. Crop Sci.
16:409.

Youngner, V. B. 1972. Physiology of defoliation and regrowth.
Biology and utilization of grasses, page 292, Academic
Press.

Ziegler, J. H., L. L. Wilson, D. S. Cable. 1971. Comparison of
certain carcass traits of several breeds and crosses of
cattle. J. Anim. Sci. 32:446.