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This is to certify that the
thesis entitled

EFFECTS OF BM3 CORN SILAGE ON THE LACTI'IONAL
PERFORMANCE OF DAIRY COWS

presented by

RICHARD A. LONGUSKI

has been accepted towards fulﬁllment
of the requirements for the

M. S. degree in Animal Science

 

 

 

 

May 30, 2003

 

Date

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6/01 cJCIRC/DatoDuo.p65—p.15

EFFECTS OF BM3 CORN SILAGE ON THE LACTATIONAL PERFORMANCE
OF DAIRY COWS

By

Richard A. Longuski

A Thesis

Submitted to
Michigan State University
in partial fulﬁllment of the requirements
for the degree of

MASTER OF SCIENCE
Department of Animal Science

2003

ABSTRACT

THE EFFECTS OF BM3 CORN SILAGE ON THE LACTATIONAL
PERFORMANCE OF DAIRY COWS

BY

Richard A. Longuski

Effects of brown midrib-3 (bm3) mutation in corn silage on lactational
performance were evaluated using 80 Holstein cows (30 primiparous and 50
multiparous) in a full lactation experiment. Treatments were diets containing bm3
or isogenic normal (control) corn hybrids. In vitro NDF digestibility at 30-h was
greater for bm3 corn silage compared with control (63.1 vs. 48.8%). Cows were
offered diets containing a forage-mix of 67% treatment silage and 33% alfalfa
silage on a DM basis. Animals were fed once and milked three times daily.
Cumulative yield of SCM was greater (P = 0.01) for cows fed bm3 treatment from
50 to 150 DIM compared with cows fed normal (3150 vs. 2948 kg) but was
similar from 0 to 50 and from 150 to 300 DIM. Cumulative yields of 3.5% fat-
corrected milk and milk fat also were greater for cows fed bm3 treatment
compared to normal from 50 to 150 DIM but were similar from 0 to 50 and from
150 to 300 DIM. Milk fat concentration was similar between treatments (3.6%).
Multiparous and primiparous cows fed bm3 treatment had higher milk protein
concentrations from 0 to 50 DIM. Primiparous cows fed bm3 treatment also had
higher milk protein concentrations from 50 to 150 and 150 to 300 DIM. Results
suggest that milk yield responses for dairy cows fed bm3 corn silage compared

with normal corn silage are greatest at peak lactation.

ACKNOWLEDGMENTS

A sincere thanks to Dr. M. S. Allen for giving me the opportunity to learn
and the passion for research. It's very convenient having a boss, major professor
and friend in one.

To the rest of my committee, Drs. D. K. Beede, M. Benson and T. Herdt, I
thank them for being patient with me and for gently prodding me on towards the
ﬁnish line.

This thesis would be several pages of white if not for the workhorse-like
efforts of the crew at the Kellogg Biological Station. Special thanks to Rob
Ashley and Jim Bronson for organizing the troops and keeping me level headed.

Kudos and thanks to David G. Main and Jackie Ying for allowing me the
space and time to conduct my research by picking up the slack I must have left in
the lab.

Without statistics the data I gathered from this experiment would still be
just a bunch of cow manure covered forms. Thanks to Dr. Rob Tempelman for
the enormous amount of time and effort put into this dataset. Thanks also to Mr.
Jim Liesman for continuously teaching me about statistics and for making sure I
didn't give up on my thesis.

Dr. Richard Aeulrich, Dr. Steve Bursian and Mr. Angelo Napolitano
sparked my interest in research. I thank them for starting my career out on the

right step through integrity and dedication in their own research.

I am extremely grateful for the support and encouragement I received from
my in-laws, Mike and Sue Fryer, during the past six years. The pond will seem
empty with two less ducks to care for.

My parents have not always agreed with me but always encouraged me in
my life decisions. I owe much of the road-less-traveled experiences that have I
gotten me this far to them.

Siblings tend to decrease the joy of life in childhood (especially when you
are the youngest of six) but increase the joy of life immensely as an adult.
Thanks to Lynn, Bob, Joe, Jim and Kirk for toughening me up in childhood and
being my friends in adulthood.

It's much easier to get through life when married to one's best friend. I
thank Annabel for listening to my gripes and groans over the past six years and
never letting me think that I couldn't ever ﬁnish my goals.

Thank Godll

TABLE OF CONTENTS

List of Tables ..................................................................................... vii
List of Figures ..................................................................................... ix
INTRODUCTION ................................................................................... 1
LITERATURE REVIEW
History of the Brown Midrib Mutations in Corn .................................... 2
The Filling Effect of NDF ................................................................ 8
NDF Digestibility Affects the Filling Effect of NDF ............................... 14
Factors Affecting the Digestibility of Forage NDF ............................... 16
Animal Performance with bm3 Corn Silage ....................................... 21
Summary ................................................................................... 32
MATERIALS AND METHODS
Experimental Treatments, Design, Diets and Cows ............................ 34
Experimental Procedures .............................................................. 37
Statistical Analyses ..................................................................... 41
RESULTS AND DISCUSSION
Nutrient Composition ................................................................... 44
Milk Yield, Milk Components, BW and BCS ....................................... 45
Inﬂuence of Diets on Production Data .............................................. 54
Treatment vs. Pen Effects ............................................................. 54
Summary ................................................................................... 55
Conclusion and Implications ......................................................... 56

Tables ...................................................................................... 57

Figures ..................................................................................... 69
Appendix .................................................................................. 79
Bibliography ............................................................................... 82

vi

LIST OF TABLES

Table 1. Ingredient and nutrient composition of experimental diets ................. 57

Table 2. Nutrient composition of corn silage used throughout the
experiment ............................................................................. 58

Table 3. Cumulative estimates, standard errors and signiﬁcance
of effects of corn silage hybrids on milk yield for the ﬁrst
300 days of lactation ................................................................. 59

Table 4. Least square means, standard errors and signiﬁcance
of effects of corn silage hybrids on milk yield (kg/d) at
25 d intervals ........................................................................... 60

Table 5. Least square means, standard errors and signiﬁcance
of effects of corn silage hybrids on milk fat yield (kg/d) at
25 d intervals ........................................................................... 60

Table 6. Least square means, standard errors and signiﬁcance
of effects of corn silage hybrids on 3.5% fat-corrected
milk yield (kg/d) at 25 d intervals ................................................. 61

Table 7. Least square means, standard errors and signiﬁcance
of effects of corn silage hybrids on milk protein concentration
(%) at 25 d intervals by parity ...................................................... 62

Table 8. Least square means, standard errors and signiﬁcance
of effects of corn silage hybrids on milk protein yield
(kg/d) at 25 d intervals by parity ................................................... 63

Table 9. Least square means, standard errors and signiﬁcance
of effects of corn silage hybrids on solids-corrected milk yield
(kg/d) at 25 d intervals ............................................................... 64

Table 10. Least square means, standard errors and signiﬁcance
of effects of corn silage hybrids on body weight (kg) at 25 d
intervals ............................................................................... 64

Table 11. Least square means, standard errors and signiﬁcance

of effects of corn silage hybrids on body condition score
at 25 d intervals ...................................................................... 65

vii

Table 12. Estimates, standard errors and signiﬁcance of effects of
corn silage hybrids on cumulative milk yield (kg) by stage
of lactation ............................................................................ 65

Table 13. Estimates, standard errors and signiﬁcance of effects of
corn silage hybrids on cumulative milk fat yield (kg) by
stage of lactation .................................................................... 66

Table 14. Estimates, standard errors and signiﬁcance of effects of
corn silage hybrids on cumulative 3.5% fat-corrected milk
yield (kg) by stage of lactation ................................................... 66

Table 15. Estimates, standard errors and signiﬁcance of effects of
corn silage hybrids on cumulative milk protein concentration
(%) by stage of lactation for primiparous cows .............................. 66

Table 16. Estimates, standard errors and signiﬁcance of effects of
corn silage hybrids on cumulative milk protein concentration
(%) by stage of lactation for multiparous cows .............................. 67

Table 17. Estimates, standard errors and signiﬁcance of effects of
corn silage hybrids on cumulative milk protein yield (kg) by
stage of lactation for multiparous cows ........................................ 67

Table 18. Estimates, standard errors and signiﬁcance of effects of
corn silage hybrids on cumulative milk protein yield (kg) by
stage of lactation for primiparous cows ........................................ 67

Table 19. Estimates, standard errors and signiﬁcance of effects of
corn silage hybrids on cumulative solids-corrected milk
yield (kg) by stage of lactation ................................................... 68

Table 20. Estimates, standard errors and signiﬁcance of effects of
corn silage hybrids on cumulative body weight (kg) by
stage of lactation .................................................................... 68

Table 21. Estimates, standard errors and signiﬁcance of effects of

corn silage hybrids on cumulative body condition score by
stage of lactation .................................................................... 68

viii

LIST OF FIGURES

Figure 1. Least square mean estimates of effects of corn silage
hybrid on milk yield (kg/d) at 25 d intervals .................................. 69

Figure 2. Least square mean estimates of effects of corn silage
hybrid on milk fat yield (kg/d) at 25 d intervals ............................... 70

Figure 3. Least square mean estimates of effects of corn silage
hybrid on 3.5% fat-corrected milk yield (kg/d) at 25 d
intervals ................................................................................ 71

Figure 4. Least square mean estimates of effects of corn silage
hybrid on milk protein concentration (%) at 25 d
intervals for primiparous cows .................................................... 72

Figure 5. Least square mean estimates of effects of corn silage
hybrid on milk protein concentration (%) at 25 d
intervals for multiparous cows .................................................... 73

Figure 6. Least square mean estimates of effects of corn silage
hybrid on milk protein yield (kg/d) at 25 d intervals for
primiparous cows .................................................................... 74

Figure 7. Least square mean estimates of effects of corn silage
hybrid on milk protein yield (kg/d) at 25 d intervals for
multiparous cows .................................................................... 75

Figure 8. Least square mean estimates of effects of corn silage
hybrid on solids-corrected milk yield (kg/d) at 25 d
intervals ................................................................................ 76

Figure 9. Least square mean estimates of effects of corn silage
hybrid on body weight (kg/d) at 25 d intervals ............................... 77

Figure 10. Least square mean estimates of effects of corn silage
hybrid on body condition score at 25 d intervals .......................... 78

INTRODUCTION

Concentration of forage NDF affects DMI by dairy cows and, thus, milk
production. Because forage NDF is ﬁlling, DMI decreases as forage NDF
increases in the diet. However, insufficient forage NDF can result in ruminal
acidosis. Forages with enhanced NDF digestibility are thought to increase DMI
by decreasing the ﬁlling effect of NDF in the rumen. The naturally occurring
genetic mutation in corn plants, designated as brown midrib-3 (bm3), has
consistently greater NDF digestibility compared with corn hybrids not containing
bm mutations.

Several short-term studies have evaluated the effects of bm3 corn silage-
based diets on milk production in dairy cows with mixed results. Differences in
dietary NDF concentrations, stage of lactation and energy balance of the cows
and source of dietary NDF among the studies make it difﬁcult to draw
conclusions regarding the expected response to bm3 corn silage by stage of
lactation. The objective of the study reported herein is to evaluate milk
production responses of lactating cows fed bm3 corn silage-based diets versus

isogenic normal control corn silage-based diets throughout a complete lactation.

LITERATURE REVIEW
This literature review begins with a history of the brown midrib mutation
starting with its discovery in the early 1920’s. The ﬁlling effect of NDF and how
NDF digestibility affects ﬁll are then discussed followed by factors that inﬂuence
NDF digestibility of forages. Finally, the effects of bm3 corn silage as it relates to

animal performance are reviewed.

History of the Brown Midrib Mutations in Corn

Discovery of the Four Brown Midn'b Mutations. Among the earliest known
published accounts describing the brown midrib mutation in corn plants was by
Kiesselbach in 1922 at the University of Nebraska (Kiesselbach, 1922). While
researching the breeding of genetically pure lines of corn, he found that one
strain yielded a corn plant that exhibited what was referred to as an orange-
colored midrib (eventually to become known as brown midrib). Kiesselbach
noted that the orange midrib phenotype was recessive in F1 hybrids and as
generations progressed the trait exhibited simple Mendelian ratios. In the
second generation, for example, 78 plants showed the orange midrib
characteristic while 273 plants maintained green midribs. This amounted to 22%
of the plants with the orange midrib, which Kiesselbach observed is similar to the
1:4 ratio typical of the Mendelian inheritance ratio for recessive genes in the F2
generation.

Eyster (1926) showed that the brown midrib trait resulted from a

homozygous recessive factor pair that he named bm bm (hereafter referred to

as bm). It also was noted that the bm gene was associated with the Pr pr factor
pair, which is responsible for the changing of the aleurone color in corn plants
from purple to red. Jorgenson (1931) conﬁrmed the linkage of the bm gene to
the Pr pr factor pair. Through the use of several chemical analyses, Jorgenson
also showed that the brown pigment characteristic of corn plants with the bm
mutation was not carotin, xanthophyll, tannin, anthocyanin or ﬂavone. It was
theorized that the pigment was either a compound of the ligniﬁed tissue or
was deposited in the interstices. of the corn plant.

The importance of light for the development of the phenotypic character of
bm mutated corn also was determined. Jorgenson planted six bm corn seeds in
each of 10 pots. Five of the pots were located in a dark room and ﬁve were
placed outside the dark room exposed to light but at the same temperature as
those pots in the dark room. At the three and four leaf stage no brown pigment
formation was noted for those plants in the dark room, however, twelve of the
plants at the four-leaf stage outside of the dark room exhibited the brown midrib
characteristic.

The discovery of a second bm gene (bm2) by Burnham and Brink in 1932
mandated that the bm factor pair described by Eyster (1926) and Jorgenson
(1931) be designated as bm1. The bm2 gene, like the bm1 gene, appeared to
be associated with the ligniﬁed tissue and was inherited as simple recessive.
The authors noted that the brown midrib plants were not visibly weaker than their
genotypically normal counterparts, however, the basis for this observation was

not given. More recent evidence suggests that brown midrib plants are slightly

more predisposed to lodging but proper genetic selection might alleviate this
potential problem (Weller and Phipps, 1985; Miller et al., 1983; Nesticky and
Huska, 1985).

Burnham and Brink (1932) also showed that the expression of the bm2
gene was linked to the P-br factor pair where br is associated with plant height.
Speciﬁcally, corn plants exhibiting the br gene yield plants one-fourth to one-half
the height of normal corn plants (Emerson et al., 1935). Others have noted
decreased plant height in brown midrib plants when compared with isogenic
normal plants and this possibly could be the reason for decreased yields
commonly associated with the brown midrib mutation (Miller et al., 1983).

A summary of genetic linkages in corn by Emerson et al. (1935) attributed
the discovery of the third brn mutation, bm3, to unpublished data by Burnham.
This memoir from the Cornell University Agricultural Experiment Station
describes the bm3 mutation to be similar to the bm1 mutation but the
chromosome as unknown. Burnham also was credited with the discovery of a
fourth bm mutation in corn known as bm4 (Coors and Lauer, 2001).

Kuc and Nelson (1964) conﬁrmed Jorgensen's theory that the brown
midrib phenotype was in some way associated with the lignin fraction of the corn
plant. Corn plants that differed only in the allelic presence of the bm mutant or
normal gene were grown and the stalks and leaves were analyzed for differences
in lignin type and/or amount. The bm mutant corn plants at maturity had 14%
less lignin when compared with normal corn plants. Using labeled precursors of

lignin formation (phenylalanine and tyrosine) Kuc and Nelson found that normal

plants incorporated more of these compounds into alkali lignin than did the bm1
plants. Alkali lignin concentration was described by Kuc and Nelson (1964) as
the fraction that represents the "core" of the lignin polymer. They hypothesized
that com plants with the bm1 allele control the type of lignin that is synthesized
thus altering the lignin. Further work has shown differences in the composition of
lignin between bm1 and normal corn plants. Gee et al. (1968) found that the
lignins of the bm1 corn plants yielded approximately 50% less p-coumaric acid
than those of normal corn plants but similar ferulic acid concentrations.
Differences in the Brown Midrib Mutations. The effects of the different bm
mutations on lignin and CP concentrations were ﬁrst evaluated by Muller et al.
(1971) at Purdue University. Two single recessive bm mutant corn hybrids (bm1
and bm3) and one double recessive bm mutant corn hybrid (bm1/bm3) and their
isogenic normal corn hybrids were evaluated in a randomized complete block
design with four blocks. Six plants from each replicate were harvested at 10, 35
and 55 d post-silking. The authors noted that most of the results presented are
from the second harvest (35 d post-silking) because the timing of the second
harvest most closely reﬂected the optimum time of silage harvest. The acid
detergent lignin (ADL) concentration was lower for the bm3 hybrid (4.37%) when
compared with the bm1 (5.13%) and normal (6.08%) hybrids. The bm3 hybrid
was statistically similar but numerically lower in ADL when compared with the
bm1/bm3 hybrid (4.37 vs. 4.60%). The bm3 hybrid also had higher CP
concentration compared with the bm1 and normal hybrids at 10.2%. In a follow-

up study using the same plant material, Barnes et al. (1971) compared the

effects of the various bm mutations on in vitro DM disappearance (IVDMD). The
bm1/bm3 and the bm3 hybrids had higher IVDMD when compared with the
normal hybrid at all three harvest times (10, 35 and 55 d post-silking) by 11.8, 8.8
and 7.5%, respectively. The bm1 hybrid had higher IVDMD when compared with
the normal hybrid at 35 and 55 d post-silking- but the hybrids were similar in
IVDMD at 10 d post-silking. The authors concluded that the bm3 mutation, either
alone or as a double mutant, had the greatest inﬂuence on IVDMD when
compared with the normal or bm1 hybrids.

The ﬁnal evidence that the bm3 mutation had the greatest potential of all
the bm mutations for increasing the forage quality of corn plants came from
Lechtenberg et al. in 1972. They compared a corn hybrid with various bm
mutations (bm1, bm2, bm3, bm4 and bm1/bm3) along with the isogenic normal
and a commercial corn hybrid for ADL and IVDMD. The bm3 hybrid was lower in
ADL concentration and higher in IVDMD% when compared with all the other
hybrids. Although only one corn hybrid was used to compare the various bm
mutations, the authors concluded that the bm3 mutation in corn plants had the
greatest potential for use as a forage source when compared with the other bm
mutations because of its consistently lower ADL concentration and greater
IVDMD%. The ease of back-crossing the mutation into high yielding corn hybrids
was also an important attribute of the bm3 mutation according to the authors.

Quality Characteristics of the bm3 Mutation. The bm3 mutation was
shown to have advantageous effects on corn silage quality in different corn

hybrid types and growing conditions. Allen et al. (1997) planted and harvested

14 different corn hybrids with the bm3 mutation and their isogenic normal
counterparts in two maturity zones in 1994 and 1995. Three plots of each hybrid
were grown in three different locations in the two maturity zones each year.
Similar NDF concentrations were observed between treatments; however, in vitro
NDF digestibility (IVNDFD) was greater by an average of 24% for the hybrids
with the bm3 mutation. Also, lignin concentration was lower and CP% greater for
the bm3 treatment compared with normal (1.7 vs. 2.8% and 8.4 vs. 8.2%,
respectively). The authors also observed that the magnitude of the effect the
bm3 mutation has on corn plant quality is dependent on the hybrid in which the
mutation is incorporated. The range of improvement in IVNDFD% for the
individual bm3 hybrids was from 15 to 38% when compared with the individual
normal hybrids but the percent improvement decreased as the IVNDFD
increased for the normal hybrids.

Ying and Allen (1997) showed that the bm3 mutation enhances in vitro
NDF digestibility by increasing both the rate and extent of NDF digestion in corn
silage. One corn hybrid with the bm3 mutation and its isogenic normal
counterpart were grown, harvested and ensiled in mini-silos in three locations in
two different years (1994 and 1995). As observed in several other studies
comparing the bm3 mutation and it‘s isogenic normal counterparts in corn silage,
NDF concentrations were similar (42.9%) and lignin concentration lower for the
bm3 hybrid (1.74 vs. 2.73%). In vitro NDF indigestible residue (120 h incubation)
was lower for bm3 compared with normal (20.7 vs. 34.4%) with a greater rate of

digestion of the potentially digestible NDF (3.84 vs. 2.89%lh).

The Filling Effect of NDF

Ruminal Receptors and Satiety. The ability of a ruminant to perceive
satiety from physical ﬁll has been attributed to sensory receptors within the
reticulorumen (Lek, 1986). These receptors, which are within the muscle layers
of the rumen, are excited upon distension of the rumen wall and have been
shown to signal the brain satiety center. The existence of mechanoreceptors and
chemoreceptors within the epithelial layer of the reticulorumen also are thought
to be involved in the regulation of DMI; Forbes (1996) suggested that the
stimulation of the tension receptors in the rumen due to distension are summed
with other signals of satiety resulting in a gradual decrease in DMI when applied
at "physiological " concentrations.

The evidence of mechanoreceptors in the rumen was presented by
Baumont et al. (1990) where they suggested that the regulation of DMI in
ruminants is, at least in part, due to mechanical stimulation of the dorsal sac of
the rumen. In sheep fed a liquid diet, pseudorumination (rumination-like jaw
movements with little or no ﬁber present) was observed when the dorsal rumen
sac was stimulated with a bottle brush or ﬂoating polystyrene cubes.
Contractions associated solely with the act of rumination imply that when these
receptors are stimulated in the dorsal sac of the rumen the act of eating has
ceased and rumination begins.

Forbes and Provenza (2000) proposed that hunger and satiety are
balanced by signals from tension-, mechano— and chemoreceptors located within

the viscera of the animal and integrated by the central nervous system (CNS) to

signal "discomfort". The animal then alleviates discomfort by adapting the
amount of feed intake, or feed type, until "discomfort" is again perceived by the
CNS.

Ballast and Neutral Detergent Fiber. The concept that ruminants consume
feed until a certain amount of “ballast” (non—digestible matter) is ingested was
presented initially by Lehmann in 1941 (as cited by Blaxter et al., 1961). Several
literature reviews have since been published acknowledging that DMI can be
limited by physical ﬁll in the gastrointestinal tract of ruminants when fed high ﬁll
diets (Baile and Forbes, 1974; Allen, 1996; Allen, 2000). Although some have
suggested that the intestines may be the rate-limiting site of DMI for ruminants on
high ﬁll diets (Waldo and Jorgenson, 1981) physical limitation generally is
thought to occur in the reticulorumen.

In an attempt to develop a prediction of DMI with forages of differing
quality, Blaxter et al. (1961) fed three hay diets varying in ﬁber concentration to
sheep. Hay quality for this experiment was poor, medium and good quality hays
with crude ﬁber concentrations of 38.5, 30.8 and 22.1%, respectively. They
showed that DMI increased as the "quality" of the hay increased.

Van Soest (1965) argued that before a correlation between "ballast" and
DMI could be valid, a more satisfactory method for determining "ballast" should
be developed. Crude ﬁber did not totally account for the hemicellulose and lignin
fractions of a forage and the neutral detergent system for determining the ﬁber
concentration of a feedstuff was proposed by Van Soest (1965). It is the NDF

concentration (including the hemicellulose, cellulose and lignin fractions) of a diet

that is the single most highly correlated chemical measure of DMI (Van Soest,
1965). Models attempting to predict the voluntary DMI of dairy cattle using NDF
concentration of the diet have been proposed-(Martens, 1987; Williams et al.,
1989)

Rumen Inert Bulk. The use of rumen inert bulk (RIB) to assess the effect
of ﬁll on DMI has been done extensively with varying results. Among the ﬁrst of
these experiments, Campling and Balch (1961) used three non-lactating, non-
pregnant cows in a 3 x 3 Latin square design in 14-d periods. The three
treatments were no bladder in the rumen (control), a bladder ﬁlled with 22.7 kg of
water inserted in the rumen and a bladder ﬁlled with 34.0 kg of water inserted in
the rumen. When these animals were offered all hay diets a decrease in
voluntary DMI of 54 g/L of water in the bladders was seen.

Anil et al. (1993) showed similar results of RIB in lactating dairy cattle fed
all hay diets. Two separate experiments with six cows each in a 3 x 3 Latin
square design were used. Cows were offered hay ad Iibitum for only 3 h per
collection period. Rubber bladders in the rumen of each animal were ﬁlled with
either 7.5 or 15.0 L of water for animals in trial 1 and 12.5 or 20 L of water in trial
2. Control animals for both trials had no RIB in the rumen. Linear decreases in
DMI were seen in both trials as RIB was increased (r2 = 0.82 for trial 1; r2 = 0.80
for trial 2) at a rate of 56 g/L of water in the bladders. In a follow up study
utilizing ryegrass silage instead of ryegrass hay, Anil et al. (1993) showed a
linear decrease in DMI as water ﬁlled bladders increased ruminal distension from

0, 15, 20 and 25 L (P < 0.01). The rate of decreased DMI was only half for

10

ryegrass silage (28 g/L) compared with ryegrass hay (56 g/L) possibly indicating
the importance of weight and weight-sensitive receptors in the rumen wall.

Other studies have shown no effect on DMI with the addition of RIB to the
rumen. Waybright and Varga (1991) inserted water-ﬁlled bags into the rumen of
sheep at the rate of 0.22, 0.44 or 0.66 UL of pre-trial ruminal volume. The sheep
were fed a high-concentrate diet with a NDF concentration of 22%, dry basis. No
effect of DMI was observed as ruminal capacity decreased. Similarly, in a series
of studies by Carr and Jacobson (1967), DMI did not decrease as RIB increased
in the rumen of 500 kg non-lactating dairy cows. In these experiments it has
been suggested that ruminal ﬁll may have not been limiting DMI even after
insertion of the RIB (Allen, 1996). Anil et al. (1993) suggested that no effect was
observed in the Carr and Jacobson study because the amount of RIB used was
not great enough.

Carr and Jacobson (1967) utilized the lower level of distension to more
closely resemble "physiological levels" of ﬁll. The animals used for the Carr and
Jacobson (1967) study were non-lactating dairy cows fed a ground hay and
concentrate diet (experiment 1) or a chopped hay diet (experiment 2). Allen
(1996) speculated that these animals met their energy requirements and
therefore, physical ﬁll did not limit voluntary DMI. Non-lactating animals consume
relatively less DM compared with lactating cows and differences may have,
therefore, been more difﬁcult to discern. The use of ground hay (experiment 1)
and chopped hay (experiment 2) also may have allowed for greater passage out

of the reticulorumen relative to coarse hay diets. Thus, a lack of physical ﬁll may

11

have negated any differences that might have been seen with the RIB because
of decreased particle size of the forages.

Stage of lactation and energy balance status also may affect DMI of
ruminants due to physical limitations of NDF in the reticulorumen. This is, at
least in part, due to the increased energy requirements associated with milk
production, especially in early lactation (NRC, 2001). A negative energy balance
develops in early lactation when the demand for energy by the cow for milk
production exceeds the energy consumed. In a review on the physical restraints
of intake in ruminants, Allen (1996) concluded that the response to inert ﬁll in the
reticulorumen is a function of the energy requirement of the animal, the caloric
density of the diet, the ﬁlling effect of the diet, the capacity of the reticulorumen,
and the passage rate of digesta from the reticulorumen of the host animal.
Johnson and Combs (1991) showed that ruminal ﬁll might depress DMI for dairy
cattle in early lactation. Rumen inert bulk was used to replace 25% of ruminal
capacity in cows averaging 49 and 73 DIM in trials 1 and 2, respectively. A
decrease in DMI of 99 g/L of added bulk was observed in trial 1 and 130 g/L of
added bulk in trial 2. Dado and Allen (1995) further studied the effect of dietary
ruminal ﬁll on DMI of cows in early lactation. Twelve animals averaging 59 DIM
were used in a 4 x 4 Latin square design. Cows were fed 25 or 35% NDF diets
with or without the addition of 25% RIB (pre-trial rumen volume). There was a
decrease in DMI of 5.1 kgld for cows fed the high NDF diet when compared with
cows fed the low NDF diet. Furthermore, the addition of the RIB had no effect on

DMI of cows on the low NDF diet but decreased DMI of cows fed the high NDF

12

diet by 2.1 kgld. The addition of ﬁll to the rumens in these experiments, whether
by RIB or an increase in the ﬁlling effect of the diet (increased NDF), limited the
potential maximum DMI in these early lactation cows.

Johnson and Combs (1992), however, observed no differences in DMI
when RIB was added to rumens of cows past peak lactation and in a greater
energy balance than early lactation cows (Johnson and Combs, 1991). Cows,
with or without RIB at 25% of pre—trial rumen volume and averaging 229 DIM,
had similar DMI when fed a 29% NDF diet. In a follow up study, diets of 27 and
34% NDF were fed to cows averaging 119 DIM with or without the addition of
25% RIB (pre—trial rumen volume). The increase in dietary NDF decreased DMI
but no differences in DMI were observed for either concentration of dietary NDF
when RIB was added.

Johnson and Combs (1992) noted that it is possible for the rumen to adapt
to physical ﬁll by altering ruminal capacity. The addition of a bladder with 19.5 L
of water to cows averaging 229 DIM caused decreases in DMI of approximately
2, 1 and 0 kgld for weeks 1, 2 and 3 of the study when compared with cows with
no bladders. The cows with the bladders compensated for the RIB with a 6 L
decrease in digesta volume and a 17.5 L increase in total reticuloruminal volume.
This ability to adapt to increasing ﬁll in the rumen also was observed by Dado
and Allen (1995) for animals on the low ﬁll diet (25% NDF); however, animals on
the high ﬁll diet (35% NDF) were not able to overcome the ﬁll effect of NDF with
early lactation cows.

It has been postulated that DMI will not be limiting until the reserve

13

capacity for ﬁll in the rumen is reached (Allen, 1996). Decreasing particle size or
increasing the NDF digestiblity of the diet may potentially allow greater ruminal

passage of NDF and thus increase DMI for cows limited by physical ﬁll.

NDF Digestibility Affects the Filling Effect of NDF

Once the rumen's capacity for ﬁll has been reached, movement of digesta
out of the rumen must occur before feed intake can resume. Early work on this
subject by Crampton (1957) showed that forages with the least amount of
cellulose and hemicellulose digestion (essentially, NDF digestibility) were
retained the longest in the rumen of sheep. He postulated that this increase in
retention time of the feed in the rumen was a major factor in decreasing voluntary
intake.

Other studies have shown how increased NDF digestibility can alleviate
the ﬁlling effect of NDF in the rumen at similar dietary NDF concentrations. Ruiz
et al. (1995) fed 48 Holstein cows averaging 110 DIM diets differing in NDF
concentration (31.0, 35.0 and 39.0%) based on four different ensiled forage
sources of differing digestibilities (twelve diets total). They found that at similar
dietary NDF concentrations the diets with the greater in situ NDF digestibilities
(whole plant corn and dwarf elephant grass) had greater NDF and DM intakes
compared with the lower digestibility forage diets. Cows fed the more digestible
forages had greater milk production compared with cows fed the lower digestible
forages. However, because the treatments in this study consisted of four

different varieties of grass, it is difﬁcult to attribute the increased intakes and milk

14

 

production solely to greater NDF digestibilities of the corn and elephant grass
silages.

Robinson and McQueen (1992) fed diets of like-forage sources to test the
effects of ruminal ﬁll on intake and milk production. Twelve multiparous and 4
primiparous Holstein cows in mid-lactation (DIM not reported) were used in a
replicated 4 x 4 Latin square design. A good timothy hay (GT) and a poor
timothy hay (PT) were used to formulate diets with similar NDF concentrations
(approximately 40.0%) but differing digestibilities. Diets were designated as
having inclusion rates of GT at 0, 33, 66 and 100% of total dietary forage. The
treatment hays accounted for 53, 50, 48 and 46 percent of diet DM for diets with
GT inclusion rates of 0, 33, 66, and 100 percent, respectively. As inclusion rate
of GT in the diets increased from 0 to 100%, the extent of NDF digestion (utilizing
chromic oxide as an external digestibility marker) increased from 64.2 to 69.7%.
No effect of diet digestibility on milk production or DMI were observed. The lack
of effect of increased NDF digestibility on DMI could possibly be due, however, to
the fact that ﬁll was not limiting intake in this study (Jung and Allen, 1995).

Dado and Allen (1996) noted the possible limitations of the previous
studies and harvested and ensiled alfalfa with similar NDF concentrations that
differed in NDF digestibility by 2.8 percentage units. Diets based on these
forages were fed to cows in early lactation (average DIM = 13 d). They found
that although NDF intakes were similar between the treatments, DMI and milk
production were greater for cows consuming the diet with the greater NDF

digestibility. This coincided with greater total tract digestibilities of both NDF and

15

 

DM.

Oba and Allen (1999b) showed the impact that NDF digestibility can have
on DMI and milk production in lactating cows. From the literature, 13 sets of
forage comparisons from seven different studies were evaluated to determine the
effects of NDF digestibility on DMI, milk yield, FCM yield, BW change and
ruminal pH. Studies were included if the NDF digestibilities of the forages
compared, determined in situ or in vitro, were different (P < 0.10) and if the
comparisons were of forages within the same forage family (e.g., legume or
grass). Not included in the database were studies not reporting dietary NDF
concentration because dietary NDF concentration was used in the model as a
covariate. The authors concluded that a one unit increase in NDF digestibility
equated to a 0.17 kgld increase in DMI and a 0.25 kgld increase in 4% FCM

yield.

Factors Affecting the Digestibility of Forage NDF

Forage Maturity. The maturity of a forage has long been thought a major
determinant of forage quality (Woodward et al., 1939). Llano and DePeters
(1985), however, were among the ﬁrst to evaluate the effect of forage maturity on
NDF digestibility in vivo. They harvested and preserved, as hays, alfalfa at 21 d
(early out) or 30 d (normal cut) intervals which were fed to both lactating and non-
lactating dairy cows in a series of experiments. Both the early and normal cut
hays were mixed with concentrates at 30 or 50% of diet DM and cubed. Dietary

NDF concentrations were similar for all four diets (approximately 32%, DM

16

 

basis). The apparent digestibilities of DM and NDF were greater for cows fed the
early out forage compared with cows fed the normal cut forage (67.4 and 45.1%
vs. 61.5 and 30.5%, respectively). Dry matter intake, however, was similar at
both maturities. Overall, the authors concluded that as plant maturity increased
apparent digestibility of NDF decreased.

Maturity not only appears to affect the digestibility of a forage but also its
rate of passage from the rumen. Llamas-Lamas and Combs (1990) harvested
alfalfa at three maturities [early vegetative (EV), late bud (LB) and full bloom
(FB)] and preserved the alfalfa as hay. Diets formulated from these forages were
balanced for 29.4% NDF and 19.3% CF and fed to six lactating cows averaging
120 DIM in a replicated 3 x 3 Latin square design. Whole tract NDF digestibility
(determined by samarium-marked grain) was greater for the diet containing EV
when contrasted with diets containing LB and FB (55.0 vs. 46.0%). Dry matter
intake and in vivo solid phase rate of passage also were greater for the EV diet
compared with the average of the LB and PB diets (26.1 vs. 24.6 kgld; 5.2 vs.
4.8%). Consequently, the authors concluded that cows fed the EV diet had
greater DMI relative to the LB and FB diets because of the increased rate of
passage and greater proportion of potentially digested NDF of the EV diet.

Dry Matter Intake. How well a forage or forage-based diet is digested by a
ruminant also is dependent on the amount of intake for which a given forage is
consumed. Colucci et al. (1982) fed whole plant corn and alfalfa silage-based
low and high forage diets with dietary NDF concentrations of 29.7 and 37.8%,

respectively, to non-lactating and lactating cows. The lactating cows had greater

17

DMI (as g/kg BW), but lower DM and NDF digestibilities than the non-lactating
animals within a diet. They observed that the intake of NDF was correlated
positively with particulate matter passage and theorized that decreased
digestibility of diets at the higher intakes was caused by a faster rate of passage
through the rumen.

Utilizing a 3 x 3 Latin square design, Shaver et al. (1986) evaluated the
effects of various intake amounts and forage particle sizes on the digestion and
passage of legume hay in dairy cattle. They fed pre-bloom alfalfa hay, either
long, chopped or pelleted, in a 60:40 hayzconcentrate diet to six Holstein cows in
early— and mid-lactation (high and medium intake groups) and in the dry period
(low intake group). Dietary NDF and CP concentrations were similar for all
treatments (30.8 and 17.4%, respectively). They observed a longer whole tract
retention time of ytterbium-marked hay (26.4 vs. 15.6 h) and greater total tract
NDF digestibility (42.5 vs. 36.5%) for the low intake group compared with the
high intake group. Like Colucci et al. (1982), the authors attributed the
depression in NDF digestibility for the high intake group to the decreased ruminal
retention time of the NDF. When the effect of particle size of the hay diets was
evaluated, DMI was similar for all treatments but the pelleted diet had lower total
tract NDF digestibility and ruminal pH compared with the long and chopped diets
(36.8 vs. 41.1% and 5.77 vs. 6.34, respectively). The authors theorized that with
high quality forages like pre-bloom alfalfa, particle size is not the factor that limits
DMI because rapid reduction in particle size due to mastication and rumination

occurs relative to lower quality forages. Therefore, the authors speculated that

18

 

trying to decrease ruminal ﬁll by reducing the particle size of a high quality forage
may not increase digestibility because smaller particles in the rumen could
decrease rumination and total chewing thereby causing a drop in ruminal pH and
thus decrease ﬁber digestibility.

Particle Size. The effect of particle size on NDF digestibility also may be
inﬂuenced by the type of forage offered. Osbourn et al. (1981) in two
experiments, fed wether lambs ﬁve hay types representing both graminaceous
and leguminous forages. Forages were fed as either long hay, pellets made from
the long hay that was ground coarsely or ﬁnely or a combination of the coarsely
and ﬁnely ground pellets (ratio of each not reported). These combinations also
were fed at different amounts of feed offered in the second experiment. Overall,
NDF digestibility decreased with a decrease in particle size and an increase in
the amount of feed offered. This decrease in NDF digestibility was more
prevalent for the grasses than the legumes.

Decreasing particle size of forages does not always decrease NDF
digestibility. Woodford et al. (1986) observed no differences in DMI or NDF
digestibility when cows were fed alfalfa hay-based diets chopped at mean
particle sizes of 0.26, 0.46, 0.64, and 0.90 cm. Cows averaged 56 DIM and the
dietary NDF concentration was 27%. It is possible, however, that ﬁll was not
limiting DMI in this study.

Environment. Forage NDF digestibility also is affected by environmental
factors such as drought stress and temperature. Allen and Oba (1996)

summarized data from 35 corn hybrids grown in two plots at two locations in two

19

maturity zones in Michigan in both 1988 and 1989. Corn grown in 1998 was
considered drought stressed relative to corn grown in 1999 because of a lower
amount of precipitation (21.3 vs. 41.4 cm) and a higher growing degree-day
value (2387 vs. 2072) from May 1 to September 1 of each year. Compared with
the non-drought stressed corn plants, the drought stressed corn plants had
slightly lower NDF and lignin concentrations (40.8 vs. 42.2% and 2.44 vs. 2.96%,
respectively) and nearly a 20% greater 30-h IVNDF D (50.3 vs. 42.0%). Although
both temperature and soil moisture are important factors affecting NDF
digestibility in forages, it has been suggested that soil moisture may be more
inﬂuential in determining forage quality than temperature (Crasta and Cox, 1996).
Increases in NDF digestibility of drought-stressed forages, however, may
not be due necessarily to decreased soil moisture but to slow maturation of the
forage itself. Deetz et al. (1996) harvested alfalfa at 21, 35 and 49 d of re-growth
in plots irrigated at 65, 88 or 112% of ﬁeld water holding capacity. Field water
holding capacities of 65 and 88% were considered water-deﬁcits. They found
that as the amount of irrigation increased, the NDF concentration of the alfalfa
increased, but ligniﬁcation and NDF digestibility was not affected by water status.
They concluded that water-stressed plants do not have greater quality
characteristics due to being water-stressed, but because a delayed maturity and
smaller concentrations of cell wall brought on by the lack of water during growth.
Lignin. A major determinant of NDF digestibility is the amount and/or the
composition of lignin within the NDF fraction of the plant (Jung, 1989). Jung and

Deetz (1993) theorized that lignin decreases the digestibility of plant NDF

20

fractions by shielding the cell wall polysaccharides from enzymatic hydrolysis.
Smith et al. (1972) harvested six legume and nine grass species at 1-wk intervals
to determine the effects of species and maturity on the indigestibility of NDF.

The rate and extent of NDF digestibility were determined by in vitro incubation.
They found that lignin concentration was correlated positively with NDF
indigestibility for both legumes (r = 0.78) and grasses (r = 0.89). The authors
concluded that lignin concentration could account for up to 75% of the variation
of in vitro NDF digestibilities across species and maturity, and that soluble DM
concentration can account for approximately 50% of the variation in NDF rates of
digestion.

Allen and Oba (1996) showed that lignin as a percent of NDF explained
about 50% of the variation in IVNDF D for alfalfa and corn forage. However, for
alfalfa the relationship between lignin as a percent of NDF and IVNDFD was
greatest for ﬁrst cutting, less for second cutting and not related for third or fourth
cutting. For corn forage grown over two years there was no relationship between
lignin as a percent of NDF and IVNDF D in a drought year but a signiﬁcant

relationship in a normal year and across both years (r2 approximately 0.50).

Animal Performance with bm3 Corn Silage

Sheep. The ﬁrst study to evaluate bm3 corn silage in vivo was published
by Muller et al. (1972). They harvested bm3, isogenic normal and conventional
corn plants and manually removed the ears prior to ensiling to avoid confounding

results because of differences in grain concentration between the hybrids. The

21

NDF concentrations were 60, 61 and 62% (dry basis) for bm3, isogenic normal
and conventional corn silages. respectively. Eighteen ram lambs were assigned
randomly to either a bm3, normal or conventional corn silage-based diet fed as
90% corn silage and 10% protein-vitamin-mineral mix. Ad Iibitum DMI as a
percent of BW for lambs on the bm3 silage diet were greater when compared
with lambs fed either the normal or conventional silage diets (2.43, 1.88 and
1.58%, respectively). Apparent digestibilities of DM, NDF and energy were all
higher for bm3 silage fed lambs when compared with normal and conventional
silage fed lambs. The authors concluded that the bm3 mutation produced corn
silage with greater digestible DM, NDF and energy when compared with normal
and conventional corn silage possibly because of decreased ligniﬁcation of the
cellulose and hemicellulose of the corn plant. They further hypothesized that the
increase in DMI for bm3 fed lambs could possibly be due to increases in the
overall digestibility of the bm3 corn silage.

Increased digestibility of bm3 corn silage has also been observed in other
studies utilizing sheep. Stallings et al. (1982) fed six yearling wethers bm3 and
isogenic normal corn silage diets in a single crossover design. Although feed
intake was restricted to 90% ad libitum intake, DMI was greater for wethers fed
the bm3 corn silage diet (1.36 vs. 1.15 kgld). Apparent DM digestibility was 6.6
percentage units greater for wethers fed the bm3 diet when compared with
wethers fed normal corn silage. Weller and Phipps (1986) noted smaller but still
signiﬁcant increases in apparent DM digestibility when feeding 18-mo old

wethers bm3 corn silage or isogenic normal corn silage. Three bm3 hybrids and

22

 

their isogenic normal counterpart hybrids were evaluated and the mean values
from the lambs fed the three bm3 hybrid silages were compared with the mean
values from the lambs fed the three normal hybrid silages. Apparent
digestibilities were higher for DM, OM, NDF, ADF, cellulose and hemicellulose for
those lambs fed the bm3 corn silage diets (2.9, 2.7, 4.5, 8.5, 6.6 and 2.0
percentage units, respectively). DMI was not reported for this study.

Dairy Cattle. Oba and Allen (19993) showed that increased NDF
digestibility observed for bm3 corn silage in vitro does not necessarily correspond
to similar NDF digestibilities in vivo. Thirty-two cows averaging 89 i 27 DIM
were fed bm3 and isogenic normal corn silage-based diets in a single crossover
design with 28 d periods. The IVNDFD of the bm3 corn silage was 9.7
percentage units greater when compared with normal corn silage. However,
when the corn silages were included in TMR diets at 45% of the diet DM the bm3
fed cows had only 2.2 percentage units greater apparent total tract NDF
digestibility when compared with cows fed the normal com silage-based diet (P =
0.02). Dry matter intake was greater (P < 0.0001) for cows fed the bm3 diet
compared with normal fed cows (25.6 vs. 23.5 kgld). The authors hypothesized
that the decrease in the in vitro and in vivo NDF digestibilities between the two
corn silage hybrids was a result of the increased DM intake observed for the bm3
fed cows. The change in the total tract NDF digestibility response to the bm3
treatment ranged from approximately plus 15% when DMI was greater for normal
fed cows to approximately minus 15% when DMI was greater for bm3 fed cows.

This relationship between DMI response to the bm3 treatment (response to bm3

23

 

corn silage minus response to normal corn silage) and the response in total tract
NDF digestibility showed a negative correlation (P < 0.001). As DMI increased,
NDF digestibility decreased. The authors speculated that this was because of
faster passage from the rumen for bm3 as DMI increased. Because a constant
retention time is used to determine in vitro digestibility values, the differences in
NDF digestibility between bm3 and normal corn silages may have been inﬂated
compared with the in vivo results.

The increases in DMI and NDF digestibility observed by Oba and Allen
(1999a) for cows fed the bm3 treatment was accompanied by a milk yield
response when compared with cows fed the isogenic normal treatment.
Speciﬁcally, cows fed the bm3 treatment yielded 2.8 kgld more milk than cows on
the normal treatment and 2.6 kgld more 3.5% FCM. Because this study was a
crossover design the authors were able to evaluate each animal's response to
the bm3 treatment. They plotted each animal's pre-trial milk yield against their
milk yield response to the bm3 treatment and observed a positive correlation. In
other words, cows that had the highest milk yields pre-trial had the greatest
response to the bm3 treatment. Conversely, those cows that had lower milk
yields pre-trial had little or no responses to the bm3 treatment.

Increases in milk yield also have been observed with cows fed bm3 corn
silage diets without increases in DMI. Keith et al. (1979) randomly assigned 12
Holstein cows past peak lactation to one of four treatment combinations in a
double switchback design. The diet combinations were bm3 and isogenic normal

corn silages fed at two forage to concentrate (F:C) ratios (75:25 and 60:40).

24

 

Cows received their assigned diet for 5 wk, were randomly switched to a second
treatment diet for 5 wk and then were switched back to the original assigned diet
for 5 wk. Although genotype or F:C ratio did not affect DMI, milk yields were
higher for cows fed the bm3 treatments. Cows on the bm3 treatment had 1.3
and 1.6 kgld greater milk yield and 0.9 and 1.0 kgld greater FCM yield than cows
fed the normal treatment at F:C ratios of 75:25 and 60:40, respectively.

Oba and Allen (2000a) also fed cows bm3 and normal corn silage diets at
two different dietary NDF concentrations (29 and 38% dietary NDF) but noted
increases in DMI at both concentrations of ﬁber for cows on the bm3 treatment.
Along with the increases in DMI, cows fed bm3 corn silage-based diets also had
higher SCM yields regardless of the forage concentration. However, because no
milk fat depression was observed for cows on the high forage bm3 diet and
solids not fat concentration also was greater for these cows when compared with
the bm3 low forage and normal diets. The authors contended that the feeding of
bm3 corn silage was more beneﬁcial in high forage diets when fed to higher
producing cows.

Frenchick et al. (1976) observed increases in milk yield for cows past peak
lactation fed a bm3 corn silage-based diet compared with cows fed an isogenic
normal diet (22.5 vs. 21.7 kgld). However, because cows fed the bm3 treatment
had a lower milk fat percentage the FCM yields between the two treatments were
similar. Body weight gains, though, were greater for cows fed the bm3 treatment
(+3.1 vs. —0.6 kg for normal treatment).

Sommerfeldt et al. (1979) theorized that BW gains of cows fed bm3 com

25

silage are due to partitioning of energy from milk production. In their study, cows
(averaging 42 DIM) fed bm3 corn silage-based diets had no advantages in DMI
nor milk yield compared with cows fed isogenic normal corn silage diets but they
did have greater (P < 0.01) daily BW gains (+584 vs. -47.3 gld). Rook et al.
(1977) also observed increased BW gains with cows fed bm3 corn silage-based
diets from 42 to 91 DIM (49.6 vs. 7.1 g/d), but there were also signiﬁcant
increases in DMI when compared with cows fed normal corn silage-based diets
(20.2 vs. 18.6 kgld). Cows beginning treatments at 7 DIM, however, had no
advantage in DMI or BW gain from the bm3 corn silage diet when fed to 56 DIM.
Milk yields were not different between treatments at either stage of lactation.

The apparent partitioning of energy toward body condition rather than milk
production for cows fed bm3 corn silage was also observed by Block et al.
(1981). From 18 to 74 DIM cows fed bm3 corn silage had increased BW (+10.2
kg), whereas cows fed the isogenic normal corn silage actually lost BW (-24.6
kg). Cows fed the bm3 treatment produced more milk throughout the study but
this was not signiﬁcant. The authors, however, noted that when the milk yield of
the two groups were analyzed by week, cows receiving the bm3 treatment
produced more actual milk in wk 5, 6 and 8 compared to cows receiving the
normal treatment. Statistics regarding these differences were not reported.

The effects of bm3 corn silage on lactational performance also have been
compared with other specialty hybrids. Ballard et al. (2001) fed late lactation
cows (204 i 104 DIM) corn silages from either leafy, brown midrib, or high grain

yield corn hybrids. Because the leafy and brown midrib hybrids are considered

26

for silage only they were compared with the grain hybrid and to each other.
Direct contrasts between the grain hybrid and either of the silage hybrids were
not performed. They found that cows fed the silage hybrids produced 1.1 kgld
more milk when compared with cows fed the grain hybrid and that the brown
midrib treatment increased milk yield over the leafy hybrid by 2.3 kgld. Yield of
3.5% FCM also was greater for cows fed the brown midrib treatment compared
with the leafy treatment (35.8 vs. 33.5 kgld) but cows receiving the silage hybrids
had similar yields to the grain hybrid treatment fed cows (34.7 vs. 33.3 kgld). An
intake study conducted with the same hybrids in growing dairy heifers showed
that the silage hybrids allowed greater consumption of DM compared with the
grain hybrid as a percent of BW (2.13 vs. 2.02%) but that body condition and
weight gains were similar between the treatments.

Transition cows have beneﬁted by bm3 corn silage-based diets. Santos et
al. (2001) fed primiparous and multiparous dairy animals non-isogenic control
corn silage-based diets at either 55:45 or 65:45 F:C ratios or a bm3 corn silage-
based diet at a 65:45 F:C ratio. Treatment diets began an average of 23 d prior
to calving and continued for 33 d postpartum. Post calving health and DMI were
similar between treatments for this study but a tendency (P = 0.09) for increased
milk yield was observed for multiparous cows receiving the bm3 treatment (+2.2
kgld).

Beef Cattle. The effects of bm3 corn silage-based diets also were
evaluated in studies with beef cattle. Keith et al. (1981) studied the effects of

bm3 corn silage with various concentrations of additional grain in both beef

27

 

steers and heifers in two different experiments. Steers fed bm3 corn silage
increased average daily gain (ADG) when compared with steers fed a
conventional corn silage only diet (0.90 vs. 0.82 kgld) but when each hybrid was
supplemented with corn at 2% of BW feed efﬁciency was similar. In the second
experiment heifers fed bm3 corn silage only had greater ADG than heifers fed
conventional corn silage only (1.03 vs. 0.90 kg) and similar ADG to conventional
corn silage plus 1% added corn (1.03 kg for both treatments). Similarly, Woody
et al. (1977) observed that beef steers fed bm3 corn silage only diets had similar
ADG when compared with steers fed conventional corn silage plus 40% com
grain.

'ljardes et al. (2000) fed eight beef steers bm3 or normal corn silage diets
at 86% of the diet DM both ad libitum and restricted intake. The bm3 treatment
increased DMI when fed ad libitum (5.06 vs. 4.44 kgld). Apparent total tract ﬁber
digestibility was 10.5 and 15.8 percentage units greater for steers on the bm3
treatment when compared with normal treatment steers when fed ad libitum and
restricted, respectively. These same diets were fed ad libitum to eight pens
(eight steers per pen) for 112 d as a grower diet and then a common ﬁnishing
diet was fed to all animals. Although DMI was greater for steers on the bm3 diet
(0.43 kgld increase) during the growing phase no advantages in either DMI or
ADG were observed for either treatment overall.

Lignin and Digestibility. The advantages observed for feeding bm3 corn
silage-based diets have been attributed to the increased digestibility of the ﬁber

due to decreases in the lignin concentration of the whole plant. Only one study

28

 

reported in the literature has shown similar lignin concentration between a bm3
corn hybrid and its isogenic normal counterpart (Sommerfeldt et al., 1979) but
NDF digestibility was still 9.6 percentage units greater for the bm3 corn silage
diet in that study. Kuc and Nelson (1964) determined that the lignin of brown
midrib corn plants differs from normal corn plants by not only decreased lignin
concentration, but also by altered lignin composition. Although overall NDF
digestibility is typically increased for bmr corn hybrids, there is evidence that the
NDF of bmr corn plants is less digestible per unit of lignin when compared with
normal corn plant ﬁber (Thorstensson et al., 1992). Therefore, the observation of
Sommerfeldt et al. (1979) is difﬁcult to explain.

Microbial Efﬁciency. Microbial efﬁciency, deﬁned as grams of bacterial
leg of OM truly digested in the rumen, was greater for early mid-lactation cows
fed bm3 corn silage (Oba and Allen, 2000c) but was signiﬁcantly decreased for
late lactation cows (Greenﬁeld et al., 2001) when compared with isogenic normal
corn silage diets. The differences observed between these studies may be
accounted for by the DMI for cows fed bm3 treatments compared with normal
treatments. The early mid-lactation cows of the Oba and Allen study (2000a)
increased DMI by 4.8% whereas late lactation cows in the Greenﬁeld et al. study
(2001) showed similar DMI between the two treatment diets. Greenﬁeld et al.
(2001) attributed the differences in microbial efﬁciency between the early mid-
lactation and late lactation cow studies to the differences observed in rumen
retention times.

Physical Effectiveness. Although bm3 corn hybrids typically are superior

29

to isogenic normal corn hybrids in NDF digestibility the NDF of both hybrid types
has been shown to be similar in physical effectiveness (Oba and Allen, 2000).
Oba and Allen (2000b) observed that the turnover rate of ruminal digesta NDF
was greater for bm3 corn silage diets fed to lactating cows but that the pool size
of the NDF remained similar to the normal corn silage fed cows due to an
increase in DMI of cows fed the bm3 treatment. No effects on eating or
ruminating time were observed for cows on the bm3 treatment in this study when
compared with the normal treatment.

Milk Composition. The effects of bm3 corn silage-based diets on milk
composition and yield have given mixed results. Several studies have shown no
effect on concentration or yield of milk components with bm3 corn silage diets
[Rook et al. (1977), Keith et al. (1979), Sommerfeldt et al. (1979), Stallings et al.
(1982), Ballard et al. (2001), Greenﬁeld et al. (2001) and Tine et al. (2001)].

Oba and Allen (1999a) observed increases in milk protein concentration
and yield with cows fed bm3 corn silage diets of 2.4 and 8.1%, respectively,
compared with cows fed isogenic normal corn silage diets. In a subsequent
study, Oba and Allen (2000a) again noted increases in milk protein yield for cows
fed the bm3 corn silage diets compared with cows fed normal corn silage diets
but not for milk protein concentration. Oba and Allen (2001c) attributed the
increased milk protein concentration and yield observed in these two studies to
the greater microbial N production of cows on the bm3 treatments.

Block et al. (1981) observed decreases in milk fat concentration of 8.9%

for cows fed bm3 corn silage diets compared with isogenic normal fed cows. The

30

bm3 corn silage in this study was lower in NDF concentration compared with the
normal corn silage and the diets were balanced for the same forage to
concentrate ratio rather than for NDF concentration. It is possible that the lower
milk fat concentrations observed for by Block et al. (1981) was due to lower NDF
dietary concentrations for the bm3 treatments.

Oba and Allen (2000a) observed lower milk fat concentrations for cows
fed bm3 corn silage diets compared with isogenic normal corn silage diets at low
(29%) but not high (38%) NDF concentrations. Two concentrations of dietary
NDF with bm3 and normal corn silage hybrids were fed to lactating cows in a 4 x
4 Latin square design with a 2 x 2 factorial arrangement of treatments. Milk fat
concentration was depressed greatly for the bm3 treatment compared with
normal treatment for the low NDF concentration diets (3.28 vs. 3.67%) but not for
the high NDF concentration diets (3.86 vs. 3.90%). However, milk fat yield was
similar among treatments (1.24 kgld). The milk fat depression observed for the
bm3 treatment in the low NDF concentration diet was hypothesized by the
authors to be a dilution effect resulting from a greater rate of milk ﬂuid synthesis
relative to milk fat synthesis.

Ruminal pH. In the ﬁve studies that reported ruminal pH values when
feeding bm3 and isogenic corn silage-based diets to lactating dairy cows, four of
the studies noted decreases in ruminal pH for bm3 corn silage fed cows. Oba
and Allen (2000b) observed depressed ruminal pH values for bm3 corn silage fed
cows compared with isogenic normal corn silage fed cows (5.68 vs. 5.84)

although chewing activity and OM truly fermented in the rumen were similar

31

between treatments. Similarly, Greenﬁeld et al. (2001), Frenchick et al. (1976)
and Block et al. (1981) observed lower ruminal pH values for bm3 treatment
cows compared with isogenic normal treatment cows by 0.11, 0.18 and 0.52 pH
units, respectively.

In an attempt to explain ruminal pH value differences by salivary buffering
capacity without measuring saliva ﬂow to the rumen directly, Oba and Allen
(2000b) measured chewing activity because of the expected relationship
between saliva production and total chewing time. However, because chewing
activity and OM truly fermented in the rumen were similar between the bm3 and
normal corn silage treatments in their study no explanation for the depressed
ruminal pH was evident. The authors speculated that factors other than chewing
time, which affect rate of absorption and passage along with the neutralization of
fermentation acids, may explain the decreased ruminal pH with the bm3 corn

silage diets.

SUMMARY

Several short-term studies have evaluated the effects bm3 corn silage-
based diets on lactational performance of dairy cows, however, the results from
these studies have been inconsistent. Increases in milk production of 1.6 kgld
(Keith et al., 1979), 2.8 kgld (Oba and Allen, 1999a) and 3.5 kgld (Oba and Allen,
2000a) were observed for cows fed bm3 corn silage-based diets when compared
with cows fed isogenic normal corn silage-based diets. Others comparing cows

fed bm3 and isogenic normal corn silage-based diets have observed no milk

32

production differences (Rook et al., 1977; Sommerfeldt et al., 1979; Stallings et
al., 1982). The varied responses observed could be because of the different
stages of lactation of the cows in these studies.

Negative energy balance in early lactation occurs because energy intake
lags behind the energy demands of milk production. The reasons for this are
unknown but might be because feed intake is limited by physical ﬁll in early
lactation. The ﬁlling effects of a diet are affected primarily by NDF concentration
and its digestibility. Brown midrib-3 corn silage is expected to increase feed
intake when it is limited by ﬁll because of its greater NDF digestibility relative to
corn silage hybrids not containing bm mutations. The hypothesis for this
experiment is that bm3 corn silage based-diets will increase milk yield of cows
compared with normal corn silage and that the response will be greater in early
lactation compared with late lactation. Therefore, the objective of the experiment
reported herein is to evaluate milk production responses of lactating cows fed

bm3 corn silage-based diets throughout a complete lactation.

33

MATERIALS AND METHODS

Experimental Treatments, Design, Diets and Cows

This experiment was conducted at the Michigan State University dairy
facility at the Kellogg Biological Station in Hickory Corners, Michigan. The All-
University Committee on Animal Use and Care of Michigan State University
approved the animal care protocol (approval number 02/98-033-00). The
experiment began on May 16, 1998 and ended on November 11, 1999.

Com Hybrids Compared. The two corn hybrids used for the experiment
were Cargill F657 (bm3) and Cargill 6208FQ (isogenic normal control). Each
hybrid was planted, harvested and stored in 1997 (Year 1) and 1998 (Year 2).
The normal hybrid was planted in Year 1 from 04/23l97 through 04/25/97 and
again on 04/28/97. The bm3 hybrid was planted in Year 1 on 04/24/97 and
04/28/97. The normal hybrid in Year 2 was planted on 04/24/98, 04/30198 and
05/06/98. The bm3 hybrid in Year 2 was planted on 05I06/97 and 05/07/97.

Harvest in 1997 and 1998 was initiated for each hybrid at approximately
30% whole plant DM. The bm3 hybrid in Year 1 was harvested from 10/07/97
through 10/11/97 and the normal hybrid was harvested from 09/30l97 through
10/02/97 and from 10/06/97 through 10l07l97. Both the bm3 and normal hybrids
were harvested from 08/29/98 through 09/02/98 and from 09l07/98 through
09109/98 in Year 2. The theoretical length of chop was one-half inch for each
hybrid in both years. The chopped whole plant corn of each hybrid was stored
separately in both concrete bunker silos and 2.5-m silage bags (150 tons, Ag

Bag®, Ag-Bag International, LTD., Warrenton, OR) in both Year 1 and Year 2.

34

Storage of each corn hybrid in silage bags was necessary to allow the bunker
silos to be available for ﬁlling the following fall of each respective harvest year.
This also ensured that enough silage was available for the experiment, and that
silage available for feeding was well fermented.

Design. A randomized complete block design was utilized with 80
Holstein cows. Cows were blocked on their actual calving day by parity
(multiparous or primiparous), previous experimental treatment, and calving date.
Of the 80 cows blocked, 50 were multiparous and 30 were primiparous. Prior to
being utilized for this experiment each cow was a test subject in an experiment
about dietary cation—anion difference (DCAD) pre—partum. There were a total of
ﬁve DCAD diets before calving, and each cow was assigned randomly to only
one of the diets. The DCAD diets were fed starting approximately 21 d before
each cow's anticipated calving date and feeding of DCAD diets was terminated at
calving.

Within 24 h of calving, cows within a block were assigned randomly to one
of the two treatment diets (Appendix). Treatments were diets containing bm3 or
isogenic normal corn silages. Termination of treatment diets occurred when a
cow had a milk yield of less than 13.6 kgld for a 7 d average, was approximately
60 d from anticipated calving date or because a cow was in poor health. The
experiment was considered complete when all cows had reached a minimum of
305 DIM.

Diets. Two diets with conceptually different nutrient densities were utilized

for each treatment for this experiment (Table 1). The diet each cow received at

35

calving and until at least 8413 DIM was balanced for 30% NDF and 18% CP.
This high nutrient dense (HND) diet consisted of the respective treatment corn
silage (67% of forage DM), alfalfa silage (33% of forage DM), dry ground corn,
high moisture com, a protein, mineral and vitamin supplement, whole-linted
cottonseed and a salt mix. Cows remained on their respective corn silage
treatment but were switched to a low nutrient dense (LND) diet after 84:3 DIM if
their BCS exceeded 3.0 (erdman et al, 1982; on the ﬁve-point scale where 1 =
thin to 5 = fat) and their milk production dropped below 31.8 kgld for a
multiparous cow or 24.5 kgld for a primiparous cow. If poor health and/or
environmental factors (e.g., hot weather, high humidity, etc.) were suspected to
have decreased a cow's milk production below the LND criteria then the cow was
not switched to the LND diet. The LND diets were balanced for the maximum
concentration of NDF possible utilizing the treatment hybrid with the lowest ﬁber
concentration, and were formulated to 17% CP. Ingredients used for the LND
were the respective treatment corn silage (67% of forage DM), alfalfa silage
(33% of forage DM), a protein, mineral and vitamin supplement, a salt mix and
dry ground shelled corn if adjustment of dietary NDF% was needed.

The bm3 and normal HND diets were simultaneously adjusted 20 times
throughout the trial with each diet lasting an average of 20 d before the following
diet adjustment. Brown midrib-3 corn silage and alfalfa silage accounted for 41.6
and 20.8%, respectively, of the bm3 HND diet (DM basis). Normal corn silage
and alfalfa silage accounted for 40.4 and 20.2%, respectively, of the normal HND

diet (DM basis).

36

Cows. Cows were housed in a free-stall barn separated into pens by
treatment (bm3 or normal) and diet (HND or LND). Because of limited space
availability, some non-experimental cows were co-mingled with experimental
cows. The stalls of each free-stall pen had rubber-ﬁlled mattress bases and were
bedded with wood shavings. The aisles within each pen were cleaned once daily
of manure, urine and dirty bedding. Two small free-stall pens at the east end of
the facility were used to house cows at the beginning of the experiment when few
cows were on treatment. As more cows began the experiment the two groups of
HND cows were housed in larger pens at the west end of the facility. The two
smaller pens at the east end of the facility were then used for the LND cows
when it became necessary.

Cows had continuous access to their respective treatment diets with the
following exceptions: during milkings (3x/d), during BW measurements, during
herd health checks and between orts removal (1x/d) and feeding (1x/d). Fresh
water was continuously available to all cows with the following exceptions: during

milkings, during BW measurements and during herd health checks.

Experimental Procedures

All treatment diets were mixed each morning using a model 3300 Knight
mixer wagon. Cows were fed once per day following the mixing of each diet.
Groups were fed at 110% of the expected intake. Samples of each TMR and
individual diet ingredients were sampled each Monday and frozen immediately.

A second sample of both treatment corn silages and the alfalfa silage was taken

37

and frozen immediately. Orts for each treatment diet were sampled each
Tuesday and frozen immediately. Frozen samples were thawed and composited
by type every 2 wk on a Friday. Composited samples were dried in a 55° C
forced-air oven for at least 48 h and DM concentrations were determined.
Samples were ground (6 mm screen) with a Wiley® Mill, sub-sampled
(approximately 30 g) and subsequently ground through a 1 mm screen. Forage
samples were analyzed for NDF (Van Soest et al, 1991; method A) and CP
(Hach et al, 1987) concentrations. Rations were adjusted if the NDF
concentrations of forages increased dietary NDF greater than one percentage
unit from the target NDF value of 30% for HND diets or if treatment diets were
divergent greater than one percentage unit. Rations were always adjusted when
a silage bag or bunker were newly opened. Post-trial end corn silage samples
were analyzed for IVNDFD and IVTDMD with a 30 h incubation time (Goering
and Van Soest, 1970).

The second sample of each corn silage treatment and the alfalfa silage
were thawed every other Friday, composited by type and re-frozen. These
samples were analyzed for fermentation acid and toluene DM (AOAC, 1990)
concentrations as well as pH post-trial end.

For analysis of VFA and lactate concentrations in the forages, 15 g of
each sample and 150 ml of de-ionized water was weighed into a 250 ml Sorvall®
brand stainless steel container. The samples were mixed at setting three for one
min using a Sorvall® Omni-mixer (model 17150). Samples were strained through

two layers of two-ply cheesecloth and pH was determined immediately using an

38

Orion Research” Expandable ionAnalyzer (model EA 940). Five ml aliquouts of
each sample were centrifuged at 26,000 x g for 15 min, and supernatant (600 pl)
was mixed with 600 pl Ca(OH)2 and 300 pl of CuSO4 containing crotonic acid as
an internal standard in 1.7 ml microcentrifuge tubes and frozen. Samples were
thawed, centrifuged at 12,000 x g for 10 min, and supernatant (1000 pl) was
taken and mixed with 28 pl of H2804 in 1.5 ml microcentrifuge tubes. Samples
were frozen and thawed twice, and centrifuged at 12,000 x g for 10 min to
precipitate and remove protein thoroughly. Supernatant was transferred to HPLC
vials. Concentrations of VFA and lactate were determined by HPLC as
described by Dado and Allen (1995).

Alfalfa silage and both the bm3 and normal corn silages were sampled
each Monday for particle size evaluation. Determination of particle size was
performed on fresh samples using the Penn State Particle Size separator
(Lammers et al., 1996).

The same person throughout the experiment scored cows within 21 d
before their anticipated calving date for body condition each Friday of the
experiment. Cows that calved since the previous Friday also were scored. The
BCS that was closest to each cow's actual calving date was designated as the
initial BCS on experiment. Body condition scores were determined on Friday of
each week. The ﬁrst scheduled BCS was determined at 14:3 DIM for each cow.
The second scheduled BCS was determined at 28:3 DIM for each cow.
Thereafter, the BCS of each cow was determined every 28:3 DIM throughout the

experiment. The last BCS was assigned for each cow at the end of treatment.

39

Body weights were measured within 48 h post calving. All other
scheduled BW measurements were measured on Friday of each week during the
experiment. The ﬁrst scheduled BW measurement was at 14:3 DIM for each
cow. The second scheduled BW measurement was at 28:3 DIM for each cow.
Thereafter, the BW measurement of each cow was every 28:3 DIM throughout
the experiment. The last BW measurement was at the end of treatment for each
cow. Cows were weighed using a stationary electronic ﬂoor scale that was
calibrated prior to the experiment and approximately every three months,
thereafter, during the experiment. A lightning storm on 06/25/98 disabled the
electronic scale until it was repaired on 08/07/98. All initial and scheduled BW
measurements during this time period were missed.

Cows were milked three times per day at approximately 0500 (Milking 1),
1230 (Milking 2) and 1900 h (Milking 3) in a six by six herringbone style parlor.
Milk yield data was collected both manually and electronically. The primary
source of milk yield data were the manually recorded values. Electronically
captured milk yields were used only when manually recorded data were missed.
Headgates in each freestall pen were closed prior to moving cows to the milking
parlor, thus prohibiting the consumption of the incorrect treatment diets. From
the beginning of the experiment (May 16, 1998) through March 8, 1999 the
milking parlor was operated using Boumatic parlor equipment and electronics for
data capture to computer. On March 9, 1999 the parlor was renovated using
Surge brand equipment and electronics for data capture to computer.

Milk samples for composition were taken approximately once every 28 d

40

by a Michigan Dairy Herd lmprovementAssociation (DHIA) technician. Samples
were composited in equal amounts across all three milkings for each cow. These
samples were sent to Michigan DHIA for analysis of milk fat and milk protein
concentrations by infrared spectroscopy along with somatic cell count.
Calculations used to determine SCM yield, solids-not fat (SNF) concentration
(Tyrell and Reid, 1965) and 3.5% FCM yield (NRC, 1989) are as follows:
SCM, kgld = (12.3)(fat, kg) + (6.56)(SNF, kg) - (0.0752)(milk, kg)
where SNF, kg =
[(%milk protein + %milk lactose + %milk ash)/100] (milk, kg)

3.5% FCM, kgld = (milk, kg)(0.43 + (0.162)(%milk fat))

For determination of SCM yield, milk lactose and milk ash concentrations were

assumed to be 4.9 and 0.7%, respectively.

Statistical Analyses

Statistical analysis of milk production, BCS and BW data was based on a
fourth order polynomial of DIM including cow-speciﬁc random regression curves
for each given variable. If any‘of the polynomial by time terms was signiﬁcant (P
s 0.05), treatment by time interaction was indicated. Data were analyzed using

the Proc Mixed procedure of SAS (SAS, 1999) according to the following model:

Yijklmn = dieti + silyrj + tdate(silyri) + pretrtk + trtl + cowm + morpn +
block(morpn) + dim1 + dim2 + dim3 + dim4 + pretrtk*trt| + pretrtk*morpn +

pretrtk*block(morpn) + trt|*morpn + trt|*block(morpn) + trt|*dim1 + trt|*dim2 +

41

trt|*dim3 + trt|*dim4 + cowm*dim1 + cowm*dim2 + morpn*dim1 + morpn *dim2 +

morpn*dim3 + morpn*dim4 + trt|*morpn*dim1 + trt|*morpn*dim2 + trt|*morpn*dim3

+ trtrmorpn *dim4 + Bijklmn
where:

Yijklmn
dieti

silyrj
tdate(silyri)

pretrtk
trtj
COWm

morph
block(morpn)
dim1

dim2

dim3

dim4
pretrtk*trt|
pretrtk*morpn

pretrtk*block(morpn)

trt|*morpn
trt|*block(morpn)
trt|*dim1
trt|*dim2
trt|*dim3
trt|*dim4
cowm*dim1
cowm*dim2
morpn*dim1
morpn*dim2

response variable

ﬁxed effect of diet

ﬁxed effect of silage year

ﬁxed effect of milk test date nested within
silage year

ﬁxed effect of pre-experimental diet

ﬁxed effect of treatment assignment
random effect of cow

ﬁxed effect of parity

ﬁxed effect of block nested within parity
effect of DIM

quadratic effect of DIM

cubic effect of DIM

quartic effect of DIM

effect of interaction of pretrtk and trtl
effect of interaction of pretrtk and morpn
effect of interaction of pretrtk and
block(morpn)

effect of interaction of trtl and morpn
effect of interaction of trtj and block(morpn)
effect of interaction of trtl and dim1
effect of interaction of trtl and dim2
effect of interaction of trtl and dim3
effect of interaction of trtl and dim4
effect of interaction of cowm and dim1
effect of interaction of cowm and dim2
effect of interaction of morpn and dim1
effect of interaction of morpn and dim2

42

morpn*dim3 = effect of interaction of morpn and dim3

morpn*dim4 = effect of interaction of morpn and dim4

trt|*morpn*dim1 = effect of interaction of trtl and morpn and
dim1

trt|*morpn*dim2 = effect of interaction of trtl and morpn and
dim2

trt|*morpn*dim3 = effect of interaction of trtl and morpn and
dim3

trt|*morpn*dim4 = effect of interaction of m. and morpn and
dim4

eijklmn = residual, assumed normally distributed.

If a signiﬁcant treatment by time or treatment by time by parity interaction
was observed for a given variable then cumulative differences of treatments were
estimated by deriving contrast coefﬁcients for the following time periods: 0 to 50
DIM, 50 to 150 DIM and 150 to 300 DIM. Signiﬁcance for interactions was
determined at P < 0.10. The estimated cumulative treatment differences were
calculated by contrasts based on the area under the lactation curve using integral
calculus for each time period. Also, differences of least squares mean estimates
between treatments for variables with signiﬁcant treatment by time or treatment
by time by parity interactions at 25 d intervals through 300 DIM were analyzed.
Both the cumulative treatment and the 25 d interval treatment differences were
analyzed using the following model:

Yijklmn = dieti + silyrj + pretrtk + trt. + cowm + morpn + block(morpn) +
pretrtk*trt. + pretrtk*morpn + pretrtk*block(morpn) + trt."morpn + trt.*block(morpn) +
eijklmn

All data comparing the chemical analyses of the treatment corn silages

were analyzed by t-test procedure of JMP (version 4, SAS Institute, Cary, NC).

43

RESULTS AND DISCUSSION
Nutrient Composition

The nutrient compositions of the treatment corn silages are shown in
Table 2. Dry matter percentages, based on 55° C oven-dried samples, were
similar between the treatment corn silages (33.4%); but DM percentage by
toluene distillation was 2.4 percentage units lower (P < 0.01) for the bm3 corn
silage compared with the normal corn silage (31.4 and 33.8%, respectively). The
reason for this discrepancy is not known.

Neutral detergent ﬁber and starch concentrations, as a percentage of DM,
were similar for the two treatment corn silages (39.9 and 30.6%, respectively).
Acid detergent ﬁber concentration was 1.3 percentage units lower (P < 0.01) for
bm3 corn silage compared with normal corn silage (22.7 and 24.0%,
respectively). Crude protein concentration was higher (P < 0.05) by 0.4
percentage units for bm3 corn silage compared with normal corn silage. Both
lignin concentration and lignin as a percentage of NDF were lower for bm3 corn
silage compared with normal corn silage (P < 0.001). The lower concentration of
ADF for the bm3 corn silage is attributed partially to the lower concentration of
lignin, which is a component of ADF. In vitro true DM digestibility and IVNDFD
were greater (P < 0.001) for bm3 corn silage compared with normal corn silage
(85.4 vs. 79.4% and 63.1 vs. 48.8%, respectively).

Particle size distribution was similar for both treatment silages. The top,
middle, and bottom screens of the Penn State Particle Size Separator retained

11.0, 74.9 and 14.2% of the treatment silage samples as a percentage of wet

44

sample weight.

Acetic acid concentration, as a percent of silage DM, was greater (P =
0.001) for bm3 corn silage compared with the normal corn silage (2.18 vs.
1.69%). However, lactic acid and propionic acid concentrations were similar
between the treatment silages (Table 2). The silage pH also was similar

averaging 3.8 for both silages.

Milk Yield, Milk Components, BW and BCS

Treatment effects on milk yield, BCS and BW are in Table 3 for the ﬁrst
300 DIM. Cows fed bm3 or normal corn silage based-diets had similar milk yields
from 0 to 300 DIM (9111 kg), but there was a treatment by time interaction (P <
0.01). At 75 and 100 DIM the bm3 corn silage treatment resulted in 6.2 and
4.9% greater milk yield, respectively, than the normal corn silage treatment
(Table 4; Figure 1). There also was a tendency (P = 0.09) for the bm3 treatment
to increase milk yield at 50 DIM by 5.1% compared with the normal treatment.
Milk yields were similar for all 25 d interval comparisons before 50 DIM and after
100 DIM. When analyzed by stage of lactation (Table 12), cows fed the bm3
treatment tended (P = 0.06) to increase cumulative milk yield by 4.2% from 50 to
150 DIM compared with those fed the normal treatment (3421 vs. 3278 kg,
respectively) but yields were similar from 0 to 50 DIM (1608 kg) and from 150 to
300 DIM (4153 kg).

Milk fat percentage was similar between treatments for the ﬁrst 300 DIM

and no interactions were detected. Milk fat yield was also similar between

45

treatments for the ﬁrst 300 DIM (313 kg), but there was a treatment by time
interaction (P < 0.05). At 50, 75 and 100 DIM the bm3 treatment had 8.5, 8.8
and 8.3% greater milk fat yield, respectively, than the normal treatment (Table 5;
Figure 2). There was also a tendency (P = 0.07) for the bm3 treatment to
increase milk fat yield at 125 DIM by 6.1% compared with the normal treatment.
Milk fat yields were similar for all 25 d interval comparisons before 50 DIM and
after 125 DIM. When analyzed by stage of lactation (Table 13), milk fat yield
increased from 50 to 150 DIM (P = 0.02) by 7.5% for the bm3 treatment
compared with the normal treatment (119.3 vs. 110.3 kg, respectively) but
treatments were similar from 0 to 50 (65.5kg) and from 150 to 300 DIM (132.6
kg).

Cows fed bm3 or normal corn silage diets had similar cumulative 3.5%
FCM yields from 0 to 300 DIM (8932 kg), but there was a treatment by time
interaction (P < 0.01). At 50, 75 and 100 DIM the bm3 corn silage treatment
resulted in 8.2, 8.1 and 7.0% greater 3.5% FCM yield, respectively, than the
normal corn silage treatment (Table 6; Figure 3). There was also a tendency (P
= 0.10) for the bm3 treatment to increase 3.5% FCM yield at 125 DIM by 4.3%
compared with the normal treatment. Yields of 3.5% FCM were similar for all 25
d interval comparisons before 50 DIM and after 125 DIM. When analyzed by
stage of lactation (Table 14), the bm3 treatment resulted in 6.2% greater (P =
0.02) cumulative 3.5% FCM yields from 50 to 150 DIM compared with the normal
treatment (3410 vs. 3198 kg, respectively) but was similar from 0 to 50 DIM
(1766 kg) and from 150 to 300 DIM (3862 kg).

46

The increased milk yields around peak lactation for cows fed bm3 corn
silage-based diets in the current study is supported by the ﬁndings of Oba and
Allen (1999a). They observed that cows with the highest pre-trial milk production
had the greatest response to a bm3 corn silage-based diet compared with cows
fed an isogenic normal corn silage-based diet; whereas, little beneﬁt was
observed in cows with lower pre-trial milk production fed the bm3 corn silage-
based diet. Peak milk production in dairy cows typically occurs between 28 to 74
d postpartum (Clark and Davis, 1980) so the observation that the bm3 treatment
began to increase milk yields at 50 DIM in the current study is not unexpected.
Conversely, the lack of treatment differences in milk yield before 50 DIM and
after 150 DIM is also reasonable.

Increased milk yields around peak lactation for cows fed bm3 corn silage-
based diets also have been observed in other studies comparing bm3 and
isogenic normal corn silages. Block et al. (1981) fed cows either bm3 or normal
corn silage-based diets from 18 to 74 DIM and found no differences in milk yield
when analyzed cumulatively. However, when the data were analyzed as weekly
averages, increased milk yields (P < 0.05) were observed for cows fed bm3 at wk
5, 6 and 8 of the study, corresponding to 53, 60 and 74 DIM. Oba and Allen
(2000a) fed bm3 or normal corn silage-based diets to high producing (averaging
33.6 kgld) dairy cows averaging 70 DIM at trial start and observed that cows on
the bm3 treatment had increased SCM yields compared with cows fed the
normal treatment (P < 0.05).

If it is true that higher producing cows beneﬁt more from bm3 corn silage-

47

based diets (Oba and Allen, 1999a), then the relative beneﬁt a cow receives from
consuming a bm3 corn silage-based diet must be reduced as milk yield declines.
Studies that compared cows fed bm3 and isogenic normal corn silage-based
diets without increases in milk yield used lower producing cows in later stages of
lactation (Stallings et al., 1982; Tine et al., 2001; Greenﬁeld et al., 2001).

The idea that physical ﬁll limits intake of feedstuffs for dairy cattle in early
lactation may, therefore, not be true because milk yield, or sOme other indicator
of increased energy intake (i.e., BW gain or increased BCS), would logically be
greater for cows fed bm3 corn silage-based diets compared to cows fed normal
corn silage-based diets. This is mainly because of increased NDF digestibility
associated with bm3 corn silage. Therefore, because higher producing cows
beneﬁt more from bm3 corn silage-based diets (Oba and Allen, 1999a) it is
possible that factors other than physical ﬁll are limiting intake in early lactation
and that physical ﬁll is more limiting around peak lactation where increased milk
yields (Oba and Allen, 1999a and Oba and Allen, 2000a) and BW gains (Rook et
al., 1977 and Sommerfeldt et al., 1979) have been observed for bm3 corn silage
fed cows.

One study did observe increased milk yields for later lactation cows fed bm3
corn silage but the diets may have favorably biased the bm3 treatment. Keith et
al. (1979) fed 12 Holstein cows past peak lactation (DIM not reported) bm3 and
isogenic normal corn silage-based diets at two F:C ratios (75:25 and 60:40) and
observed increases (P < 0.01) in both milk and 3.5% FCM yields for the bm3

corn silage-fed cows. However, the bm3 corn silage was lower in NDF

48

concentration (P < 0.05), but was included in the bm3 diets at the same
proportion as the isogenic corn silage in the normal diets. Also, the bm3 corn
silage analyzed higher in GP concentration and an increase in ground corn in the
bm3 diets was needed to offset increases in soybean meal additions to the
normal corn silage-based diets to make the diets isonitrogenous. Both of these
dietary differences could have biased the results in favor of the bm3 diets by
decreasing the NDF concentration of the rations. It has been observed that diets
lower in ﬁber concentration can decrease the physical ﬁll of the rumen possibly
resulting in greater DMI and milk production (Dado and Allen, 1995).

A treatment by time by parity interaction was observed for milk protein
concentration in the current study (P = 0.05). Primiparous cows fed the bm3 corn
silage treatment had greater milk protein concentration compared with
primiparous cows fed the normal corn silage treatment at every 25 d interval from
25 to 300 DIM (Table 7; Figure 4). There was also a tendency (P < 0.10) for
primiparous cows fed the bm3 treatment to have greater milk protein
concentration at 0 DIM compared with cows fed the normal corn silage treatment.
Multiparous cows fed the bm3 corn silage treatment had greater milk protein
concentration compared with multiparous cows fed the normal corn silage
treatment at 25 and 50 DIM (Table 7; Figure 5). There was also a tendency for
cows fed the bm3 corn silage treatment to have greater milk protein
concentration at 75, 225 and 250 DIM compared with cows fed the normal corn
silage treatment. Milk protein concentrations were similar between treatments for

multiparous cows when compared at 0, 100, 125, 150, 175, 200, 275 and 300

49

DIM. When analyzed by stage of lactation, primiparous cows fed the bm3
treatment had greater milk protein concentration from 0 to 50, 50 to 150 and 150
to 300 DIM compared with primiparous cows fed the normal treatment (Table
15). Multiparous cows fed the bm3 treatment tended to have greater milk protein
concentration from 0 to 50 DIM but similar milk protein concentration from 50 to
150 and 150 to 300 DIM when compared with cows fed the normal treatment
(Table 16).

The increase in milk protein concentration observed in the current study
supports the ﬁndings of others. Oba and Allen (1999a) observed increases in
milk protein concentration for early- to mid-lactation cows fed bm3 corn silage-
based diets compared with cows fed isogenic normal corn silage-based diets. In
a subsequent study, Oba and Allen (2000a) again observed greater milk protein
concentration for early— to mid-lactation cows fed bm3 com silage-based diets
compared with cows fed isogenic normal corn silage-based diets. Associated
with the increased milk protein concentration, Oba and Allen (20000) noted
greater microbial nitrogen ﬂow to the duodenum for cows fed bm3 corn silage-
based diets compared with cows fed normal corn silage-based diets. It is
possible that cows fed bm3 corn silage-based diets in the current study had
increased milk protein concentrations because of an increase in microbial
nitrogen ﬂow (not measured).

A treatment by time by parity interaction was observed for milk protein
yield in the current study (P < 0.10). Primiparous cows fed the bm3 corn silage

treatment had greater milk protein yield compared with primiparous cows fed the

50

normal corn silage treatment at 75 DIM (Table 8; Figure 6). There was also a
tendency for primiparous cows fed the bm3 corn silage treatment to have greater
milk protein yields at 50 and 100 DIM compared with primiparous cows fed the
normal corn silage treatment. Yields of milk protein were similar for all 25 d
interval comparisons before 50 DIM and after 100 DIM for primiparous cows.
Multiparous cows fed the bm3 corn silage treatment had greater milk protein
yields compared with multiparous cows fed the normal corn silage treatment at
50, 75, 100 and 125 DIM (Table 8, Figure 7). Multiparous cows fed the normal
corn silage treatment had a tendency for greater milk protein yield compared with
multiparous cows fed the bm3 corn silage treatment at 0 DIM (P = 0.08). Milk
protein yields were similar between treatments for multiparous cows when
compared at 25, 150, 175, 200, 225, 250, 275 and 300 DIM. When analyzed by
stage of lactation, multiparous cows fed the bm3 treatment had greater milk
protein yield from 50 to 150 DIM compared with multiparous cows fed the normal
treatment. Milk protein yields were similar between treatments from 50 to 150
and from 150 to 300 DIM for multiparous cows (Tables 17). There was a
tendency (P = 0.07) for primiparous cows fed the bm3 treatment to have a
greater milk protein yield from 50 to 150 DIM but milk protein yields were similar
between treatments for primiparous cows from 0 to 50 and 150 to 300 DIM.

Solids-corrected milk yields were similar between treatments from 0 to 300
DIM (8366 kg), but there was a treatment by time interaction (P < 0.01). At 50,
75 and 100 DIM the bm3 corn silage treatment had 7.3, 8.6 and 7.2% greater

SCM yield, respectively, than the normal corn silage treatment (Table 9; Figure

51

8). There was a tendency for cows on the bm3 treatment to increase SCM yield
at 125 DIM by 4.6% compared with cows on the normal treatment. Solids-
corrected milk yields were similar for all 25 d interval comparisons before 50 DIM
and after 125 DIM. When analyzed by stage of lactation (Table 19) SCM yield
was greater from 50 to 150 DIM (P < 0.01) for cows fed the bm3 treatment
compared with those fed the normal treatment (3150 vs. 2948 kg, respectively)
but were similar from 0 to 50 (1581 kg) and 150 to 300 DIM (3737 kg).

Cows fed bm3 or normal corn silage diets had similar BW from 0 to 300
DIM (593 kg), but there was a treatment by time interaction (P < 0.05). However,
no differences were observed when analyzed by 25 d intervals (Table 10; Figure
9) or stage of lactation (Table 20) between treatments for BW. Although
treatment differences across time for BW were not detected with the parameters
chosen to compare treatment by time interactions (25 d intervals at points in time
along the BW polynomial curve and 0 to 50, 50 to 150 and 150 to 300 DIM
cumulative differences along the BW polynomial curve), analysis of BW data
deﬁned by parameters with smaller increments (Le, 10 d intervals) may detect
treatment by time differences.

Shorter term studies by others have noted increases in BW changes for
cows fed bm3 corn silage-based diets with no concurrent increases in milk
production (Rook et al., 1977; Sommerfeldt et al., 1979). Another study noted
increases in both milk production and BW gains for bm3 fed cows. Block et al.
(1981) observed increases in BW change for cows fed a bm3 corn silage-based

diet from 18 to 74 DIM with increased milk production for the bm3 fed cows only

52

at 53, 60 and 74 DIM.

Cows fed bm3 or normal corn silage diets had similar body condition
scores from 0 to 300 DIM (2.43), but there was a tendency for a treatment by
time interaction (P < 0.10). No differences in BCS due to treatments were
observed when analyzed by 25 d intervals (Table 11; Figure 10) or stage of
lactation (Table 21). As discussed with BW, treatment differences by time may
be detectable for BCS data if analyzed by parameters smaller than 25 d intervals
(e.g., 10 d interval comparisons).

The idea that milk yield in early lactation dairy cows is limited to less than
optimal energy intake because of physical ﬁll of the diet may not be true.
Voluntary intake is regulated by many factors besides physical ﬁll (Allen, 2000)
and the degree to which each factor affects intake, and thus milk production, may
change as energy status of the cow changes throughout a lactation. For
instance, it has been suggested that intake in early lactation is controlled partially
by an increase in B-oxidation of non-esteriﬁed fatty acids in the liver brought on
by the mobilization of lipids from body fat reserves (Emery et al., 1992). In this
case, body condition at calving may have more of an inﬂuence on voluntary DMI
than physical characteristics of the diet consumed. Cows near peak lactation fed
diets with higher NDF digestibility have greater increases in DMI and milk yield
(Oba and Allen, 1999a; Oba and Allen, 2000a). Dry matter intake and milk yield
in around peak lactation, thus, may be more inﬂuenced by physical ﬁll than by

other factors.

53

Inﬂuence of Diets on Production Data

Of the 80 cows that began this study, only ten cows met the criteria to
switch to the LND diet prior to 300 DIM. Four cows on the bm3 treatment and six
cows on the normal treatment were switched to their respective LND diets,
averaging 166 and 208 DIM at the time of switch for the bm3 and normal
treatments, respectively. The production data from this study were deﬁned by
10,906, 10,501, 732, and 487 cow-days for the bm3-HND, normal-HND, bm3-
LND and normal-LND diets, respectively. The HND diets of both treatments
were assumed to have been more inﬂuential on the parameters measured in this
experiment than the LND diets because of the relative difference of cow-days

between diets HND and LND (averaging 10,704 vs. 610 cow-days, respectively).

Treatment vs. Pen Effects

Although cows were group-fed treatment diets during this experiment,
inferences on the effects of bm3 corn silage on the lactational performance of
dairy cows were made using the cow as the experimental unit. However,
treatment effects in this experiment are confounded with potential pen effects
because cows on each treatment were housed in separate pens. A pen effect,
however, is not expected because the two pens in which the cows were housed
for the majority of the experiment were similar in location, size, number of cows
per pen and design. Ideally this experiment would have been conducted with
cows randomly assigned to individual stalls with a random allocation of

treatments. The resources required for such an experiment were not available.

54

Therefore, the results of this experiment should be interpreted and applied in

conjunction with results of other studies.

Summary

In this complete lactation experiment, cows fed bm3 corn silage-based
diets had greater cumulative milk, milk fat, 3.5% FCM and SCM yields from 50 to
150 DIM compared with cows fed isogenic normal corn silage-based diets.
Yields of milk and milk fat were similar from 0 to 50 and from 150 to 300 DIM.
Milk fat concentration was similar for both treatments throughout the study. Milk
protein concentration and milk protein yield was dependent on treatment, DIM
and parity. Speciﬁcally, primiparous cows on the bm3 treatment had greater
cumulative milk protein concentration from 0 to 50, 50 to 150 and 150 to 300 DIM
compared with primiparous cows on the normal treatment. Multiparous cows on
the bm3 treatment had greater milk protein concentration compared with
multiparous cows on the normal treatment, but only from 0 to 50 DIM.
Primiparous and multiparous cows fed the bm3 treatment had greater milk
protein yields compared to primiparous and multiparous cows fed the normal
treatment from 50 to 150 DIM but treatments were similar for both parities from 0
to 50 and from 150 to 300 DIM. Body weights and BCS were similar for both

treatments throughout 300 d.

55

Conclusion and Implications

Cows beneﬁted more from bm3 corn silage-based diets during, and
around, peak lactation by increasing milk yield and milk protein concentration
without sacriﬁcing body condition or milk fat concentration. The results from this
experiment do not agree with the concept that cows in negative energy balance
in early lactation would beneﬁt most from bm3 corn silage. This might be true if
voluntary DMI was limited in early lactation by physical ﬁll because the increased
NDF digestibility of bm3 corn silage would most likely increase ruminal NDF
turnover. However, no study has yet to observe signiﬁcant increases in voluntary
DMI for cows fed bm3 corn silage in early lactation but several studies have
noted increases in voluntary DMI for cows near or past peak lactation (Rook et
al., 1977; Tine et al., 2001; Block et al., 1981; Sommerfeldt et al., 1979; Oba and
Allen, 1999a; Oba and Allen, 2000a). It is most likely that factors other than
physical ﬁll are limiting intake, and thus, milk yield, in very early lactation.

Hybrid seed corn with the brown midrib mutation is typically more than
twice as expensive and lower yielding (an average of 9% lower in the current
study) than conventional seed corn. Use of bm3 corn silage might not be
economically beneﬁcial if it is fed to all cows in the herd. Targeting cows when
they are most responsive by increasing milk yield will increase the economic
beneﬁt of bm3 corn silage. Brown midrib-3 corn silage fed to cows around peak
lactation may be most effective, whereas conventional corn silage might be fed to

early and late lactation cows.

56

 

Table 1. Ingredient and nutrient composition of experimental diets.

 

 

 

 

 

HND‘ LND2
bm3 3 Normal bm3 Normal
(% of DM)
Ingredient
bm3 corn silage 41.6 55.7
Normal corn silage 40.4 53.8
Alfalfa silage 20.8 20.2 31.5 31.2
Dry ground corn 8.3 9.0 0.4 1.9
High moisture corn 8.3 8.9
Protein, mineral and
vitamin supplement5 13.0 13.3 11.7 12.3
Whole linted cottonseed 7. 4 7.4
Salt mix‘5 0. 74 0.74 0.85 0.85
Nutrient

0M7 41.7 42.1 35. 4 36. 5
NDF7 30.0 30.0 34.7 34.5
ADF8 20.0 20.0 23. 4 23 3
CP7 17.9 18.0 17.0 17.0
NEL: , Mcal/kg 1.70 1.70 1. 57 1 57
Ash“ 5. 7 5. 7 7. 5 7. 5
Ca8 0. 90 0. 91 0. 99 1. 00
P8 0. 44 0. 44 0.41 0.42
Mags 0. 25 0. 25 0.23 0.23
K 1.55 1.53 1.85 1.31
Na8 0.18 0.18 0.18 0.19
CI8 0.35 0.35 0.41 0.41
s8 0.19 0.19 0.18 0.18
Cu:, mg/kg 16.74 16.99 16.95 17.43
Fe, mg/kg 212 211 247 247
Mn“, mg/kg 75.1 75.9 80.2 81.8
2n", mg/kg 55.9 57.9 57.5 59.5

 

;High nutrient density diet.
:Low nutrient density diet.

:Brown midrib mutant for corn

Dry ground corn was used to maintain similar dietary NDF concentrations between LND

treatments.

5Protein, mineral and vitamin supplement was a contract mix with the following proﬁle as a
percentage of DM: 1.88 Mcal/kg NEL, 51 .6% CP, 42. 0% undegradable protein, 3.48% Ca,

60.,59%P 0.,54%Mg1.9,8%K 0.52% Na, 0..82%C|and046°/oS,

6Salt mix formulated for the following proﬁle as a percentage of DM: 12.53% Ca, 13. 9%P
12 2% Na, 18.9% CI, 6. 3 ppm Co and 9042 ppm Fe.

zFrom laboratory analysis.

8From diet formulation and nutrient compositions of individual ingredients from NRC (1989).

57

Table 2. Nutrient composition of corn silages used throughout the experiment.

 

 

Item bm31 Normal SE P
DM% (oven-dried at 55°C) 33.0 33.7 0.59 0.22
DM% (toluene distillation) 31.4 33.8 0.77 0.003
_(% of DM)—
NDF 39.5 40.3 0.59 0.16
ADF 22.7 24.0 0.40 0.002
Lignin 1.8 2.8 0.14 <0.001
Lignin, % of NDF 4.5 7.0 0.31 ‘ <0.001
OF 8.6 8.2 0.18 0.025
Ash 4.2 4.1 0.14 0.65
Starch 30.6 30.6 0.74 0.92
IV TDMD2 85.4 79.4 0.36 <0.001
IV NDFD, % of NDF3 53.1 48.8 0.72 <0.001
bm31 Normal SE P
Particle size4 ,
% of wet sample weight
Top 11.02 10.90 0.73 0.87
Middle 74.32 75.40 0.69 0.12
Bottom 14.65 13.69 0.69 0.17
bm3 I Normal SE P
Fermentation Acids,
% of DM
Lactic Acid 5.27 5.86 0.39 0.14
Acetic Acid 2.18 1.69 0.15 0.001
Propionic Acid 0.30 0.23 0.05 0.17
pH 3.82 3.78 0.03 0.20

 

1Brown midrib 3 mutant for corn.

2IV TDMD = In vitro true DM digestibility estimated after 30 h incubation.
3IV NDFD = In vitro NDF digestibility estimated after 30 h incubation.
‘Determined with Penn State Particle Size Separator.

58

Table 3. Estimates, standard errors and signiﬁcance of effects of corn silage
hybrids on milk yield for the ﬁrst 300 d of lactation.

 

Treatment Effect1

 

 

bm32 Normal SE H HxT HxTxP

 

 

Cumulative Yield, kg

Milk 9165 9057 285 0.91 *** NS

Fat 322 304 12.5 0.28 ** NS

Protein 273 256 8.7 0.13 *** 1‘

3.5% FCM 9116 8747 304 0.47 *** NS

SCM 8536 8196 271 0.45 *** NS
Milk composition, %

Mean Fat 3.68 3.54 0.07 0.37 NS NS
Mean Protein 3.07 2.92 0.05 0.02 NS *
Mean BW, kg 588 597 12.5 0.92 ** NS
Mean BCS 2.38 2.47 0.10 0.80 1' NS

 

1H = Effect of hybrid type, H x T = interaction of hybrid type and time, and
H x T x P = interaction of hybrid type, time and parity.

2Brown midrib 3 mutation for corn.

1'P < 0.10

*P = 0.05

**P < 0.05

***P < 0.01

59

Table 4. Least square means, standard errors and
signiﬁcance of effects of corn silage hybrids on milk
yield (kg/_d) at 25 d intervals.

 

 

 

Days Treatment

In Milk bm3 1 Normal SE P
0 26.5 31.4 3.3 0.14
25 32.3 32.6 1.7 0.88
50 35.0 33.2 1.1 0.09
75 35.5 33.3 0.8 0.007
100 34.7 33.0 0.8 0.025
125 33.1 32.4 0.8 0.35
150 31.4 31.6 0.9 0.88
175 29.8 30.5 1.0 0.49
200 28.6 29.4 1.2 0.49
225 27.6 28.0 1.3 0.74
250 26.7 26.5 1.4 0.84
275 25.7 24.6 1.5 0.48
300 23.9 22.5 1.9 0.44

 

1Brown midrib 3 mutation for corn.

Table 5. Least square means, standard errors and
signiﬁcance of effects of corn silage hybrids on milk fat
yield (kg/d) in 25 d intervals.

 

 

 

Days Treatment
In Milk bm3 1 Normal SE P
0 1.35 1.43 0.12 0.52

25 1.33 1.28 0.06 0.42
50 1.30 1.19 0.05 0.02
75 1.25 1.14 0.04 0.006
100 1.20 1.10 0.04 0.01
125 1.14 1.07 0.04 0.07
150 1.08 1.03 0.04 0.30
175 1.01 0.99 0.04 0.52
200 0.96 0.93 0.05 0.55
225 0.90 0.86 0.05 0.43
250 0.85 0.79 0.06 0.28
275 0.81 0.73 0.07 0.21
300 0.78 0.69 0.09 0.35

 

1Brown midrib 3 mutation for com.

60

Table 6. Least square means, standard errors and
signiﬁcance of effects of corn silage hybrids on 3.5%
fat-corrected milk yield (kg/d) at 25 d intervals.

 

 

 

Days Treatment

In Milk bm3 1 Normal SE P

0 33.7 36.8 3.1 0.33
25 35.9 35.0 1.6 0.57
50 36.4 33.7 1.1 0.02
75 35.7 32.8 1.0 0.003
100 34.4 32.0 0.9 0.009
125 32.6 31.2 0.9 0.10
150 30.8 30.1 1.0 0.49
175 29.0 28.8 1.1 0.85
200 27.4 27.3 1.2 0.90
225 26.0 25.5 1.3 0.69
250 24.8 23.6 1.5 0.43
275 23.5 21.7 1.7 0.28
300 22.0 19.9 2.3 0.37

 

rBrown midrib 3 mutation for corn.

61

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63

 

 

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E8 00 $803 00 8:85:03 0cm 20:0 285% .959: 96:0» 88.. .0 0.55.

Table 9. Least square means, standard errors and
signiﬁcance of effects of corn silage hybrids on solids-

corrected milk yield (kg/d) at 25 d intervals.

 

 

 

Days Treatment
In Milk bm3 1 Normal SE P
0 29.3 33.1 3.1 0.22
25 31.9 31.4 1.6 0.76
50 32.9 30.5 1.0 0.016
75 32.7 29.9 0.7 0.0004
100 31.8 29.5 0.7 0.0017
125 30.4 29.0 0.8 0.07
150 29.0 28.3 0.9 0.47
175 27.6 27.4 1.0 0.86
200 26.3 26.1 1.1 0.88
225 25.2 24.6 1.2 0.65
250 24.2 23.0 1.4 0.37
275 23.3 21.4 1.5 0.20
300 22.1 20.0 1.8 0.26

 

1Brown midrib 3 mutation for corn.

Table 10. Least square means, standard errors and
signiﬁcance of effects of corn silage hybrids on body
weight (kg) at 25 d intervals.

 

 

 

Days Treatment
In Milk bm3 1 Normal SE P

0 609 628 34 0.22
25 576 591 29 0.25
50 563 573 29 0.40
75 562 569 28 0.60
100 568 572 28 0.79
125 577 579 28 0.89
150 586 587 28 0.89
175 592 596 28 0.78
200 597 603 28 0.59
225 600 61 1 29 0.41
250 604 619 30 0.28
275 614 631 32 0.24
300 635 651 38 0.34

 

1Brown midrib 3 mutation for com.

64

Table 11. Least square means, standard errors and
signiﬁcance of effects of corn silage hybrids on body
condition score at 25 d intervals.

 

 

 

Days Treatment
In Milk bm3 1 Normal SE P
0 3.10 3.22 0.14 0.43
25 2.66 2.78 0.12 0.32
50 2.42 2.52 0.11 0.38
75 2.31 2.38 0.11 0.53
100 2.28 2.32 0.10 0.70
125 2.29 2.32 0.10 0.81
150 2.31 2.33 0.10 0.80
175 2.32 2.37 0.10 0.65
200 2.32 2.40 0.10 0.44
225 2.30 2.42 0.11 0.27
250 2.29 2.45 0.12 0.17
275 2.32 2.50 0.13 0.16
300 2.42 2.59 0.16 0.32

 

1Brown midrib 3 mutation for corn.

Table 12. Estimates, standard errors and Signiﬁcance
of effects of corn silage hybrids on cumulative milk
yield (kg) by stage of lactation.

 

 

 

Stage of
Lactation Treatment
(DIM) bm3 1 Normal SE P
0 - 50 1591 1625 90 0.70
50 - 150 3421 3278 75 0.06
150 - 300 4152 4153 182 1.00

 

1Brown midrib 3 mutation for com.

65

Table 13. Estimates, standard errors and signiﬁcance
of effects of corn silage hybrids on cumulative milk fat
yield (kg) by stage of lactation.

 

 

 

Stage of
Lactation Treatment
(DIM) bm3 1 Normal SE P
0 - 50 66.4 64.5 3.32 0.56
50 - 150 119.3 110.3 3.67 0.02
150 - 300 136.4 128.7 7.75 0.32

 

1Brown midrib 3 mutation for corn.

Table 14. Estimates, standard errors and signiﬁcance
of effects of corn silage hybrids on cumulative 3.5% fat
corrected milk yield (kg) by stage of lactation.

 

 

 

Stage of
Lactation Treatment
(DIM) bm3 " Normal SE P
0 - 50 1779 1753 83 0.75
50 - 150 3410 3198 86 0.02
150 - 300 3927 3796 196 0.50

 

1Brown midrib 3 mutation for corn.

Table 15. Estimates, standard errors and signiﬁcance
of effects of corn silage hybrids on weighted average milk
protein concentration by stage of lactation for primiparous cows.

 

 

 

Stage of
Lactation Treatment

(DIM) bm3 ‘ Normal SE P

0 - 50 2.85 2.66 0.07 0.01
50 - 150 2.91 2.73 0.08 0.03
150 - 300 3.23 3.00 0.08 0.009

 

1Brown midrib 3 mutation for com.

66

Table 16. Estimates, standard errors and signiﬁcance
of effects of corn silage hybrids on weighted average milk
protein concentration by stage of lactation for multiparous cows.

 

 

Stage of
Lactation Treatment
(DIM) bm3 I Normal SE P
0 - 50 2.92 2.83 0.06 0.08
50 - 150 2.93 2.85 0.06 0.14
150 - 300 3.23 3.14 0.06 0.17

 

1Brown midrib 3 mutation for corn.

Table 17. Estimates, standard errors and signiﬁcance
of effects of corn silage hybrids on cumulative milk protein
yield (kg) by stage of lactation for multiparous cows.

 

 

Stage of
Lactation Treatment

(DIM) bm3 1 Normal SE P

0 - 50 51.5 52.3 3.2 0.79
50 - 150 106.0 96.6 3.2 0.003
150 - 300 125.3 116.5 6.9 0.21

 

1Brown midrib 3 mutation for corn.

Table 18. Estimates, standard errors and signiﬁcance
of effects of corn silage hybrids on cumulative milk protein
yield (kg) by stage of lactation for primiparous cows.

 

 

Stage of
Lactation Treatment
(DIM) bm3 I Normal SE P
0 - 50 41.3 37.6 0.04 0.33
50 - 150 92.4 84.7 0.04 0.07
150 - 300 129.1 123.3 0.09 0.51

 

1Brown midrib 3 mutation for com.

67

Table 19. Estimates, standard errors and signiﬁcance
of effects of corn silage hybrids on cumulative solids-
corrected milk yield (kg) by stage of lactation.

 

 

 

Stage of
Lactation Treatment

(DIM) bm3 I Normal SE P

0 - 50 1583 1578 84 0.95
50 - 150 3150 2948 71 0.0045
150 - 300 3803 3670 176 0.45

 

1Brown midrib 3 mutation for corn.

Table 20. Estimates, standard errors and signiﬁcance
of effects of corn silage hybrids on cumulative body weight
(kg) by stage of lactation.

 

 

Stage of
Lactation Treatment
(DIM) bm31 Normal SE P

 

0 - 50 28,958 29,716 665 0.26
50 - 150 56,997 57,440 1,257 0.72
150 - 300 90,375 91,928 4,345 0.43

 

1Brown midrib 3 mutation for corn.

Table 21. Estimates, standard errors and signiﬁcance
of effects of corn silage hybrids on weighted average
body condition score by stage of lactation.

 

 

 

Stage of
Lactation Treatment
(DIM) bm3 1 Normal SE P
0 - 50 2.70 2.81 .12 0.34
50 - 150 2.31 2.36 .10 0.64
150 - 300 2.32 2.43 -17 0.30

 

1Brown midrib 3 mutation for com.

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Appendix. Block and treatment end summary.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Block Parity1 Cow Treatment2 Pre—treatment DIM at Reason for
ID diet3 EOT‘1 treatment end5
A M 1429 normal DCAD 1 375 A
A M 3227 bm3 DCAD 1 523 C
A M 1331 normal DCAD 2 62 D
A M 1469 bm3 DCAD 2 285 A
A M 1424 normal DCAD 3 208 D
A M 1492 bm3 DCAD 3 283 B
A M 1236 normal DCAD 4 302 A
A M 1473 bm3 DCAD 4 401 B
A M 1515 normal DCAD 5 283 A
A M 1266 bm3 DCAD 5 479 B
C P 1608 bm3 DCAD 1 249 D
C P 1627 normal DCAD 1 337 A
C P 1601 bm3 DCAD 2 283 A
C P 1602 normal DCAD 2 538 C
C P 1657 bm3 DCAD 3 338 A
C P 1642 normal DCAD 3 420 C
C P 1628 bm3 DCAD 4 352 A
C P 1651 normal DCAD 4 304 A
C P 1619 bm3 DCAD 5 503 C
C P 1623 normal DCAD 5 470 C
D M 1450 bm3 DCAD 1 400 C
D M 1346 normal DCAD 1 292 A
D M 1411 bm3 DCAD 2 283 A
D M 3273 normal DCAD 2 257 B
D M 1426 bm3 DCAD 3 197 D
D M 1532 normal DCAD 3 417 B
D M 3269 bm3 DCAD 4 423 D
D M 1534 normal DCAD 4 341 C
D M 1316 bm3 DCAD 5 363 A
D M 1336 normal DCAD 5 313 B

 

 

 

 

 

 

 

1 Multiparous (M); Primiparous (P)

2 brown midrib mutant for corn (bm3); isogenic corn hybrid to bm3 (normal)
3 Dietary cation-anion difference rations fed until calving (DCAD 1 - 5)
‘1 Days in milk at end of treatment (DIM at EDT)

5 Reason cow ended treatment

A = approximately 60 d from calving

B = milk yield is below 13.6 kgld for 7d average

C = study completed
D = culled due to health problem

79

 

 

Appendix. Block and treatment end summary (continued).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Block Parity1 Cow Treatment2 Pre-treatment DIM at Reason for
ID diet3 EOT‘1 treatment end5
E M 1486 normal DCAD 1 307 A
E M 1438 bm3 DCAD 1 280 A
E M 1495 normal DCAD 2 249 B
E M 1338 bm3 DCAD 2 359 A
E M 1327 normal DCAD 3 439 C
E M 1529 bm3 DCAD 3 252 D
E M 1481 normal DCAD 4 299 D
E M 1474 bm3 DCAD 4 492 C
E M 3271 normal DCAD 5 233 B
E M 1419 bm3 DCAD 5 347 C
F M 1430 bm3 DCAD 1 283 A
F M 1432 normal DCAD 1 313 A
F M 1521 bm3 DCAD 2 282 A
F M 1531 normal DCAD 2 364 A
F M 1445 bm3 DCAD 3 296 B
F M 1323 normal DCAD 3 286 B
F M 1504 bm3 DCAD 4 404 B
F M 1518 normal DCAD 4 338 A
F M 1435 bm3 DCAD 5 407 A
F M 1501 normal DCAD 5 340 A
G P 1647 bm3 DCAD 1 375 A
G P 1650 normal DCAD 1 299 A
G P 1612 bm3 DCAD 2 441 C
G P 1653 normal DCAD 2 414 C
G P 1621 bm3 DCAD 3 390 A
G P 1617 normal DCAD 3 287 A
G P 1641 bm3 DCAD 4 424 C
G P 1632 normal DCAD 4 386 C
G P 1634 bm3 DCAD 5 361 A
G P 1643 normal DCAD 5 413 C

 

 

 

 

 

 

 

1 Multiparous (M); Primiparous (P)
2 brown midrib mutant for corn (bm3); isogenic corn hybrid to bm3 (normal)
3 Dietary cation-anion difference rations fed until calving (DCAD 1 - 5)

‘1 Days in milk at end of treatment (DIM at EOT)
5 Reason cow ended treatment
A = approximately 60 d from calving

B = milk yield is below 13.6 kgld for 7d average
C = study completed

D = culled due to health problem

80

 

 

Q.

Appendix. Block and treatment end summary (continued).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Block Parity1 Cow Treatmentz i Pre-treatment DIM at Reason for
ID - diet3 EOT‘1 treatment end5
H M 1335 normal DCAD 1 124 D
H M 1535 bm3 DCAD 1 288 A
H M 1477 normal DCAD 2 359 A
H M 1337 bm3 DCAD 2 330 C
H M 1527 normal DCAD 3 353 C
H M 1333 bm3 DCAD 3 324 C
H M 1483 normal DCAD 4 291 B
H M 1 510 bm3 DCAD 4 400 C
H M 1434 normal DCAD 5 363 D
H M 1459 bm3 DCAD 5 383 C
l P 1629 bm3 DCAD 1 31 1 C
I P 1646 normal DCAD 1 288 A
I P 1640 bm3 DCAD 2 400 A
l P 1648 normal DCAD 2 369 C
| P 1661 bm3 DCAD 3 357 C
l P 1667 normal DCAD 3 316 A
I P 1659 bm3 DCAD 4 284 A
l P 3383 normal DCAD 4 26 D
| P 1666 bm3 DCAD 5 353 C
I P 1644 normal DCAD 5 340 C

 

 

 

 

 

 

 

1 Multiparous (M); Primiparous (P)
2 brown midrib mutant for corn (bm3); isogenic corn hybrid to bm3 (normal)
3 Dietary cation-anion difference rations fed until calving (DCAD 1 - 5)

4 Days In milk at end of treatment (DIM at EOT)
5 Reason cow ended treatment
A = approximately 60 d from calving

B = milk yield is below 13.6 kgld for 7d average

C = study completed

D = culled due to health problem

81

 

 

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