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This is to certify that the

dissertation entitled

Neutral Detergent Fiber Concentration and Digestibility
in Corn Silage Influences Digesta Kinetics, Dry Matter
Intake, and Performance of Growing Steers

presented by

Kent Eric Tjardes

has been accepted towards fulﬁllment
of the requirements for

 

 

Doctor of philosophy degree in Animal Science

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NEUTRAL DETERGENT FIBER CONCENTRATION AND DIGESTIBILITY IN
CORN SILAGE INFLUENCES DIGESTA KINETICS, DRY MATTER INTAKE,
AND PERFORMANCE OF GROWING STEERS
By

Kent Eric Tjardes

A DISSERTATION

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

DOCTOR OF PHILOSOPHY
Department of Animal Science

2001

ABSTRACT
NEUTRAL DETERGENT FIBER CONCENTRATION AND DIGESTIBILITY IN
CORN SILAGE INFLUENCES DIGESTA KINETICS, DRY MATTER INTAKE,
AND PERFORMANCE OF GROWING STEERS
By

Kent Eric Tjardes

It is our hypothesis that corn silage high in ﬁber potentially limits dry matter intake
(DMI) and performance of growing beef steers. Improving ﬁber digestibility and(or)
reducing ﬁber concentration in corn silage should improve intake and performance if
intake is limited by ruminal ﬁll. The brown midrib-3 (bm) gene mutation has been
incorporated into corn plants to improve ﬁber digestibility. In Experiment 1, the objective
was to determine the effect of bm3 corn silage on digestion (Trial 1) and performance
(Trial 2) of growing steers. In Trial 1, eight ruminally ﬁstulated Angus steers (224 :l: 24
kg) were used in a replicated 4 X 4 Latin square design with a 2 X 2 factorial arrangement
of treatments and 21-d periods. Steers had ad libitum access or were restricted to 80%
intake of diets containing 86% bm3 corn silage (BMCS) or corn silage from its isogenic
normal counterpart (Control). BMCS resulted in increased DMI (P < 0.01) and 1
improved total-tract digestibility of dry matter (DM) and neutral detergent ﬁber (NDF; P
< 0.05). In Trial 2, 128 steer contemporaries to Trial 1 (245 i 13 kg) were offered ad
libitum access to BMCS or Control diets. Aﬁer a 112-d treatment period, steers received
a common ﬁnishing diet. During the 112-d treatment period, steers fed BMCS had higher
DMI (P < 0.05) and similar body weight gain (P > 0.10), resulting in poorer feed

efﬁciency (P < 0.01). Finishing and overall performance of steers was not different due to

treatment (P > 0.10). The objectives of Experiments 2 and 3 were to determine if corn
silage high in NDF concentration would limit DMI and performance by physical ﬁll. In
Experiment 2, eight ruminally ﬁstulated Holstein steers (198 i 13 kg) were used in a
replicated 4 X 4 Latin square design with a 2 X 2 factorial arrangement of treatments and
16-d periods. Treatment diets contained a normal hybrid (33.8% NDF; low-ﬁber; LF) or
male-sterile (50.8% NDF; high-ﬁber, HF) corn silage. Diets were offered ad libitum to
steers without or with rumen inert bulk (RIB) added at 25% of pretrial ruminal volume.
Feeding I-IF reduced DMI and ruminal NDF turnover time (P < 0.01), but had no effect on
ruminal digesta volume (P > 0.10). Addition of RIB also reduced DMI and NDF turnover
time (P < 0.01). The RIB increased digesta + RIB volume (P < 0.01), but had no effect
on digesta (minus RIB) volume (P > 0.10). In Experiment 3, twelve Angus (237 i 13 kg)
and twelve Holstein (235 i 15 kg) steers were used in a crossover design consisting of six,
l4-d periods. The LP and HF diets were alternated each period. The HP diet decreased
DMI and gain over the entire trial (P < 0.01), and HF depressed DMI to a greater extent
as steers increased body weight when compared to LP (P < 0.01). Holstein steers
consumed more DM and gained faster than Angus steers (P < 0.01). Difference in total-
tract DM digestibility was negatively correlated to difference in DMI (:2 =0.23; P < 0.01)
for LF minus HF within Angus steers, but not for Holstein steers. Results from these
experiments suggest that DMI of light-weight steers receiving corn silage diets within a
wide range of NDF concentration was controlled by a combination of both physical and
metabolic factors. In addition, the use of bm3 to improve ﬁber digestibility of a corn silage

based diet containing less than 40% NDF improved DMI but did not affect feedlot ADG.

ACKNOWLEDGMENTS

I would like to express my appreciation to the people who gave me guidance,
assistance, and friendship during my educational experience at Michigan State University.
I would like to thank my graduate committee: Dr. Daniel Buskirk, for his friendship,
guidance, help with data collection, and ﬁnancial support that allowed me to complete my
degree; Dr. Michael Allen, for his friendship, expertise, and counseling that allowed me to
develop my projects; and Drs. Leslie Bourquin, Steven Rust, and Harlan Ritchie for their
expertise and support that contributed to my dissertation research and education at MSU.
In addition to committee members, I would like to thank ioel Cowley, Mark McCully, and
Drs. Kent Ames, Robert Tempelman, Margaret Benson, David Hawkins, Herb Bucholtz,
Michael VandeHaar, and Ted Ferris for their help, advice, and friendship.

I would like to acknowledge Cargil Hybrid Seeds and United Agri Products, Dyna-
Gro for there support of corn silage research at Michigan State University. Thanks also
goes out to Robert Burnett, David Main, Dewey Longuski, Jackie Ying, Masahito Oba,
and Jill Davidson for assistance in the laboratory and making it more enjoyable. I would
like to thank Ken Metz, the farm crew at BCRC, Phil Summer, John Bufﬁngton, and Fred
Openlander; and my undergraduate employees, Holly Weldon, Casey Bradley, Michelle
Currell, and Mandy Rust, for help with feeding, animal handling, data collection and
analysis. In addition, I would like to thank all the graduate students, faculty and staff that
helped with my research and made being here fun. A special thanks goes out to Dr. Roy
Radcliff, Mike and Tonia Peters, Matt and Dr. Jennifer Fenton, and Tom Pilbeam for all

the times we enjoyed nature. Sometimes we actually saw the wildlife we were hunting.

iv

Finally, I am truly appreciative to my family and the role they played. I would like
to thank my mother Gale, father Harry, and grandparents Eugene and Gladis for their
continued love and ﬁnancial support during my “long" college career. I want to thank my
brother Kurt, my sisters Kara and Kristin, their husbands Al and Wade, and my future
family Mike, Pam and Stacy, for there continual support towards me “ﬁnally” ﬁnishing.
Last but not least, I would like to acknowledge the patience, encouragement, and love of
my ﬁance, Michelle Smiricky. I also appreciated her help dumping rumens, even though

she reﬁised to wear gloves.

CHAPTER 1

CHAPTER 2

TABLE OF CONTENTS

LIST OF TABLES .................................................. ix
LIST OF FIGURES .................................................. xi
LIST OF ABBREVIATIONS ......................................... xiv
INTRODUCTION .................................................... 1
Literature Review .............................................. 4
Regulation of Intake ....................................... 4

Physical regulation ................................... 4

Metabolic regulation ................................. 8

Integration of regulating factors ........................ 13

Fiber digestibility ......................................... 15

Effect of ﬁber modiﬁcation on digestibility ................ 18

Effect of the brown midrib mutation on plant composition . . . . 21
Effect of the brown midrib mutation an intake and performance

........................................... 22

Effect of the brown midrib mutation on digestion ........... 23

Fiber concentration ....................................... 25

Effects of fiber concentration on intake and performance ..... 25
Effects of ﬁber concentration on digestion and digesta

characteristics ................................ 27

Rumen inert bulk ........................................ 28

Effects of rumen inert bulk an intake .................... 29

Effects of rumen inert bulk on digesta characteristics ........ 30

Effects of rumen inert bulk on total-tract diet digestibility . . . . 3]
Effects of cattle breed on intake, performance, and maintenance

requirements ...................................... 3 1
Summary ............................................... 33
Literature Cited .......................................... 3 5

Brown Midrib-3 (bm3) Corn Silage Improves Digestion but not Performance

of Growing Beef Steers .................................... 49
Abstract ................................................ 49
Introduction ............................................ 50
Materials and Methods .................................... 51

vi

Trial 1 ........................................... 52

Trial 2 ........................................... 54
Sample Analysis .................................... 5 5
Statistical Analysis .................................. 5 7
Results and Discussion .................................... 58
Trial 1 ........................................... 59
Trial 2 ........................................... 65
Implications ............................................. 67
Tables and Figures ....................................... 68
Literature Cited .......................................... 76

CHAPTER 3

Neutral Detergent Fiber Concentration of Com Silage and Rumen Inert Bulk
Inﬂuences Dry Matter Intake and Ruminal Digesta Kinetics of

Growing Steers .......................................... 79
Abstract ................................................ 79
Introduction ............................................ 80
Materials And Methods .................................... 81

Sample Analysis .................................... 83

Statistical Analysis .................................. 85
Results And Discussion .................................... 85
Implications ............................................. 93
Tables and Figures ....................................... 95
Literature Cited ......................................... 102

CHAPTER 4

Neutral Detergent Fiber Concentration in Corn Silage Inﬂuences Dry Matter
Intake, Diet Digestibility, and Performance of Angus and Holstein

Steers ................................................. 105
Abstract ............................................... 105
Introduction ........................................... 1 06
Materials And Methods ................................... 107

Sample Analysis ................................... 109

Statistical Analysis ................................. l 10
Results And Discussion ................................... l 1 1
Implications ............................................ l 15
Tables and Figures ...................................... l 16
Literature Cited ......................................... 124

vii

CHAPTER 5
Interpretive Summary ......................................... 126
Fiber digestibility ........................................ 126
Fiber concentration ...................................... 127
Recommendation ........................................ l 29
Tables and Figures ...................................... 132
APPENDICES
APPENDIX A ................................................ 137
APPENDIX B ................................................ 141
VITA ...................................................... 144

viii

44* —

CHAPTER 1

LIST OF TABLES

Table l-l. The inﬂuence of hormones and neurotransmitters in

CHAPTER 2

voluntary dry matter intake .................................. 12

Table 2-1. Post-ensiled nutrient composition and fermentation

characteristics of isogenic normal and brown midrib-3 (bm3)
corn hybrids ............................................. 68

Table 2-2. Ingredient and nutrient composition of isogenic normal

control (Control) and brown midrib-3 (BMCS) corn silage
diets fed during the growing and ﬁnishing phases ................. 69

Table 2-3. Dry matter intake, fecal output, apparent total-tract

digestibility, and energy concentration of isogenic normal

control (Control) and brown midrib-3 (BMCS) corn silage

diets offered ad libitum or 80% of ad libitum to steers (Trial

1) ..................................................... 70

Table 2-4. Ruminal digesta characteristics and kinetics for steers

receiving isogenic normal control (Control) and brown
midrib-3 (BMCS) corn silage diets offered ad libitum or
80% of ad libitum (Trial 1) .................................. 71

Table 2-5. Ruminal VFA concentration for steers receiving

isogenic normal control (Control) and brown midrib-3
(BMCS) corn silage diets offered ad libitum or 80% of ad
libitum (Trial 1) .......................................... 72

Table 2-6. Performance for steers receiving isogenic normal

CHAPTER 3

control (Control) and brown midrib-3 mutation (BMCS)
corn silage based diets for 112 d (Trial 2) ....................... 73

Table 3-1. Post-ensiled nutrient composition and fermentation

characteristics of normal and male-sterile corn hybrids ............. 95

Table 3-2. Ingredient and nutrient composition of normal (Low-

ﬁber) and male-sterile (High-ﬁber) corn silage diets ............... 96

ix

Table 3-3. Dry matter intake, NDF intake, and ruminal digesta
characteristics and kinetics of normal (Low ﬁber) and male-
sterile (High ﬁber) corn silage based diets with and without
rumen inert bulk (RIB) ..................................... 97

Table 3-4. Ruminal pH, lactate, and VFA of normal (Low-ﬁber)
and male-sterile (High-ﬁber) corn silage-based diets with
and without rumen inert bulk (RIB) ........................... 98

Table 3-5. Apparent total tract digestibility, and energy
concentration of normal (Low ﬁber) and male-sterile (High
ﬁber) corn silage based diets with and without rumen inert
bulk (RIB) .............................................. 99

CHAPTER 4

Table 4-1. Post-ensiled nutrient composition and fermentation
characteristics of normal and male-sterile corn hybrids ............ 116

Table 4-2. Ingredient and nutrient composition of normal (Low-
ﬁber) and male-sterile (High-ﬁber) corn silage-based diets ......... 117

Table 4-3. Dry matter intake, average daily gain, apparent total
tract digestibility, and energy concentration of low-ﬁber
(LF) and high-ﬁber (HF) corn silage-based diets fed to
growing Angus and Holstein steers ........................... 118

CHAPTER 5

Table 5-1. Beef growing phase partial budget for steers receiving
brown midrib-3 (BMCS) and isogenic normal (Control)
corn silage based diets (Based on Experiment 1) ................. 132

Table 5-2. Feed proportions and prices of isogenic normal
(Control) corn silage based growing diet ....................... 133

Table 5-3. Feed proportions and prices of brown midrib-3 (BMCS)
corn silage based growing diet .............................. 133

Table 5-4. Beef growing phase partial budget for steers receiving
brown midrib-3 (BMCS) and isogenic normal (Control)
corn silage based diets .................................... 134

LIST OF FIGURES

CHAPTER 2

Figure 2-1. Effects of feeding ad libitum isogenic normal control
(AC), ad libitum brown midrib-3 (AB), limited isogenic
normal control (LC), or limited brown midrib-3 (LB) corn
silage diets on ruminal pH over time (Trial 1). Feed offered
at 0, 8, and 16 h. Time X DMI interaction (P < 0.001).
SEM = 0.065. ........................................... 74

Figure 2-2. Effects of feeding ad libitum isogenic normal control
(AC), ad libitum brown midrib-3 (AB), limited isogenic
normal control (LC), or limited brown midrib-3 (LB) corn
silage diets on ruminal NH3 N over time (Trial 1). Feed
offered at 0, 8, and 16 h. Time X DMI >< hybrid interaction
(P<0.05). SEM= 1.13. ................................... 75

CHAPTER 3

Figure 3-1. Effects of feeding a normal corn hybrid (low-ﬁber; LF)
or its male-sterile counterpart (high-ﬁber; HF), without or
with rumen inert bulk (RIB) on ruminal pH over time. Feed
offered at 0, 12 h. Time >< ﬁber level interaction (P <
0.0001). SEM = 0.09. .................................... 100

Figure 3-2. Effects of feeding a normal corn hybrid (low-ﬁber; LF)
or its male-sterile counterpart (high-ﬁber; HF), without or
with rumen inert bulk (RIB) on molar percentage of

propionate over time. Feed offered at 0, 12 h. Time >< ﬁber
level interaction (P < 0.0001). SEM = 0.61 ..................... 101

CHAPTER 4

Figure 4-1. Effects of feeding low-ﬁber (LF) and high-ﬁber (HF)
corn silage-based diets on growing steer a) dry matter
intake least squares mean (DMI) over period and b) dry
matter intake as a percentage of body weigh least squares
mean (DMI, % BW) over period. Period >< ﬁber level
interactions (P < 0.0001). .................................. l 19

Figure 4-2. Relationship between difference in DMI for low-ﬁber

(LF) minus high-ﬁber (HF) and average crossover body
weight of Angus and Holstein steers. Difference in DMI

xi

thrust

(LF - HF) = -l .856 + 0.011 X average crossover body
weight (r2 = 0.24; P < 0.001). ............................... 120

Figure 4-3. Relationship between difference in apparent total-tract
DM digestibility and difference in DMI for low-ﬁber (LF)
minus high-ﬁber (HF) within a) Angus steers (r2 = 0.23; P <
0.001) and b) Holstein steers (r2 = 0.01; P = 0.42).
Difference in apparent total-tract digestibility (LF - I-IF) of
Angus steers = 12.54 - 9.45 X difference in Angus steer
DMI. ................................................. 121

Figure 4-4. Relationship between difference in DE intake and
difference in DMI for low-ﬁber (LF) minus high-ﬁber (HF)
within a) Angus steers (r2 = 0.01; P = 0.57) and b) Holstein
steers (r2 = 0.23; P < 0.001). Difference in DE intake (LF -
HF) of Holstein steers = 1.294 + 2.080 x difference in
Holstein steer DMI. ...................................... 122

Figure 4-5. Relationship between difference in DE intake for low-
ﬁber (LF) minus high-ﬁber (HF) and average crossover
body weight of Angus and Holstein steers. Difference in
DE intake (LF - HF) = -3.499 + 0.025 X average crossover
body weight (r2 = 0.08; P < 0.01). ........................... 123

CHAPTER 5

Figure'S-l. Return to labor and management ($/steer) as a result of
difference in average daily gain (ADG) and feed efﬁciency
(GainzFeed). Based on the isogenic normal (Control) corn
silage diet in Table 5-4. Assumes that cost of producing
silage does not change. .................................... 135

APPENDIX A

Figure A—l. Effects of feeding ad libitum isogeneic normal control
(AC), ad libitum brown midrib-3 (AB), limited isogeneic
normal control (LC), or limited brown midrib-3 (LB) corn
silage diets on total ruminal VFA concentration over time
(Trial 1). Feed offered at 0, 8, and 16 h. Time >< hybrid
interaction (P < 0.001). SEM = 4.14 .......................... 137

Figure A-2. Effects of feeding ad libitum isogeneic normal control
(AC), ad libitum brown midrib-3 (AB), limited isogeneic
normal control (LC), or limited brown midrib-3 (LB) corn
silage diets on molar percentage of acetate over time (Trial

xii

1). Feed offered at 0, 8, and 16 b. Time X hybrid
interaction (P < 0.001). SEM = 2.64 .......................... 138

Figure A-3. Effects of feeding ad libitum isogeneic normal control
(AC), ad libitum brown midrib-3 (AB), limited isogeneic
normal control (LC), or limited brown midrib-3 (LB) corn
silage diets on molar percentage of propionate over time
(Trial 1). Feed offered at 0, 8, and 16 h. Time X hybrid
interaction (P < 0.001). SEM = 1.30 .......................... 139

Figure A-4. Effects of feeding ad libitum isogeneic normal control
(AC), ad libitum brown midrib-3 (AB), limited isogeneic
normal control (LC), or limited brown midrib-3 (LB) corn
silage diets on molar percentage of butyrate over time (Trial
1). Feed offered at O, 8, and 16 h. Time X hybrid
interaction (P < 0.05). SEM = 0.70 ........................... 140

APPENDIX B

Figure B-l. Effects of feeding a normal corn hybrid (low-ﬁber; LF)
or its male-sterile counterpart (high-ﬁber; HF), without or
with rumen inert bulk (RIB) on total ruminal VFA
concentration over time. Feed offered at 0, 12 h. Time X
ﬁber level interaction (P < 0.0001). SEM = 4.9 .................. 141

Figure B-2. Effects of feeding a normal corn hybrid (low-ﬁber; LF)
or its male-sterile counterpart (high-ﬁber; HF), without or
with rumen inert bulk (RIB) on molar percentage of acetate
over time. Feed offered at 0, 12 h. Time X ﬁber level X
bulk interaction (P < 0.01). SEM = 0.54. ...................... 142

Figure B-3. Effects of feeding a normal corn hybrid (low-ﬁber; LF)
or its male-sterile counterpart (high-ﬁber; HF), without or
with rumen inert bulk (RIB) on molar percentage of
butyrate over time. Feed offered at O, 12 h. Time X ﬁber
level interaction (P < 0.0001). SEM = 0.40 ..................... 143

xiii

ADF
ADG
ADIN
ADL
bm3
BMCS
BW
CF

CP
Control
cwt

(1

DE
DM
DMI
GE

h

HF

i.d.
iNDF
kd

kp

LF

ME

n

NDF
NE
NEE
OM
P

r2
RIB
SAS
s.c.
SD
SEM
VFA

X

m

LIST OF ABBREVIATIONS

acid detergent ﬁber

average daily gain

acid detergent insoluble nitrogen

acid detergent lignin

brown midrib-3 mutation

brown midrib-3 corn silage based diet
body weight

crude ﬁber

crude protein

isogenic normal corn silage diet

100 pounds of body weight

day(s)

digestible energy

dry matter

dry matter intake

gross energy

hour(s)

high ﬁber diet containing male-sterile corn silage
internal diameter

indigestible neutral detergent ﬁber
digestion rate in the rumen

passage rate for the rumen

low ﬁber diet containing normal corn silage
metabolizable energy

number

neutral detergent ﬁber

net energy of maintenance

net energy of gain

organic matter

probability that difference was due to chance alone
coefficient of determination

rumen inert bulk

Statistical Analysis System
subcutaneous

standard deviation

standard error of the least squares mean
volatile fatty acids

mean

xiv

INTRODUCTION

Many producers background cattle or feed them a high forage growing ration
before they are ﬁnished on a high concentrate ration. The use of backgrounding allows
producers to 1) increase frame size of cattle and thereby increase their ﬁnal weight at a
similar body composition, 2) utilize less expensive feedstuffs, resulting in cheaper weight
gains, and 3) hold cattle in order to sell them during the high part of the annual price cycle.
In the southern part of the United States and Plains States, producers have the ability to
use grazing as a method to background cattle. In these situations, cattle graze either cool-
season native range or improved cool-season pastures (e. g. ryegrass, winter wheat, and
rye). In the upper Midwest, because freezing temperatures and snow cover limits the use
of year-round grazing, harvested forages are fed in many backgrounding or growing diets.
Corn silage is often the primary ingredient in these growing rations in the upper Midwest.

Concentration of cell wall material in forage plants has been implicated as a major
factor that inﬂuences forage intake by cattle. Many different molecules and molecular
polymers make up the cell wall of corn plants. The number and structural interactions of
these molecules and polymers can change during maturation of the plant and can vary due
to genetic differences in hybrids. These variations contribute to differences in ﬁber
concentrations and digestibility, and ultimately affect intake and performance of cattle.

Light-weight cattle have a relatively smaller ruminal capacity compared to mature
cattle, and therefore have the potential for intake to be relatively more limited when diets
contain a high concentration of ﬁber. However, it has been proposed that several

mechanisms work in concert with one another to inﬂuence feed intake. These mechanisms

produce a number of signals that are summarized by intake centers of the central nervous
system, which ultimately determine commencement and cessation of eating. These
potential signals include rumen distension, propionate ﬂux, circulating hormones and(or)
neurotransmitters.

Being able to accurately estimate voluntary dry matter intake is important when
trying to determine the nutrient requirements of cattle. Accurately estimating intake is
also critical for predicting performance and efficiency of gain of cattle. Accurate
predictions of feed eﬂiciency and gain allow producers to estimate proﬁtability and
determine breakeven prices for buying and selling cattle. The understanding of how fiber
concentration and digestibility in corn silage affects intake is important when considering
the proﬁtability in producing cattle. If intake can be manipulated through corn hybrid
selection, harvesting hybrids at the Optimal time, and(or) post-harvest modiﬁcations to
improve gain and(or) feed efﬁciency, this could have dramatic effects on returns to
management and labor.

The overall hypothesis of the research described in this dissertation is that corn
silage high in ﬁber potentially limits intake and performance of light-weight steers by
physical constraints in the rumen. Therefore, improving ﬁber digestibility or decreasing
ﬁber concentration in corn silage should reduce the ﬁlling effect in the rumen, and increase
intake and performance. The objectives of this research project were to:

1) determine the effects of increasing ﬁber digestibility of corn silage on

digesta kinetics, DMI, growth, and feed efficiency of light-weight steers;

2) challenge growing steers with ruminal ﬁll in the form of dietary NDF and
inert bulk to determine if increased NDF concentration in corn silage limits
DMI by rumen ﬁll and inﬂuences digesta kinetics and diet digestibility;

3) determine if increased NDF concentration in corn silage depresses DMI
and performance and inﬂuences diet digestibility as steers increase in BW;
and

4) determine if Holstein and Angus steers respond differently to increased
NDF concentration in corn silage.

Chapter 2 describes a digestion trial using 8 ruminally ﬁstulated Angus steers and a
performance trial using 128 Angus steers comparing brown midrib-3 corn silage to its
isogenic normal control to address Objective 1. Chapter 3 describes an experiment in
which 8 ruminally ﬁstulated Holstein steers were challenged with rumen ﬁll in the form of
NDF and rumen inert bulk (Objective 2). Objectives 3 and 4 were addressed by feeding
either a low-ﬁber or high-ﬁber diet to 12 Angus and 12 Holstein steers using a crossover

design consisting of six, 14-day periods (Chapter 4).

CHAPTER 1

Literature Review

Regulation of Intake

Animal and dietary factors that control satiety and hunger, in turn regulating
intake, are complex and not ﬁilly understood. The regulation of DMI has been
differentiated into those factors that affect long-term and short-term control (Baile and
Forbes, 1974). Long-term control of intake is regulated by factors involved in
maintenance of energy inputs and outputs to achieve balance in body weight and
productive functions. Short-term regulators are those factors associated with controlling
meal initiation and termination, which have inﬂuence over meal size and inter-meal interval
within a clay. Factors associated with short-term regulation of intake may more accurately
deﬁne daily ﬂuctuations in intake. Factors that inﬂuence intake regulation have been
categorized into those associated with physical limitations, metabolic signals, and social
and environmental factors (Forbes, 1996). Physical regulation of DMI implies that intake
is limited by maximum ﬂow of digesta throughout the gastrointestinal tract or physical
capacity of the gastrointestinal tract. Metabolic regulation occurs when absorbed ﬁJClS
trigger feedback mechanisms to terminate intake. These factors, involved in intake

regulation of forage, will be further discussed in the following sections.

Physical regulation
The theory that DMI is regulated by physical ﬁll was ﬁrst proposed sixty years ago

when (Lehmann, 1941) suggested that indigestible organic matter residue created bulk in

the gastrointestinal tract, limiting intake. Since that time, the theory has become widely
accepted and much research has been conducted to better understand the mechanisms by
which DMI is limited with physical control. Although the abomasum and large and small
intestines have ﬁnite volumes, there is a general consensus that the physical capacity of
these organs does not limit voluntary intake (Grovum, 1987; Forbes, 1995). The site in
which physical distension regulates DMI generally has been regarded to be the reticulo-
rumen. Ash and Kay (195 7) reported that the reticulo-omasal oriﬁce was sensitive to
mechanical stimuli and its distension evoked rumination, indicating that the reticulo-
omasal oriﬁce may be a control mechanism for passage of particles from the reticulo-
rumen. The discovery of tension receptors and mechanoreceptors concentrated in the
reticulum and cranial rumen further suggest that the site of physical control of intake is the
reticulo-rumen (lggo, 1955; Leek, 1969). These tension receptors have been shown to
send nerve impulses via the vagus and splanchnic nerves to brain centers when stimulated
by distension (Leek, 1969). Epithelial mechanoreceptors are stimulated by both light
mechanical and chemical stimuli (Leek, 1969).

Physical limitations to intake can be separated into animal and dietary affects. The
primary animal effect that can impact DMI is capacity of the reticulo-rumen. Wardrop
(1960) found a positive correlation between intake and weight of the empty reticulo—
rumen in lambs. An increase in size of other abdominal organs, such as the pregnant
uterus, reduces capacity of the reticulo-rumen and decreases DMI (Forbes, 1995). An
increase in abdominal fat was also negatively correlated to DMI (NRC, 1987) and this
may be due to a reduction on gut capacity and(or) may be due to satiety signals via leptin.

Cattle with similar body fat but larger skeletal size have increased DMI (NRC, 1987).

Further discussion of differences in DMI between Holstein and beef breeds will be
discussed later in this review.

Dietary characteristics which inﬂuence the digesta ﬂow from the reticulo-rumen
can play an important role in physical limitation of intake. The ﬂow rate of digesta can be
inﬂuenced by particle size, fragility, density, and chemical composition. Passage rate of
particles is controlled by the reticulo-omasal oriﬁce. Size reduction of large particles is
required for passage from the reticulo-rumen. Poppi et al. (1985) reported that resistance
to escape the reticulo-rumen increases for particles retained on a sieve aperture of 1.18
mm, for sheep and cattle. However, higher threshold sieve aperture sizes have been
reported for steers (Dixon and Milligan, 1985) and dairy cattle (Cardoza and Mertens,
1986), in the range of 3 to 4 mm. Breakdown of large particles is primarily done through
the process of rumination, with little or no further particle size reduction occurring once
particles leave the reticulo-rumen (Poppi et al., 1980; Okine and Mathison, 1991). It has
also been reported that rate of particle size reduction decreases with increasing BW
(W elch, 1982; Illius and Gordon, 1991). Welch (1982) reported the rumination time per
gram of cell wall contents decreased exponentially with increasing BW for sheep, goats
and steers.

Increasing forage particle fragility increases the rate of particle size reduction and
reduces particle retention time in the reticulo-rumen (Poppi et al., 1981; McLeod and
Minson, 1988). Ulyatt et a1. (1986) found a greater reduction in particle size by chewing
for mature ryegrass that contained higher cell wall content and lower digestibility than for
less mature ryegrass. They suggested that this greater particle size reduction was due to

“brittleness” (i. e. fragility) which increased as the ryegrass matured.

Particle density also has an effect on physical control of intake. In order for a
particle to pass from the reticulo-rumen, it must come into close proximity of the reticulo-
omasal oriﬁce at the second phase of reticular contraction (Allen and Mertens, 1988). The
ability of a particle to come within close proximity of the oriﬁce is dependent on particle
density (Allen, 1996). Small, dense particles fall into the ventral rumen where they ﬂow
with the ventral currents into the reticulum (Wyburn, 1980). These particles are then
1 close to the reticulo-omasal oriﬁce and are expelled as it opens during the second reticular
contraction (Midasch et al., 1994). Less dense particles are either trapped in the rumen
mat (Faichney, 1986) or become propelled ﬁirther away from the reticulo-omasal oriﬁce
when the rumen contracts (Lechner-Doll et al., 1991), resulting in these less dense
particles having a slower rate of passage. Negative relationships between particle density
and retention time in the reticulo-rumen have been reported in experiments using inert
particles (Balch and Kelly, 1950; King and Moore, 1957; desBordes and Welch, 1984;
Murphy et al., 1989) and experiments using labeled indigestible cell walls (Ehle, 1984;
Ehle and Stern, 1986). Lechner-Doll et al. (1991) reported that the relationship between
particle density and retention time in the reticulo-rumen was nearly linear. As density of
inert particles increased from 0.9 to 1.5 g/mL, retention time decreased from 91 to 19 h
for experiments using inert particles with different densities (Lechner-Doll et al., 1991).

In spite of the fact that digesta particles typically have a true speciﬁc gravity of 1.3
to 1.5 (Siciliano-J ones and Murphy, 1991), most digesta particles in the rumen are initially
buoyant (Sutherland, 1988). This process is described in detail in a review by Allen
(1996). As particles are swallowed, air becomes trapped within the void spaces, but this

air eventually dissolves. Actively fermented particles remain buoyant because carbon

dioxide and methane are produced by fermentation of the potentially digestible organic
matter and thereby decrease particle density. Density increases as fermentation continues
and the amount of potentially fermentable organic matter is reduced, cell walls are
disrupted, and less gas is associated with the digesta particles. This allows these particles
to come into close proximity with the reticulo-omasal oriﬁce and pass from the reticulum

(Allen, 1996).

Metabolic regulation

If physical constraints on the gastrointestinal tract were the only method by which
voluntary DMI were regulated, then more digestible feeds would be consumed at a much
higher level than less digestible feeds. However, DMI of highly digestible feeds is not
always greater, and their intake may be controlled by metabolic regulation. One theory of
metabolic control of intake is based on the premise that an animal will consume nutrients
until energy balance is achieved (Jones, 1972; Joumet and Remond, 1976; De Jong,
1986). Illius and J essop (1996) stated that an animal has, at any point in time, some
maximal productive capacity. This capacity depends on the animal’s genetic potential for
growth and(or) lactation, and will vary over the animal’s lifetime, according to stage of
growth, reproductive status, physical and climatic environment, the animal’s ability to
store energy surpluses, etc. This theory is disputed by a review on intake control, in
which Grovum (1987) cited several studies conducted with sheep, beef cattle, and dairy
cattle where digestible energy intakes were relatively constant at moderate dietary energy

densities, but declined at high dietary energy concentrations. He suggested that

maintenance of rumen function received priority over maintaining energy intake under high
concentrate feeding.

A second theory states that metabolic feedback stemming from the animal’s ability
to utilize nutrients interacts with the balance of absorbed nutrients to regulate intake (Illius
and J essop, 1996). The ability to utilize nutrients depends on the animal’s production
potential. The metabolic feedback can be in the form of metabolites associated with
energy metabolism, and hormones associated with homeorhetic and digestive control
(Illius and Jessop, 1996).

In support of this second theory, epithelium chemoreceptors have been observed in
the reticulum and the cranial sac of the rumen. These receptors are stimulated by acids,
alkali, and hypo- and hyper-osmotic solutions (Leek, 1969). The osmolality of ruminal
ﬂuid can be highly variable depending on mineral salt content and fermentability of the diet
(Allen, 2000). Satiety may be triggered by the osmolality stimulating the epithelial
receptors in the reticulo-rumen (Grovum, 1995). However, Leek and Harding (1986)
reported that the threshold for stimulation of receptors in response to hyper-osmotic
solutions is between 700 and 1700 mOsm/kg, which is not in the physiological range.
Osmolality of ruminal contents has been reported to be 250-3 00 mOsm/kg pre-feeding and
increase within a few hours after a large meal to as high as 500 mOsm/kg (Warner and
Stacy, 1968).

Large quantities of VFA are produced during ruminal fermentations. Therefore,
several studies have investigated the possibility of these metabolites being associated with
intake regulation. Undissociated VFA have been found to stimulate reticulo-rumen

epithelial receptors in the range of 40 to 100 mM (Harding and Leek, 1972). Crichlow

and Leek (1980) reported that butyrate had a greater stimulatory effect on the epithelial
receptors as compared to propionate, and that the stimulation was greater at lower pH.
This is likely the effect of VFA absorption rate, because this rate is negatively associated
with ruminal pH. Relative rate of absorption has been demonstrated to be butyrate >
propionate > acetate (Dijkstra et al., 1993). It has been reported that VFA, particularly
acetate and propionate, depress intake when infused into the rumen (Baile and Forbes,
1974; Forbes, 1995). However, De Jong et al. (1981) reported that the acetate
concentration infused in the studies was unphysiological. De Jong et a1. (1981) could not
repeat the depression in intake when physiological levels were inﬁised. Anil et al. (1993)
inﬁised sodium acetate continually into the rumen of lactating cows for 3 h. They
observed little or no signiﬁcant effects on intake when the rate of acetate infusion was
similar to that normally produced in the rumen. Depression of intake only became obvious
when inﬁrsion produced at least twice the normal concentration of acetate (Anil et al.,
1993). Anil and Forbes (1980) observed that inﬁision of propionate into the hepatic vein
depressed intake in sheep, but infusion into the jugular vein had no effect on intake. They
also reported that denervation of the liver prevented the intake depressing effect of hepatic
vein propionate inﬁlsion. Anil and Forbes (1980), therefore concluded that there may be
propionate receptors in the liver.

Chemoreceptors, sensitive to only propionate, have not been identiﬁed in the liver
to date (Allen, 2000). Andrews (1987) did report that there are thermo- and osmo-
receptors in the liver that may be involved in satiety. Therefore, oxidizable ﬁJElS in the
liver may have the ability to stimulate these receptors, and if the animal is unable to utilize

these ﬁiels, their buildup may shutdown intake.

10

Reductions in intake, as a result of propionate inﬁrsion, may also be mediated by
an increase in insulin (Grovum, 1995). Plasma insulin has been shown to increase in
response to hepatic infusion of propionate, but not inﬁision of acetate or jugular infusion
of propionate in sheep (Manns and Boda, 1967). Secretions of insulin also may be
induced by the sight of food in sheep (Bassett, 1975) and cattle (Vasilatos and Wangsness,
1980; Faverdin, 1986). Small doses of insulin have been shown to reduce intake in sheep
(Dulphy and Faverdin, 1987; Foster et al., 1991)

Besides insulin, regulation of intake also can be controlled by additional hormones
associated with energy status. Hormones associated with peripheral metabolism (e. g.
glucagon, glucocorticoids, etc.) and the gut hormones associated with feeding (e. g.
gastrin, secretin, cholecystokinin, etc.), as well as various neurotransmitters (e. g.
serotonin, opioid peptides, neuropeptide Y, etc.) that have potential roles in intake control
are reviewed in detail by Forbes (1995). The inﬂuence that several hormones and
neurotransmitters potentially have on intake are summarized in Table 1-1. Understanding
the interactions of these and other hormones and how they transmit signals to the

hypothalamus are important areas for continued research.

11

Table 1-1. The inﬂuence of hormones and neurotransmitters in voluntary dry matter

intakea

Hormones and neurotransmitters

Effect on dry matter intake

 

Metabolic hormones
Glucagon
Grth hormone
Adrenaline

Gut peptides
Cholecystokinin (CCK)
Pentagastrin
Somatostatin
Bombesin

Hormones associated with growth
Cortisol
B-agonists

Other hormones
Estrogen
Vasopressin
Endorphins

Satietin

depresses
may stimulate

depresses

depresses
no effect
depresses

depresses

stimulates

no effect

low doses stimulate, high doses depress
depresses
not enough information

may depress

Neurotransmitters and hormones associated with the central nervous system

Serotonin
Opioid peptides
Neuropeptide Y and peptide YY

Grth hormone releasing factor

depresses
stimulates
stimulates

stimulates

 

aAdapted from Forbes (1995).

12

Integration of regulating factors

The physical and metabolic factors that have potential to affect intake of forages
by ruminants include 1) distension of the gastrointestinal tract, 2) effects of ruminal ﬂuid
osmolality, 3) ability of tissues to metabolize nutrients (Forbes, 1996), 4) effects of VFA
on the stomach, ruminal veins, and liver, 5) effect of peptides on smooth muscle tone in
the digestive tract, 6) effects of circulating hormones, and 7) effects of various
neurotransmitters (Grovum, 1987). Nerve impulses and chemical signals created by these
factors are transmitted to the hypothalamus and(or) other satiety centers of the brain to
control the initiation and termination of eating. The presence of multiple control
mechanisms implies that intake may result from the summation of several responses.
According to Illius and Jessop (1996), voluntary intake is ultimately a psychological
phenomenon. It involves integration of various signals, and is a reﬂection of the biological
system’s ﬂexibility to cope with variations in food supply, composition, and animal state
(Illius and Jessop, 1996). Forbes and Provenza (2000) further theorized that animals
integrate signals from the various visceral receptors, adipose tissue, social stimuli, and
environmental factors, to generate a signal of total ‘discomfort’. The animal then adjusts
its DMI in attempt to minimize this discomfort.

The majority of research elucidating intake mechanisms has evaluated factors
separately. There have been several studies, however, that have evaluated multiple factors
affecting intake simultaneously, to determine possible synergy between factors. Adams
and Forbes (1981) found that sodium acetate infusion into the rumen of sheep depressed
intake by 12%, and a balloon in the rumen inﬂated with 1 L of water reduced intake by

18%. A combination of these two factors was apparently additive and depressed intake by

13

50%. In studies using dairy cattle, Anil et al. (1987) and Mbanya et a1. (1993) reported
that intake depressions from ruminal distension (balloon inﬂated with water) and the
addition of VFA (either sodium acetate or sodium propionate) had either slight or non-
signiﬁcant affects alone, but in combination, resulted in a signiﬁcant reduction in intake.

Because factors regulating intake in ruminants are not completely understood,
many of the models predicting intake are empirical by nature rather than being
mechanistic. There are numerous equations that predict voluntary intake of beef cattle.
Intake has been found to be a ﬁinction of body weight (Fox and Black, 1984),
metabolizable energy (ARC, 1980), net energy of maintenance (N Em; NRC, 1984, 1996),
and dietary concentration of crude protein, ADF, and total digestible nutrients (Moore and
Kunkle, 1999). The equations used by the NRC (1996) describe DMI as a function of
dietary NE,n concentration, with adjustments for body fat, breed (beef vs Holstein or
Holstein X beef), feed additives (monensin), temperature, and mud. The base equation for
growing calves is:

DM] = (SBWO'75 * (0.2435 NE,n - 0.0466 NE",2 - 0.1128))/NEm
and for growing yearlings is:

DMI = (SBWO'75 * (0.2435 NEm - 0.0466 NE",2 - 0.0869))/NEm
where:

DM] is dry matter intake in kg/d,

SBW is shrunk body wieght in kg, and

NEm is net energy value of diet for maintenance in Mcal/kg.
These intake equations do not account for all the interactions between physiological,

environmental, and management factors that regulate intake. However, the NRC (1996)

14

demonstrated during validation, that the growing calf equation accounted for 76.5% of the
variation with a bias of only +0.16% for a data set containing the middle to upper range of
dietary NEm concentrations (Cornell data set), and 79.3% of the variation with a bias of
only -0.49% for a data set containing the lower to middle range of dietary NEm
concentrations (Guelph data set). However, this same growing calf equation accounted
for only 30.8% of the variation with a bias of -8.4% for a data set containing cattle fed all-
forage diets (Alberta data set). The NRC (1996) subcommittee stated that no single,
general equation can be applied in all production situations, and thereby recommend that
beef cattle producers should develop intake prediction equations speciﬁc to given
production situations. Such equations should account for a greater percentage of the

variation in intake than would be possible with a generalized equation.

Fiber digestibility

Ruminants have evolved the ability to utilize forage as their sole source of
nutrients (Hoﬁnann, 1988). Forages remain an important feedstuff in ruminant animal
productions systems within the United States, even though modern agricultural practices
utilize substantial quantities of concentrate feeds in diets fed to both beef and dairy cattle
(Jung and Allen, 1995). Forages alone may not meet the energy requirements of high
producing dairy cows or rapidly growing steers (Galyean and Goetsch, 1993), therefore
the quality of forage used in these production systemsis of great importance when feeding
high forage diets. According to Nelson and Moser (1994), forage quality is mainly
considered in terms of plant factors affecting availability and digestibility of forage

produced. Forage cell wall fractions have been implicated as a control mechanism for

15

forage intake (Waldo, 1986). Concentration and digestibility of cell walls potentially limits
intake and energy availability of forage crops in both beef and dairy production systems
(Jung and Allen, 1995). Oba and Allen (1999) evaluated the effects of the digestibility of
NDF from forage on performance of dairy cows using treatment means across 13 sets of
forage comparisons reported in the literature. They concluded that enhanced NDF
digestibility of forage signiﬁcantly increases DMI and milk yield. They ﬁirther reported
that for every one-unit increase in NDF digestibility in vitro or in situ, DMI was increased
by 0.17 kg/d and 4% fat corrected milk was improved by 0.25 kg/d (Oba and Allen,
1999b). Buxton and Fales (1994), stated that no single factor impacts forage quality more
than plant maturity.

The maturation of plant cells has been discussed in great detail in several reviews
(Hatﬁeld, 1993; Jung and Deetz, 1993; Moore and Hatﬁeld, 1994; Jung and Allen, 1995).
During the ﬁrst stages of plant cell wall growth and development, the primary wall
increases in size through elongation. The primary cell wall is composed of a composite of
polysaccharides, proteins, and phenolic acids. Pectins, xylans, and cellulose are all
deposited during primary growth, however, during this phase of growth no lignin is
deposited (Jung and Allen, 1995). During the second phase, when cell elongation has
ceased, the plant cell switches to secondary wall thickening. The cell wall becomes
progressively thicker as it grows towards the center of the plant cell (Bacic et al., 1988).
The polysaccharide material deposited during secondary thickening contains higher
concentrations of cellulose than xylans, and pectins are no longer added to the walls (Jung

and Allen, 1995). Lignin polymer deposition also begins with secondary wall thickening

l6

(Terashima et al., 1993), beginning at the middle lamella/primary cell wall region and
proceeding into the secondary wall (Jung and Allen, 1995).

As ligniﬁcation proceeds from the primary to the secondary cell wall, there is a
shift from guaiacyl- to syringyl-type lignin deposited (Terashima et al., 1993). In addition
to continual ligniﬁcation during secondary thickening as the plant matures, there is
incorporation of arabinoxylan ferulate esters in the primary wall which forms cross-
linkages between the xylans to lignin. The increase in lignin concentration and formation
of cross-linkages between lignin and xylans potentially reduces cell wall digestibility. Akin
and Chesson (1989) stated that lignin is the only internal chemical factor that has been
demonstrated conclusively to negatively affect the extent of cell wall polysaccharide
digestion. Merchen and Bourquin (1994) stated that the accumulation of phenolic
material on plant cell surfaces could change surface chemistry sufficiently to inhibit cell
wall digestion by ruminal microorganisms, thereby protecting the underlying cell wall from
further attack.

There are also several extramural plant factors, external to the plant cell wall, that
are detrimental to cell wall polysaccharide degradation. These factors include the cuticle,
warty layer, and middle lamella of secondary thickened cell walls (Merchen and Bourquin,
1994). Akin (1979) stated that the cuticle is indigestible, and therefore one of the primary
reasons ruminal microbes attack plant tissues at inner surfaces of broken cells. The warty
layer, which is a lining on the inner surface of ligniﬁed cell walls (Engels and Brice, 1985)
and middle lamella are probably poorly digested due to degree of ligniﬁcation within these

tissues (Engels and Schuurrnans, 1992).

17

Effect of fiber modiﬁcation on digestibility

In production systems where forage quality cannot be optimized, post-harvest
treatments to improve forage digestibility and quality may be implemented. Techniques to
modify forage digestibility include physical (e. g. grinding, pelleting and mechanical
separation of plant parts) and chemical treatments (e. g. hydrolytic and oxidative
treatments). Grinding or pelleting decreases particle size, increases surface area, and
increases bulk density of leaf and stem fractions of forages (Laredo and Minson, 1975).
Feed intake is consistently increased with grinding and pelleting. Greenhalgh and Reid
(1973) reported that intake responses to grinding were greater for sheep than cattle (45 vs
11%) and greater in young animals than in mature ones (38 vs 17%). The intake of most
ground forages generally increases with decreasing particle size and does not reach
maximum until the mean particle size is less than 1 mm (Osbourn et al., 1976). Grinding
and(or) pelleting generally reduces digestibility of the forage and the depression due to
processing increases with increasing intake (Blaxter et al., 1956). The primary reduction
in ﬁber digestion is due to shorter residence time in the gastrointestinal tract (Minson,
1963; Alwash and Thomas, 1974). The reduction in ﬁber digestibility may also be due to
a depression in ruminal pH. Fine grinding and pelleting of forages drastically reduces the
time that ruminants spend eating and ruminating (Weston and Hogan, 1967; Osuji et al.,
1975). This consequently reduces saliva production (Osuji et al., 1975; Thomson and
Beever, 1980) and decreases buffering capacity, which results in a depression in ruminal
pH and a decrease in cell wall carbohydrate fermentation (Moore, 1964; Grant and
Mertens, 1992a). The depression in digestion of grasses due to particle size reduction is

greater than that of legumes (Waldo et al., 1972). This difference may exist because

18

grasses have a higher percentage of organic matter as structural carbohydrates (Thomson
and Beever, 1980) and(or) grasses have higher concentrations of water-soluble
carbohydrates which would more drastically depress ruminal pH (Osbourn et al., 1976).

Mechanical separation of plant materials is another method of physically
processing forage in an attempt to improve quality. The simplest form involves leaf/stem
fractionation of dried forage or crop residues. More involved processes include whole
crop cereal harvesting and leaf protein concentration isolation from fresh forages. The
processes are generally quite expensive, and they may not provide economic beneﬁts
(Berger et al., 1994).

Chemical treatments using hydrolytic and oxidative agents can be used to improve
forage digestibility. Hydrolytic agents include alkali metal hydroxides (e. g. NaOH, KOH,
and Ca(OH)2 ), ammonia and urea. Sodium hydroxide is the most widely used alkali metal
hydroxide, because it is more effective in improving forage digestibility and is less
expensive when compared to KOH or Ca(OH)2 (Bass et al., 1982; Owens et al., 1984).
Alkali hydroxides improve forage digestibility by solubilizing hemicellulose, lignin and
silica, and by hydrolyzing uronic and acetic acid esters (Rexen and Thomsen, 1976;
Jackson, 1977; Klopfenstein, 1978; Chesson, 1981; Chesson et al., 1983). These
chemicals may also increase rate of hydration, which is a necessary component of
microbial degradation of ﬁber.

Ammonia and urea have similar modes of action, but are not as affective as NaOH
in improving digestibility of forage. Ammoniation of forage has been shown to reduce the
concentrations of NDF and hemicellulose, with no effect on cellulose, ADL and ADIN

(Van Soest et al., 1984). The effect of urea on ﬁber digestibility is variable and may be the

19

result of urea having to be broken down to ammonia before it becomes active (Berger et
al., 1994). Additionally, the water content of roughages, as well as temperature and
intrinsic urease activity play a role in the breakdown of urea to ammonia Williams and
Innes, 1983).

Oxidative agents actively attack and degrade a major proportion of cell wall lignin
(Chang and Allen, 1971). The net effects of oxidative agents on forage digestibility are
due to the signiﬁcant decrease in lignin content and increase in soluble carbohydrate
concentration (Ben-Ghedalia et al., 1982; Ben-Ghedalia et al., 1983). Peroxides have
similar effects on digestibility when compared to NaOH, but are more expensive (Berger
et al., 1994). Ben-Ghedalia and Shefet (1983) reported that ozone treatment makes cell
wall polysaccharides more available for digestion by microbes when compared to either
untreated or NaOH treated forage. However, ozone treatment is impractical due to
possible hazards and cost (Berger et al., 1994). Chlorine has been shown to improve ﬁber
digestion, but potentially reduces DMI by as much as 50% (Yu et al., 1975; Ford et al.,
1987). One oxidant that has shown potential for usage on residues in ruminant diets is
$0,. Sulfur dioxide-treatment of wheat straw has been shown to increase DMI, improve
ﬁber digestibility (Ben-Ghedalia and Miron, 1987), and produce comparable gains to a
barley-com based diet when fed to sheep (Ben-Ghedalia et al., 1988).

Chemical treatments have the greatest improvements on ﬁber digestibility when
used on mature ligniﬁed substrates, while reducing digestibility when used on more
immature substrates that have high contents of cell solubles (Atwell et al., 1991; Cameron

et al., 1991). They also have more inﬂuence on the digestibility of grasses as compared to

20

legumes, because grasses have a greater concentration of esteriﬁed hydroxycinnamic acids

and potentially larger number of polysaccharide-lignin cross-linkages.

Effect of the brown midrib mutation on plant composition

Eyster (1926) was one of the earliest to report a brown pigment developing in cells
in the midrib and leaf sheaths of maize (Zea mays L.). He found this characteristic to be
homozygous recessive and designated it as brown midrib (bm). Jorgenson (1931) further
observed that this pigmentation was found in the leaf midrib, stem, tassel, cob, and roots,
but he could not identiﬁed any chemical that caused this pigmentation. It was later
determined that the pigment was associated with all ligniﬁed tissues. To date, four
mutations (bmh bmz, bm3, and bm4) have been reported in maize (Neuffer et al., 1997).

Kuc and Nelson (1964), and Gee et al.. (1968) were the ﬁrst to observe that the
brown midrib mutants were associated with lower lignin content, and less
p-hydroxycinnamic acid bound to the lignin core, when compared to isogenic normal
strains. Chabbert et al. (1994) reported that bm3, when compared to isogenic normal,
reduced lignin content by 18 to 30%, and content of p-coumaric acid was reduced 40 to
51%. They did not observe any difference in content of ester-bound ferulic acid between
the two hybrids, but they found a 50% decrease in syringyl content and a slight increase in
5-OH guaiacyl residues in lignin from bm, (Chabbert et al., 1994). Grand et al. (1985)
observed that the enzyme, O-methyltransferase, was reduced ten—fold for bm3 when
compared to isogenic normal. O-methyltransferase is involved in synthesis of
methyloxylated ferulic and sinapic acids, which are precursors of guaiacyl and syringyl

units of lignin, respectively (Grand et al., 1985; Vignols et al., 1995). Therefore,

21

improvements in cell wall digestibility of bm3 could be a result of both reduction in lignin
concentration and reduction in syringyl lignin content. Normally, syringyl-type lignin is
more linear in structure and extends further into the secondary wall, thereby protecting a
greater proportion Of polysaccharides in the secondary wall from digestion compared to
guaiacyl-type lignin. With bm, lignin would be more condensed and protective of the
primary cell wall, however, the secondary cell wall would have greater potential for
degradation because of less encroachment of lignin into this region (Jung and Deetz,
1993). Muller et al. (1972) showed that the in vitro digestion rates of DM, NDF,
cellulose, and hemicellulose were faster for corn silage with bm3 compared to isogenic

normal.

Effect of the brown midrib mutation an intake and performance

Increased voluntary DMI has been observed for early (Rook et al., 1977; Block et
al., 1981) and mid to late lactation (Sommerfeldt et al., 1979; Stallings et al., 1982) dairy
cows fed bm, corn silage. In a majority of these experiments, increased DMI generally
resulted in increased milk yield and(or) greater body weight gain. Oba and Allen (1999)
reported a 9% increase in DMI and a 7% increase in milk yield when diets fed to dairy
cows contained bm, over those fed isogenic normal corn silage. Tine et al. (2001)
observed that DMI was 10.5% higher but milk yield was similar when bm, was compared
to isogenic normal in diets fed to early lactating dairy cows. Keith et al. (1981) observed
an increase in DMI when bm3 was compared with isogenic normal corn silage fed to
steers. They also reported improvements in ADG of steers fed bm, compared with

isogenic normal, but did not observe any differences in feed conversion. When steers were

22

fed a 92% corn silage diet containing bm, compared to diets using a variety of commercial
hybrids, ADG was increased (McEwen et al., 1996). McEwen et al. (1996) also reported
that feeding a bm3 corn silage diet resulted in increased feed efﬁciency compared with
diets containing corn silage from commercial hybrids.

In more recent studies, Oba and Allen (2000a, 2000b) stated that improvements in
DMI observed when feeding bm3 compared to isogenic normal hybrids may be due to
alterations in meal size and frequency in addition to the increase in passage rate. They
proposed that ﬂuctuations in ruminal pH and supply of metabolites may increase insulin
release and absorption of glucose, thereby increasing the frequency of meals and

improving DMI.

Effect of the brown midrib mutation on digestion

In previous literature, when bm3 was compared with isogenic normal corn silage,
no difference in apparent total-tract DM digestibility was observed for lactating dairy
cows (Rook et al., 1977; Sommerfeldt et al., 1979; Oba and Allen, 1999a). However, a
6.6 percentage unit improvement in DM digestibility has been reported for sheep
consuming bm3 (Stallings et al., 1982). In a study by Oba and Allen (1999), bm3 was
compared with isogenic normal corn silage diets fed to lactating dairy cows in a crossover
design. As DMI increased with bm3 compared to control, total-tract digestibility of NDF
decreased. When cows consumed similar amounts of bm3 and isogenic normal silage
diets, there was a 6 unit increase in apparent total-tract digestibility of NDF for bm3
compared with normal silage. However, this improvement in total-tract digestibility of

NDF for bm3 corn silage was diminished when DMI increased. Oba and Allen (1999)

23

explained that higher passage rate associated with increased DMI could have reduced
ruminal retention time for bm3 corn silage, which would have reduced total-tract
digestibility of NDF. In a later study, Oba and Allen (2000) observed an increase in
passage rate of NDF and a reduction in ruminal digestion rate of potentially digestible
NDF in dairy cows fed diets containing bm3 relative to isogenic normal corn silage. Rook
et al. (1977) and Sommerfeldt et al. (1979) reported no differences in energy digestibility
for dairy cows fed diets containing either bm3 or isogenic normal corn silage. Tine et a1.
(2001) found that bm, corn silage provided greater amounts of energy when fed to dry
cows at maintenance due to increased ﬁber digestibility. However, difference in energy
digestibility between bm, and isogenic normal were small when diets were fed to early
lactating dairy cows. They concluded that the increases in milk production for bm,
compared to isogenic normal in previous studies was likely due to the increases in DMI
for the bm, diet (Tine et al., 2001), which was previously pointed out by Oba and Allen
(1999)

Block et al. (1981) observed that bm3 corn silage, fed at 65% of the diet to
lactating dairy cows, decreased acetate and increased molar proportion of propionate,
when compared to isogenic normal. In contrast, Rook et al. (1977) reported no difference
in molar proportions of either acetate or propionate between bm3 and isogenic normal
when a 60% corn silage diet was fed to lactating dairy cows. However, when the
percentage of corn silage was 85%, Rook et al. (1977) did observe increases in molar
proportions of both acetate and propionate for bm3. Rook et al. (1977), Block et al.

(1981), and Oba and Allen (2000a) reported that bm3 reduced ruminal pH.

24

Fiber concentration

The NDF concentration of well-cared corn silage can range from less than 35% to
greater than 55% (NRC, 1996). As discussed previously, the concentration of cell walls
can have dramatic effects on intake as well as performance of animals. Besides modifying
the ﬁber digestibility post-harvest, the concentration of ﬁber can be changed by altering
the forage to concentrate ratio in the diet. A second method to alter ﬁber concentration
can be accomplished by selecting hybrids with different NDF concentrations. As discussed
previously, stage of maturation can also have a dramatic impact on ﬁber concentration.
With corn hybrids, as the plant matures, there is a quadratic response on ﬁber
concentration (St-Pierre et al., 1983; Bal et al., 1997). The ﬁlling of corn kernels with
starch dilutes the NDF concentration of the entire plant. Once grain ﬁlling ceases and the
corn plant continues to mature, subsequent NDF concentration increases with increasing
dry matter content (Weaver et al., 1978; St-Pierre et al., 1983). A third method to alter
ﬁber concentration of silage would be to use male-sterile corn hybrids compared to their
isogenic normal counterparts. The use of male-sterile hybrids would prevent grain ﬁlling,

therefore preventing starch from diluting the ﬁber concentration of the plant.

Effects of ﬁber concentration on intake and performance

Increasing dietary NDF concentration by increasing roughage to concentrate ratio
has been shown to depress DMI of sheep (Aitchison et al., 1986) and dairy cows (Llamas-
Lamas and Combs, 1991; Dado and Allen, 1995). This reduction is likely to occur when
intake is being controlled by physical constraints on the rumen. Decreasing dietary NDF

concentration by increasing concentrate in the diet may increase DMI if physical

25

constraints of the reticulo-rumen are limiting intake (Woody et al., 1983; Brennan et al.,
1987). However, negative associative effects may occur with increasing concentrates in
the diet, resulting in decreased ﬁber digestibility (Joanning et al., 1981; Grant and
Mertens, 1992a; Grant and Mertens, 1992b). Intake may also become controlled by
metabolic regulation with high levels of grain, resulting in decreased DMI (Muhamad et
al., 1983; Woody et al., 1983).

Selecting hybrids with different ﬁber concentrations can have varied results on
DMI and animal performance. These variations may be the result of the difference in ﬁber
concentration being confounded by the differences in cell wall digestibility between
hybrids. Orskov’s group (Orskov et al., 1988; Reid et al., 1988; Orskov et al., 1991)
found that straw produced from different barley hybrids contained different concentrations
of NDF, and those with greater NDF concentration reduced DMI and performance of
steers. In contrast, Bal et al. (2000a) found when comparing a corn hybrid (Garst 8751,
39.2% NDF) with a lower NDF corn hybrid (Cargill 3677, 32.8% NDF) that DMI was
greater for the higher NDF corn hybrid, with no effect on milk production in dairy cows.
The researchers also reported higher in situ NDF disappearance for the higher NDF corn
hybrid (Bal et al., 2000b), and they concluded that the differences in intake were not
affected by NDF content of the hybrid, but were likely the result of increased ﬁber
digestibility (Bal et al., 2000a). However, the cows in this study were in mid to late
lactation, and the high ﬁber diets contained approximately 29% NDF. Therefore, ruminal
distension might not have been the major factor controlling DMI, but intake may have

been regulated by metabolic factors. If this is true, then the higher propionate ﬂux

26

associated with the lower ﬁber corn hybrid might have been more hypophagic than the
higher ﬁber corn silage.

As discussed previously, as corn plants mature, there is a quadratic effect on ﬁber
concentration. This has resulted in observed quadratic effects on DMI with feeder heifers
(Chamberlain et al., 1971) and Holstein cows (St-Pierre et al., 1983). Intake was the
lowest when com was harvested at milk stage or when it was mature, but highest when it
was harvested at the dough stage. Chamberlain et al. (1971), also observed a depression
in ADG with the most mature corn silage. Bal et al. (1997), found that milk production
was the lowest when dairy cows were fed a diet containing corn silage from immature
corn plants. In a study using growing British breed steers, Joanning et al. (1981) observed
that feeding immature corn silage reduced daily DMI, but had no effect on steer ADG. In
contrast, Calder et al. (Calder et al., 1977) reported that stage of corn silage maturity had
no affect on either DMI or ADG of yearling Hereford steers.

In a study comparing male-sterile to its isogenic normal corn hybrid, Stake et al.
(1973) reported that steers consumed similar amounts of both silages when they received
1.81 kg/d of a protein/ grain supplement and there was no difference in crude ﬁber between
the hybrids. These researchers also reported no difference in steer ADG or efﬁciency of

gain.

Effects of ﬁber concentration on digestion and digesta characteristics
Johnson and Combs (1992) and Dado and Allen (1995) found that, when ruminal
distension was potentially limiting DMI of early lactating dairy cows, increasing dietary

NDF concentration increased digesta volume and wet weight, decreased digesta DM

27

percentage, and thus resulted in no effect on weight of digesta DM. They also reported an
increase in ruminal NDF weight (Johnson and Combs, 1992; Dado and Allen, 1995).

Dado and Allen (1995) also found, with lactating dairy cows that increasing dietary ﬁber
resulted in a faster passage rate of NDF and increased the amount of time spent
ruminating and chewing. They reported that these factors likely compensated for the
increased rumen ﬁll and helped to maintain intake (Dado and Allen, 1995).

Johnson and Combs (1992) and Dado and Allen (1995) found that increasing
dietary ﬁber concentration increased ruminal pH and acetate percentage, but reduced
propionate percentage. Improved NDF digestibility for the high ﬁber diets was likely the
result of improved conditions for ﬁber-digesting microorganisms within the
gastrointestinal tract (Woodford et al., 1986; Grant and Mertens, 1992a, 1992b). Stake et
al. (1973) reported that ruminal pH was greater, but concentration of total VFA and
percentage of acetate were not affected, for male-sterile compared to normal corn silage
fed to growing Holstein steers.

Dado and Allen (1995) found that increasing the dietary ﬁber concentration in
diets fed to dairy cows decreased the apparent total-tract digestibilities of both DM and
NDF. In previous research, when male-sterile was compared to normal corn silage in diets
fed to growing steers, total-tract digestibility of crude ﬁber was improved, but digestibility

of DM and energy were not inﬂuenced (Perry and Caldwell, 1969; Stake et al., 1973).

Rumen inert bulk
Addition of various quantities of rumen inert bulk (RIB) via permanent ruminal

cannulae has been used to investigate physical capacity of the rumen. If rumen capacity is

28

limiting intake, then decreasing volume by reducing the utilizable reticulo-rumen space by
addition of RIB should result in reduced dry matter intake. If intake is not reduced, it is

concluded that intake is being limited by some factor other than physical ﬁll.

Effects of rumen inert bulk an intake

Dado (1993) summarized 38 RIB treatments from 11 published studies, and
reported that 92% of all treatments depressed intake. Average depression in dry matter
intake was 94 :t 78 g of DM/L of RIB, with a minimum of -39 and a maximum of 300 g/L.
The sources of RIB in these studies consisted of water-ﬁlled bladders, air-ﬁlled bladders,
and polystyrene cubes. Experiments were conducted using sheep, steers, and lactating
dairy cows. Dado (1993) also performed multiple regression analysis with the data to
determine which factors signiﬁcantly (P > 0.01) contributed to the variation in intake
depression with RIB. It was concluded that 1) sheep had higher depressions compared to
cattle, 2) animals of relatively smaller body weight within a species had greater
depressions in intake, and 3) animals that tended to have higher requirements due to
physiological states (i. e. growth or lactation) had greater depressions in intake compared
to those at maintenance (Dado, 1993).

In a trial using mature steers (550 kg) fed low quality orchardgrass hay, Schettini
et al. (1999) added either 50 or 100 tennis balls, weighted to speciﬁc gravity of either 1.1
or 1.3. They concluded that both volume and weight of the RIB were capable of
depressing intake by 157 g of diet DM per L of RIB and 112 g of diet DM per kg of RIB,
respectively. Since the RIB potentially had higher speciﬁc gravity than that of hay in the

rumen, the RIB may have migrated out of the mat layer and sank. This would have

29

increased the potential for the tennis balls to migrate into the cardiac sac of the rumen and
the reticulum. As a result, the weight of the RIB in the reticulum could have altered
ruminal contractions (Kaske and Midasch, 1997) and(or) stimulated the mechanoreceptors

around the cardia (Leek, 1969), which would reduce dry matter intake.

Effects ofrumen inert bulk on digesta characteristics

When ruminal distension was potentially limiting to DMI of early lactating dairy
cows, Dado and Allen (1995) observed that RIB, when added at 25% of pre-trial digesta
volume to a diet containing 35% NDF, increased total ruminal volume (digesta + RIB) by
only 9.2%, but decreased digesta volume by 14.3% and decreased DMI. This reduction in
digesta volume suggests that the diet was potentially limiting to intake of these early
lactation dairy cows due to physical constraints on the rumen. Johnson and Combs (1991)
also found that when 25% RIB reduced DIVII of early lactation dairy cows fed diets that
contained either 26.1 or 28.5% NDF, total rumen volume increased an average of 15.2%
and digesta volume decreased an average of 7.2%. In contrast, Johnson and Combs
(1992) found that when 25% RIB did not inﬂuence DM] of late lactation dairy cows
receiving diets containing less than 33% NDF, total ruminal volume increased 18.0%, but
digesta volume was not signiﬁcantly inﬂuenced. Since digesta volume was not inﬂuenced,
this suggests that there was residual space in the rumen and the diet fed to these late
lactation cows was not limiting intake by physical ﬁll. Schettini et al. (1999) did not
report the effect of RIB on ruminal volume when beef steers were fed low quality hay
(70.3% NDF). However, they observed that addition of RIB decreased DMI and reduced

digesta wet weight. Addition of RIB to dairy cows reduced digesta wet weight (Johnson

30

and Combs, 1991; Johnson and Combs, 1992), decreased amount of digesta DM and NDF
(Johnson and Combs, 1991; Johnson and Combs, 1992; Dado and Allen, 1995), and
increased passage rate of NDF (Dado and Allen, 1995). Johnson and Combs (1992) and
Dado and Allen (1995) also found that the addition of RIB increased ruminal pH and
acetate percentage, but reduced propionate percentage. Ruminal VFA concentrations may
have been altered by RIB because of increased dilution rate of the ruminal contents,
increased rate of VFA absorption as a result of increased mixing in the rumen, and(or) by
a more rapid breakdown of ﬁbrous particles caused from mechanical action of the RIB

and(or) increased chewing.

Effects of rumen inert bulk on total-tract diet digestibility

Previous research with lactating dairy cows (Johnson and Combs 1991, 1992;
Dado and Allen 1995) and beef steers (Schettini et al., 1999) reported that RIB had no
effect on apparent total-tract digestibility of DM, NDF, or ADF, regardless of whether or
not DMI was inﬂuenced. Waybright and Varga (1991) did report reductions in total-tract
digestibility of DM, NDF, and ADF when RIB was added to sheep fed a 75% concentrate
diet. They also reported that DMI and water intake were not affected by addition of RIB.
The reduction in total-tract digestibility may have been the result of increased passage rate

of the digesta through the gastrointestinal tract (W aybright and Varga, 1991).

Effects of cattle breed on intake, performance, and maintenance requirements
As discussed previously, increasing frame size of animals can increase dry matter

intake. Frame sizes among beef breeds can vary considerably. The current NRC (1996)

31

intake prediction equations are adjusted by scaling frame sizes to an equivalent mature
weight (frame-size equivalent weight) and this adjustment should account for the
difference between beef breeds (Fox et al., 1988). However, these adjustments may not
account for the differences in intake between Holsteins and beef breeds (Fox et al., 1988).
Previous researchers have reported that Holstein and Holstein crossbred steers have 4.2 to
17.0% greater DMI when compared to British steers (Garrett, 1971; Dean et al., 1976;
Thonney et al., 1981; Fox and Black, 1984). Fox et al. (1988) suggested that, relative to
British-bred cattle, intake predictions should be increased 8% for Holsteins and 4% for
Holstein X British-breed crosses.

The inﬂuence of breed-type on ADG in previous studies has been variable. Garrett
(1971) reported no difference in ADG between Holstein and Hereford steers when they
were fed either 70% sorghum or 44% barley diets. Dean et al. (1976) found a reduction
in ADG of 0.2 to 0.4 kg/d for Holstein crossbred steers compared to British steers when
they received a 65% sorghum diet. In a more recent study, Thonney et al. (Thonney,
1987) reported that Holstein steers gained 11% faster than Angus or Hereford steers when
fed either high-moisture ear corn or corn silage based diets.

Equations by Fox and Black (1984) predict that Holstein steers require 12% more
NEm and NEg than British breed steers. These equations are based on trials from Garrett
(1971), Ayala (1974), Anrique (1976), and Crickenberger et al. (1978). In these trials,
body weight gains for Holstein and beef steers were not signiﬁcantly different. Garrett
(1971) reported that protein gain per unit of food above maintenance was almost identical
between Holstein and Hereford steers. The difference in energetic efﬁciency between the

two breeds was related to the higher fat gain for Herefords, resulting in Herefords having

32

more energy retention (Garrett, 1971). Nour et al. (1981) also observed, when comparing
steers at the same weight, that Holstein steers gained more muscle and less fat than Angus
steers. The same group of researchers reported that Holstein steers consumed 10% more
DM/d and gained 0.2 kg/d faster than Angus steers, but they did not report if there were
any differences in energetic efficiency between the two breeds (Thonney et al., 1981).
Aﬁer completing an extensive review of previous literature pertaining to the differences in
maintenance requirements among cattle of different breeds, the NRC (1996) subcommittee
generalized that in growing cattle 1) Bos indicus breeds of cattle require 10% less energy
for maintenance than beef breeds of Bos taurus cattle, with crossbreeds being
intermediate, and 2) dairy or dual-purpose breeds of Bos taurus cattle apparently require

about 20% more energy than beef breeds, with crossbreeds being intermediate.

Summary

Voluntary DMI of ruminants is controlled by physical and metabolic regulation.
Distension in the gastrointestinal tract can limit voluntary DMI of ruminant animals, and
may be the primary factor when they are fed high forage diets. Ruminal distension signals
satiety through discomfort and the animal will adjust its DMI in attempt to minimize this
discomfort. However, the reduction in DMI may reduce the supply of metabolic ﬁiels
thereby stimulating discomfort due to hunger. Determining how satiety and hunger
interact to signal discomfort is an important area for ﬁiture research. An understanding of
these interactions is necessary to more clearly deﬁne how intake of higher ﬁber diets is

regulated.

33

A knowledge of the plant factors that affect ﬁber digestibility and contribute to
intake regulation is important. This knowledge allows us to determine the optimal time to
harvest forage, select hybrids with improved digestibility, and apply post-harvesting
methods to improve ﬁber digestion. These improvements in ﬁber digestibility may not

only improve efﬁciency of forage utilization, but may also inﬂuence voluntary DMI.

34

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4s

CHAPTER 2
Brown Midrib—3 (bm3) Corn Silage Improves Digestion but not Performance of
Growing Beef Steers

Abstract

The brown midrib-3 (bm,) gene mutation has been incorporated into corn plants to
potentially improve ﬁber digestibility. The objectives of this study were to determine the
effect of bm3 corn silage on digestion and performance of growing beef steers and to
determine whether limiting intake would ﬁrrther enhance ﬁber digestibility of bm3 corn
silage. A bm3 hybrid and its isogenic normal counterpart were harvested at three-quarters
kernel milk line. Neutral detergent ﬁber, ADF, and ADL were 4.5, 6.9, and 1.9 units
lower, respectively, and DM was 5.4 units higher for bm3 than for normal silage. In Trial
1, eight ruminally ﬁstulated Angus crossbred steers (224 i: 24 kg) were randomly assigned
to a 2 X 2 factorial arrangement of treatments in a replicated 4 X 4 Latin square design.
Steers had ad libitum feed access or were restricted to 80% of ad libitum intake of diets
containing 86% normal corn silage (Control) or bm3 corn silage (BMCS). The remainder
of the diets consisted of soybean meal, urea, monensin, vitamins, and minerals. Dry matter
intake was greater (P < 0.01) for steers offered ad libitum access to BMCS than for those
with ad libitum access to the Control diet. The BMCS treatment resulted in improved (P
< 0.05) apparent total-tract digestibility of DM, OM, NDF, and ADF. Mean
concentration of total VFA and molar proportions of acetate were increased (P < 0.05) by
feeding BMCS. There tended to be a DMI X hybrid interaction (P = .16) for apparent
total-tract digestibility of NDF. When diets were offered ad libitum, BMCS increased

NDF digestibility by 10.5 percentage units compared to with Control, but, when DMI was

49

limited, BMCS increased NDF digestibility by 15.8 percentage units. In Trial 2, 128 steer
contemporaries of those used in Trial 1 (245 i 13 kg) were offered ad libitum access to
BMCS or Control diets as used in Trial 1. After a 1 12-d treatment period, concentrate in
the diet was increased, and all steers were fed a common ﬁnishing diet. During the 112-d
treatment period, steers receiving BMCS consumed 0.45 kg more DM/d (P < 0.05) and
had similar ADG (P > 0.10), compared with those steers receiving the Control silage.
This resulted in poorer (P < 0.01) feed efficiency for steers receiving BMCS. Finishing
phase and overall performance of the steers was not different (P > 0.10) due to treatment.
Although feeding BMCS in growth-phase diets resulted in increased daily DMI and
improved digestibility of DM and ﬁber, it did not result in improved steer feedlot ADG

compared with Control silage.

Introduction

Brown midrib mutations have been incorporated into corn plants to lower lignin
concentration (Kuc and Nelson, 1964) and improve ﬁber digestibility compared with
normal corn without the mutation. Muller et al. (1972) showed that the in vitro digestion
rates of DM, NDF, cellulose, and hemicellulose were faster for corn silage with the brown
midrib-3 (bm3) mutation. Increased voluntary DMI has been observed for early (Rook et
al., 1977; Block et al., 1981) and mid to late lactation (Sommerfeldt et al., 1979; Stallings
et al., 1982) dairy cows fed bm3 corn silage. In a majority of these experiments, increased
DMI generally resulted in increased milk yield and(or) greater BW gain. Oba and Allen
(1999) reported a 9% increase in DMI and a 7% increase in milk yield when diets fed to

dairy cows contained him over those fed isogenic normal corn silage.

50

High levels of corn silage are often fed during the growth phase of beef cattle
feeding systems in the upper Midwest (Ritchie et al., 1992). During this phase, the extent
of ruminal ﬁll and digestibility of ﬁber may limit animal performance. Feeding corn silage
with the bm3 mutation might improve growth performance as a result of increased ﬁber
digestion and DMI.

Limit-feeding of a high roughage diet has been shown to improve total-tract
digestibility of NDF in sheep (Colucci et al., 1989) and cattle (Colucci et al., 1989;
Murphy et al., 1994). Oba and Allen (1999) reported a negative relationship between
difference in NDF digestibility and difference in DMI for brn3 and isogenic normal corn
silage, for lactating dairy cows. Therefore, the objectives of this study were to determine
the effects of bm3 corn silage on ﬁber digestibility, voluntary DMI, growth, and feed
efficiency of weanling beef steers and to determine whether limiting intake would ﬁrrther

enhance ﬁber digestibility of the bot, corn silage.

Materials and Methods

A com hybrid containing bm3 (F657, Cargill Hybrid Seeds, Minneapolis, MN) and
the same hybrid without the mutation (isogenic normal; 6208, Cargill Hybrid Seeds), were
grown in adjoining 14.6-ha ﬁeld plots at Michigan State University, East Lansing. Both
hybrids were seeded on the same day in 76.2-cm rows to achieve a population of 69,200
seeds per hectare. As the corn approached maturity, DM for each hybrid was determined
every third day to estimate desired time of harvest. Immediately before harvest, estimates
of plant population were determined for each hybrid by counting the number of plants

found in 5.3 m of a row, in 10 randomly selected sites. Four plants from each site were

51

weighed, chopped (Mighty Mac, Amerind MacKissic Inc., Parker Ford, PA), and DM was
determined by oven drying at 57°C. An estimate of DM yield per hectare was determined
by multiplying the plant population estimate by the plant DM weight. The two ﬁeld plots
were harvested with a three-row silage chopper (Model 900, New Holland North America
Inc, New Holland, PA) set at 9.5-mm theoretical cut length, and ensiled in adjacent ISO-T
concrete bunker silos at the Michigan State University Beef Cattle Teaching and Research
Center. Samples from every fourth silage load were collected, frozen immediately at -
20°C, and analyzed for CP by macro-Kjeldahl N (AOAC, 1984) before formulating the
experimental diets. Post-ensiled nutrient composition and fermentation characteristics of

the silages are presented in Table 2-1.

Trial 1

Eight Angus crossbred steers (224 i 24 kg) were surgically ﬁtted with 7.5-cm i.d.
ruminal cannulas (Model 4C, Bar Diamond Inc., Parma, ID) 4 wk before the start of the
trial. Eighteen days after surgery, cannulas were replaced with lO-cm i.d. ruminal
cannulas (Model 2C, Bar Diamond Inc). At this time, steers were weighed and moved to
individual metabolism stalls for acclimation. Steers had ad libitum access to water and a
common corn silage diet (Table 2-2). Corn silage was the primary dietary ingredient, with
soybean meal and supplement added to meet or exceed requirements for metabolizable
protein, minerals, and vitamins (NRC, 1996). Feed ‘offered and I'CfUSCd was recorded
daily, and, when DMI reached a plateau (< 5% difference in DMI for 4 (1), DM] as a

percentage of body weight was calculated.

52

After acclimation, a 2 X 2 factorial arrangement of treatments was applied to a
replicated 4 X 4 Latin square design balanced for carryover effects. Treatment periods
were 21 d (14 d of adaptation and 7 d of collection). Treatment diets contained corn
silage from a normal corn hybrid (Control) or the same hybrid with the brown midrib-3
mutation (BMCS; Table 2-2). The two diets were offered ad libitum or limited to 80% of
ad libitum normal DMI. Preceding each period, steers were weighed, and ad libitum DMI
as a percentage of body weight was estimated from DMI determined during acclimation.
Treatments with limited DMI were fed 80% of this ad libitum DMI estimate. This
procedure adjusted DMI for increasing BW during the 84-d trial.

Diets were mixed daily and fed at 1400, 2200, and 0600 the following day.
Amounts fed and reﬁised were recorded daily. Representative samples of complete mixed
diets, individual ingredients, and orts were taken at each feeding on d 14 through 21 of
each period and frozen immediately at -20°C.

Fecal output was determined using total fecal collection on d 15 through 18 of
each period. Fecal collection bags were placed on each steer at 1400 on collection days.
Accumulated feces were removed and weighed at each 24-h interval for the 4 d. A 0.5-kg
representative sample was frozen at -20°C until analysis.

Five subsamples of whole ruminal contents from representative areas of the rumen
were collected and composited every hour for 8 h starting at 0600 on d 15, 1400 on d 16,
and 2200 on d 17, to represent an entire 24-h period. Fluid was separated from the
particulate fraction by squeezing through four layers of cheesecloth. Ruminal ﬂuid pH

was determined immediately after collection. A 50-mL aliquot was frozen immediately at

53

-20°C for later analysis of VFA. An additional 50-mL aliquot was acidiﬁed with 1 mL of
6 N HCl and frozen at -20°C for later analysis of ruminal ammonia N concentration.
Total ruminal contents were removed at 1000 on d 19 and 1800 on d 21 of each
period to determine ruminal volume and passage rate. Each animal’s digesta was
removed and placed in a 114-L open barrel. Ruminal content was weighed, and volume
was determined. A 2.7-kg subsample was collected, and digesta were replaced. The
subsample was frozen immediately at -20°C for later determination of indigestible NDF

COIIICIII.

Trial 2

One hundred twenty-eight weanling Angus crossbred beef steers (245 i 13 kg)
were used to determine the effects of feeding bm3 corn silage on growth performance.
Steers were blocked by weight and randomly assigned to eight replications of two dietary
treatments with eight animals per pen (4.3 X 13.1 m, partially covered). Steers were fed
once daily and had ad libitum access to Control and BMCS diets, as used in Trial 1, for
112 (1. After this time, the percentage of concentrate in the diet was increased stepwise
(four diets over 16 (1) until steers were adapted to a common ﬁnishing diet that contained
15% normal corn silage (Table 2-2). Orts were weighed every 28 (1 during the entire
feeding period. Complete mixed diets and individual feedstuffs were sampled every 15 d
and frozen at -20°C until analysis. Steer weights at 0, 112, and 200 d were the average of
full weights taken on two consecutive days. Steers were implanted at d 0 and 112 with
200 mg of progesterone and 20 mg of estradiol benzoate (IMPLUS-S, Upjohn Co.,

Kalamazoo, MI ). Estimates of 5c. fat thickness and longissimus muscle area were

54

determined at d 0 and 112 using real-time ultrasound (Model SLC 200V Pie Medical,
Classic Medical Supply Inc., Tequesta, FL) between the 12th and 13th rib. All steers were
harvested at a commercial packing plant (Moyer Packing Co., Souderton, PA) on d 202 of
the trial. Carcass measurements were recorded after a 48-h chill.

For both trials, experimental and surgical procedures were conducted according to
those approved by the Michigan State University All University Committee on Animal Use

and Care (AUF No. 07/97-093-00).

Sample Analysis

Feed and fecal samples were dried at 57°C and ground through a Wiley mill
(Arthur H. Thomas, Philadelphia, PA) equipped with a 1-mm screen. Samples of rations
and individual feedstuffs were composited for each period, and fecal samples were
composited by animal for each period. Samples were then analyzed for DM, OM
(Goering and Van Soest, 1970), NDF, ADF, and ADL (Van Soest et al., 1991; method A
for NDF). Neutral detergent ﬁber, ADF, and ADL were corrected for ash. Feed samples
were analyzed for CP by macro-Kjeldahl N (AOAC, 1984). Feed and fecal starch were
measured by an enzymatic method (Karkalas, 1985) using a spectrophotometer (Spectra
Max 190, Molecular Device Corp, Sunnyvale, CA) after samples were gelatinized with
sodium hydroxide. Gross energy was determined for both feed and fecal samples by bomb
calorimetry (1241 Adiabatic Calorimeter, Parr Instruments, Moline, IL; AOAC, 1984).
Digestible energy was determined as the difference between intake of diet gross energy
and output of fecal gross energy. Concentration of ME, NE“, and NEg in the diets were

calculated from DE using NRC (1996) equations.

55

Ruminal VFA samples were allowed to thaw completely at room temperature (22
°C) before analysis. Samples were then mixed thoroughly, and S-mL subsamples were
transferred to high-speed centriﬁrge tubes. Samples were then acidiﬁed (pH < 3) with 90
uL of 12 N H280,” vortexed, and centriﬁrged (Model J2-21, Beckman Instruments Inc.,
Arlington Heights, IL) at 26,000 X g for 30 min. Concentrations of VFA in the supernate
were then determined by HPLC (Waters 410 Differential Refractometer, Millipore Corp,
Milford, MA) using an organic acid analysis column (300 mm X 7.8 mm id; AMINEX
HPX 87H Ion Exchange, Bio-Rad Laboratories, Hercules, CA) and 0.005 M H280, at 0.6
mL-min'l as the mobile phase.

Silage samples were allowed to thaw completely at room temperature before
analysis. A 50-g subsample of silage plus 450 mL of distilled water were blended (Model
STO-3 500, STOMACHER Lab-Blender, Teckmar, Cincinnati, OH) for 5 min. Samples
were strained through four layers of cheesecloth, and pH was determined. Five milliliters
of solution was transferred to a high-speed centrifuge tube and acidiﬁed (pH < 3) with 90
uL of 12 N HZSO4 and centrifuged at 26,000 X g for 30 min. Concentrations of VFA in
the supernate were determined by HPLC.

Ruminal samples were thawed completely at 22°C, mixed, and S-mL subsamples
were transferred to high-speed centrifuge tubes. Samples were then centriﬁiged at 26,000
X g for 30 min. Ruminal ammonia N concentrations were determined using a
spectrophotometer (Model DU 7400, Beckman Instruments Inc., Schaumburg, IL)
following the procedure described by Chaney and Marbach (1962).

Indigestible residues in feed and ruminal contents were determined using 120-h in

vitro digestion according to procedures described by Dado and Allen (1995). Passage rate

56

of indigestible NDF from the rumen (k1,) was determined by dividing the rate of
indigestible NDF intake by the indigestible NDF pool size, based on the two-pool, ﬁrst-
order model of rumen ﬁber digestion (Waldo et al., 1972). Ruminal NDF turnover time
was determined by dividing ruminal NDF pool size by NDF intake per hour. These
calculations assume that ruminal NDF pool sizes and ﬂuxes are at steady state, and that

120-h in vitro indigestible NDF is an accurate measure of indigestible ﬁber in vivo.

Statistical Analysis

Intake, digestibility, VFA, digesta characteristics, and kinetic data for Trial 1 were
analyzed using the Mixed Models procedure (SAS, 1996) as a 2 X 2 factorial arrangement
of treatments. Compound symmetry was determined as the most appropriate covariance
structure using the Schwarz Bayesian criterion (Littell et al., 1998). The model contained
animal as a random effect and period, DMI level, hybrid, and DMI X hybrid as ﬁxed
effects. Interactions were considered signiﬁcant at P < 0.10. In Trial 1, one steer that had
ad libitum access to BMCS would not consume expected DMI of feed prior to collection
for reasons unrelated to treatment. Therefore, data were omitted for this steer during that
period. Due to the unbalanced design, data are presented as least squares means.

Ruminal pH and NH3 N data for Trial 1 were analyzed using the Mixed Models
procedure (SAS, 1996) as a 2 X 2 factorial arrangement of treatments with repeated
measures over time. The covariance structure using unstructured correlation for period
and autoregressive correlation for time was determined to be the most appropriate

according to the Schwarz Bayesian criterion (Littell et al., 1998). The model contained

57

animal as a random effect and period, DMI level, hybrid, time, and their 2- and 3-way
interactions as ﬁxed effects. Interactions were considered signiﬁcant at P < 0.10.

Data for Trial 2 were analyzed using the Mixed Models procedure (SAS, 1996) as
a randomized complete block design using pen as the experimental unit. The model
statement contained ADG, DMI, feed efﬁciency, and ultrasound data as the dependent
variables and weight-block and treatment as the independent variables. Carcass data for
19 steers in Trial 2 were not obtained at the packing plant. Treatment effects for all data

were considered different at a signiﬁcance level of P < 0.05.

Results and Discussion

Isogenic normal corn was harvested 140 (1 following planting and was 4
percentage units higher in DM than the bm3 at this time. The brn3 corn was harvested 147
(1 following planting. Both hybrids were ensiled at three-fourths kernel milk line, but the
DM concentration was greater for bm3 than isogenic normal (Table 2-1). Previous
literature indicates that adding the bin, mutation to corn results in slower growth (Miller
and Geadelmann, 1983), delayed silking (Miller et al., 1983; Weller et al., 1985), and
slower grain ﬁlling (Miller and Geadelmann, 1983), which may delay maturity by 7 to 14 d
(Weller et al., 1985). Allen et al. (1997) compared 14 bm3 corn hybrids with their
respective isogenic normal counterparts and determined, that when the hybrids were
harvested on the same date, the bm3 hybrids were 3 percentage units lower in DM. In the
current research, the percentage of CP was similar between the two hybrids. There was
6.3% more starch in the bin, corn silage compared with the isogenic normal corn silage.

Neutral detergent ﬁber, ADF, and ADL were 4.5, 6.9, and 1.9 units lower, respectively,

58

for bat, than for isogenic normal. Oba and Allen (1999) observed reductions of 1.8, 1.3,

and 0.8 units in NDF, ADF, and lignin for bm3 corn silage.

Trial 1

Steers with ad libitum access to BMCS had a higher (P < 0.01) daily DMI than
steers with access to Control silage. This increase in DMI could be partially due to the
lower NDF concentration and(or) increased NDF digestibility of BMCS. Oba and Allen
(1999) reported a 9% increase in DMI when dairy cows received bm3 corn silage
compared with normal and attributed much of this increase to bm3 silage being more
readily degraded in the rumen and having a faster passage rate.

Digestibility of DM and OM was improved (P < 0.05) by feeding BMCS
compared with Control silage. The higher DM digestibility for BMCS could be due to the
higher ﬁber digestibility and(or) the higher starch content in the diet. In previous
literature, when brn3 was compared with isogenic normal corn silage, no difference in
apparent total-tract DM digestibility was observed for lactating dairy cows (Rook et al.,
1977; Sommerfeldt et al., 1979; Oba and Allen, 1999); however, a 6.6 percentage unit
improvement in DM digestibility has been reported for sheep (Stallings et al., 1982).

There was a trend for a DMI level X hybrid interaction (P s 0.16) for apparent
total-tract digestibility of NDF and ADF (Table 2-3). The magnitude of improvement in
total-tract digestibility of NDF and ADF by feeding BMCS was dependent on DMI level.
When BMCS. was compared with Control at ad libitum intakes, there were 10.5 and 9.4
percentage unit improvements in total-tract digestibility of NDF and ADF, respectively.

When intake was held constant between the two hybrids by limiting DMI, feeding BMCS

59

resulted in 15.8 and 15.4 percentage unit improvements in total-tract digestibility of NDF
and ADF, respectively. Similar results were reported by Oba and Allen (1999), when brn3
was compared with isogenic normal corn silage diets fed to lactating dairy cows in a
crossover design. In that study, as DMI increased with bm3 compared with control, total-
tract digestibility of NDF decreased. When cows consumed similar amounts of bm3 and
isogenic normal silage diets, there was a 6 unit increase in apparent total-tract digestibility
of NDF for bm3 compared with normal silage. However, this improvement in total-tract
digestibility of NDF for brn3 corn silage was diminished when DMI was increased. Oba
and Allen (1999) explained that higher passage rate associated with increased DMI could
have reduced ruminal retention time for bm3 corn silage, which should have reduced total-
tract digestibility of NDF. Differences in apparent total-tract digestibility of NDF and
ADF in the current trial can be explained in a similar manner. Limiting intake would have
decreased passage rate and increased the ruminal retention time of the bm3 corn silage,
allowing a greater extent of fermentation in the rumen. Murphy et al. (1994) reported
that, for every l-kg reduction in DMI below ad libitum for steers fed corn silage-based
diets, total-tract digestibility of NDF increased 4.1 units.

Apparent total-tract digestibility of starch was not affected (P > 0.20) by either
hybrid or level of intake (Table 2-3). Oba and Allen (1999) also reported no difference in
total-tract starch digestibility when either bm3 or the same hybrid without the mutation
was fed to lactating dairy cows. Murphy et al. ( 1994) observed that reducing DMI from
ad libitum to 80% of ad libitum did not inﬂuence total-tract starch digestibility.

Gross energy digestibility tended to be improved (P = 0.07) by feeding BMCS

compared with Control (Table 2-3). With a 10.5 percentage unit greater apparent total-

60

tract digestibility of NDF for BMCS than for Control silage and similar starch digestibility,
GE digestibility would be predicted to be higher. The reason for lack of a signiﬁcant
increase in GE digestibility is not known but may be due to a decreased protein
digestibility of BMCS. Rook et al. (1977) and Sommerfeldt et al. (1979) reported no
differences in energy digestibility for dairy cows fed diets containing either bm3 or isogenic
normal corn silage. In the current study, the increased DMI and total-tract digestibility of
energy by steers offered ad libitum intake of BMCS resulted in increased (P < 0.05)
digestible energy intake for BMCS compared with Control silage.

Ruminal digesta characteristics and passage rate data are presented in Table 2-4.
There were DMI level X hybrid interactions (P < 0.10) for digesta dry weight, digesta
volume, percentage of ruminal NDF, and ruminal NDF turnover time. When steers had ad
libitum access to BMCS and Control silage, digesta dry weight and digesta volume were
increased by 5.2 and 4.1%, respectively. However, when intake was held constant by
restricting DMI, feeding BMCS resulted in digesta dry weight and digesta volume being
decreased by 7.7 and 7.0%, respectively. Ruminal NDF turnover time was 9% slower for
ad libitum Control silage than for ad libitum BMCS. When intake was restricted, ruminal
NDF turnover time was 23% slower for Control silage than for BMCS. Ruminal NDF
turnover time for BMCS was similar (P > 0.20) when diets were fed at either DMI level.
Ruminal passage rate of indigestible NDF was reduced (P < 0.01) by restriction of DMI
but was not signiﬁcantly affected by hybrid. The faster passage rate and similar turnover
time for ad libitum BMCS than for limited BMCS suggests that digestion rate of BMCS
was reduced by increasing DMI. Similar results were reported by Oba and Allen (2000),

who observed an increase in passage rate ofNDF and a reduction in digestion rate of

61

potentially digestible NDF when bm3 relative to isogenic normal corn silage was fed to
dairy cows,

Hybrid did not signiﬁcantly inﬂuence ruminal pH (P > 0.10). There was a time X
DMI interaction (P < 0.001) for ruminal pH. Therefore, ruminal pH data are presented as
treatment least squares means over time after initial feeding (Figure 2-1). Ruminal pH
reached the lowest point approximately 3 h after each feeding for both limit-fed treatments
and then increased until the next feeding. Ruminal pH for steers receiving the limited diets
continued this cyclic pattern for each additional feeding. Steers offered ad libitum access
had decreasing ruminal pH from initial feeding until approximately 4 to 6 h aﬁer feeding.
Aﬁer this time, ruminal pH remained fairly constant with only slight ﬂuctuations when
additional feed was offered. The limited intake steers consumed all of their allotted feed
rapidly at each of the feeding times, which would supply a large amount of fermentable
substrate to the ruminal microbes in a short period of time, explaining the cyclic pattern
for ruminal pH. Steers receiving the diets at ad libitum intakes were observed to consume
feed throughout the period, which would result in a more constant pool of fermentable
substrate in the rumen and a more consistent pH. A pattern in ruminal pH similar to the
ad libitum treatments was observed by Rook et al. (1977), who reported that ruminal pH
reached the lowest point approximately 4 h after feeding and then increased until the next
feeding when an 85% corn silage diet was offered at ad libitum to lactating dairy cows. In
contrast to these results, Rook et al. (1977) and Block et al. (1981) reported lower
ruminal pH when bm3 was compared to isogenic normal corn silage diets offered ad

libitum to dairy cows.

62

Ruminal ammonia data are presented in Figure 2-2 as treatment least squares
means over time after initial feeding, because of the time X DMI X hybrid interaction (P <
0.05). Ruminal ammonia followed a cyclic pattern over the 24-h period for all treatments.
In all four treatments, NH, N peaked approximately 1 h after each of the three feeding
times. Limit-feeding resulted in higher (P < 0.05) NH, N at each of the peaks compared
with ad libitum feeding. After reaching the peak, NH, N in both limit-fed treatments
reached the lowest point approximately 4 h after feeding. Ruminal ammonia concentration
in steers offered diets ad libitum declined more slowly and did not reach the lowest point
until after 4 h after feeding. Murphy et al. (1994) found that restricting intake of steers
fed a 7 5% corn silage diet resulted in higher peak conCentrations of NH, N when
compared with ad libitum DMI. In that study, the diets were balanced to contain similar
daily intakes of CP by adding higher concentrations of soybean meal and urea to the limit-
fed diets. As a result, steers receiving the limit-fed diets consumed more total protein
shortly after feeding, resulting in a higher NH, N peak (Murphy et al., 1994). In the
present study, even though the diets were balanced to contain similar concentrations of
protein, the higher NH, N peak for steers receiving the limited intake diets could be
explained in a similar manner. The feed-restricted steers probably consumed a larger
initial meal size, which could be the cause of higher NH, N peak.

Steers with ad libitum access to Control silage had signiﬁcantly higher NH, N
concentration than those receiving ad libitum BMCS at l h after initial feeding. Limit-fed
Control silage- and BMCS-fed steers had similar NH, N at l h after initial feeding. At 2
and 3 h after initial feeding, NH, N was higher (P < 0.05) for limit-fed Control steers than

for limit-fed BMCS steers. The two treatments remained similar from 4 h after initial

63

feeding until additional feed was offered, at which time limit-fed Control steers again had
higher concentrations NH, N after feeding. Murphy et al. (1994) observed that, as time
after feeding increased, NH, N concentration of steers fed restricted intakes increased
compared with steers offered ad libitum intakes. They explained that this could be from
lack of NH, N assimilation into microbial protein as a result of decreased availability of
fermentable substrate. In the present study, differences in ruminal ammonia
concentrations between the limit-fed treatments could be due to an increase in availability
of fermentable substrate for BMCS compared with Control silage. The lower
concentration of NH, N caused by ad libitum BMCS compared to ad libitum Control
silage could have resulted from an increased availability of fermentable substrate, a smaller
initial meal size, faster liquid passage rate, lower protein digestibility, or any combination
of these factors. When bm, was compared with isogenic normal corn silage in lactating
dairy rations, no differences in NH, N were observed (Rook et al., 1977; Sommerfeldt et
al., 1979; Block et al., 1981).

There was trend for a DMI level X hybrid interaction (P < 0.15) for total VFA
concentration, and there was a DMI level X hybrid interaction (P < 0.10) for molar
proportions of butyrate (Table 2-5). Steers with ad libitum access to BMCS had the
highest (P < 0.05) concentration of total VFA compared with those fed the otherthree
treatments. Total VFA were higher (P < 0.05) for ad libitum-fed Control steers than for
limit-fed Control steers. There was a hybrid effect (P < 0.001) for molar proportions of
acetate, and feeding BMCS at both DMI levels resulted in increased proportions of
acetate. Feeding BMCS did not affect (P < 0.20) molar proportions of propionate. When

bm, silage was fed to lactating dairy cows in rations containing 65% corn silage, Block et

64

al. (1981) observed an increase in molar proportion of propionate and a decrease in
acetate. Rook et al. (1977) reported no difference in molar proportions of either acetate
or propionate between bm, and isogenic normal when a 60% corn silage diet was fed to
lactating dairy cows. When the percentage of corn silage was 85%, Rook et al. (1977) did
observe increases in molar proportions of both acetate and propionate for bm,.
Restricting DMI resulted in a reduction (P < 0.01) in total VFA concentration but
increased (P < 0.01) molar proportions of acetate. Feeding both corn silage diets ad
libitum resulted in a higher (P < 0.05) proportion of propionate. Rumsey et al. (1970)
observed that increasing DMI from 0.5 to 2% of body weight for diets containing either
all-concentrate or 88% hay resulted in increased concentration of total VFA, increased
molar proportion of propionate, and decreased molar proportion of acetate. Galyean et al.
(1979) also reported that feeding an 84% concentrate diet at increasing levels from one to
two times maintenance tended to increase propionate and decrease acetate proportions.
Total VFA concentration and molar percentages of acetate, propionate and butyrate over

time, for this trial, are presented in APPENDIX A (Figures A-l to A-4, respectively).

Trial 2

Feeding BMCS compared with Control silage during the 112-d growth phase
resulted in a 0.43-kg increase in daily DMI (Table 2-6). The increase in DW for steers
receiving BMCS was consistent with the digestion trial data. Keith et al. (1981) also
observed an increase (0.47 kg/d) in DMI when bm, was compared with isogenic normal
corn silage fed to steers. When bm, was compared to isogenic normal in diets fed to

lactating dairy cows, increases in DMI ranged from 3 to 9% (Sommerfeldt et al., 1979;

65

Stallings et al., 1982; Oba and Allen, 1999). Although there were improvements in ﬁber
and energy digestibility when ﬁstulated steers received BMCS in Trial 1, ADG of feedlot
steers in Trial 2 was not inﬂuenced (P > 0.20) by hybrid. In addition, hybrid did not affect
(P > 0.20) change in so. fat thickness or longissimus muscle area (0.20 vs 0.20 cm, and
17.6 vs 18.1 cm2 for Control and BMCS, respectively). Based on energy concentration of
the diets from Trial 1 and DMI and BW from Trial 2, shrunk weight gain was predicted
(NRC, 1996) to be 0.13 kg/d greater for steers with ad libitum access to BMCS than for
Control steers. A possible explanation for the absence of observed ADG response in Trial
2 could be an increase in passage rate and a reduction in digestion rate of NDF for BMCS
by increasing DMI, as suggested by results in Trial 1. Steers in Trial 2 consumed 26%
more DM as a percentage of BW compared with cannulated steers in Trial 1 that had ad
libitum access to feed. This greater DMI in Trial 2 could have further increased passage
rate of BMCS and depressed DM digestion of BMCS, resulting in similar digestible DM
intake for both treatments. Oba and Allen (1999) observed that a large increase in DMI
resulted in lower digestibility of DM for bm, relative to isogenic normal corn silage. In the
current research, the increase in DMI and no change in ADG resulted in steers fed BMCS
having poorer (P < 0.01) feed efﬁciency. Keith et al. (1981) observed improvements in
ADG of steers fed bm, compared with isogenic normal but did not observe differences in
feed conversion. When steers were fed a 92% corn silage diet containing bm, compared
to diets using a variety of commercial hybrids, ADG was increased (McEwen et al., 1996).
McEwen et al. (1996) also reported that feeding a bm, corn silage diet resulted in
increased feed efﬁciency compared with diets containing corn silage from commercial

hybrids.

66

Average daily gain, daily DMI, and gain efﬁciency during the ﬁnishing phase and
for the entire feeding period were not different (P > 0.05 ) between steers that had either
received Control silage or BMCS during the growing period (Table 2-6). Consistent with
there being no difference in ADG over the entire feeding period, there was no difference
(P > 0.10) in ﬁnal weight between the two treatments (Table 2-6). In addition, hot
carcass weight, dressing percentage, so. fat thickness, longissimus muscle area,
percentage of kidney-pelvic-heart fat, and marbling score were not signiﬁcantly different

between BMCS and Control steers (data not shown).

Implications

Although brown midrib-3 corn silage resulted in increased feed intake and
improved digestibility of ﬁber, and was predicted to improve daily gains by 0.13 kg/d, no
improvement in average daily gain was observed in the performance trial. In addition,
poorer feed efﬁciency was observed for steers receiving brown midrib-3 corn silage in this
trial. Reasons for the discrepancy between predicted and actual daily gains are not known
and ﬁrrther research is warranted. Restricting feed intake may further improve ﬁber
digestibility of brown midrib-3 corn silage. Knowledge gained from additional trials will
be necessary for feedlot managers to make informed decisions on potential advantages or

disadvantages of producing and feeding brown midrib corn silage.

67

Tables and Figures

Table 2-1. Post-ensiled nutrient composition and fermentation characteristics of isogenic
normal and brown midrib-3 (bm,) corn hybrids

 

 

 

 

Corn hybrid
Item Isogenic normal bm,
Nutrient composition % in silage DM
DM 29.8 35.2
OM 96.3 96.6
CP 7.06 7.03
Starch 37.5 43.8
NDFal 44.0 39.5
ADFa 29.3 22.4
ADL’l 3.68 1.78
Fermentation characteristics
pH 3.66 3.79
Acetate, g/100 g DM 2.98 2.27
Propionate, g/ 100 g DM 0.37 1.00
Lactate, g/ 100 g DM 13.0 8.73

 

2'Corrected for ash.

68

Table 2-2. Ingredient and nutrient composition of isogenic normal control (Control) and
brown midrib-3 (BMCS) corn silagﬂliets fed during the growing and ﬁnishingghases

 

 

Growing dietal

Item Control BMCS Finishgg diet

Ingredient composition, % in diet DM
Isogenic corn silage 86.3 — 15.0
Brown midrib corn silage - 86.3 -
Soybean meal, 44% CP 10.38 10.38 6.25
Cracked high-moisture corn - — 76.2
Ground shelled corn 0.21 0.21 0.17
Trace-mineralized salt" 0.64 0.64 0.5
Urea 0.47 0.47 0.37
Potassium chloride 0.36 0.36 0.28
Selenium 90c 0.07 0.07 0.05
Vitamin A6 0.01 0.01 0.01
Rumensin 80c 0.02 0.02 0.02
Dicalcium phosphate 0.14 0.14 0.11
Calcium carbonate 1.41 1.41 1.11

Nutrient composition, % in diet DM
DM 35.6 43.2 64.6
OM 93.9 94.2 96.3
CP 12.9 12.9 12.7
NDFf 39.4 35.5 13.9
ADFf 26.4 20.4 7.1
ADLf 3.24 1.60 .95
Starch 33.6 39.0 53.7

 

alControl = isogenic normal corn silage diet; BMCS = brown midrib-3 corn silage
diet.

bComposition (%): NaCl, 96-98.5; Zn, >035; Mn, >02; Fe, >02; Cu, >003; l,
>0007; Co, >0005.

cComposition (%): Ca, >285; Se, 0.02.

dContains 30,000 IU of vitamin A per gram.

°Contains 176 g of monensin per kg.

fCorrected for ash.

69

Table 2-3. Dry matter intake, fecal output, apparent total-tract digestibility, and energy
concentration of isogenic normal control (Control) and brown midrib-3 (BMCS) corn
silage diets offered ad libitum or 80% of ad libitum to steers (Trial 1)

 

 

 

 

 

Ad Libitum Limited Effect," P-value

Item Control BMCS Control BMCS SEM‘I I H I X H
n 8 7 8 8
DMI, kg/d 4.44 5.06 3.49 3.50 0.214 <00] <00] <00]
Fecal output, kg/d 1.32 1.38 1.14 0.96 0.058 <00] 0.23 <001
Apparent total-tract digestibility

DM, % 70.4 73.1 67.4 72.7 1.29 0.29 0.02 0.33

OM, % DM 72.5 74.9 69.7 74.9 1.22 0.38 0.02 0.28

NDF, % DM 53.1 63.6 49.5 65.3 2.12 0.69 <0.01 0.16

ADF, % DM 56.1 65.5 52.1 67.5 2.04 0.69 <0.01 0.12

Starch, % DM 89.] 88.2 86.8 88.0 1.06 0.23 0.89 0.31

GE digestibility, % 72.1 74.1 70.7 74.0 1.22 0.58 0.07 0.61
DE intake, Mcal/d 13.7 15.6 10.5 10.9 0.79 <001 0.04 0.10
Energy concentration of dietsc

ME, McaI/kg DM 2.53 2.55 2.48 2.55 0.042 0.72 0.42 0.61

NEm, Mcal/kg DM 1.63 1.65 1.58 1.65 0.037 0.73 0.41 0.63

NEg,Mcal/ngM 1.02 1.04 0.983 1.04 0.033 0.73 0.42 0.64

 

“Standard error of the least squares mean.
bI = DMI main effect; H = hybrid main effect; I X H = DMI X hybrid interaction.
°Calculated from DE using NRC (1996) equations.

70

Table 2-4. Ruminal digesta characteristics and kinetics for steers receiving isogenic
normal control (Control) and brown midrib-3 (BMCS) corn silage diets offered ad libitum
or 80% of ad libitum (Trial 1)

 

 

 

 

Ad Libitum Limited Effect,b P-value
Item Control BMCS Control BMCS SEMa I H I X H
n l6 l4 l6 16
DM, % at 57°C 11.85 12.46 11.06 11.33 0.432 <00] 0.15 0.58
DM, kg 2.68 2.82 2.35 2.17 0.208 <0.0l 0.86 0.09
Ruminal digesta
volume, L 27.2 28.3 25.3 23.5 2.2 <00] 0.66 V 0.07
Ruminal digesta
density, kg/L 0.857 0.826 0.878 0.851 0.011 0.02 <00] 0.83
Ruminal NDF, % DM 59.5 57.2 61.0 53.9 0.88 0.29 <001 <00]
Ruminal NDF
turnover time, h 23.8 21.8 27.6 22.5 0.97 <0.01 <0.01 0.05
kp, %/hc 3.16 3.50 2.79 2.92 0.239 0.01 0.20 0.57

 

3Standard error of the least squares mean.
1’I = DMI main effect; H = hybrid main effect; I X H = DMI X hybrid interaction.
cRuminal passage rate of indigestible NDF.

71

Table 2-5. Ruminal VFA concentration for steers receiving isogenic normal control

(Control) and brown midrib-3 (BMCS) corn silage diets offered ad libitum or 80% of ad

libitum (Trial 1)

 

 

 

 

 

Ad Libitum Limited Effect," P-value
Item Control BMCS Control BMCS SEMa I H I X H
n 192 168 192 192
Total VFA, mM 105 108 103 103 2.1 <0.01 0.02 0.15
VFA, mol/100 mol
Acetate 62.7 64.5 65.4 66.2 0.45 <001 <00] 0.30
Propionate 20.8 207 19.9 19.4 0.58 0.04 0.53 0.61
Butyrate 11.5 9.8 10.0 9.7 0.43 0.03 <001 0.06
Valerate 0.53 1.07 0.51 1.10 0.07 0.95 <0.01 0.66
Branched chainc 3.06 2.74 3.04 2.61 0.14 0.56 0.01 0.64
AcetatezPropionate 3.10 3.17 3.37 3.49 0.11 0.01 0.32 0.77

 

3'Standard error of the least squares mean.
"I = DMI main effect; H = hybrid main effect; I X H = DMI X hybrid interaction.
cIsobutyrate and isovalerate.

72

Table 2-6. Performance for steers receiving isogenic normal control (Control) and brown

midrib-3 mutation (BMCS) corn silage based diets for 112 d (Trial 2)

 

 

Items Control BMCS SEM“ P-value
No. of pens 8 8
Initial wt, kg 244 246 0.06 0.15
Growing period
112-d wt, kg 359 359 2.01 0.90
ADG, kg 1.02 1.01 0.02 0.55
DMI, kg/d 7.04 7.47 0.12 0.04
Gain:Feed 0.145 0.135 0.001 <001
Subsequent ﬁnishing period
Final wt, kg 509 516 3.52 0.17
ADG, kg 1.72 1.80 0.02 0.06
DMI, kg/d 9.98 10.08 0.10 0.49
Gain:Feed 0.172 0.179 0.004 0.23
Growing and ﬁnishing period
ADG, kg 1.33 1.35 0.01 0.23
DMI, kg/d 8.35 8.63 0.08 0.06
Gain:Feed 0.159 0.157 0.002 0.52

 

3'Standard error of the mean.

73

 

 

—o—AC—A—AB--o-IC--A-LB

 

 

 

 

 

 

 

 

7.1
73 : z i '\ r".
: I .1 I ‘, 0. ﬁx
.. ' I . A. I I " \l
6.97 ‘ ' “ l 0 a
I p I “I I 0 ‘
“ '0 o .2 , l |
E. \ . ‘ \, I ." 0'
.‘s‘ 68 - -' -‘
. I
=51 1 ' - , g
m 4 A
\ i
6.7" ' \. I
a \ I
l \ I r
I ‘ / LA...
6.6“ X r
r \ I
: ‘a’
6.5 I I I l l l l I l l I l I I l I I I I l
-2 0 4 6 8 10 12 14 16 18 20 22

Tune post initial feeding, h

Figure 2-1. Effects of feeding ad libitum isogenic normal control (AC), ad libitum brown
midrib-3 (AB), limited isogenic normal control (LC), or limited brown midrib-3 (LB) corn

silage diets on ruminal pH over time (Trial 1). Feed offered at 0, 8, and 16 h. Time X
DMI interaction (P < 0.001). SEM = 0.065.

74

 

+AC+AB--o-LC--A-LB

 

 

 

 

 

 

25 a
l r. -"
- ; ‘, 2
d : \\ . ‘
20 r I \ : \.
-i :l‘“: :‘\ "
A _. |' 2'. .' \ I
“a .1 " “ I. 1 "
3’ ‘5 i -: 3 1 ‘.
z“ - .1 ‘3‘ I: A ~‘
n " . I. ‘
g : -- -: ~ 1'.
— _, ‘l ' \
.g 10 - : ‘\ 1"
E " I 1‘ \
= - . ' ‘ \
K _ i I ‘
' I
5 a \‘
V a ‘ ‘.
0.: 1A
0 l I I l I I I I l I l I I I 7 I

 

 

-2 0 2 4 6 8 10 12 14 16 18 20 22
Time post initial feeding, b

Figure 2-2. Effects of feeding ad libitum isogenic normal control (AC), ad libitum brown

midrib-3 (AB), limited isogenic normal control (LC), or limited brown midrib-3 (LB) corn
silage diets on ruminal NH, N over time (Trial 1). Feed offered at 0, 8, and 16 h. Time X
DMI X hybrid interaction (P < 0.05). SEM = 1.13.

75

Literature Cited

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forage quality and yield of corn hybrids. J. Dairy Sci. 80(Suppl. 1):157(Abstr.).

AOAC. 1984. Official Methods of Analysis. 14th ed. Association of Ofﬁcial Analytical
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Block, E., L. D. Muller, L. C. Griel, Jr., and D. L. Garwood. 1981. Brown midrib-3-com
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Chaney, A. L., and E. P. Marbach. 1962. Modiﬁed reagents for determination of urea and
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Colucci, P. E., G. K. Macleod, W. L. Grovum, L. W. Cahill, and I. McMillan. 1989.
Comparative digestion in sheep and cattle fed different forage to concentrate ratios
at high and low intakes. J. Dairy Sci. 72: 1774-1785.

Dado, R. G., and M. S. Allen. 1995. Intake limitations, feeding behavior, and rumen
function of cows challenged with rumen ﬁll from dietary ﬁber or inert bulk. J.
Dairy Sci. 78:118-133.

Galyean, M. L., D. G. Wagner, and F. N. Owens. 1979. Level of feed intake and site and
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Goering, H. K., and P. J. Van Soest. 1970. Forage ﬁber analysis (apparatus, reagents,
procedures and some applications). Agric. Handbook No. 379. ARS-USDA,
Washington, DC.

Karkalas, J. 1985. An improved enzymatic method for the determination of native and
modiﬁed starch. J. Sci. Food Agric. 36:1019-1027.

Keith, E. A., V. F. Colenbrander, T. W. Perry, and L. F. Bauman. 1981. Performance of
feedlot cattle fed brown midrib-three or normal corn silage with various levels of
additional corn grain. J. Anim. Sci. 52:8-13.

Kuc, J ., and O. E. Nelson. 1964. The abnormal lignins produced by the brown-midrib
mutants of maize. Arch. Biochem. Biophys. 105:103-113.

Littell, R. C., P. R. Henry, and C. B. Ammerman. 1998. Statistical analysis of repeated
measures data using SAS procedures. J. Anim. Sci. 76: 1216-1231.

McEwen, P. L., J. G. Buchanan-Smith, and M. G. Cameron. 1996. The inﬂuence of corn

silage hybrid variety on beef steer growth performance. Ontario Beef Res. Update
Univ of Guelph. pp43-48

76

Miller, J. E., and J. I. Geadelmann. 1983. Effect of the brown midrib-3 allele on early
vigor and growth rate of maize. Crop Sci. 23:510-513.

Miller, J. E., J. L. Geadelmann, and G. C. Marten. 1983. Effect of the brown midrib-allele
on maize silage quality and yield. Crop Sci. 23:493-496.

Muller, L. D., V. L. Lechtenberg, L. F. Bauman, R. F. Barnes, and C. L. Rhykerd. 1972.
In vivo evaluation of a brown midrib mutant of Zea mays L. J. Anim. Sci. 35:883-
889.

Murphy, T. A., S. C. Loerch, and B. A. Dehority. 1994. The inﬂuence of restricted
feeding on site and extent of digestion and ﬂow nitrogenous compounds to the
duodenum in steers. J. Anim. Sci. 72:2487-2496.

NRC. 1996. Nutrient Requirements of Beef Cattle. 7th ed. National Academy Press,
Washington, DC.

Oba, M., and M. S. Allen. 1999. Effects of brown midrib 3 mutation in corn silage on dry
matter intake and productivity of high yielding dairy cows. J. Dairy Sci. 82:135-
142.

Oba, M., and M. S. Allen. 2000. Effects of brown midrib 3 mutation in corn silage on
productivity of dairy cows fed two concentrations of dietary neutral detergent
ﬁber: 3. Digestibility and microbial efﬁciency. J. Dairy Sci. 83: 1350-1358.

Ritchie, H., R. Black, A. Booren, L. Copeland, J. Ferris, J. Lloyd, T. Louden, H. Person,
and S. Rust. 1992. Type of Farming Systems Study: Beef feedlot survey. Agric.
Exp. Station Res. Rep. 522. Michigan State University, East Lansing, MI.

Rook, J. A., L. D. Muller, and D. B. Shank. 1977. Intake and digestibility ofbrown-midrib
corn silage by lactating dairy cows. J. Dairy Sci. 60:1894-1904.

Rumsey, T. S., P. A. Putnam, J. Bond, and R. R. Oltjen. 1970. Inﬂuence of level and type
of diet on ruminal pH and VFA, respiratory rate and EKG patterns of steers. J.
Anim. Sci. 31:608-616.

SAS. 1996. SAS/STAT User's Guide (Release 6.12). SAS Inst. Inc., Cary, NC.

Sommerfeldt, J. L., D. J. Schingoethe, and L. D. Muller. 1979. Brown-midrib corn silage
for lactating dairy cows. J. Dairy Sci. 62:1611-1618.

Stallings, C. C., B. M. Donaldson, J. W. Thomas, and E. C. Rossman. 1982. In vivo

evaluation of brown-midrib corn silage by sheep and lactating dairy cows. J. Dairy
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77

Van Soest, P. J ., J. B. Robertson, and B. A. Lewis. 1991. Methods of dietary ﬁber, neutral
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Dairy Sci. 74:3583-3597.

Waldo, D. R., L. W. Smith, and E. L. Cox. 1972. Model of cellulose disappearance from
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78

CHAPTER 3

Neutral Detergent Fiber Concentration of Com Silage and Rumen Inert Bulk
Inﬂuences Dry Matter Intake and Ruminal Digesta Kinetics of Growing Steers

Abstract

The concentration of NDF in corn silage ranges from less than 35% to over 55%.
Corn silage with high NDF concentration has the potential to reduce DMI because it has a
greater ﬁlling effect in the rumen than low NDF corn silage. Our objective was to
determine if high NDF corn silage-based diets limit intake of light-weight growing steers
by challenging them with ruminal ﬁll. Eight ruminally cannulated Holstein steefs (198 :1:
13 kg) were randomly assigned to a 2 X 2 factorial arrangement of treatments in a
replicated 4 X 4 Latin square design with 16-d periods. Treatments were diets containing
corn silage from a normal hybrid (low-ﬁber; LF) or its male-sterile isogenic counterpart
(high-ﬁber; HF), offered ad libitum to steers with or without rumen inert bulk (RIB). The
LP and HF diets contained 33.8 and 50.8% dietary NDF, respectively. Rumen inert bulk
was added at 25% of pretrial ruminal volume in the form of plastic-coated tennis balls
ﬁlled with sand to achieve a speciﬁc gravity of 1.1 (7.5 L). No ﬁber level X inert bulk
interactions were detected for DMI or NDF intake (P > 0.10) suggesting that DMI was
limited by physical ﬁll at both levels of dietary ﬁber. Addition of RIB decreased DMI by
an average of 10.7%, which was 65.5 g/L of added bulk. The HF treatment depressed
DMI by an average of 15.5%, increased NDF intake 27.1%, and reduced ruminal NDF
turnover time by 21.0% compared to LP (P < 0.001) with no effect on ruminal volume or
amount of NDF in the rumen (P > 0.10). Addition of RIB also reduced ruminal NDF
turnover time and amount of NDF in the rumen (l 1.8% and 20.7%, respectively; P <

0.001) with no change in ruminal digesta volume (P > 0.10). The HP treatment decreased

79

digestibility of DM and GE (5.5 and 5.7%, respectively; P < 0.001), but increased NDF
digestibility (10.4%; P < 0.001) compared to LF. Rumen inert bulk had no effect on
digestibility of DM, NDF, or GE (P > 0.10). Results from this trial suggest that DMI of
light-weight steers receiving corn-silage based diets within a wide range of NDF
concentration might be regulated by ruminal distension and metabolic signals to maintain

the balance between satiety and hunger.

Introduction

Distension in the gastrointestinal tract can limit voluntary DMI of ruminant animals
(Baile and Forbes, 1974; Forbes, 1996). Previous researchers have examined the effect of
reticulo-rumen ﬁll on DMI by adding rumen inert bulk (RIB) to sheep (Egan, 1972;
Waybright and Varga, 1991), steers (Carr and Jacobson, 1967; Schettini et al., 1999), and
lactating dairy cows (Campling and Balch, 1961; Johnson and Combs, 1991, 1992; Dado
and Allen, 1996). A review of several studies by Dado (1993) indicated that the average
reduction in DMI, from RIB addition, was 94 g/L of RIB, and ranged from no change to a
depression in DMI of 300 g/L. The depression in intake was greatest for a) sheep, b)
animals with relatively lighter body weight within a species, and c) animals that tended to
be in physiological states with higher nutrient requirements (Dado, 1993).

Neutral detergent ﬁber is a measure of total insoluble ﬁber, and is related to the

ﬁlling effects of feeds in the rumen. Increasing the dietary NDF concentration, by
increasing roughage to concentrate ratio, depressed DMI of sheep (Aitchison et al., 1986)

and dairy cows (Llamas-Lamas and Combs, 1991; Dado and Allen, 1995). Increasing

80

dietary NDF concentration by addition of straw also reduced DM1 and performance of
steers (Orskov et al., 1988, 1991).

High levels of roughage are often fed during the growth phase of beef cattle
feeding systems in the upper Midwest, and corn silage is the primary roughage source
(Ritchie et al., 1992). Fiber concentration of corn silage can vary greatly; the average
NDF for well-cared corn silage is 46.0% with a standard deviation of 6.5% (NRC, 1996).
We hypothesized that corn silage high in NDF concentration limits DMI and animal
performance of light-weight steers fed high roughage diets. Therefore, the objective of

this trial was to determine if high NDF corn silage limits DMI by increasing ruminal ﬁll.

Materials And Methods

A com hybrid (5456, UAP Dyna-Gro, East Lansing, MI) and its male-sterile
isogenic counterpart were planted in separate ﬁelds on the same day to achieve a
population of approximately 66,700 plants/ha. The male-sterile hybrid was isolated from
all other com hybrids to prevent pollination. As the corn approached maturity, DM for
each hybrid was determined every third day to estimate the desired time of harvest. The
normal and male-sterile corn hybrids were harvested with a three-row silage chopper
(Model 900, New Holland North America Inc., New Holland, PA) set at 1.3 cm
theoretical cut length, and ensiled separately in adjacent 2.4-m dia. plastic silage bags (Ag
Bag International, Warrenton, OR) at the Michigan State University Beef Cattle Teaching
and Research Center. Before feeding, forages were analyzed for DM, NDF, CP, pH, and
VFA. Post-ensiled nutrient composition and fermentation characteristics of the silages are

presented in Table 3-1.

81

Experimental and surgical procedures in this trial were conducted according to
those approved by the Michigan State University All University Committee on Animal Use
and Care (AUF No. 07/99-089-00).

Eight Holstein steers (198 :l: 13 kg) were surgically fitted with 7.5-cm i.d. rumen
cannulas (Model 4C, Bar Diamond Inc., Parma, ID) 4 weeks before trial initiation. Eight
days aﬁer surgery, cannulas were replaced with 10-cm i.d. rumen cannulas (Model 2C,
Bar Diamond Inc.). At this time, steers were weighed and moved to individual
metabolism stalls for acclimation for 14 days. Steers had ad libitum access to water and a
common corn silage diet (Table 3-2). Corn silage from the normal (low-ﬁber) corn hybrid
was the primary dietary ingredient, with soybean meal and supplement added to meet or
exceed requirements for metabolizable protein, minerals, and vitamins (NRC, 1996). Feed
offered and reﬁrsed were recorded daily.

The eight ﬁstulated steers were assigned to duplicated 4 X 4 Latin squares
balanced for carryover effects with a 2 X 2 factorial arrangement of treatments. Steers
were randomly assigned to treatment sequences within square. Factors evaluated were
dietary NDF content and amount of rumen inert bulk. Concentrations of NDF in the diets
were 33.8% (low-ﬁber; LF) or 50.8% (high-ﬁber; HF). The amount of RIB was 0 or
25% of the average pretrial ruminal digesta volume. Pretrial ruminal digesta volume was
measured by manual evacuation of digesta. Rumen inert bulk consisted of 52 plastic-
coated tennis balls (7.5 L; 1.1 speciﬁc gravity; Schettini et al., 1999). Treatment periods
were 16 d, with 10 d for adaptation and the ﬁnal 6 d for collection.

Diets were mixed once daily and offered at 0700 and 1900 daily to allow steers ad

libitum access (210% orts) to the total mixed ration. Amounts fed and reﬁised were

82

recorded daily. Representative samples of complete mixed diets, individual ingredients,
and orts were taken at each feeding on d 10 through 16 of each period.

Fecal output was determined using total fecal collection for 4 (1 each period. Fecal
collection bags were placed on each ﬁstulated steer at 1300 on collection days starting on
d 11. Accumulated feces were removed, weighed at each 24-h interval for the 4 d, and a
0.5 kg representative sample was retained.

Four subsamples of whole ruminal contents from representative areas of the rumen
were collected and composited every 3 h for a 24-h period starting before morning feeding
on d 11. Ruminal ﬂuid was separated from the particulate fraction by squeezing through
four layers of cheesecloth. Ruminal pH was determined immediately after collection. A
45-mL aliquot of ﬂuid was frozen immediately at -20°C for later analysis of ruminal VFA.

Total ruminal contents were removed at 1300 on d 15 and 16 of each period.

Each animal’s digesta was manually removed via the cannula and placed in a 114-L barrel.
Weight and volume of the rumen contents were determined, and a l-kg subsample was
collected before replacing digesta. Immediately before digesta removal, headspace volume
in the dorsal rumen was estimated at both evacuation times by ﬁlling the space with
unweighted tennis balls of known volume. Following the evacuation on d 16, ruminal
contents including RIB were switched among steers, within each square, to assist in

adaptation to the next treatment.

Sample Analysis
Diets, individual ingredients, orts, ruminal contents, and fecal samples were dried

immediately after collection at 57°C for 72 h in a forced-air oven and analyzed for DM

83

content. All samples were ground through a Wiley mill (Arthur H. Thomas, Philadelphia,
PA) equipped with a 1-mm screen. Samples of the diets and dietary ingredients were
composited for each period, and fecal samples were composited for each animal within
period. Diets, individual ingredients, fecal, and ruminal content samples were analyzed for
percentages of NDF, ADF, ADL, indigestible NDF, and ash. Neutral detergent ﬁber,
ADF, and ADL were determined according to Van Soest et al. (1991; Method A for
NDF) and corrected for ash. Ash content was determined after 5 h of oxidation at 500°C
in a muffle furnace. Diet and individual ingredient samples were analyzed for CP by the
combustion method (AOAC, 1990; Model FP-2000, LECO, St. Joseph, MI). Free
glucose in the diets and feed ingredients was measured by an enzymatic method (Karkalas,
1985; glucose kit #510-A, Sigma Diagnostics Inc., St. Louis, MO) using a microplate
reader (Spectra Max 190, Molecular Device Corp, Sunnyvale CA) after samples were
extracted with deionized water. Starch in the diets, feed ingredients, and feces were
measured by an enzymatic method (Karkalas, 1985; glucose kit #510-A) after samples
were gelatinized with sodium hydroxide and digested with amylase (CRYSTALZYME 40
L, Vally Research Inc., South Bend, IN). Gross energy was determined for both feed and
fecal samples by bomb calorimetry (AOAC, 1990; Model 1241 Adiabatic Calorimeter,
Parr Instruments, Moline, IL). Digestible energy was determined as the difference
between intake of diet gross energy and output of fecal gross energy. Concentrations of
ME, NE“, and NEg in the diets were calculated from DE using published equations (NRC,
1996). Ruminal VFA, silage VFA, ruminal NDF turnover time, and passage rate of

indigestible NDF were determined according to procedures described by Tjardes et al.

84

(2000). The concentrations of all nutrients were expressed as percentage of DM

determined from drying at 57°C.

Statistical Analysis

Intake, digestibility, VFA, digesta characteristics, and kinetic data were analyzed
based on a mixed effects model using MIXED procedure of SAS (SAS Inst. Inc., Cary,
NC). The model contained animal as a random effect and period, ﬁber level, RIB, and
ﬁber level X RIB as ﬁxed effects. Using the Schwarz Bayesian criterion (Littell et al.,
1998), a ﬁrst-order autoregressive error structure was determined as the most appropriate
residual covariance structure for repeated measures over period within animals. Main
effects were considered signiﬁcant at P < 0.05 and two-way interactions were considered
signiﬁcant at P < 0.10. One steer that had access to the high ﬁber diet with additional RIB
would not consume the expected DMI of feed before collection. Therefore, data were
omitted for this steer during that period. Due to the unbalanced design, data are presented

as least squares means.

Results And Discussion

Normal and male-sterile hybrids were harvested 127 (1 following planting. At time
of harvest, the male-sterile hybrid had 4.8% less DM than the normal hybrid (31.5 vs
36.3% DM, respectively). The DM of silage from the male-sterile hybrid was 5.7% lower
after ensiling (Table 3-1). Stake et al. (1973) reported that the male-sterile corn silage
contained 2.0% less DM even when the male-sterile corn hybrid was harvested one week

after a regular dent corn hybrid. Perry and Caldwell, (1969) harvested a male-sterile com

85

hybrid one month after a typical dent corn hybrid and observed that the male-sterile corn
silage contained 13.2% less DM. Neither trial reported if the male-sterile and normal corn
hybrids were of similar genetics or if the hybrids required a similar number of growing
degree days for maturation.

Since the male-sterile corn hybrid was barren and devoid of grain, the male-sterile
as compared to normal corn silage had lower starch (3.3 vs 32.0%, respectively) but
greater NDF and ADF concentration (Table 3-1). The male-sterile corn silage contained
0.7% less CP than normal. Stake et al. (1973) observed no difference in crude ﬁber value
between normal and male-sterile hybrids, however, the male-sterile contained 2.4%
greater CP. Perry and Caldwell (1969) reported that both crude ﬁber and CP were higher
for male-sterile when compared to normal (30.3 vs 21.3%, and 10.9 vs 8.4%, for crude
ﬁber and CP, respectively).

Total soluble carbohydrate content of male-sterile corn hybrids ranges from 15 to
16% as compared to 8 to 10% for normal corn hybrids (Fisher and Fairey, 1979). During
the ensiling process, the soluble carbohydrates would have been readily fermented (Stake
et al., 1973). Stake et al. (1973) reported that the soluble carbohydrates would have been
transformed to lactic acid, however, they failed to report if the ethanol content of male-
sterile corn silage increased during fermentation. In the current study, the male-sterile
corn silage had greater concentrations of acetate, propionate, lactate, and ethanol as
compared to the normal corn silage (0.6, 0.3, 2.2, and 7.0%, respectively). The higher
concentration of fermentation acids resulted in the male-sterile corn silage having 0.15 unit
lower pH compared to the normal corn silage. Since the male-sterile corn silage contained

a greater concentration of ethanol, steers receiving HF would have consumed up to 350

86

mL of ethanol over the entire day. No adverse signs related to ethanol ingestion were
observed among steers. Previous research has shown that steers weighing 227 kg were
able to tolerate 140 mL of ethanol pulse dosed into the rumen, however, they exhibited
signs of intoxication when they received a pulse dose of 250 mL (Bruning and Yokoyama,
1988)

Feeding HF compared to LF resulted in an average reduction in steer DMI of 0.7
kg/d (P < 0.001; Table 3-3). Previous research has demonstrated that increased dietary
NDF by straw addition, decreased DMI of steers (Reid et al., 1988; Orskov et al., 1991).
Stake (1973) reported that steers consumed similar intakes of male-sterile and normal corn
silage when they were receiving 1.81 kg/d of a protein/ grain supplement and there was no
difference in the crude ﬁber values between the two hybrids.

Addition of RIB depressed DMI of both LF and HF diets an average of 65 g/L of
RIB (P < 0.001). Schettini et al. (1999) reported a reduction of 157 g/L of RIB when low
quality orchard grass hay (70.3% NDF) was fed to beef steers with an initial weight of 550
kg. Mowat (1963) reported a reduction of up to 112 g/L of RIB when good quality hay
(37.8% NDF) was fed to Holstein steers with an initial weight of 227 kg. Dado and Allen
(1995) reported that DMI of a 25% NDF diet fed to early lactation dairy cows (17 d
postpartum) was not affected by RIB addition, however, DMI of a 35% NDF diet was
depressed by 95 g/L of RIB. They concluded that DMI of cows receiving the high ﬁber
diet was under greater control by ruminal distension (Dado and Allen, 1995). In the
current study, the fact that RIB decreased DMI in both diets and the lack of a ﬁber level X
RIB interaction suggests that DMI was limited by physical ﬁll at both levels of dietary

ﬁber.

87

Increasing concentration of dietary ﬁber did not affect ruminal digesta volume or
wet digesta weight (P > 0.10), but decreased digesta DM percentage and weight (P <
0.05; Table 3-3). Feeding HF compared to LP increased the concentration of NDF and
indigestible NDF of the ruminal digesta (P < 0.001), however, amount of both NDF and
indigestible NDF in the rumen was not affected by ﬁber treatments (P > 0.10). Johnson
and Combs (1992) and Dado and Allen (1995), found that with early lactating dairy cows,
increasing dietary NDF concentration increased digesta volume and wet weight, decreased
digesta DM percentage, resulting in no effect on weight of digesta DM. They also
reported an increase in ruminal NDF weight when concentration of dietary NDF was
increased (Johnson and Combs, 1992; Dado and Allen, 1995). Inthese previous studies
with early lactation dairy cows, DMI of the low NDF diets was likely not regulated by
ruminal distension. When dietary NDF concentration was increased, the digesta volume
was increased and ruminal ﬁll began to limit DMI. In the current study, digesta volume
was not increased when the dietary NDF concentration was increased, suggesting that
DMI was limited by ruminal distension at both levels of dietary ﬁber.

Addition of RIB to both LF and HF, increased total ruminal volume (digesta +
RIB) by 23.2% (P < 0.01), but did not inﬂuence digesta volume (P > 0.10; Table 3-3).
The addition of RIB, increased wet weight of digesta + RIB (P < 0.01), but had no effect
on wet digesta weight alone (P > 0.10). Dado and Allen (1995) observed that when a diet
containing 35% NDF was fed to early lactating dairy cows, RIB added at 25% of pre-trial
digesta volume increased total ruminal volume by only 6.2%, but decreased digesta
volume by 16.3%. In the same trial, when the diet contained 25% NDF and 25% RIB was

added, total ruminal volume was increased by 11.3% and digesta volume was decreased

88

by 12.1% (Dado and Allen, 1995). Johnson and Combs (1991) found that when 25% RIB
reduced DMI of early lactation dairy cows fed diets that contained either 26.1 or 28.5%
NDF, total rumen volume increased an average of 15.2% and digesta volume decreased an
average of 7.2%. However, Johnson and Combs (1992) found that when 25% RIB did
not inﬂuence DMI of late lactation dairy cows, total ruminal volume increased 18.0%, but
digesta volume was not signiﬁcantly inﬂuenced. Schettini et al. (1999) did not report the
effect of RIB on ruminal volume, when beef steers were fed low quality hay (70.3%
NDF), however they observed that addition of RIB reduced digesta wet weight. The lack
of reduction in digesta volume in the current study, suggest that ruminal distension was
not the only factor regulating DMI of the LF and HF diets. The addition of the RIB is
expected to have increased stimulation of the tension receptors (Leek, 1969) contributing
to satiety. However, the reduction in DMI would have reduced the amount of absorbed
metabolic ﬁiels potentially increasing the stimulation of hunger (Illius and Jessop, 1996)
and DMI was the result of a balance between hunger and satiety (Forbes and Provenza,
2000)

Addition of RIB reduced the percentages and amounts of digesta DM, NDF, and
indigestible NDF (P < 0.01; Table 3-3). These reductions are consistent with Dado and
Allen (1995) who found that RIB not only reduced percentage DM of digesta, but also
reduced the amounts of digesta DM, NDF and indigestible NDF. Johnson and Combs
(1991, 1992) also reported that RIB reduced digesta wet weight and decreased amounts
of digesta DM and NDF.

Increasing dietary ﬁber concentration and the addition of RIB both increased

ruminal NDF turnover rate (P < 0.05). Similar results were observed by Dado and Allen

89

(1995), who found that with lactating dairy cows, passage rate of NDF was faster when
dietary ﬁber and RIB were increased. They also noted that increasing dietary ﬁber and the
addition of RIB increased the amount of time spent ruminating and chewing. Dado and
Allen (1995) reported that these factors likely compensated for the increased rumen ﬁll
and helped to maintain intake. In the current study, increased NDF turnover rate and the
faster passage rate of indigestible NDF were potentially due to the increased ruminal ﬁll
and(or) increased ruminating and chewing. However, RIB weight in the reticulum (Kaske
and Midasch, 1997) and(or) RIB stimulation of mechanoreceptors around the cardia
(Leek, 1969) may have also contributed to the faster passage rates, because a few of the
weighted tennis balls were observed to be in the reticulum during ruminal content
evacuation.

Ruminal pH, lactate, and VFA data are presented in Table 3-4. Ruminal pH was
decreased and concentrations of lactate and total VFA were increased by feeding LF
compared to HF (P < 0.05). In addition, molar percentages of propionate and butyrate
were greater and acetate was reduced for LF (P s 0.05). This was likely the result of
having greater starch content in the LF diet (Grant and Mertens, 1992b). Stake et al.
(1973) reported that ruminal pH was greater, but concentration of total VFA and
percentage of acetate were not affected for male-sterile compared to normal corn silage
fed to growing Holstein steers.

Fiber level X RIB interactions were detected for total VFA concentration, and
molar percentages of acetate and butyrate (P < 0.10). Addition of RIB to LF decreased
total VFA concentration and butyrate percentage by 10.3 and 18.3%, respectively. Total

VFA concentration and butyrate percentage were only decreased by 6.2 and 12.9% when

90

RIB was added to HF. Molar percentage of acetate was increased by 4.7 and 2.6%, when
RIB was added to LF and HF, respectively. There was no ﬁber level X RIB interaction for
molar percentage of propionate (P > 0.05). Ruminal VFA concentrations may have been
altered by RIB because of increased dilution rate of the ruminal contents, increased rate of
VFA absorption from increased mixing in the rumen, and(or) by a more rapid breakdown
of ﬁbrous particles. Similar to the current study, Johnson and Combs (1992) and Dado
and Allen (1995) found that both the addition of RIB and increasing dietary ﬁber
concentration increased ruminal pH and acetate percentage, but reduced propionate
percentage.

Feeding LF as compared to HF not only reduced ruminal pH and resulted in higher
molar percentages of propionate, but resulted in more daily variations in pH (Figure 4-1)
and percentage of propionate (Figure 4-2). Greater ﬂuctuation in ruminal pH and
percentage of propionate might indicate a more pulsatile energy supply to the blood from
the rumen. This agrees with Oba and Allen (2000) who reported that the more pulsatile
supply of energy may have increased the rate of metabolite utilization which would have
stimulated hunger sooner, shortening intermeal interval which would have the potential to
increase DMI. However, blood metabolite and feeding behavior data collected
concurrently would be necessary to conﬁrm this hypothesis. Total ruminal VFA
concentrations, molar percentages of acetate and butyrate over time, for this trial, are
presented in APPENDIX B (Figures B-l to B-3, respectively).

Addition of RIB had no effect on apparent total-tract digestibility of DM, NDF,
ADF, starch, or GE (P > 0.10; Table 3-5). Previous research with lactating dairy cows

(Johnson and Combs 1991, 1992; Dado and Allen 1995) and beef steers (Schettini et al.,

91

1999) also reported that RIB had no effect on apparent total-tract digestibility of DM,
NDF, or ADF. Waybright and Varga (1991) did report reductions in total-tract
digestibility of DM, NDF and ADF when RIB was added to sheep fed a 75% concentrate
diet. In the current study, even though there was no decrease in total-tract digestibility of
GE with the addition of RIB, the decrease in DMI resulted in there being an average
reduction in DE intake of 1.45 Mcal/d (P < 0.001).

The HF compared to the LF treatment had lower apparent total-tract digestibility
of DM and GE (P < 0.001; Table 3-5), but greater total-tract digestibility of NDF and
ADF (P < 0.01). The difference in DM and GE digestibility was primarily the result of the
male-sterile hybrid having a higher NDF and lower starch content than the normal corn
silage. Improved NDF digestibility for the HF treatment was likely the result of improved
conditions for ﬁber-digesting microorganisms within the gastrointestinal tract (W oodford
et al., 1986; Grant and Mertens, 1992a, 1992b) as suggested by the greater ruminal pH
and percentage of acetate. In previous research, when male-sterile was compared to
normal corn silage in diets fed to growing steers, crude ﬁber digestibility was improved,
but digestibility of DM and energy were not inﬂuenced (Perry and Caldwell, 1969; Stake
et al., 1973). Stake et al. ( 1973) reported no difference in ADG or efﬁciency of gain when
steers had ad libitum access to either male-sterile or a normal corn hybrid. In the current
study, increasing dietary ﬁber decreased NEm and NEg by 17.3 and 28.4%, respectively (P
< 0.001). Based on energy concentrations, feeding HF as compared to LF reduced
predicted shrunk weight gain (NRC, 1996) by 71.7% (0.15 vs 0.53 kg/d for HF and LF,
respectively). The HF treatment also had a 67.6% poorer predicted efﬁciency of gain,

when compared to LF.

92

Illius and Jessop (1996) suggested that voluntary DMI is ultimately a
psychological phenomenon, involving the integration of many metabolic signals by the
central nervous system. Forbes and Provenza (2000) ﬁirther theorized that animals
integrate signals from the various visceral receptors, adipose tissue, social stimuli, and
environmental factors, to generate a signal of total ‘discomfort’. The animal then adjusts
its DMI in attempt to minimize this discomfort. In the current study, the lack of reduction
in digesta volume with a depression in DMI as a result of RIB addition and increase of
ﬁber concentration, suggests that the steers might have regulated DMI in an attempt to
minimize discomfort. The RIB addition and increase in NDF concentration would have
distended the rumen and would have potentially increased animal discomfort. The
reduction in DMI would have reduced absorbed metabolic fuels causing increased
discomfort due to hunger. The steers might have altered meal size and inter-meal interval
in an attempt to reduce discomfort from ruminal distension, but would have attempted to
consume enough DM in order to reduce the stimulus of hunger. Feeding behavior and
blood metabolite data collected simultaneously would be necessary to conﬁrm this

hypothesis of animals eating to minimize discomfort.

Implications

Results from this study indicate that the NDF content of corn silage can limit
intake when fed to light-weight steers. The lack of reduction in digesta volume with
addition of inert ﬁll suggests that feed intake was not regulated by ruminal distension
alone. Intake regulation of corn silage diets may be the result of steers attempting to

minimize discomfort due to satiety and hunger as a result of ruminal distension and lack of

93

metabolic fuels. Further research is necessary to more directly deﬁne how the metabolic

signals interact to regulate intake of corn silage-based diets.

94

Tables and Figures

Table 3-1. Post-ensiled nutrient composition and fermentation characteristics of normal
and male-sterile corn hybrids

 

 

Corn hybrid
Item Normal Male-sterile
Nutrient composition, % in silage DMa
DM 36.7 31.0
CP 6.91 6.18
NDF" 38.6 56.7
ADF" 22.7 32.3
Starch 32.0 3.3
Fermentation characteristicsc
pH 3.61 3.46
Acetate, g/ 100 g DM 0.80 1.42
Propionate, g/ 100 g DM - 0.30
Ethanol, g/100 g DM 0.52 7.57
Lactate, g/ 100 g DM 5.67 7.88

 

“During trial analysis.
"Corrected for ash.
cPre-trial analysis.

95

Table 3-2. Ingredient and nutrient composition of normal (Low-ﬁber) and male-sterile
tHigh—ﬁber) corn silge diets

Item Low-ﬁber High-ﬁber

 

Ingredient composition, % in diet DM

Normal corn silage 87.72 —
Male-sterile corn silage - 85.76
Soybean meal, 44% CP 9.04 11.07
Ground shelled corn 0.21 0.20
Trace mineralized salt“ 0.62 0.61
Urea 0.46 0.45
Potassium chloride 0.34 0.34
Selenium 90b 0.07 0.06
Vitamin Ac 0.01 0.01
Rumensin 80d 0.02 0.02
Dicalcium phosphate 0.13 0.13
Calcium carbonate 1.37 1.34
Nutrient composition

DM, % 39.3 30.3
CP,%DM 11.4 11.2
NDF, % DMc 33.8 50.8
indigestible NDF, % NDF 43.2 36.0
ADF, % DM" 20.3 30.1
ADL, % DMc 2.07 2.72
ADL, %NDF 6.12 5.35
Starch, % DM 29.1 4.2
Free glucose, % DM 0.12 0.05

 

 

“Composition (%): NaCl, 96-985; Zn, > 0.35; Mn, > 0.2; Fe, > 0.2; Cu, > 0.03; l,
> 0.007; Co, > 0.005.

"Composition (%): Ca, > 28.5; Se, 0.02.

cContains 30,000 IU of vitamin A per gram.

dContains 176 g of monensin per kg.

6Corrected for ash.

96

Table 3-3. Dry matter intake, NDF intake, and ruminal digesta characteristics and kinetics
of normal (Low ﬁber) and male-sterile (High ﬁber) corn silage based diets with and
without rumen inert bulk (RIB)

 

 

 

 

 

Low ﬁber High ﬁber Effect", P-value

Item Control RIB Control RIB SEM“ Fiber RIB F X B
DMI, kg/d 4.92 4.47 4.23 3.70 0.14 <0.001 <0.001 0.63
NDF intake, kg/d 1.66 1.51 2.15 1.88 0.06 <0.001 <0.001 0.13
Ruminal volume, L

Digesta + RIB 28.7 35.5 29.1 35.2 2.14 0.98 <0.001 0.73

Digesta 28.7 28.0 29.1 27.6 2.14 0.98 0.29 0.73

Headspace‘ 3.22 3.88 4.24 5.58 0.52 0.02 0.08 0.28
Digesta composition

DM, % at 57°C 13.1 11.3 11.7 9.4 0.38 <0.001 <0.001 0.20

NDF, % DM 56.0 52.9 61.2 55.3 1.02 <0.001 <0.001 0.03

iNDF, % DMd 37.6 34.8 42.1 37.6 1.25 0.004 0.004 0.39
Rumen mass, kg

Wet digesta + RIB 24.3 33.3 25.9 35.1 1.84 0.03 <0.001 0.86

Wet digesta 24.3 24.4 25.9 26.3 1.84 0.03 0.71 0.86

DM 3.16 2.78 3.03 2.50 0.20 0.04 <0.001 0.42

NDF 1.78 1.46 1.84 1.41 0.13 0.92 <0.001 0.42

iNDFd 1.18 0.96 1.30 0.94 0.72 0.48 <0.001 0.24
Density, kg/L 0.85 0.88 0.89 0.95 0.01 <0.001 <0.001 0.12
iNDF kp, %/h6 2.68 2.98 2.65 3.24 0.18 0.37 0.001 0.19
Ruminal NDF
turnover time, h 25.9 23.2 20.8 18.0 1.40 <0.001 0.002 0.97

 

“Standard error of the least squares mean.

"Fiber = Fiber level main effect; RIB = rumen inert bulk main effect; F X B = Fiber
level X rumen inert bulk interaction.

CVolume of space in dosal rumen.

dIndigestible NDF.

°Passage rate of indigestible NDF.

97

Table 3-4. Ruminal pH, lactate, and VFA of normal (Low-ﬁber) and male-sterile (High-
ﬁber) corn silage-based diets with and without rumen inert bulk (RIB)

 

 

 

 

Low-ﬁber High ﬁber Effect", P-value

Item Control RIB Control RIB SEM“ Fiber RIB F X B
pH 6.43 6.56 6.72 6.74 0.08 0.003 0.20 0.38
Lactate, mM 0.70 0.60 0.47 0.41 0.11 0.02 0.38 0.84
Total VFA, mM 112.6 101.0 94.2 88.4 3.2 <0.001 <0.001 0.01
VFA, mol/ 100 mol

Acetate 62.1 65.0 68.7 70.5 0.4 <0.001 <0.001 0.03

Propionate 23.8 22.7 18.5 18.0 0.5 <0.001 0.05 0.41

Butyrate 10.30 8.41 9.39 8.18 0.33 0.05 <0.001 0.06

Valerate 0.96 1.12 0.93 0.99 0.04 0.02 0.001 0.03

Isobutyrate 1.04 1.12 0.88 0.89 0.03 <0.001 0.05 0.11

Isovalerate 1.92 1.72 1.55 1.48 0.14 0.002 0.16 <0.001

 

“Standard error of the least squares mean.

"Fiber = ﬁber level main effect; RIB = rumen inert bulk main effect; F X B = ﬁber

level X rumen inert bulk interaction.

98

Table 3-5. Apparent total tract digestibility, and energy concentration of normal (Low
ﬁber) and male-sterile (High ﬁber) corn silage based diets with and without rumen inert
bulk (RIB)

 

 

 

 

 

Low ﬁber High ﬁber Effect", P-value

Item Control RIB Control RIB SEM“ Fiber RIB F X B
Apparent total tract digestibility

DM, % 70.1 69.6 65.6 63.2 0.87 <0.001 0.12 0.27

NDF, % DM 47.8 46.0 58.8 55.7 1.35 <0.001 0.11 0.64

ADF, % DM 50.7 49.1 60.0 57.1 1.21 <0.001 0.11 0.59

Starch, % DM 98.8 98.8 98.8 97.1 1.06 0.44 0.42 0.42

GE digestibility, % 69.6 69.3 65.0 62.6 0.87 <0.001 0.14 0.27
DE intake, Meal/d 13.7 12.4 10.5 8.9 0.43 <0.001 <0.001 0.49
Energy concentration of dietsc

ME, Mcal/kg DM 2.28 2.27 2.04 1.97 0.03 <0.001 0.15 0.27

NEm, Mcal/kg DM 1.41 1.40 1.19 1.12 0.03 <0.001 0.15 0.27

NEg, Mcal/kg DM 0.82 0.82 0.63 0.56 0.02 <0.001 0.15 0.27

 

“Standard error of the least squares mean.

"Fiber = Fiber level main effect; RIB = rumen inert bulk main effect; F X B = Fiber
level X rumen inert bulk interaction.

cCalculated from DE using NRC (1996) equations.

99

Ruminal pH

 

 

—o—LF- -o - LF+RIB+HF- i - HF+ RIB

 

 

 

7.1 ,
6.9 E
6.7 E

6.5 f

5.9 3

5.7 1

 

 

5.5 '

j T j I I I I T l I I I I I I I I I l I

 

2 4 6 8 10 12 l4 16 18 20 22
Time post initial feeding, h

Figure 3-1. Effects of feeding a normal corn hybrid (low-ﬁber; LF) or its male-sterile
counterpart (high-ﬁber; HF), without or with rumen inert bulk (RIB) on ruminal pH over
time. Feed offered at 0, 12 h. Time X ﬁber level interaction (P < 0.0001). SEM = 0.09.

100

 

—o—LF- -o - LF+RIB+HF- -A - HF+ RIB

 

 

 

27

 

25‘

23

21:

Propionate, mol/100 mol

 

17:

 

 

 

15 ' I I —I I I r l I I H I ' l ' l 7 l I l ' l T
-2 0 2 4 6 8 10 12 14 16 18 20 22
Time post initial feeding, h

Figure 3-2. Effects of feeding a normal corn hybrid (low-ﬁber; LF) or its male-sterile
counterpart (high-ﬁber; HF), without or with rumen inert bulk (RIB) on molar percentage
of propionate over time. Feed offered at 0, 12 h. Time X ﬁber level interaction (P <
0.0001). SEM = 0.61.

101

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evaluation of pH effects on ﬁber digestion in vitro. J. Dairy Sci. 75: 1581-1587.

Grant, R. J ., and D. R. Mertens. 1992b. Inﬂuence of buffer pH and raw corn starch
addition on in vitro ﬁber digestion kinetics. J. Dairy Sci. 75:2762-2768.

Illius, A. W., and N. S. Jessop. 1996. Metabolic constraints on voluntary intake in
ruminants. J. Anim. Sci. 74:3052-3062.

Johnson, T. R, and D. K. Combs. 1991. Effects of prepartum diet, inert rumen bulk, and
dietary polyethylene glycol on dry matter intake of lactating dairy cows. J. Dairy
Sci. 74:933-944.

Johnson, T. R, and D. K. Combs. 1992. Effects of inert rumen bulk of dry matter intake
in early and midlactation cows fed diets differing in forage content. J. Dairy Sci.
7 52508-5 19.

Karkalas, J. 1985. An improved enzymatic method for the determination of native and
modiﬁed starch. J. Sci. Food Agric. 36:1019-1027.

Kaske, M., and A. Midasch. 1997. Effects of experimentally-impaired reticular
contractions on digesta passage in sheep. Br. J. Nutr. 78:97-110.

Leek, B. F. 1969. Reticulo-ruminal mechanoreceptors in sheep. J. Physiol. (Lond).
202:585-609.

Littell, R. C., P. R. Henry, and C. B. Ammerman. 1998. Statistical analysis of repeated
measures data using SAS procedures. J. Anim. Sci. 76:1216-1231.

Llamas-Lamas, G., and D. K. Combs. 1991. Effect of forage to concentrate ratio and
intake level on utilization of early vegetative alfalfa silage by dairy cows. J. Dairy
Sci. 74:526-536.

Mowat, D. N. 1963. Factors affecting rumen capacity and the physical inhabition of feed
intake. Ph.D. dissertation, Cornell University, Ithaca, NY.

NRC. 1996. Nutrient Requirements of Beef Cattle. 7th ed. National Academy Press,
Washington, DC.

103

Oba, M., and M. S. Allen. 2000. Effects of brown midrib 3 mutation in corn silage on
productivity of dairy cows fed two concentrations of dietary neutral detergent
ﬁber: 1. Feeding behavior and nutrient utilization. J. Dairy Sci. 83:1333-1341.

Orskov, E. R, G. W. Reid, and M. Kay. 1988. Prediction of intake by cattle from
degradation characteristics of roughages. Anim. Prod. 46:29-34.

Orskov, E. R, G. W. Reid, and M. Kay. 1991. Inﬂuence of straw quality and level of
concentrate in a completely mixed diet on intake and growth rate in steers. Anim.
Prod. 52:461-464.

Perry, T. W., and D. M. Caldwell. 1969. Comparative nutritive value of silages made from
high-sugar male sterile hybrid corn and regular starchy corn. J. Dairy Sci. 5221119-
1121.

Reid, G. W., E. R. Orskov, and M. Kay. 1988. A note on the effect of variety, type of
straw and ammonia treatment on digestibility and on growth rate in steers. Anim.
Prod. 47:157-160.

Ritchie, H., R. Black, A. Booren, L. Copeland, J. Ferris, J. Lloyd, T. Louden, H. Person,
and S. Rust. 1992. Type of Farming Systems Study: Beef feedlot survey. Agric.
Exp. Station Res. Rep. 522. Michigan State University, East Lansing, MI.

Schettini, M. A., E. C. Prigge, and E. L. Nestor. 1999. Inﬂuence of mass and volume of
ruminal contents on voluntary intake and digesta passage of a forage diet in steers.
J. Anim. Sci. 77:1896-1904.

Stake, P. E., M. J. Owens, D. J. Schingoethe, and H. H. Voelker. 1973. Comparative
feeding value of high-sugar male sterile and regular dent corn silages. J. Dairy Sci.
56:1430-1444.

Tjardes, K. E., D. D. Buskirk, M. S. Allen, N. K. Ames, L. D. Bourquin, and S. R. Rust.
2000. Brown midrib-3 corn silage improves digestion but not performance of
growing beef steers. J. Anim. Sci. 78:2957-2965.

Van Soest, P. J ., J. B. Robertson, and B. A. Lewis. 1991. Methods of dietary ﬁber, neutral
detergent ﬁber, and nonstarch polysaccharides in relation to animal nutrition. J.
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Waybright, T. R, and G. A. Varga. 1991. Effect of water-ﬁlled bags in the rumen of
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Woodford, J. A., N. A. Jorgensen, and G. P. Barrington. 1986. Impact of dietary ﬁber and
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104

 

CHAPTER 4
Neutral Detergent Fiber Concentration in Corn Silage Inﬂuences Dry Matter

Intake, Diet Digestibility, and Performance of Angus and Holstein Steers

Abstract

Twelve Angus (237 i 13 kg) and twelve Holstein (235 i 15 kg) steers were used
to determine if a corn silage-based diet high in NDF depresses DMI as steers increase in
body weight and to determine if a diet high in NDF has the same inﬂuence on Angus and
Holstein steers. Steers were randomly assigned to individual slatted-ﬂoor pens and used
in a crossover design consisting of six 14—d periods. Experimental diets contained corn
silage from a normal hybrid (low-ﬁber; LF) and its male-sterile counterpart (high-ﬁber;
HF) and were alternated each period. The LP and HF diets contained 33.8 and 50.8%
NDF, respectively. The HF diet decreased overall steer mean DMI 14.0% relative to LP
(P < 0.001), with mean differences increasing as steers increased in body weight (P <
0.001). Feeding HF also reduced ADG by an average of 13.8% relative to LF (P <
0.001). Holstein steers consumed 14.4% more DM, and gained 14.3% faster than Angus
steers (P < 0.001). There was a ﬁber level X breed-type interaction (P = 0.08) for
efﬁciency of gain. Angus steers receiving HF had greater efﬁciency of gain than Angus
steers consuming LF; however, Holstein steers consuming LF had greater efﬁciency of
gain than those receiving HF. The HF treatment reduced total-tract digestibility of DM
and GE by 4.6 and 4.5%, respectively (P < 0.001) and decreased DE intake 20.5% (P <
0.001), but increased apparent total-tract digestibility of NDF and ADF (9.4 and 8.4%,
respectively; P < 0.001). Holstein steers had similar digestibility of DM and GE (P >

0.10), but had greater DE intake (P < 0.01) when compared to Angus steers. There were

105

 

ﬁber level X breed-type interactions for total-tract digestibility of NDF and ADF (P s
0.06). Difference in DM digestibility was negatively associated with difference in DMI (r2
= 0.23; P < 0.001) for LP minus HF within Angus steers, but not within Holstein steers (P
= 0.42). Total-tract digestibility of NDF and ADF was 4.1 and 3.4% lower for HF, but
was only 1.1 and 0.6% lower for LP when fed to Holsteins compared to Angus. Results
from this trial demonstrate that high NDF corn silage-based diets reduced intake of both
Angus and Holstein steers, and this reduction in DMI continues as steers increase in body

weight from 235 to 330 kg.

Introduction
Many cattle receive a growing diet before being placed on a high-concentrate
ﬁnishing diet. Growing diets often contain high levels of corn silage in upper Midwest
beef cattle feeding systems (Ritchie et al., 1992). Concentration of NDF in corn silage can
vary greatly (46.0 i: 6.5% NDF, >‘< i SD; NRC, 1996). In a previous study, corn silage
high in NDF fed to light-weight steers (198 :t 13 kg) depressed DMI (Tjardes et al.,
2001). A review of several studies indicates that depression in intake, as a result of
physical ﬁll in the form of inert bulk, was greatest for animals with relatively lighter body
weight within a species, and for animals in physiological states with higher nutrient
requirements (Dado, 1993). It is uncertain whether the ﬁlling effect of a high-ﬁber corn
silage-based diet continues to limit DMI as steers increase in body weight.
In addition to dietary effects, DMI may be inﬂuenced by steer breed-type.
Holstein and Holstein crossbred steers have DMI that is 4.2 to 17.0% greater compared to

Other breeds (Garrett, 1971; Fox and Black, 1984). Due to differences in DMI, it was our

106

hypothesis that physical ﬁll in the rumen may depress DMI to a lesser extent for Holsteins
compared to steers of beef breeding. Therefore, our objectives were to determine if a high
NDF corn silage-based diet depresses DMI as steers increased in body weight and to

determine if the depression in DMI was different for Holstein compared to Angus steers.

Materials And Methods

A com hybrid (5456, UAP Dyna-Gro, East Lansing, MI) and its male-sterile
isogenic counterpart were planted in separate ﬁelds on the same day to achieve a
population of approximately 66,700 plants/ha. The male-sterile hybrid was isolated from
all other com hybrids to prevent pollination. As the corn approached maturity, DM for
each hybrid was determined every third day to estimate the desired time of harvest. The
normal and male-sterile corn hybrids were harvested with a three-row silage chopper
(Model 900, New Holland North America Inc., New Holland, PA) set at 1.3 cm
theoretical cut length, and ensiled separately in adjacent 2.4-m dia. plastic silage bags (Ag
Bag International, Warrenton, OR) at the Michigan State University Beef Cattle Teaching
and Research Center. Before feeding, forages were analyzed for DM, NDF, CP, pH, and
VFA. Post-ensiled nutrient composition and fermentation characteristics of the silages are
presented in Table 4-1.

Animal handling and experimental procedures in this trial were conducted
according to those approved by the Michigan State University All University Committee
on Animal Use and Care (AUF No. 07/99-089-00).

Twelve Angus (237 :t 13 kg) and twelve Holstein (235 :l: 15 kg) steers were

randomly assigned to individual 2.1X 1.8 m slotted-ﬂoor metabolism pens for a lO-d

107

.21.! 3'

acclimation period. Steers had ad libitum access to water and a common corn silage-based
diet (Table 4-2). Corn silage was the primary dietary ingredient, with soybean meal and
supplement added to meet or exceed requirements for metabolizable protein, minerals, and
vitamins (NRC, 1996). After acclimation, diets were formulated using either the male-
sterile (low-ﬁber diet; LF) or normal (high-ﬁber diet; HF) corn hybrids resulting in LF and
HF containing 33.8% and 50.8% dietary NDF, respectively (Table 4-2). Steer diets were l

mixed once daily and offered at 0730 and 1930 to allow steers ad libitum access (210%

 

orts) to the total mixed ration. Amounts fed and reﬁised were weighed daily for each L
steer. Representative samples of the complete mixed diets, individual ingredients, and orts
were taken twice weekly. Samples were dried immediately at 57°C in a forced-air oven
for 72 h to determine DM. A crossover design, consisting of six 14-d periods (ﬁve
crossovers), was used to determine the effect of dietary NDF concentration on diet
digestion and steer performance as steers increased in body weight. Dietary treatments
were switched on d 14 of each period.

Steer weights were the average of ﬁrll weights taken on two consecutive days at d
0, l, 13, and 14 of each period throughout the trial. Steers were implanted with 200 mg
of progesterone and 20 mg of estradiol benzoate (IMPLUS-S, Upjohn Co., Kalamazoo,
MI) before acclimation. Fecal grab samples were collected at 1900 on d 12, 0700 and
1900 on d 13, and 0700 on d 14 and immediately frozen at -20°C. Fecal samples were

later dried at 57 °C in a forced-air oven for 72 h to determine DM.

108

Sample Analysis

Diets, individual ingredients, and fecal samples were ground through a Wiley mill
(Arthur H. Thomas, Philadelphia, PA) equipped with a 1-mm screen. Samples of diets
and individual ingredients were then composited for each stage, and fecal samples were
composited by animal for each stage. Diet, individual ingredient, and fecal samples were
then analyzed for percentages of NDF, ADF, ADL, indigestible NDF, and ash. Neutral
detergent ﬁber, ADF, and ADL were analyzed according to procedures of Van Soest et al.
(1991; method A for NDF) and corrected for ash. Ash content was determined after 5 h
of oxidation at 500°C in a muffle ﬁrmace. Diets and individual ingredients were analyzed
for CP by the combustion method (AOAC, 1990; Model FP-2000, LECO, St. Joseph,
MI). Free glucose in the diets and feed ingredients were measured by an enzymatic
method (Karkalas, 1985; glucose kit #510-A, Sigma Diagnostics Inc., St. Louis, MO)
using a microplate reader (Spectra Max 190, Molecular Device Corp, Sunnyvale, CA)
after samples were extracted with deionized water. Starch in the diets, feed ingredients,
and feces were measured by an enzymatic method (Karkalas, 1985; glucose kit #510-A)
after samples were gelatinized with sodium hydroxide and digested with amylase
(CRYSTALZYME 40 L, Vally Research Inc., South Bend, IN). Fecal output and
apparent total-tract digestibility of dietary nutrients were calculated using indigestible
NDF as an internal marker (Cochran et al., 1986). Indigestible NDF residues in feed and
feces were quantiﬁed as NDF content of samples following in vitro fermentation in
buffered rumen media (Goering and Van Soest, 1970) for 120-h without addition of
pepsin. Gross energy was determined for both feed and fecal samples by bomb

calorimetry (AOAC, 1990; Model 1241 Adiabatic Calorimeter, Parr Instruments, Moline,

109

IL). Digestible energy was determined as the difference between intake of dietary gross
energy and output of fecal gross energy. Concentration of ME, NEm, NEg in the diets
were calculated from DE using published equations (NRC, 1996). The concentrations of

all nutrients were expressed as percentage of DM determined from drying at 57 °C.

Statistical Analysis

Intake, performance, and digestibility data were analyzed based on a mixed effect
model using the MIXED procedure of SAS (SAS Inst. Inc., Cary, NC). The model
contained animal nested within breed-type as a random effect, and period, ﬁber level,
breed-type, and ﬁber level X breed-type as ﬁxed effects. Using the Schwarz Bayesian
criterion (Littell et al., 1998), a ﬁrst-order compound symmetry error structure was
determined as the most appropriate residual covariance structure for repeated measures
over period within animals. Main effects were considered signiﬁcant at P < 0.05, and
two-way interactions were considered signiﬁcant at P < 0.10.

Difference in DMI, DIVII as a percentage of BW, DMI as a percentage of BW‘m,
DE intake, DE intake as a percentage of BW, DE intake as a percentage of BW’”, and
apparent total-tract DM digestibility between the two treatments were calculated by
subtracting the high-ﬁber diet from the low-ﬁber diet (LF-HF) data for each steer within
each of the ﬁve crossovers. Relationships between the factors were then determined using
the simple linear regression procedure of SAS (PROC REG). Slopes of regression lines
for Angus and Holstein steers were tested using dummy variables to set the Holstein slope
equal to zero and determine if the Angus slope was different from zero. Slopes of the

regressions lines were considered signiﬁcantly different at P < 0.10.

110

Results And Discussion

The normal and male-sterile corn silages in the current study were the same as
those used in Tjardes et al. (2001). Since the male-sterile corn silage contained greater
concentration of ethanol (7.0%), steers receiving HF would have consumed up to 550 mL
of ethanol over the entire day. No adverse signs related to ethanol ingestion were
observed among steers.

The HF diet decreased steer DMI 14.6% when summarized over the entire trial
(Table 4-3; P < 0.001). This reduction in DMI agrees with Tjardes et al. (2001), who
reported a 14.0% reduction in DMI when a similar diet was fed to cannulated steers.
There was a period X ﬁber level interaction for DMI (P < 0.001; Figure 4-1a), and DMI as
a percentage of BW (P < 0.001; Figure 4-1b). In addition, there was a positive
relationship between average steer BW for each crossover and the difference in steer DMI
for LP minus HF, (r2 = 0.24; P < 0.001; Figure 4-2). There was also a positive
relationship (P < 0.001) between average steer BW for each crossover and difference in
DMI whether DMI was expressed as a percentage of BW (y = -O.319 - 0.002x; r2 = 0.13)
or expressed as a percentage ofBW"75 (y = -1.678 - 0.011x; r2 = 0.18). These data
suggest that when steers increased in body weight, the HF diets became more limiting to
DMI as compared to LF. In addition to the reduction in DMI, feeding HF also reduced
ADG by an average of 13.8% (P < 0.001; Table 4-3). In contrast to the current study,
Stake et al. (1973) reported that steers consumed similar intakes of male-sterile or normal
corn silage when they were receiving 1.81 kg/d of a protein/grain supplement and there

was no difference in the crude ﬁber value between the normal and male-sterile hybrids.

111

The researchers also reported no difference in steer ADG due to treatment (Stake et al.,
1973)

Holstein steers consumed 14.4% more DM, and gained 14.3% faster than Angus
steers (P < 0.001; Table 4-3). Previous researcher has indicated that Holstein and
Holstein crossbred steers have 4.2 to 17.0% greater DMI when compared to British steers
(Garrett, 1971; Dean et al., 1976; Thonney et al., 1981; Fox and Black, 1984). The
inﬂuence of breed-type on ADG in previous studies has been variable. Garrett (1971)
reported no difference in ADG between Holstein and Hereford steers when they were fed
either 70% sorghum or 44% barley diets. Dean et al. (1976) found a reduction in ADG of
0.2 to 0.4 lb/d for Holstein crossbred steers compared to British steers when they received
a 65% sorghum diet. In contrast, Thonney et al. (1981) reported that Holstein steers
gained 0.4 lb/d faster that small-framed Angus calves when they were fed either com- or
silage-based diets.

There was no breed-type X ﬁber level X period interaction (P = 0.88) for DMI and
the slope of the relationship between average steer body weight for each crossover and the
difference in steer DMI for LF minus HF were not different for the two breeds (P = 0.18).
This suggests that the diet high in NDF had the same inﬂuence over DMI for both breed
types.

The HF treatment reduced total-tract digestibility of DM and gross energy (GE)
by 4.6 and 4.5%, respectively (P < 0.001), but increased apparent total-tract digestibility
ofNDF and ADF (9.4 and 8.4%, respectively; P < 0.001) compared to LF.

Since steers receiving HF consumed less DM and had lower digestibility of GE, digestible

energy intake was reduced by 20.5% (P < 0.001). Similar results were reported by

112

 

Tjardes et al. (2001), where feeding HF compared to LP increased digestibility of NDF
and ADF (11.0 and 9.3%, respectively), but decreased digestibility of DM and GB (4.5
and 4.7%, respectively), and reduced digestible energy intake 23.4%.

Holstein steers had similar digestibility of DM and GE (P > 0.10), but had greater
digestible energy intake (P = 0.002) when compared to Angus steers. There were ﬁber

level X breed-type interactions for total-tract digestibility of NDF and ADF (P s 0.06).

F '-

4

Within the HF diet, total-tract digestibility of NDF and ADF was 1.1 and 0.6% lower,

 

respectively, for Holstein compared to Angus steers. When steers received the LF [3.
treatment, total-tract digestibility of NDF and ADF was 4.1 and 3.4% lower, respectively,
for Holstein compared to Angus steers. The decline in ﬁber digestibility for Holstein
steers receiving LF could be due to a greater amount of starch fermented in the rumen
(Grant and Mertens, 1992) and(or) an increased passage rate resulting in more potentially
digestible ﬁber escaping ruminal degradation (Oba and Allen, 2000).

There was a negative relationship between difference in apparent total-tract DM
digestibility and difference in DMI (LF-HF) for Angus steers (r2 = 0.23; P < 0.001; Figure
4-3a). There was also a negative relationship (P < 0.001) when DMI was expressed as a
percentage of BW"75 (y = 13.82 0 -7.30x; r2 = 0.25). These data suggest that when there
was no difference in DMI due to ﬁber level, LF had a higher total-tract DM digestibility.
However, when steers consumed greater levels of LF as compared to HF, the total-tract
DM digestibility of LF was reduced. The reduction in DM digestibility may have been
because of an increase in passage rate for LP in association with the higher DMI. Similar
responses were reported by Oba and Allen (1999, 2000) when they compared diets fed to

early lactation dairy cows containing corn hybrids with different digestibilities of NDF.

113

 

No relationship was reported between difference in apparent total-tract DM digestibility
and difference in DMI for Holstein steers (P = 0.42; Figure 4-3b) or when DMI was
expressed as a percentage of BW“75 (P = 0.45). Reasons for the different relationship for
Holstein steers compared to Angus steers might be because of differences between the
breeds in ruminal retention time of digesta for the two diets.

There was no relationship between difference in DE intake and difference in DMI
for Angus steers (P = 0.57; Figure 4-4a). This was due to the negative relationship
between difference in DM digestibility and difference in DMI. In contrast, there was a
positive relationship between difference in DE intake and difference in DMI for Holstein
steers (r2 = 0.23; P < 0.001; Figure 4-4b). The relationship between differences in DE
intake and DMI were consistent with difference in ADG for each breed type. Within the
Angus steers, there was no relationship between differences in DE intake and DMI which
corresponded to only a 0.1 kg/d difference in ADG between the LF and HF diets.
However, for the Holstein steers, there was positive relationship between differences in
DE intake and DMI, and the Holstein steers receiving LF gained 0.2 kg/d faster than those
receiving HF.

There was a ﬁber level X breed-type interaction for efﬁciency of gain (P = 0.08;
Table 4-3). Angus steers receiving HF had greater efﬁciency of gain than Angus steers
consuming LF. The reduction in efficiency of gain for the Angus steers receiving LF is
consistent with the negative relationship between difference in DM digestibility and
difference in DMI. In contrast, the Holstein steers consuming LF had greater efﬁciency of
gain than those receiving HF. Previous research has reported that Holstein and Holstein

crossbred steers range from having greater efﬁciency of gain (Thonney et al., 1981) to

114

 

having lower efﬁciency of gain (Dean et al., 1976; Wyatt et al., 1977) when compared to

British steers.

Implications

Corn silage high in ﬁber has the potential to limit intake of light-weight steers. As
steers increased in body weight, intake of the high-ﬁber corn silage diet was depressed to a
greater extent compared to the lower-ﬁber diet. The two breeds responded differently to

the different ﬁber levels. Although the Holstein steers consumed more dry matter and

 

gained faster than the Angus steers, the increased ﬁber concentration appeared to be more
detrimental to performance of the Holstein steers as compared to the Angus steers.
Further research is needed to more clearly deﬁne the factors controlling intake of com-
silage based diets and the determination of ruminal digesta kinetics of both breed-types
would be beneﬁcial to determine the reasons for the breed difference between the two

ﬁber levels.

115

Tables and Figures

Table 4-1. Post-ensiled nutrient composition and fermentation characteristics of normal
and male-sterile corn hybrids

 

 

 

Corn hybrid
Item Normal Male-sterile
Nutrient composition, % in silage DM“
DM 36.7 31.0
CF 6.91 6.18
NDF" 38.6 56.7
ADF" 22.7 32.3
Starch 32.0 3.3
Fermentation
pH 3.61 3.46
Acetate, g/ 100 g DM 0.80 1.42
Propionate, g/100 g DM - 0.30
Ethanol, g/100 g DM 0.52 7.57
Lactate, g/ 100 g DM 5.67 7.88

 

“During trial analysis.
"Corrected for ash.
cPre-trial analysis.

116

Table 4-2. Ingredient and nutrient composition of normal (Low-ﬁber) and male-sterile
(High-ﬁber) corn silage-based diets

Item Low-ﬁber High-ﬁber
Ingredient composition, % in diet DM

Normal corn silage 87 .72 —
Male-sterile corn silage - 85.76
Soybean meal, 44% CP 9.04 11.07
Ground shelled corn 0.21 0.20
Trace mineralized salt“ 0.62 0.61
Urea 0.46 0.45
Potassium chloride 0.34 0.34
Selenium 90" 0.07 0.06
Vitamin Ac 0.01 0.01
Rumensin 80d 0.02 0.02
Dicalcium phosphate 0.13 0.13
Calcium carbonate 1.37 1.34

Nutrient composition

DM, % 39.3 30.3
CP,%DM 11.4 11.2
NDF, % DMe 33.8 50.8
indigestible NDF, % NDF 43.2 36.0
ADF, % DM" 20.3 30.1
ADL, % DM° 2.07 2.72
ADL,%NDF 6.12 5.35
Starch, % DM 29.1 4.2
Free glucose, % DM 0.12 0.05

 

“Composition (%): NaCl, 96-98.5; Zn, > 0.35; Mn, > 0.2; Fe, > 0.2; Cu, > 0.03; I,
> 0.007; Co, > 0.005.

"Composition (%): Ca, > 28.5; Se, 0.02.

cContains 30,000 IU of Vitamin A per gram.

dContains 176 g of monensin per kg.

°Corrected for ash.

117

Table 4-3. Dry matter intake, average daily gain, apparent total tract digestibility, and
energy concentration of low-ﬁber (LF) and high-ﬁber (HF) corn silage-based diets fed to
growing Angus and Holstein steers

 

 

 

 

 

Angus Holstein Effect", P-value

Item LF HF LF HF SEM“ Fiber Breed F X B
DMI, kg/d 5.98 5.05 6.76 5.85 0.13 <0.001 <0.001 0.85
DMI, % BW 2.19 1.86 2.44 2.11 0.05 <0.001 0.006 0.18
NDF intake, kg/d 2.10 2.51 2.37 2.91 0.05 <0.001 <0.001 0.004
ADG, kg/d 1.05 0.95 1.25 1.03 0.05 0.002 0.006 0.18
Gain:Feed 0.173 0.188 0.186 0.174 0.008 0.97 0.80 0.08
Apparent total tract digestibility

DM, % 63.3 60.0 62.1 59.6 0.61 <0.001 0.26 0.43

NDF, % DM 47.4 55.3 43.3 54.2 0.83 <0.001 0.009 0.05

ADF, % DM 48.5 55.2 45.1 54.6 0.82 <0.001 0.04 0.06

Starch, % DM 94.2 96.5 94.5 96.9 0.69 <0.001 0.69 0.13

GE digestibility, % 63.3 60.3 62.1 59.5 0.59 <0.001 0.11 0.66
DE intake, Mcal/d 14.8 11.5 16.4 13.3 0.35 <0.001 0.002 0.81
Energy concentration of diets"

ME, Mcal/kg DM 2.03 1.88 1.99 1.85 0.02 <0.001 0.11 0.65

NEm, Mcal/kg DM 1.18 1.03 1.14 1.01 0.02 <0.001 0.13 0.65

NEg,Mcal/ngM 0.61 0.48 0.58 0.46 0.02 <0.001 0.13 0.65

“Standard error of the least squares mean.

"Fiber = Fiber level main effect; Breed = steer breed-type main effect; F X B = ﬁber
level X steer breed-type interaction.

"Calculated from DE using NRC (1996) equations.

 

118

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Figure 4-1. Effects of feeding low-ﬁber (LF) and high-ﬁber (HF) corn silage-based diets
on growing steer a) dry matter intake least squares mean (DMI) over period and b) dry
matter intake as a percentage of body weigh least squares mean (DMI, % BW) over
period. Period X ﬁber level interactions (P < 0.0001).

119

 

 

O Holstein steers
2. 5 — X Angus Steers

 

Difference in DMI (LF-HF), kg/d

 

 

 

- 1 l I l l I T 7 I I l I I T l
200 220 240 260 280 300 320 340 360
Average crossover BW, kg
Figure 4-2. Relationship between difference in DMI for low-ﬁber (LF) minus high-ﬁber

(HF) and average crossover body weight of Angus and Holstein steers. Diﬁerence in
DMI (LF - HF) = -1.856 + 0.011 X average crossover body weight (r2 = 0.24; P < 0.001).

120

a
W
O

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3s 25 ‘
73 A 20 -
84b.- 15 -
H LL.
5 cl 10 -
3 a
0.: 5 _
3‘5
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d)
D -15 -
'20 I I I I I
-0.5 0 0.5 1 1.5 2 2.5
Difference in DMI (LF- HF), kg/d
b 30
2 5 _ O Holstein steers
‘5
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4. A o
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é o —15 - 0
Q
'20 I I I I I
~O.5 O 0.5 l 1.5 2 2.5

Diﬁerence in DMI (LF- HF), kg/d

Figure 4-3. Relationship between difference in apparent total-tract DM digestibility and
difference in DMI for low-ﬁber (LF) minus high-ﬁber (HF) within a) Angus steers (r2 =
0.23; P < 0.001) and b) Holstein steers (r2 = 0.01; P = 0.42). Difference in apparent
total-tract digestibility (LF - HF) of Angus steers = 12.54 - 9.45 X difference in Angus
steer DMI.

121

 

 

 

 

 

 

lO .
{xAngussteers

82
34’ x
‘3 X
“-0 XX X
.E% 6- >$<x xx
LL10 X X
a: X >¢Ex %

X X X

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-0.5 O 0.5 1 1.5 2 ' 2.5 3
Difference in DMI (LF- HF), kg/d

 

 

 

 

 

 

b
10 .
o Holstein steers 0
Q) 8-
ﬁt,
5% 6-
LL10
DE
3:: .
-—A 4"
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£5 2‘
D
0..
-2 I r T I r I

 

 

 

-0.5 0 0.5 l 1.5 2 2.5 3
Difference in DMI (LF- HF), kg/d

Figure 4-4. Relationship between difference in DE intake and difference in DMI for low-
ﬁber (LF) minus high-ﬁber (HF) within a) Angus steers (r2 = 0.01; P = 0.57) and b)
Holstein steers (r2 = 0.23; P < 0.001). Difference in DE intake (LF - HF) of Holstein
steers = 1.294 + 2.080 X difference in Holstein steer DMI.

122

 

 

y—n
N

 

 

 

 

 

OHolsteinSteers
xAnngteers
1:: 10* .
E o
A 8‘
Q)
”E?
.E 4-
u.)
C3
.5 21
8
c:
8
a o—
.5
'2 I T I I I I I I

 

 

 

200 220 240 260 280 300 320 340 360
Average crossover BW, kg

Figure 4-5. Relationship between difference in DE intake for low-ﬁber (LF) minus high-
ﬁber (HF) and average crossover body weight of Angus and Holstein steers. Difference in
DE intake (LF - HF) = -3.499 + 0.025 X average crossover body weight (r2 = 0.08; P <
0.01).

123

 

 

Literature Cited

AOAC. 1990. Official Methods of Analysis. 15th ed. Association of Official Analytical
Chemists, Washington, DC.

Cochran, R. C., D. C. Adams, J. D. Wallace, and M. L. Galyean. 1986. Predicting
digestibility of different diets with internal markers: Evaluation of four potential
markers. J. Anim. Sci. 63:1476-1483.

Dado, R. G. 1993. Voluntary intake and feeding behavior of dairy cows in response to
rumen ﬁll from forage ﬁber. Ph. D. dissertation, Michigan State University, East
Lansing.

Dean, R. A., J. W. Holloway, J. V. Whiteman, D. F. Stephens, and R. Totusek. 1976.
Feedlot performance of progeny of Hereford, Hereford x Holstein and Holstein
cows. J. Anim. Sci. 42:1290-1296.

Fox, D. G., and J. R. Black. 1984. A system for predicting body composition and
performance of growing cattle. J. Anim. Sci. 58:725-739.

Garrett, W. N. 1971. Energetic efficiency of beef and dairy steers. J. Anim. Sci. 32:451-
456.

Goering, H. K., and P. J. Van Soest. 1970. Forage ﬁber analysis (apparatus, reagents,
procedures and some applications). Agric. Handbook No. 379. ARS-USDA,
Washington, DC.

Grant, R. J ., and D. R. Mertens. 1992. Inﬂuence of buffer pH and raw corn starch addition
on in vitro ﬁber digestion kinetics. J. Dairy Sci. 7 522762-2768.

Karkalas, J. 1985. An improved enzymatic method for the determination of native and
modiﬁed starch. J. Sci. Food Agric. 36:]019-1027.

Littell, R. C., P. R. Henry, and C. B. Ammerman. 1998. Statistical analysis of repeated
measures data using SAS procedures. J. Anim. Sci. 76:1216-1231.

NRC. 1996. Nutrient Requirements of Beef Cattle. 7th ed. National Academy Press,
Washington, DC.

Oba, M., and M. S. Allen. 1999. Effects of brown midrib 3 mutation in corn silage on dry
matter intake and productivity of high yielding dairy cows. J. Dairy Sci. 82:135-
142.

Oba, M., and M. S. Allen. 2000. Effects of brown midrib 3 mutation in corn silage on

productivity of dairy cows fed two concentrations of dietary neutral detergent
ﬁber: 3. Digestibility and microbial efficiency. J. Dairy Sci. 83:1350-1358.

124

 

Ritchie, H., R. Black, A. Booren, L. Copeland, J. Ferris, J. Lloyd, T. Louden, H. Person,
and S. Rust. 1992. Type of Farming Systems Study: Beef feedlot survey. Agric.
Exp. Station Res. Rep. 522. Michigan State University, East Lansing, MI.

Stake, P. E., M. J. Owens, D. J. Schingoethe, and H. H. Voelker. 1973. Comparative
feeding value of high-sugar male sterile and regular dent corn silages. J. Dairy Sci.
56:1430-1444.

Thonney, M. L., E. K. Heide, D. J. Duhaime, A. Y. M. Nour, and P. A. Oltenacu. 1981.
Growth and feed efficiency of cattle of different mature sizes. J. Anim. Sci.
53:354-362.

Tjardes, K. E., D. D. Buskirk, M. S. Allen, N. K. Ames, and S. R. Rust. 2001. Neutral
detergent ﬁber concentration of corn silage and rumen inert bulk inﬂuences dry
matter intake and ruminal digesta kinetics of growing steers. J. Anim. Sci.
(submitted).

Van Soest, P. J ., J. B. Robertson, and B. A. Lewis. 1991. Methods of dietary ﬁber, neutral
detergent ﬁber, and nonstarch polysaccharides in relation to animal nutrition. J.
Dairy Sci. 743583-3597.

Wyatt, R. D., K. S. Lusby, M. B. Gould, L. E. Walters, J. V. Whiteman, and R. Totusek.

1977 . Feedlot performance and carcass traits of progeny of Hereford, Hereford X
Holstein and Holstein cows. J. Anim. Sci. 45:1131-1137.

125

CHAPTER 5

Interpretive Summary

Fiber digestibility

The overall hypothesis of the research described in this dissertation is that corn
silage high in ﬁber potentially limits intake and performance of light-weight steers by
ruminal distension. Therefore, improving ﬁber digestibility or decreasing ﬁber
concentration in corn silage should reduce ruminal distension and increase intake and
performance. In Experiment 1, feeding BMCS compared to Control improved NDF
digestibility and increased DMI but did not improve steer ADG. Reasons for the lack of
improvements in ADG are unclear.

In Experiment 1, the brown midrib-3 and its isogenic control corn hybrids were
planted to achieve similar populations, but the bm3 resulted in a 19% reduction in as-is
silage yield per hectare (Table 5-1). In addition, the bm3 seed typically costs $100 more
per bag when compared to its isogenic normal counterpart. Assuming the normal corn
silage would cost $27.60/t of wet silage delivered to the bunk, the bm3 corn silage would
cost an additional $7.36/t of wet silage as a result of the higher seed cost and yield
reduction (Table 5-1). During the performance trial, feeding BMCS increased steer DMI,
but had no effect on ADG and resulted in poorer feed efficiency. The higher DMI and
cost of silage production would have resulted in a $9.16/steer increase in feed cost for
steers receiving BMCS compare to Control (Table 5-4). Total operating costs (excluding
animal purchase price) would have been $9.53/steer greater for BMCS, resulting in the

cost of gain (excluding animal purchase price) being increased from $0.87/kg for Control,

126

 

to $0.97/kg for BMCS. Assuming steers were purchased at $1 .82/kg ($82.40/cwt)1 and
sold aﬁer the 112-d growing period at $1.67/kg ($75.60/cwt)2, feeding BMCS would
have reduced the return to labor and management by $12.14/steer when compared to
Control (Table 5-4). Finally, kilograms of gain per hectare of corn was reduced 11% for
BMCS when compared to Control as a result of the reduction in silage yield, with no

improvements in steer ADG (2,850 vs 2,530 kg/ha for Control and BMCS, respectively).

Fiber concentration

In Experiment 2, feeding HF compared to LP reduced DMI, and the addition of
RIB to both diets depressed DMI. These data appear to agree with the hypothesis that
increasing ﬁber concentration in corn silage reduces voluntary DMI by ruminal distension.
Digesta volume was also similar between LF and HF, suggesting that animals were eating
to maintain a similar digesta volume ﬁthher suggesting that ruminal distension may be
regulating DMI. However, when RIB was added at 25% of pre-trial ruminal volume, total
ruminal volume was increased by approximately 25% for both LF and HF treatments.
These data suggest that steers with the RIB adapted to additional ﬁll in an attempt to
minimize the discomfort from satiety as well as hunger. The RIB addition was expected
to distend the rumen and increase the stimulation of tension receptors in the rumen. The
tension receptors would have sent nerve impulses to the brain via the vagus nerve that
would have contributed to satiety. However, the reduction in DMI due to ruminal

distension would have reduced the amount of absorbed metabolic ﬁiels, resulting in

 

lCATTLE-F AX lO-year average (1990-2000) for 250 kg feeder calves during October.
2CATTLE-FAX 10-year average (1990-2000) for 363 kg feeder calves during February.

127

 

stimulation of hunger. The steers would have integrated the competing Signals of
discomfort ﬁom hunger and satiety. The steers might have then adjusted the threshold for
the tension receptors to signal discomfort in attempt to consume enough DM in order to
reduce the stimulus of hunger. Feeding behavior and blood metabolite data collected
simultaneous would be necessary to conﬁrm this hypothesis.

In Experiment 3, the HF treatment when compared to LF, reduced DMI of both
the Angus and Holstein steers. As the steers increased in body weight, differences in DMI
and DE intake between LF and HF became greater and it appears that the HF diet became
more limiting to DMI as compared to LP. The reason for this difference in DMI as steers
increase in BW is unclear. A possible explanation might be that the balance between
hunger and satiety may have become different between the two treatments as the steers
increased in BW. Ruminal distension was potentially the major constraint regulating DMI
of both treatments when the steers were of lighter BW. However, the energy
concentration of the HF diet was lower than that of the LF diet. This would have resulted
in a reduction of absorbed metabolic fuels and may have increased the discomfort due to
hunger for the steers receiving HF as compared to those receiving LF. Therefore, when
the steers had lighter BW, hunger may have been the predominant factor controlling DMI
of HF, but DMI of LF may have been regulated to a greater extent by satiety. As the
steers increased in BW, they consumed more DM. This increase in DMI might have
provided more absorbed metabolic fuels, potentially reducing the discomfort due to
hunger. The reduction in hunger would have potentially switched the balance of intake
regulation towards those signals producing satiety. Since the HF diet contained greater

NDF concentrations, it would have potentially increased ruminal distension to a greater

128

 

extent when compared to the LF diet. Therefore, at the heavier BW, ruminal distension
might have became a greater factor regulating DMI for steers receiving HF when
compared to those receiving LF.

Holstein steers consumed more DM than Angus steers. The higher DMI may have
been a result of Holstein steers having larger skeletal size, larger rumen capacity, and(or)
higher energy requirements as compared to Angus steers. The skeletal sizes of the two
breeds were not measured, but visually the Holsteins appeared to be roughly two frame
score sizes larger than the Angus. There was a negative relationship between the
difference in apparent total-tract DM digestibility and the difference in DMI for LP minus
HF with Angus steers. When there was no difference in DMI due to ﬁber concentration,
LF had a greater total-tract DM digestibility. When the Angus steers consumed greater
amounts of LF as compared to HF, total-tract DM digestibility of LF was reduced. This
reduction in DM digestibility may have been due to increased passage rate for LP in
association with greater DMI, resulting in more potentially digestible DM escaping
fermentation. In contrast, no relationship was observed for Holstein steers. The reasons
for the breed differences are not clear, but might be because of differences between breeds
in ruminal retention time of digesta for the two diets. Further studies using cannulated
steers of both breeds would be helpful in determining if digestion kinetics and efficiency of

metabolite utilization are different between the two breeds.

Recommendation
When determining if a hybrid has economic potential for use in growing diets, one

must ﬁrst determine if there will be any added production costs associated with the hybrid.

129

Higher seed costs and yield reductions are two of the major factors associated with added
production costs. Improvements in ADG and feed efficiency can also have great impacts
on proﬁtability. Average daily gain impacts the number of days on feed to reach a certain
ﬁnal weight and inﬂuences the cost of yardage, feed, and interest of money borrowed to
purchase cattle and feed. Feed costs and interest on feed also are affected by feed
efficiency. An analysis of returns to labor and management as a result of altering ADG
and gain to feed ratio is presented in Figure 5-1. This analysis was based on the partial
budget and assumptions for steers receiving the isogenic normal (Control) diet in
Experiment 1, and assumes that there is no added production cost for different hybrids.
An improvement in feed efficiency of 0.01, with no change in ADG, increased returns to
labor and management by $6.55/steer. A 0.09 kg/d improvement in ADG, with no change
on feed efficiency, resulted in a $4.03/steer increase in returns. Therefore, selecting
hybrids that would increase or decrease ADG and(or) feed efficiency slightly can have
dramatic effects on proﬁtability.

Feeding the brown midrib-3 corn silage during the 112-d growing period in
Experiment 1 did not change ADG, but resulted in poorer feed efficiency. Ignoring the
higher productions costs, this reduction in gainzfeed of 0.01 would have reduced returns
to labor and management by $7.52/steer. Therefore, it may not be economical to feed
corn silage with higher ﬁber digestibility in diets that contain less than 40% NDF, unless
increases in ADG can offset the potential decreases in feed efficiency. In Experiment 3,
feeding the corn silage diet that contained greater than 50% NDF did not affect feed
efficiency, but reduced ADG by 0.32 kg/d. This reduction in ADG would have reduced

returns by greater than $10.39. Therefore, selecting corn hybrids that contain less than

130

 

 

50% NDF should be beneﬁcial in improving proﬁtability unless declines in feed efficiency
offset the improvements in ADG. Further research needs to be performed to determine if
improvements in ﬁber digestibility of corn silage diets that contain greater than 50% NDF

are economical for light-weight steers.

 

131

 

 

Tables and Figures

Table 5-1. Beef growing phase partial budget for steers receiving brown midrib-3
(BMCS) and isogenic normal (Control) corn silage based diets (Based on Experiment 1)

Corn silage diet

 

Item Control BMCS
Production
Seed cost, $/bag 80.00 180.00
Corn silage DM, % i . 29.8 35.2
Corn silage as-is yield, t/ha 57.6 45.8
Corn silage DM yield, t/ha 16.9 16.2
Partial budget
Additional seed cost, $/t -- 2.33
Additional cost for yield reduction, $/tb -- 5.03
As-is silage delivered to bunlg $/t 27.60 34.96

 

alOne bag is required for each 1.09 hectares at 69,200 plants per hectare.
bAssumes that Control costs $27.60/t wet silage delivered and harvesting cost per
hectare are the same for both hybrids.

132

 

 

 

 

 

 

 

 

133

 

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Table 5-4. Beef growing phase partial budget for steers receiving brown midrib-3
(BMCS) and isogenic normal (Control) corn silagibased diets

 

 

Item Control BMCS
Weights and Prices
Purchase weight, kg 244.0 246.3
Shrunk sale weight, kg 358.3 359.3
Delivered purchase price, $/kg" 1.82 1.82
Purchase cost, $/steer 443.31 447.43
Sale price, $/kgb 1.67 1.67
Gross revenue, $/steer 597.24 598.75
Gross margin. $/steer 153.93 151.32
Performance
Daily gain, kg 1.02 1.01
Gain:Feed, DM basis 0.145 0.135
Out shrink,% 0.00 0.00
Death loss, % 1.00 1.00
Days on feed, d 1 12 112
Feed costs
Feed price, $/t DM 127.00 130.65
Feed cost, $/steer 100.00 109.16
Other operating costs
Yardage rate, $/steer/d 0.30 0.30
Yardage amount, $/steer 33.60 33.65
Veterinary and medication, $/ steer 10.00 10.00
Death loss, $/steer 4.43 4.47
Operating cost subtotal, $/steer 48.03 48.12
Interest rate 9.50 9.50
Interest on cattle, $/steer * 1.00 13.23 13.38
Interest of feed, $/steer * 0.50 1.48 1.62
Interest on other operating, $/steer * 0.50 0.64 0.65
Total interest, $/hd 15.36 15.64
Total operating cost, $/steerc 163.39 172.92
Return to labor and management, $/steer (9.46) (21.60)
Feed cost of gain, $/kg 0.87 0.97
Total cost of gain, $/k,gc 1.43 1.53

 

“CATTLE-FAX, average (1990-2000) for 250 kg feeder calves during October.
aCATTLE-FAX, average (1990-2000) for 363 kg feeder calves during February.

cExcludes animal purchase price.

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135

 

APPENDICES

136

APPENDIX A

 

 

—o—AC—t—-AB--o-LC--k-LB

 

 

 

 

 

 

 

130
120 - 9.
- . ‘ F.- " \‘
0 - \‘ . .
§ . \ 3.. A : ‘\

. _ ’ . - ' 0 ' \ \
<1110 ‘1‘ﬁ‘ , .
“I ) . \ ‘ ' ' ’ _ a
> { ~ ' A\
_. \ . a \
N I ‘ \

8 J ‘ ’\ x

\ ‘ I
P‘ 100 . 1 ,. 0‘ ‘ .
' ‘0 ‘ "I. ‘ ‘u ‘
‘\ ' ~ ‘ .I ‘ I l
1 . b“. A. 0‘ . ,‘
‘ o. ' . '- ‘
90 "‘ " : \k : ‘
. ' ' \\ ..
'\ C v
. '.
80 I I I I fr . I . I I I I I I a I T I T I
-2 0 2 4 6 8 10 12 14 16 18 20 22

Time post initial feeding, b

Figure A-l. Effects of feeding ad libitum isogeneic normal control (AC), ad libitum brown
midrib-3 (AB), limited isogeneic normal control (LC), or limited brown midrib-3 (LB)
corn silage diets on total ruminal VFA concentration over time (Trial 1). Feed offered at
O, 8, and 16 h. Time >< hybrid interaction (P < 0.001). SEM = 4.14.

137

 

 

—o—AC-A—AB--o-Lc--A--LB

 

 

 

 

80
..
.’\ O I\
75 ‘ ,' \ ". .' ‘.
' \
\ o . I n
| ..A\ |‘ 'ﬂ I '1
r ‘ ‘ . .
_ . ‘ '. 0“ 1' * A“ A. t‘ I‘
O 70 - ‘ '. ) g ' = I
a - . , \ .x . .
g _‘ \ U \ \ ‘ ’ n
S i r, "A I ‘ ' \‘o
) I
O 65 '1 1 ‘ I ‘\ l ’3
E ‘ a ‘ \ \ I.
a 'l ‘ \A ' .‘ ‘.
8 . . \ g \ \ e '
a q \ 'n \ ‘0
B \ I ‘ . \ '
0 60 ‘ .0, . \ '
< d ' ‘ ..
" \
i '. .' o. .0
. ‘ .
55 — I.
50 I I I I I I I I I I I I I I I l I I I I I I

 

 

 

-2 0 2 4 6 8 10 12 14 16 18 20 22
Time post initial feeding

Figure A-2. Effects of feeding ad libitum isogeneic normal control (AC), ad libitum brown
midrib-3 (AB), limited isogeneic normal control (LC), or limited brown midrib-3 (LB)
corn silage diets on molar percentage of acetate over time (Trial 1). Feed offered at O, 8,
and 16 h. Time >< hybrid interaction (P < 0.001). SEM = 2.64.

138

 

 

 

—o—AC+AB--O-LC--A-LB

 

 

 

 

 

 

 

28
26 ‘. r.
. I .
-I ' “ ‘-
.: ' . .. .’
I: 24 . : l‘ “ I ‘.
/ \
g - ' ‘0 ﬁ " ‘LI .
S 22 - ' I ‘1 \ \ I; 3.
O ‘ \ II A . ; \ ‘
E A . ‘ 'I \ | ‘
a I ' ‘5‘ I' \A‘ 5' .’
o ‘ -
a 20:- -.' ‘A". ' -. i ‘o
= 4 ‘ 'g \ ' “ f
.2 .1 I. x I . ‘, I
e . 5." 1. I 1 ~ I
o . \
" ' I s ‘ .' ‘-
-I \.' .‘ ‘\ e
16 l ‘ \ U. ‘5 0’
., \‘ ' .
1 9
14 I I I I I I I I I I I I 1 I I I I I

 

-2 0 2 4 6 8 10 12 l4 16 18 20 22
Time post initial feeding, h

Figure A-3. Effects of feeding ad libitum isogeneic normal control (AC), ad libitum brown
midrib-3 (AB), limited isogeneic normal control (LC), or limited brown midrib-3 (LB)
corn silage diets on molar percentage of propionate over time (Trial 1). Feed offered at 0,
8, and 16 h. Time >< hybrid interaction (P < 0.001). SEM = 1.30.

139

 

 

+AC+AB--O-LC--t-LB

 

 

 

15

14:

13“

 

Butyrate, mol/100 mol

 

 

 

 

6 I I I I I I I I f I I I I I ' I I I I I ' I '
-2 0 2 4 6 8 10 12 l4 16 18 20 22
Time post initial feeding, h

Figure A-4. Effects of feeding ad libitum isogeneic normal control (AC), ad libitum brown
midrib-3 (AB), limited isogeneic normal control (LC), or limited brown midrib-3 (LB)
corn silage diets on molar percentage of butyrate over time (Trial 1). Feed offered at 0, 8,
and 16 h. Time X hybrid interaction (P < 0.05). SEM = 0.70.

140

APPENDIX B

 

+LF- -O- - LF+RIB +HF' " " HF+ RIB

 

 

 

 

140
130 —:

120

 

y—t

.—A

C
I

100 1

Total VFA, mM

VD
c
1111

 

 

 

 

60 I T I I I I I I I I I I I I I I I I I I I I I
-2 0 2 4 6 8 10 12 14 l6 18 20 22
Time post initial feeding, h

Figure B-l. Effects of feeding a normal corn hybrid (low-ﬁber; LF) or its male-sterile
counterpart (high-ﬁber; HF), without or with rumen inert bulk (RIB) on total ruminal

VFA concentration over time. Feed offered at 0, 12 h. Time X ﬁber level interaction (P <
0.0001). SEM = 4.9.

141

 

—o—LF- -o - LF+RIB +HF- -A - HF+ RIB

 

 

 

 

74

111111

72

685

Acetate, mol/ 100 mol

 

 

 

 

-2 0 2 4 6 8 10 12 14 16 18 20 22
Time post initial feeding, h

Figure B-2. Effects of feeding a normal corn hybrid (low-ﬁber; LF) or its male-sterile
counterpart (high-ﬁber; HF), without or with rumen inert bulk (RIB) on molar percentage
of acetate over time. Feed offered at 0, 12 h. Time X ﬁber level X bulk interaction (P <
0.01). SEM = 0.54.

142

 

 

—o—LF- -o - LF+RIB +HF- -‘ - HF+ RIB

 

 

 

12‘
11‘

10" ,7

 

 

 

_
E
9 a
Q
S d
a 9‘ 0.“‘
a I .-...,-—--o. .' ~.
H q 9“. ~- “ . .--‘
E . 0‘ . "x' 3%.
b 8—4 ’ A§-.' .~ ‘
g j I 0
I 9,
.1
I
I . A
1 A
7—1
6 I I 7 I I I 1 [ﬁ' I I I r l I I Ij U i I Iﬁ

-2 0 2 4 6 8 10 12 l4 16 18 20 22
Time post initial feeding, h

Figure B-3. Effects of feeding a normal corn hybrid (low-ﬁber; LF) or its male-sterile
counterpart (high-ﬁber; HF), without or with rumen inert bulk (RIB) on molar percentage
of butyrate over time. Feed offered at 0, 12 h. Time X ﬁber level interaction (P <
0.0001). SEM = 0.40.

143

VITA

Kent Eric Tjardes was born on February 4, 1972, in Gibson City, Illinois, son of
Harry and Gale Tjardes. Kent was raised on a grain and cattle farm and was a 10-year
active member of the Illinois Junior Polled Hereford Association. He graduated as
valedictorian from Gibson City Junior-Senior High School in 1990. In 1994, Kent
received a 38., with honor, in Animal Science from the University of Illinois, Urbana-
Champaign. He continued at the University of Illinois and received a M.S., in Ruminant
Nutrition, in 1996, and began work on his Ph.D. at Michigan State University in August of
1996. Kent is a member of the American Society of Animal Science, and American Dairy
Science Association. He is also a member of the Gamma Sigma Delta honorary society
and alumni of the Alpha Chapter of Alpha Gamma Rho social/professional fraternity.
After completion of his Ph.D., Kent will become a faculty member in the Department of
Animal and Range Science at South Dakota State University. Kent and his ﬁancé,

Michelle Smiricky, will be wed on June 1, 2002.

144

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