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6/01 cJCIRC/Dateoue.p65-p.15

 

PELLETED BEET PULP SUBSTITUTED FOR HIGH-MOISTURE CORN:
EFFECTS ON FEED INTAKE, RUMINAL FERMENTATION, DIGESTION, AND
MILK PRODUCTION OF DAIRY cows
By

Jennifer Anne Voelker

A THESIS

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

MASTER OF SCIENCE
Department of Animal Science

2002

ABSTRACT
PELLETED BEET PULP SUBSTITUTED FOR HIGH-MOISTURE CORN:
EFFECTS ON FEED INTAKE, RUMINAL FERMENTATION, DIGESTION, AND
MILK PRODUCTION OF DAIRY cows
By

Jennifer Anne Voelker

Grain is Often substituted for forage in diets for high-producing dairy cows
tO increase feed intake, diet fermentability, and milk yield, but greater dietary
starch concentration can also reduce performance. Beet pulp contains 65-75%
insoluble ﬁber and pectin, SO it is frequently included in low-forage diets tO
moderate ruminal fermentation. TO investigate the range Of inclusion rates for
beet pulp, low-forage diets in which pelleted beet pulp replaced high-moisture
corn grain at 0%, 6%, 12%, and 24% Of diet dry matter were fed tO eight
ruminally and duodenally cannulated dairy cows. Substituting beet pulp for high-
moisture corn decreased dry matter intake, but milk yield was unaffected and
milk fat yield was slightly improved for low inclusion rates. Ruminal pH was
unexpectedly similar among treatments. Substituting beet pulp for high-moisture
corn improved ﬁber digestion and dramatically shifted the dominant Site Of starch
digestion from the rumen tO the intestines without reducing whole tract starch
digestibility. However, efﬁciency Of microbial protein production was not different
among treatments. The results Of this experiment suggest that substituting beet
pulp at low inclusion rates can improve diet digestibility and might improve milk

fat yield in high-producing dairy cows.

For Howard and Mary Voelker, who Showed me how tO learn and tO live.

ACKNOWLEDGEMENTS

I am grateful tO Dr. Allen for his guidance and for providing Opportunities
for me tO learn, from arranging my ﬁrst hands-on experiences in dairy nutrition,
through hours Of interpreting mind-bending results Of “just a Simple experiment,”
to the transformation Of a backup plan into a fascinating project. Thanks
especially tO both Dr. Allen and to the MSU Graduate School for providing the
ﬁnances that gave me freedom to pursue a new ﬁeld Of applied knowledge, to
complete this and other research, and to learn from others in the ﬁeld.

I would like tO thank Dr. Beede, Dr. Benson, and Dr. Bourquin for their
advice and suggestions as members Of my graduate committee. Each one has
contributed in a speciﬁc, important way tO my understanding and research
experience; they have been part Of my broader experience as a graduate student
at MSU as well, and I’m glad tO have worked with them. Thanks also tO Dr.
Ames for performing the ruminal and duodenal cannulation surgeries.

NO research like this could be completed without a team Of people to
Share the intellectual, physical, and emotional load, and this is a great team.

This experiment should actually have been named “00-JVDMDLYYCSMMO-2, et
al.” That would include Dave Main, Dewey Richard Longuski, Jackie Yun Ying,
C. Steve Mooney, (Dr.) MasahitO Oba, and others. It’s impossible tO thank yOU
Speciﬁcally for everything you’ve done, and the only way I can think Of tO repay
you is tO explain what we’ve discovered as well as I can tO people, and tO pass

on what you’ve taught me and done for me tO others. Christy Taylor and Kevin

Harvatine, thanks for helping me interpret the results and for being interested in
this research, especially in the last critical weeks. Thanks also tO everyone else
who got covered in rumen ﬂuid tO help out with this research project.

I’m very grateful tO the crew at the MSU dairy farm —BOb Kreft, the full-
time crew, and the student employees— for making the day-tO-day aspects Of this
research happen. Being able to depend on them tO do things and tO do them
well made a world Of difference.

Many thanks to those who helped me learn ﬁrst-hand what it means to
feed cows and run a dairy farm: the crew at the MSU campus dairy farm; the
folks at the UP. Experiment Station in Chatham for an incredible month Of
farming experience and a taste Of small-town U.P. life; and Steve Mooney for
(along with an armload Of helpful farm management bOOkS) a video on how to get
a 1700-pound animal tO do what you want her to do without getting hurt.

Finally, thanks to Mom, Dad, John and James for challenging me tO grow
and learn, for encouraging me tO lOOk beyond (geographically, spiritually, and
philosophically), for letting me be myself (and leading by example), for helping

me deal with the challenges that that brings, and for loving me.

TABLE OF CONTENTS

LIST OF TABLES .................................................................................. ix
LIST OF FIGURES ................................................................................. xi
LIST OF ABBREVIATIONS .................................................................... xii
INTRODUCTION ................................................................................... 1
CHAPTER 1
A REVIEW OF LITERATURE
Beet Pulp ..................................................................................... 3
Pectin .......................................................................................... 5
Fermentation of Pectin .................................................................... 6
Fermentation of Beet Pulp In VitrO ................................................... 1O
Beet Pulp Substituted for Grain In Dairy Cattle Rations ....................... 12
Beet Pulp and Regulation Of Feed Intake ........................................... 15
Effects of Beet Pulp on Chewing Behavior ........................................ 25
Beet Pulp and Microbial Efﬁciency ................................................... 26
Effects of Beet Pulp on Milk Production ............................................ 31
Effects Of Beet Pulp on Energy Partitioning ........................................ 35
Summary .................................................................................... 35
CHAPTER 2

Pelleted beet pulp substituted for high-moisture corn: Effects on feed
intake, chewing behavior, and milk production of lactating dairy cows

ABSTRACT ................................................................................. 39
INTRODUCTION ......................................................................... 40

vi

MATERIALS AND METHODS

Treatments and Cows .......................................................... 42
Data and Sample Collection .................................................. 43
Sample and Statistical Analysis .............................................. 44

RESULTS AND DISCUSSION

Feed Intake ........................................................................ 47

Regulation Of Feed Intake ..................................................... 48

Milk Production and Nutrient Partitioning ................................. 53

Plasma Insulin .................................................................... 53

SUMMARY ................................................................................. 56
CHAPTER 3

Pelleted beet pulp substituted for high-moisture corn: Effects on digestion
and ruminal digestion kinetics of lactating dairy cows

ABSTRACT .................................................................................. 70
INTRODUCTION ......................................................................... 71
MATERIALS AND METHODS
Treatments and Cows .......................................................... 73
Data and Sample Collection .................................................. 74
Sample and Data Analysis .................................................... 75

RESULTS AND DISCUSSION

Ruminal NDF Digestion ........................................................ 79
Ruminal pH and NDF Digestion ............................................. 80
Whole Tract NDF Digestion ................................................... 81
Ruminal Starch Digestion Kinetics .......................................... 81

vii

Site of Starch Digestion ......................................................... 82

Digestion of DM and OM ...................................................... 84

SUMMARY ................................................................................. 85
CHAPTER 4

Pelleted beet pulp substituted for high-moisture corn: Effects on ruminal
fermentation, pH, and microbial protein efﬁciency of lactating dairy cows

ABSTRACT ............................................................................... 94
INTRODUCTION ......................................................................... 95
MATERIALS AND METHODS ......................................................... 96
Treatments and Cows .......................................................... 96
Data and Sample Collection .................................................. 97
Sample and Statistical Analysis ............................................ 100
RESULTS AND DISCUSSION
Ruminal pH ...................................................................... 103
Ruminal Volatile Fatty Acid Concentration and Removal ........... 104
Ruminal pH and Volatile Fatty Acids ..................................... 106
Ruminal Nitrogen Digestion ................................................. 107
Microbial Nitrogen Efﬁciency ................................................ 107
Microbial Nitrogen Efﬁciency and Fermentation ....................... 108
Microbial Nitrogen Efﬁciency and Ruminal Passage Kinetics ...... 109
SUMMARY ............................................................................... 112
CHAPTER 5
CONCLUSIONS AND IMPLICATIONS .................................................... 123
REFERENCES .................................................................................. 127

viii

LIST OF TABLES

CHAPTER 1

Table 1. Chemical composition Of dried, unmolassed beet pulp ..................... 38
CHAPTER 2

Table 1. Nutrient composition of high-moisture corn and dried, pelleted beet

pulp .................................................................................................... 58
Table 2. Ingredient and nutrient composition of experimental diets ................. 58

Table 3. Effects Of substitution Of pelleted beet pulp for high-moisture corn on
nutrient intake and ruminal pool ............................................................... 59

Table 4. Effects of substitution Of pelleted beet pulp for high-moisture corn on
meal patterns and water consumption ....................................................... 60

Table 5. Effects of substitution Of pelleted beet pulp for high-moisture corn on
chewing time ........................................................................................ 61

Table 6. Effects of substitution Of pelleted beet pulp for high-moisture corn on
chewing activity .................................................................................... 62

Table 7. Pearson correlation coefﬁcients between DMI and eating or chewing
behavior .............................................................................................. 63

Table 8. Pearson correlation coefﬁcients between DMI and characteristics Of
ruminal fermentation and pH ................................................................... 63

Table 9. Effects of substitution of pelleted beet pulp for high-moisture corn on
milk production ...................................................................................... 64

Table 10. Effects Of substitution Of pelleted beet pulp for high-moisture corn on
energy balance and plasma insulin ........................................................... 65

Table 11. Pearson correlation coefﬁcients between plasma insulin and
characteristics Of intake, production, and energy balance ............................... 65

CHAPTER 3

Table 1. Nutrient composition of high-moisture corn and dried, pelleted beet
pulp .................................................................................................... 87

Table 2. Ingredient and nutrient composition of experimental diets ................. 87

Table 3. Effects of substitution Of pelleted beet pulp for high-moisture corn on
ruminal digestion kinetics ........................................................................ 88

Table 4. Correlation coefﬁcients for ﬁber digestion kinetics and ruminal pH ...... 88

Table 5. Effects Of substitution of pelleted beet pulp for high-moisture corn on
digestion of total NDF and potentially digestible NDF (pdNDF) ....................... 89

Table 6. Effects Of substitution Of pelleted beet pulp for high-moisture corn on
digestion of starch .................................................................................. 90

Table 7. Effects of substitution of pelleted beet pulp for high-moisture corn on

digestion of DM and OM ......................................................................... 91

CHAPTER 4

Table 1. Nutrient composition Of high-moisture corn and dried, pelleted beet

pulp ................................................................................................... 1 13
Table 2. Ingredient and nutrient composition Of experimental diets ............... 113

Table 3. Effects of substitution Of pelleted beet pulp for high-moisture corn on
ruminal pH .......................................................................................... 114

Table 4. Effects of substitution of pelleted beet pulp for high-moisture com on
ruminal fermentation and VFA removal ..................................................... 115

Table 5. Pearson correlation coefﬁcients for ruminal VFA concentration and
related variables .................................................................................. 116

Table 6. Effects of substitution Of pelleted beet pulp for high-moisture corn on N
digestion ............................................................................................ 116

Table 7. Pearson correlation coefﬁcients for microbial efﬁciency and related
variables ............................................................................................ 117

LIST OF FIGURES

CHAPTER 2

Figure 1. Relationship between DMI (kg/d) and (a) average kg DMI/meal; (b)
mean ruminal pH; and (c) pH standard deviation ......................................... 66

Figure 2. Relationship between sorting against NDF (%NDF in orts - %NDF in
feed) and 3.5% FCM yield ...................................................................... 68

Figure 3. Relationship between milk fat concentration and mean ruminal pH...69

CHAPTER 3

Figure 1. Relationship between rate Of digestion of potentially digestible NDF
(%lh) and mean ruminal pH .................................................................... 92

Figure 2. Relationship between (a) starch digested (kg/d) and duodenal starch
ﬂow; and (b) starch digestibility (% duodenal ﬂow) and duodenal starch ﬂow....93
CHAPTER 4

Figure 1. Relationship between VFA concentration in rumen ﬂuid and (a) rate Of
valerate absorption; (b) liquid passage rate; and (c) mean ruminal pH ........... 118

Figure 2. Relationship between microbial N efﬁciency (9 microbial N / kg
TRDOM) and (a) 24-h mean ruminal pH; (b) concentration Of ammonia in rumen
ﬂuid; (C) concentration Of VFA in rumen liquid; (d) ruminal starch digestion rate;
(e) starch passage rate; and (f) liquid passage rate .................................... 120

xi

ADF
BCS
BP
BW
CP
DM
DMI
F:C
FCM
HMC
INDF

kabs

kd

MN
MNE
MY
NAN
NANMN
NDF

NEL

LIST OF ABBREVIATIONS

Acid Detergent Fiber

Body Condition Score

Beet Pulp

Body Weight

Crude Protein

Dry Matter

Dry Matter Intake
Forage-to-Concentrate Ratio
Fat-corrected Milk
High-Moisture Corn
lndigestible NDF

Absorption Rate

Digestion Rate

Passage Rate

Microbial Nitrogen

Microbial Nitrogen Efﬁciency
Milk Yield

Non-Ammonia Nitrogen
Non-Ammonia, Non-Microbial Nitrogen
Neutral Detergent Fiber

Net Energy of Lactation

xii

NEM
NFFS
(MA
pdNDF
SD
TCT
'ﬂWR
TRDOM

VFA

Net Energy of Maintenance

Non-Forage Fiber Source

Organic Matter

Potentially Digestible NDF

Standard Deviation

Total Chewing Time

Total Mixed Ration

Truly Ruminally Degraded Organic Matter

Volatile Fatty Acids

xiii

INTRODUCTION

Grain is Often used to increase the energy intake and milk yield of dairy
cows. Substituting grain for forage can increase feed intake by reducing the
ﬁlling effect Of a diet (Allen, 2000) and Often increases energy intake. In some
cases, adding grain can also increase ruminal microbial protein production.
Greater energy intake and microbial protein production increase the ability Of
cows to attain their maximum genetic potential for milk production. Increasing
milk yield per cow reduces the amount of energy used for maintenance per
kilogram Of milk produced, thereby increasing the efﬁciency of milk production.

However, increasing dietary starch concentration while decreasing neutral
detergent ﬁber (NDF) from forage can have several negative effects. Feeding
less forage NDF reduces chewing (Allen, 1997). Fiber digestibility is reduced
when dietary starch concentration is increased, leading to altered volatile fatty
acid production in the rumen (Grant and Mertens, 1992). Propionate production
is increased, which can depress dry matter intake (DMI; Anil and Forbes, 1980)
and potentially reduce milk yield or milk fat concentration. Excessive
fermentation of starch can decrease the efﬁciency of microbial protein production
because of energy spilling (Strobel and Russell, 1986). Total tract digestibility of
starch and of total nutrients can be reduced if increasing starch intake leads to
drastic increases in passage rate. While lowering forage intake and increasing
grain intake has the potential to increase energy intake and milk yield, this

strategy can also have the opposite effect.

There are several alternative strategies for increasing dietary energy
content while reducing the risk of negative side effects. One such strategy is to
add carbohydrate sources that are more rapidly and extensively fermented than
forage NDF and that mimic some of its beneﬁcial effects, but do not bring the
same negative effects as starch fermentation. Many non-forage ﬁber sources ﬁt
that description, and beet pulp has been studied in this role because Of its high
concentrations Of rapidly-fermented soluble and insoluble ﬁber (Mansﬁeld et al.,
1994; Swain and Armentano, 1994; O’Mara et al., 1997; Clark and Armentano,
1997). However, the effects of substituting beet pulp for grain on ruminal
digestion kinetics and microbial protein production have not been investigated in
dairy cattle; most studies have focused on feed intake, chewing response, and
milk production.

It might be possible to partially replace grain with beet pulp in energy-
dense diets to moderate the negative effects of starch while avoiding the
negative effects of a higher forage NDF content. Therefore, the Objective of this
research was to evaluate the effects Of increasing substitution of beet pulp for
high-moisture corn on feed intake and chewing behavior, ruminal fermentation,

nutrient digestion, and milk production.

CHAPTER 1

A REVIEW OF LITERATURE

Beet Pulp

Beet pulp is a byproduct Of the extraction of sucrose from the sugar beet
(Beta vulgaris). The sugar beet industry originated in Europe in the early 18005
but was not successful in the United States until around 1900, and it has been
limited to north-central and western states (Bichsel, 1988). The sugar industry is
dominated by cane sugar, most of which is imported, but maintenance Of the
capacity to produce sugar domestically has traditionally been a priority,
especially in time of war (Winner, 1993). In Michigan, nearly all cultivation of
sugar beets takes place in the lowlands around Saginaw. In 2000, the state Of
Michigan ranked fourth in the nation in sugar beet production with 166,000 acres
and over 3 million tons of beets (MDA, 2002).

Sugar beets grown in the northern states are generally harvested between
September and November and stored in piles to permit more extended Operation
Of processing plants. (In California, beets must be processed immediately due to
warmer air temperatures, and part of the crop is left in the dry ground for spring
harvest.) A sugar beet weighs about 1-2.5 kg at harvest and contains
approximately 25% dry matter (Bichsel 1988). Of that dry matter, 74% is
sucrose, 3% is ash, 18% is soluble organic non-sugars (such as carbohydrates,

organic acids, protein, amino acids, amides, betaine, and saponins), and 5% is

insoluble organic non-sugars (hemicellulose, cellulose, pectin, and lignin;
Tjebbes 1988). To extract the sucrose, the beets are cut into “cossettes”
approximately 5 mm2 and 5-7.5 cm long. There are several different methods for
extracting sucrose, but the process generally uses hot water (which disrupts cell
walls) and counter-current diffusion in several steps, along with pressing.
Approximately 98% of the sucrose is removed, producing a juice containing
approximately 12% sugar, which is puriﬁed by precipitation and ﬁltering. The
resulting solution is reduced to a concentrate, and the sucrose is crystallized
(Bechsel 1988).

Byproducts Of beet sugar extraction include lime sludge from the
precipitation of impurities, which is sometimes used as a soil improver (Tjebbes
1988); beet pulp, which is sold wet or dried for numerous uses (to be described
further); and molasses from the sugar crystallization, which is either added back
to the pulp before drying or used to produce citric acid, antibiotics, yeast, and
other biological and Chemical commodities (Bechsel 1998).

One metric ton Of sugar beets will produce approximately 149 kg Of sugar
and 50 kg of pulp (Tjebbes 1988). The chemical composition of the pulp varies
depending on location, year, and processing methods, but dried, unmolassed
beet pulp used in several feeding experiments with ruminants has contained, on
average (% DM): 6% ash, 23.6% ADF, 46.0% NDF, 11.7% CP, 1.5% ether
extract, and 4.5% Iignin (Table 1). Beet pulp also contains a signiﬁcant
concentration Of gums, Speciﬁcally pectic substances, an amorphous class of

polysaccharides which comprises approximately 25% Of dried beet pulp (Thibault

et al., 1991 ). The usefulness of these pectic substances for adding texture and
ﬁber to human food products has been widely known, and the fermentation Of

pectin has been studied in nonruminants (including humans) and in ruminants.

Pectin

Pectic substances are a Class of polysaccharides that are partially, and
variably, soluble in water, and are especially known for their gelling properties in
the presence of sugar or acid. (Therefore, the chemistry of pectin is the subject
Of much industrial, nutritional, and medical study.) Pectin is found in greatest
concentrations in the middle lamella Of plant cells, and the pectin concentration
decreases from the exterior to the interior of the cell wall (Mauseth, 1988).
Pectin adheres plant cells to each other and strengthens the cell wall. The
chemical composition and molecular weight of pectin vary among sources, but
the deﬁning structural element of pectin is D-galacturonic acid, joined by cat-1,4
linkages (Van Buren, 1991). Galacturonic acid may be present as both the acid
(COOH) and the methyl ester (COOCHa). The length Of the polymers is affected
by species type and by growing and storage conditions, and other neutral sugars
and organic acids are present in varying proportions. Rhamnose units are
inserted at irregular intervals between the galacturonic acid units; these introduce
a kink into the structure and often are linked to arabinan, galactan, or
arabinogalactan Side Chains (Van Buren, 1991). Beet pulp pectin contains high
concentrations Of these neutral sugars relative to other pectins from other

common sources such as apple and citrus pulp. This, in combination with low

 

molecular weights and a high degree of acetylation, may prevent the alignment
required for gelation, so that beet pulp pectin is not as valuable as other pectins
for use as a gel (Van Buren, 1991).

Among common components of dairy rations, beet pulp has the highest
concentration of pectin, approximately 25% Of DM (Thibault et al., 1991). Citrus
pulp also has a large concentration of pectin but also has a large concentration of
soluble sugars. Legume forages such as alfalfa and clover contain 5 to 10%
pectic substances (Gaillard, 1962), whereas grasses contain 2 to 4% pectin

(Waite and Gorrod, 1959). Grains contain very little pectin (Kertesz, 1951 ).

Fermentation of Pectin

Some Of the ﬁrst characterizations of microbial fermentation Of pectin were
published by Bryant and coworkers in the 19503 and 19603. They identiﬁed
Butyrivibrio ﬁbrisolvens, Prevotella (formerly Bacteroides) ruminicola,
Lachnospira mulitparus, Succinivibrio dextn'nosolvens, and Fibrobacter (formerly
Bacteroides) succinogenes as pectin-fermenting species (Bryant and Doetsch,
1954; Bryant and Small, 1956a; Bryant and Small, 1956b; Bryant et al., 1958).
Dehority (1969) reported that B. ﬁbrisolvens, P. ruminicola, and L. multiparus
grew using puriﬁed pectin as the sole added energy source. In the same
experiment, L. multiparus did not grow on puriﬁed galacturonic acid, and the
authors suggest that the species has an enzyme system that carries out trans-
elimination to cleave the pectin chains (pectinglycosidase), or enzymes that

Cleave the methyl ester bond (pectinesterase). Other species that can utilize

galacturonic acid monomers have a different pectinglycosidase, which directly
hydrolyzes the Ot-1,4 bonds, perhaps in addition to other pectin-degrading
enzymes (Dehority, 1969).

Fermentation of pectin by L. multiparus may be further limited by its
inability to degrade cellulose and hemicellulose in order to gain access to pectin
(Osborne and Dehority, 1989). These researchers also found that the cellulolytic
Fibrobacter succinogenes and hemicellulolytic P. ruminicola have very limited
ability to ferment or utilize puriﬁed pectin alone or in mixed culture but are able to
degrade and utilize forage pectin synergistically in mixed culture. Therefore,
tests of pectin fermentation by isolated bacteria have limited application to the
rumen environment.

Efforts have been made to characterize the growth Of pectinolytic bacteria
in response to feeding, diet composition, and ruminal pH. Leedle and coworkers
(1982) reported that, on a high-forage diet, pectinolytic bacteria had the lowest
population 2 hr after feeding, and the highest population from 8-12 h after
feeding. This is likely caused by a reduction in pH shortly after feeding, when
fermentation of readily-available starch and sugars rapidly produces volatile fatty
acids (VFA). The pectinolytic and cellulolytic populations responded similarly
after feeding, but pectin degraders recovered more quickly than the cellulolytic
population. Like cellulose, pectin fermentation is sensitive to low pH. Marounek
and coworkers (1985) found that when pectin was the sole carbohydrate, rate Of
total VFA production and ﬁnal concentration in vitrO was greater when pH was

6.5-7.0 than when pH was 5.7-6.4. The sensitivity Of pectin degraders to low pH

has also been demonstrated by in vitro fermentations at pH 6.7 or pH 6.0
(Strobel and Russell, 1986). Reducing pH from 6.7 to 6.0 decreased pectin
utilization by 53%, while the utilization of starch and sucrose was not affected by
pH. Bacterial protein production on pectin was also reduced (by 69%) at lower
pH, due in part to greater energy spilling (Strobel and Russell, 1986).

Fermentation Of pectin is carried out through more than one chemical
pathway. Methyl groups can be hydrolyzed by pectin esterase (pectase) to yield
pectic acid and methanol, and polygalacturonase (pectinase or
polygalacturonidase) catalyzes the hydrolysis of 1,4-glycosidic linkages in pectin
to form galacturonic acid (Leng, 1970). Several strains Of B. ﬁbrisolvens have
shown higher esterase activity when grown on pectin compared with glucose,
indicating that one mechanism to Obtain energy from pectin is by hydrolyzing the
ester bonds on methylated pectin chains (Hespell and O’Bryan-Shah, 1988).
Leng (1970) suggested, and others have agreed (Fahey and Berger, 1988; Van
Soest, 1994), that polygalacturonide is cleaved by polygalacturonase into
galacturonic acid monomers. Galacturonic acid is converted to pyruvate through
the pentose phosphate pathway and glycolysis, then further metabolized to VFA,
especially acetate (Leng, 1970; Van Soest, 1994). An alternate, modiﬁed Entner—
Doudoroff pathway has been proposed for pectin degradation by B. ﬁbrisolvens
and P. ruminicola, in which galacturonic acid monomers are not formed, but
pyruvate is still the end product (Marounek and Duskova, 1999). Acetate was
the dominant VFA product from pectin fermentation, and the experiment

demonstrated that the two species produced more acetate when grown on pectin

than when grown on D-glucose (Marounek and Duskova, 1999). The dominance
of acetate as a product Of pectin fermentation is well established (Marounek et.
al., 1985; Strobel and Russel, 1986; Leedle and Hespell, 1983). Pectin
fermentation also produces much less lactate than does the fermentation of
starch or glucose (Marounek et al., 1985; Strobel and Russell, 1986; Leedle and
Hespell, 1983).

The fermentation rate of pectin is generally intermediate between the rates

 

Of fermentation Of soluble carbohydrates, such as starch and sugars, and
insoluble carbohydrates such as cellulose and hemicellulose. In in vitro
experiments utilizing rumen inocula from goats fed hay and concentrates, rate of
VFA production with pectin as the substrate was more rapid than with
hemicellulose at both high and low ends Of the typical range Of ruminal pH
(Marounek et al., 1985). VFA production was more rapid for pectin than for
starch in a higher pH range (above 6.5) and was slower for pectin than for starch
at a lower pH range (below 6.5; Marounek et al., 1985). Pectin is fermented
more rapidly than insoluble ﬁber components, but like cellulose and
hemicellulose, pectin fermentation is inhibited at low pH. Therefore, pectin can
increase the rate of carbohydrate fermentation; replacing starch with pectin may
also attenuate the postfeeding pH decline, which can improve digestion of
cellulose and hemicellulose.

Because the peak in pectin fermentation is delayed for several hours after
feeding; because pectin fermenters Slow their production of VFA as pH declines;

and because pectin fermentation produces very little lactate, adding feeds with

high pectin contents (such as beet pulp) may provide more rapidly and more
thoroughly-fermented carbohydrate in diets for dairy cattle without negatively

affecting the digestion Of cellulose and hemicellulose.

Fermentation of Beet Pulp In Vitro

Among the feeds commonly included in diets for dairy cows, beet pulp has
one Of the highest pectin contents. This, and the rapid and extensive digestion of
its insoluble ﬁber components (Torrent et al., 1994; Bhatti and Firkins, 1995),
have made beet pulp attractive as an alternative to grain and forages for
increasing diet digestibility. Several comparisons have been made of the in vitro
and in Situ fermentation Of beet pulp, other byproducts, forages, and grains
(Chester-Jones et al., 1991; Sunvold et al., 1995; Sanson, 1993; Bach et al.,
1999; Mansﬁeld et al., 1994). However, only a few directly compare grains and
beet pulp.

One group (Mansﬁeld et al., 1994) studied production and intake in dairy
cattle fed diets with 30% com or 15% com plus 15% beet pulp, then used 10-day
continuous culture to estimate characteristics of digestion and fermentation.
Digestibility Of OM, OM, NDF, ADF, and non-structural carbohydrates (NSC) was
not affected by treatment. Acetate concentration was greater, and butyrate and
branched-Chain VFA concentrations were lower, for the beet pulp diet than for
the high-com diet. Total VFA and propionate concentrations were not different
between treatments. Fluid ammonia concentration and efﬂuent ammonia ﬂow

were greater for the all-corn diet.

10

Chester-Jones and coworkers (1991) replaced rolled corn with dried beet
pulp at 0%, 15%, and 30% of diet DM using eight-day continuous culture in vitro
experiments. The experiment also compared two protein sources, and
interactions between carbohydrate and protein sources complicate interpretation
of beet pulp effects. No effects Of beet pulp concentration were found for
digestibility Of OM, OM, NDF, or NSC, perhaps due to differences in effects Of
protein sources. Replacing the high-starch corn with high-ﬁber beet pulp
increased the concentration Of acetate and decreased butyrate and isobutyrate
content, but did not affect propionate concentration. These results are similar to
the work by Mansﬁeld et al. (1994). Carbohydrate source had no effect on
bacterial N ﬂow or g bacterial N per kg truly-digested DM. When soybean meal
was the primary protein source, substitution Of beet pulp for corn decreased both
ammonia N concentration in the ﬂuid and efﬂuent ammonia N ﬂow (Chester-
Jones et al., 1991), possibly because some amylolytic bacteria are highly
proteolytic (Russell et al., 1981 ).

A third experiment compared, among other feeds, molassed beet pulp and
cracked corn as supplements tO forage, in eight-day continuous culture (Bach et
al., 1999). Because the beet pulp contained molasses, it probably contained
more sugars than would unmolassed beet pulp. In this experiment, true
digestibility Of OM, OM, and NSC were greater for corn than for beet pulp, as
might be expected, but NDF digestibility was not affected. The absence Of an
effect on NDF digestibility might be because there was no difference in pH

between the two treatments. Total VFA concentration was higher for com,

11

 

reﬂecting the greater digestibility of DM and NSC on that treatment. However,
concentrations Of individual VFA, such as acetate and propionate, and acetate-
to-propionate ratio were not different between the treatments, although a beet
pulp treatment would be expected to result in greater acetate and lower
propionate production. Lactate concentration was not reported. Carbohydrate
source did not affect ﬂuid ammonia-N concentration, bacterial N ﬂow, or g
bacterial N/ kg OM truly digested.

A primary limitation of using continuous culture and other in vitro methods
for comparing fermentation of carbohydrates is manipulation of pH. Using
buffers to maintain a speciﬁc pH range or allowing fermentation to progress
without some simulation of the extrinsic factors affecting pH reduces the
possibility of determining any effects Of carbohydrate source that would be
produced in an actual rumen environment. Speciﬁcally, the effects of
carbohydrate type on VFA production, OM and NDF digestion, and N
metabolism, which are affected in vivo by pH, may not be accurately reproduced

under in vitro conditions.

Beet Pulp Substituted for Grain in Dairy Cattle Rations

Four previous experiments have examined the substitution of dried beet
pulp for grain in which the treatments were fed ad Iibitum to lactating dairy cattle
as a total-mixed ration (T MR) with a ﬁxed forage-tO-concentrate ratio (F:C; beet
pulp included in concentrate; Mansﬁeld et al., 1994; Swain and Armentano, 1994;

Clark and Armentano, 1997; O’Mara et al., 1997). These studies provide the

12

most reliable conclusions comparing the effects Of beet pulp and grain in dairy
cows; eleven other experiments compared grain and beet pulp under less
controlled feeding conditions (Bhattacharya and Lubbadah, 1971; Huhtanen,
1987; Sutton et al., 1987; Beauchemin et al., 1991; Sievert and Shaver, 1993;
Van Vuuren et al., 1993; Friggens et al., 1995; Petit and Tremblay, 1995a,b;
Moorby et al., 1996; Dewhurst et al., 1999; and Keady et al., 1999). Responses

such as DMI and milk production from these eleven experiments will be

summarized when useful.

The experiment by Mansﬁeld and coworkers (1994) utilized 46 Holstein
cows, starting in early lactation, to measure intake, milk yield and milk
composition in a 2 x 2 factorial arrangement Of treatments. Carbohydrate source
(ground corn alone or partially replaced by beet pulp) was one set of treatments,
and protein source (soybean meal or meat and bone meal) was the second set Of
treatments. The corn diets contained 28% or 32% com (depending on protein
source); the beet pulp diets each contained 15% beet pulp substituted for the
corn.

Work by Swain and Armentano (1994) utilized 21 Holstein cows in
midlactation in an incomplete block design with seven treatments and three
periods. Treatments of interest were a basal diet containing 58% ﬁnely ground
corn, and a diet containing 16% beet pulp and 41% ground corn. The
researchers measured DMI, milk production and milk fatty acid composition,
ruminal VFA, and chewing behavior, with the main Objective Of quantifying ﬁber

effectiveness.

13

O’Mara and coworkers (1997) compared milk production, blood
metabolite, ruminal fermentation characteristics, and total tract digestion effects
of four diets, two of which contained 20% ground corn with 11% beet pulp, or no
corn with 30% beet pulp. Production was measured over the course Of 56 days
using 18 cows per treatment (15 in early lactation and 3 in midlactation), and
rumen and digestion Characteristics were measured using four cows, starting in
early lactation, in a Latin square design. These four cows were ﬁtted with
ruminal cannulas, and infused Yb was used tO measure total tract digestibility.

Work by Clark and Armentano (1997) utilized 16 cows in midlactation in a
replicated 4x4 Latin square design to study the inﬂuence Of particle size on the
effectiveness of beet pulp; the two diets of interest were the basal diet, containing
45% rolled high-moisture corn and no beet pulp, and the whole-beet—pulp diet,
containing 30% com and 16% whole, dried beet pulp. Measurements included
milk production, DMI, ruminal VFA, and chewing activity.

None of the experiments described above Speciﬁed whether the dried beet
pulp was fed in the form of “shreds” (dried without further physical processing) or
pellets. It is possible that pelleting would alter the likelihood of sorting, Chewing
behavior response, rumen ﬁll effect, or ruminal degradation of beet pulp. The
more compact form of pelleted beet pulp is more suited to storage and Shipping.

In these four experiments, the F:C and the rates Of corn and beet pulp
substitution varied widely. The goal of Swain and Armentano (1994) and Of Clark
and Armentano (1997) was to test the “effectiveness” Of ﬁber from non-forage

sources through, among other measures, milk fat concentration. Therefore their

14

 

F:C were low. In the ﬁrst experiment, the F:C was 32:68, and control and beet
pulp treatments contained 58% and 41 % corn grain, respectively (Swain and
Armentano, 1994). In the second experiment, the F:C was 38:62, and control
and beet pulp treatments contained 45% and 30% com grain, respectively (Clark
and Armentano, 1997). By contrast, the F:C for Mansﬁeld and coworkers (1994)
was 53:47; because they were directly comparing corn and beet pulp for normal
production rations, their diets started with a more moderate inclusion rate of com
(30%) in the corn diets and equal amounts of corn and beet pulp (15% for each)
in the test diets. O’Mara and coworkers (1997) fed grass-silage based diets with
a F:C of 60:40 and a different substitution method, starting with a control diet
containing 30% beet pulp and no “starch source” (corn or other high-starch grain;
all diets contained soybean meal), then replacing two-thirds of the beet pulp
(20% of diet DM) with corn grain. The variety in concentrations of forage ﬁber,
non-forage ﬁber, and starch in the diets used in these four experiments certainly
contributed to differences in relative response to beet pulp and corn grain

between experiments.

Beet Pulp and the Regulation of Feed Intake

Daily feed intake is determined by meal Size and meal frequency (Allen,
2000). The amount of feed consumed at one meal is limited by Signals Of satiety,
including distension, hypertonicity of rumen ﬂuid, and the absorption Of metabolic

fuels from the rumen and intestines (Allen, 2000). Less attention has been paid

15

to the mechanisms of hunger in ruminants and the causes Of meal initiation,
which determine meal frequency.

Physical regulation of intake, described as gut (or rumen) “ﬁlling effect,"
was ﬁrst described as the “ballast” of digesta (Lehman, 1941). In dairy cattle
whose intake is limited by ﬁll, the rumen is not actually ﬁlled to capacity (Dado
and Allen, 1995), but Signals Of distension are integrated with other signals of
hunger and satiety (Forbes, 1995). The extent to which distension limits intake
would differ between cows with varying milk yields and in different reproductive
status, and between diets with different contents of energy and other nutrients
and with different dry matter contents and physical forms (Allen, 1996).

The contribution Of ruminal distention to satiety results from both weight
and volume Of digesta. Schettini and coworkers (1999) increased volume of
ruminal contents by inserting 50 or 100 tennis balls, and changed the weight
added with the volume by using balls with different speciﬁc gravity (1.1 or 1.3),
for steers fed low-quality orchardgrass. Dry-matter intake was reduced 112 g per
kg inert weight and 157 g per liter inert volume added (Schettini et al., 1999).
Beet pulp might increase ruminal digesta weight and volume by increasing
digesta moisture content, because water contributes to the volume and
especially tO the weight Of ruminal digesta. When diet moisture content was
increased by soaking in water, DMI was not reduced (Robinson et al., 1990).
However, research with pigs found that maximum potential DMI could be

predicted using the water-holding capacity (WHC; ml H20/g insoluble DM) of

16

 

feeds (Kyriazakis and Emmans, 1995) measured by centrifugation or ﬁltration.
Similar research has not been conducted with ruminants.

Beet pulp and corn meal WHC were measured in one experiment by
centrifugation according to the American Association of Cereal Chemists and by
simple ﬁltration (Ramanzin et al., 1994). The WHC of beet pulp was 6.44 and
5.97 ml H20/g insoluble DM, and the WHC Of corn meal was 1.25 and 1.27 ml
H20lg insoluble DM, for the centrifugation and ﬁltration methods, respectively
(Ramanzin et al., 1994). For reference, the WHC of alfalfa meal was 4.25 and
3.63 ml HzO/g insoluble DM for the two methods. Although the WHO of beet pulp
has been reported differently relative to forages and other non-forage ﬁber
sources (NFFS; Bhatti and Firkins, 1995), this comparison of beet pulp and corn
meal (Ramanzin et al., 1994) suggests that substituting beet pulp for corn grain
would increase the water-holding capacity, and therefore the weight and possibly
the volume, Of ruminal digesta independent Of its effects on ruminal DM or NDF
pool. This could contribute to the limitation of DMI by distention.

Allen (2000) suggested that “when DMI is regulated by distention in the
reticulorumen, substitution of NFFS for grain might decrease DMI because Of
differences in their relative ﬁlling effects.” The review combined 33 comparisons
of DMI between grain and a variety of NFFS such as soy hulls, corn distillers
grains, whole cottonseed, and beet pulp, and found that only 8 of 33 reported
increased DMI for NFFS compared to grain, 2 of 33 had decreased DMI; overall,
there was no relationship between DMI and the percent of NFFS in the diet

(Allen, 2000). Given the wide variation in physical form, NDF content, and NDF

17

digestibility and passage rate among high-ﬁber byproducts, it is not surprising
that their effects on DMI vary greatly. In addition, ruminal ﬁll probably was not
the ﬁrst limiting factor Of DMI in all of these studies (Allen, 2000). As will be
discussed later, diet energy content probably limited intake on high-grain diets.

The distension effect of beet pulp is partly a result of its NDF content, rate
and extent of NDF digestion, and NDF passage rate. Ruminal ﬁll is often
described using NDF pool rather than DM pool (Mertens and Ely, 1979; Bywater,
1984; Mertens, 1994). Most research attempting to describe the effects Of ﬁll on
intake compares forages to grains, or different forages with varying NDF
digestibility. Some of the generalizations about the effects of NDF on ruminal ﬁll
resulting from forage research may not apply to NDF from NFFS. In a summary
Of many studies, DMI decreased with increased NDF when diet NDF was altered
by changing the forage-to-concentrate ratio (Allen, 2000). Beet pulp NDF has a
shorter initial lag time than alfalfa and is more rapidly digestible than
orchardgrass and corn silage (Bhatti and Firkins, 1995; Nocek and Russell,
1988), so slow ruminal NDF digestion (relative to ruminal starch digestion) might
be less important in the limitation of intake by ﬁll on beet pulp than it is for
forages.

Passage rate of feed NDF from the ruminoreticulum also contributes to its
ﬁlling effect. Passage rate is limited by digesta particle size and density
(Lechner—Doll et al., 1991). Particle size is decreased by mastication and by

chemical breakdown; although beet pulp is likely reduced in size as quickly as

18

grains, the initial particle size of pelleted beet pulp is larger than the particle size
of grain, especially Of processed grain.

Density is increased by hydration and by increased concentration Of
indigestible material, and it is decreased by the gas produced during
fermentation (Allen, 1996; Bailoni et al., 1998). Functional speciﬁc gravity and
volume of associated gas were similar for ﬁnely ground corn meal and beet pulp
and for their insoluble fractions both before and after soaking (Ramanzin et al.,
1994). However, this comparison does not account for original particle size and
its potential effect on density and gas retention. Beet pulp fermented in vitro had
a lower functional speciﬁc gravity than grain byproducts after 4, 8, and 27 hours
of in vitro fermentation (Bhatti and Firkins, 1995). Therefore, beet pulp particles
are probably more likely to remain suspended in the rumen mat than are grain
particles. Lower density probably also leads to a Slower passage rate for beet
pulp ﬁber than for ﬁber from grain. Therefore, beet pulp might increase the
limitation of intake by physical distention compared to grain because Of longer
retention time in the rumen.

In addition to physical regulation Of intake, chemical aspects of ruminal
fermentation and intestinal absorption contribute to the sensations of hunger and
satiety. The digestion of structural and nonstructural carbohydrates can take
place in both the rumen and the intestines, with varying efﬁciency and perhaps
with different effects on intake. AS most metabolites from fermentation and
intestinal digestion pass through the hepatic portal vein, the liver is responsible

for many Of the metabolic signals of hunger and satiety (Forbes, 1995).

19

_—T—q

The primary volatile fatty acids produced from the fermentation of starch,
cellulose, hemicellulose, and pectin are propionate, acetate, and butyrate. Of
these, only propionate is produced in great enough quantity and metabolized
sufﬁciently in the liver to affect DMI (Allen, 2000). While acetate is Often found in
greater concentration in rumen ﬂuid, it is not metabolized to any great extent in
the liver (Reynolds, 1995). Ruminal infusion of propionate (compared to acetate)
decreased meal size and tended to increase intermeal interval, resulting in
decreased DMI (Choi and Allen, 1999). Substituting beet pulp for corn dilutes
dietary starch; this would likely reduce propionate production and might increase
DMI. Replacing starch with NDF and pectin would probably reduce the rate Of
VFA production in general and would increase the proportion Of acetate
produced.

Starch not fermented in the rumen is usually digested and absorbed as
glucose in the small intestine of dairy cattle. However, in ruminants, much of the
absorbed glucose is probably utilized by the viscera, as there is little net glucose
absorption across the portal-drained viscera (Reynolds, 1995). The effect Of
postruminal glucose absorption on intake in ruminants has not been investigated
thoroughly, and various studies have produced conﬂicting results (Allen, 2000).
Because the amount Of intestinally absorbed glucose reaching the liver is usually
insigniﬁcant compared to glucose produced via gluconeogenesis (Weekes,
1991), it is unlikely that glucose absorbed in the small intestine has a signiﬁcant
direct effect on satiety. However, increased absorption Of glucose into intestinal

tissue might reduce the demand for and uptake Of circulating glucose by

20

 

intestinal tissue. This should increase the amount of circulating glucose, which
could signal satiety. In addition, dietary starch absorbed by the intestines would
be converted tO lactate in intestinal tissue; and circulating lactate could be
metabolized in the liver, thus Signaling satiety. However, the effects Of starch
digestion in the small intestine on intake have not been well examined.

It is not known how the substitution of beet pulp for corn affects the
passage rate and ruminal digestibility Of starch. If adding beet pulp increases
retention time and ruminal starch digestion, increased propionate production
could reduce intake. If beet pulp increases ruminal starch passage rate and
decreases ruminal starch fermentation, the reduction of propionate absorption
might increase intake, and little evidence exists for an effect on intake Of
increased intestinal glucose absorption.

Responses of DMI to substituting beet pulp for corn grain have varied.
Two experiments (O’Mara et al., 1997; Clark and Armentano, 1997) reported
greater DMI for the beet pulp diet, and one (Mansﬁeld et al., 1994) reported
greater DMI for the corn diet. Adding beet pulp to a high-grain TMR did not affect
DMI in one experiment (Swain and Armentano, 1994), and none Of the eleven
experiments comparing grain and beet pulp under other feeding conditions
reported effects on DMI. The differences in DMI response might be explained, in
part, by dietary characteristics.

O’Mara and coworkers (1997) measured intake for treatment groups only
and therefore did not analyze this response statistically, but DMI was numerically

1.5 kg/d greater for animals fed the beet pulp diet than the corn diet. This is a

21

 

surprising result on such a high-forage diet with additional non-forage ﬁber,
where ﬁll might be expected to be the dominant factor limiting intake and the
addition of more rapidly ferrnentable corn grain might be expected to permit
greater intake. The depression Of intake with the addition Of corn grain to a
grass-silage diet might be the result of additive effects Of ﬁll and propionate
(Mbanya et al, 1993). Ruminal distension and propionate treatments which did
not reduce intake when administered alone, depressed intake when administered
together (Mbanya et al., 1993). Plasma B-hydroxybutyrate was 10.5 mg/L higher
on the corn diet than on the beet pulp diet (O’Mara et al., 1997), which might
indicate a greater hepatic pool of acetyl-COA available for use in the TCA cycle,
increasing the hypophagic effects Of propionate (Oba, 2002). However, beet
pulp did not affect rumen ﬂuid propionate concentration collected via ruminal
cannula throughout the day (O’Mara et al., 1997). Although VFA concentration is
not necessarily indicative Of VFA production or absorption, it is not clear that
intake was limited by propionate on the corn diet. Nonetheless, the additive
satiety effect of ﬁll and metabolic fuels is the most reasonable explanation for
decreased DMI on a high-forage diet with added grain. In addition, milk yield
was low for these cows, averaging approximately 20 kg/d, so propionate (or other
metabolites) would be more likely to be limiting to feed intake for these cows than
in high-producing cows with greater energy requirements.

When beet pulp was substituted for corn in a diet containing 38% forage
and 62% concentrate, resulting in a diet containing 16% beet pulp and 29% com

grain, DMI increased by 0.4 kg/d (Clark and Armentano, 1997). Rumen ﬂuid

22

propionate concentration decreased with the addition Of beet pulp, so reduced
propionate metabolism in the liver could have allowed greater DMI. However,
samples were collected only once per period via stomach tube, and this sampling
technique and frequency is less reliable than sampling from several sites in the
rumen throughout the day. Reducing dietary starch concentration or changing
the Site of starch digestion by adding beet pulp could also Change the amount Of
starch absorbed as glucose and converted to lactate in the small intestine; and a
decrease in circulating glucose or lactate might reduce satiety.

A similar experiment measured no effect on DMI (Swain and Armentano,
1994). Cows in this experiment were also producing about 10 kg/d less milk, and
cows with lower feed intake and milk production might be expected to respond
less dramatically to dietary changes. The diets that resulted in no DMI effect of
beet pulp contained slightly less forage (32% versus 38% of DM) and more com
grain for both corn and beet pulp diets than diets fed by Clark and Armentano
(1997). Ruminal propionate was measured by Swain and Armentano (1994),
once per period via stomach tube, but was unaffected by treatment. That
experiment might have failed to improve DMI with added beet pulp because the
ratio Of beet pulp to corn was lower, so the amount Of beet pulp may have been
insufﬁcient to reduce the negative effects Of corn grain.

By contrast, substituting 15% beet pulp for corn in a diet containing 53%
forage and 47% concentrate reduced intake by 1.3 kg (Mansﬁeld et al., 1994).
When sufﬁcient ﬁber is already being consumed, the substitution of high-ﬁber

beet pulp for corn likely increases the ﬁlling effect Of the diet and thus reduces

23

intake. Forage characteristics also may have affected response to beet pulp
substitution. The forage component of this diet included corn silage, alfalfa hay,
and alfalfa pellets (Mansﬁeld et al., 1994), while Swain and Armentano (1994)
and Clark and Armentano (1997) fed only alfalfa Silage as forage. Dry alfalfa hay
may have had a larger particle size or lower digestibility than alfalfa silage, which
could have increased the ﬁlling effect of the hay-based diet in addition to the
effect of higher forage content. The addition of beet pulp to that diet probably
enhanced its ﬁlling effect. Cows in this experiment (Mansﬁeld et al., 1994) had
moderate milk yields (32 kg/d), SO DMI was probably limited by ﬁll.

Responses in DMI to beet pulp substituted for corn grain have not been
consistent. While all four experiments described here replaced corn with beet
pulp as approximately 15-20% of diet DM, the response probably was affected by
the amount and type of forage fed, and possibly by the ratio of beet pulp to corn
grain. Intake would likely respond differently to higher or lower rates of beet pulp
inclusion in the diet. The response of DMI to beet pulp is probably dominated by
ﬁll effect when added to a high-ﬁll (high-forage) diet or when fed to high-
producing cows, and DMI response is probably dominated by a reduction of
metabolic fuel absorption when beet pulp is added to a high-concentrate diet or
fed to low-producing cows. However, ﬁll and metabolic satiety signals are not

mutually exclusive and can be additive (Mbanya et al., 1993).

24

Effects of Beet Pulp on Chewing Behavior

Chewing, especially rumination, is essential for the reduction Of digesta
particle size and to stimulate the ﬂow of saliva and the buffers it contains into the
rumen. Mastication contributes especially to the ruminal digestion Of NDF by
increasing surface area available for bacterial attachment. Saliva buffers are
essential to the prevention of low ruminal pH (especially below 6.0), which
inhibits the activity of ﬁbrolytic bacteria (Russell and Wilson, 1996). Because
beet pulp can be a signiﬁcant source of NDF, its effectiveness in stimulating
chewing has been compared to forages and concentrates. The ability of a feed
to stimulate chewing, salivation, and ruminal motility is implicated in milk fat
synthesis, ruminal pH, and ﬁber digestibility. Animal responses such as chewing
time, ruminal pH, acetatezpropionate, yields Of milk and milk fat, and milk fat
content, measured in 31 to 111 experiments (depending on variable), have been
used to estimate ﬁber effectiveness (Armentano and Pereira, 1997). When
various non-forage ﬁber sources were used to increase dietary NDF
concentration, responses were Similar to, but not always equal tO, those induced
by adding NDF by adding forage (Armentano and Pereira, 1997). However,
adding NFFS reduced ruminal pH, implying that ruminal health and NDF
digestibility were not improved despite increased chewing. Using data from
Swain and Armentano (1994), Mertens (1997) determined that beet pulp's
effectiveness was Similar to that of other NFFS, assigning it a pet (physical
effectiveness) value Of 0.44, where the pef of long grass hay is the standard

(1.00).

25

Both Swain and Armentano (1994) and Clark and Armentano (1997)
compared chewing behavior for beet pulp and corn treatments. In the ﬁrst
experiment, tendencies (P s 0.10) were detected for greater time Spent in total
Chewing (eating + ruminating) and in time chewing per kg DMI for cows fed beet
pulp compared to corn (Swain and Armentano, 1994). Although increased milk
fat content was also reported for cows fed the beet pulp diet, chewing response
and milk fat percent were not correlated across NFFS types, so a direct
relationship between chewing effectiveness and milk fat synthesis cannot be
assumed. In the second experiment (Clark and Armentano, 1997), beet pulp and
corn had similar effects on time spent ruminating or eating. Treatment also did
not affect milk fat yield or content. Taken together, these studies suggest that
beet pulp is not consistently a reliable source of “effective” ﬁber by the deﬁnition

Of increasing chewing time or milk fat synthesis.

Beet Pulp and Microbial Efﬁciency

Microbial protein is the most Signiﬁcant source Of amino acids for the
lactating dairy cow, not only because Of the quantity Of protein produced in the
rumen and digested in the small intestine, but also because microbial protein is
highly digestible and its amino acid proﬁle resembles ruminants' amino acid
requirements (O’Connor et al., 1993). The efﬁciency with which dietary energy
and protein are used to produce microbial protein in the rumen varies greatly.
Microbial efﬁciency (MNE), deﬁned as g Of microbial N passing to the duodenum

per kg true ruminally degraded OM (T RDOM), ranges from approximately 10 to

26

50 g/kg TRDOM (Clark et al., 1992). Microbial efﬁciency might be affected by
carbohydrate availability, ruminal pH, passage rate, and the availability Of
ruminally degradable protein (Firkins, 1996). TO the extent that the substitution
of beet pulp for high-moisture corn affects these factors, it may affect MNE.

The availability Of carbohydrates can be increased by increasing dietary
concentrations of nonstructural carbohydrates, increasing the inherent
digestibility of structural and nonstructural carbohydrates by plant genetics and
preservation method, and reducing forage and grain particle Size (within limits).
However, the effect of diet fermentability on MNE is not consistent (Overton et
al., 1995; Plascencia and Zinn, 1996; Crocker et al., 1998; Callison et al., 2001 ).
Increasing diet fermentability can increase microbial protein production (Hoover
and Stokes, 1991), but increasing fermentability can also lead to lower ruminal
pH and to greater energy spilling by microbes (Strobel and Russell, 1986).
Increasing rate of ruminal starch digestion by changing corn grain conservation
method has decreased microbial efﬁciency (Oba and Allen, 2002b). Substituting
beet pulp for highly fermentable corn grain in a high-grain diet might increase
MNE if a similar digestibility of carbohydrates were maintained while slowing
fermentation to a rate within the ability of microbes to utilize energy for protein
synthesis and growth.

Increasing the rate of fermentation can also lead to lower ruminal pH,
which has been implicated in the reduction of microbial efﬁciency, especially as a
result Of greater energy spilling (Strobel and Russell, 1986). However, most

research linking low pH and reduced microbial efﬁciency has been conducted in

27

vitro (Firkins, 1996), and low pH has not always reduced MNE in vitro
(Calsamiglia et al., 2002). Calsamiglia and coworkers (2002) also measured the
effect of pH ﬂuctuation on microbial efﬁciency. They reduced in vitro pH twice
per day from 6.4 to 5.7, or cycled pH between 6.4 and 5.7 every four hours, to
imitate ﬂuctuations in pH that might result from meals consumed throughout the
day or from a separate grain meal (Calsamiglia et al., 2002). Fluctuations in
culture pH did not affect microbial efﬁciency.

Very little evidence exists that in vivo MNE is actually affected by ruminal
pH, though it is possible that MNE is reduced at very low pH. Therefore, if beet
pulp does increase daily average ruminal pH, that effect alone might not improve
microbial efﬁciency. Only one experiment substituting beet pulp for corn in diets
fed to dairy cattle measured ruminal pH; pH was unaffected by treatment,
possibly because of the high dietary forage content (O’Mara et al., 1997).
Microbial protein production and ruminal pH have not been measured while
substituting beet pulp for corn grain.

Increased microbial efﬁciency has been demonstrated with increasing
passage rate of digesta (Clark and Davis, 1983; Firkins, 1996; Oba and Allen,
2000; Oba and Allen, 2002b). This is probably the result Of decreased lysis and
protozoal predation (Wells and Russell, 1996). Digesta passage rate can be
increased by greater DMI and decreased ambient temperature (Kennedy and
Milligan, 1978); liquid dilution rate can be increased by greater saliva ﬂow
(Owens and Goetsch, 1986) and dietary mineral salts (Rogers et al., 1979).

However, MNE is not consistently correlated with liquid passage rate, perhaps

28

because liquid passage rate is typically high in lactating dairy total; therefore, any
increase in liquid passage rate might have little effect on overall microbial
passage (Owens and Goetsch, 1986).

The effects of various non-forage ﬁber sources on passage rate have
varied and depend on DMI, NFFS type, particle size, and marker system (Firkins,
1997). Substituting beet pulp for corn grain might decrease passage rate Of
solids if beet pulp contributes at all to rumen mat formation. Grain particles, beet
pulp particles, and forage particles likely form pools with different digestion and
passage kinetics within the rumen, SO their relative responses to beet pulp and
corn might differ. The separate passage rates of NDF and INDF from forage,
beet pulp, and other concentrates cannot be accurately measured. If beet pulp
increases the passage rate of one or more particulate fraction, MNE might be
improved. Due to its high water-holding capacity, beet pulp might reduce liquid
dilution rate; however, the potential for an effect on microbial efﬁciency is less
likely because of the inconsistent relationship between liquid dilution rate and
microbial efﬁciency (Owens and Goetsch, 1986).

The efﬁciency of microbial protein production is also limited by the
availability Of ammonia, amino acids, and peptides. Hoover (1986) summarized
a number of studies which demonstrated that maximal fermentation or microbial
production can occur at a wide range of ruminal ammonia concentrations (1 to 76
mg/dl). Therefore, factors other than ruminal ammonia concentration certainly
affect microbial efﬁciency. A deﬁciency of amino acids or peptides can also

reduce microbial efﬁciency (VanKessel and Russell, 1996); amylolytic

29

microorganisms are more dependent on amino acids and peptides (Russell et al.,
1983), while ﬁbrolytic bacteria are capable Of using only ammonia N (Bryant,
1973). Therefore, substituting high-ﬁber beet pulp for high-starch corn might
allow more extensive utilization of ammonia N and thus more efﬁcient microbial
efﬁciency. If, however, diets are formulated with sufﬁcient protein and rumen-
degraded protein, then amino acids and peptides probably would not limit growth
Of starch degraders, and N availability probably would not affect microbial
efﬁciency differently when beet pulp was substituted in part for corn grain.

When beet pulp and corn grain were compared by in vitro fermentation, N
metabolism responses were inconsistent (Mansﬁeld et al., 1994; Chester-Jones
et al., 1991; Bach et al., 1999). One experiment (Mansﬁeld et al., 1994) reported
that ﬂuid ammonia concentration and efﬂuent ammonia ﬂow were greater on the
corn diet. This implies that more protein was being degraded to ammonia on the
corn diet than on the beet pulp diet, or that N was being integrated into bacterial
protein more efﬁciently on the beet pulp diet. However, there was no effect of
treatment on dietary CP degradation or on microbial N efﬁciency (Mansﬁeld et
al., 1994). Chester-Jones and coworkers (1991) and Bach and coworkers (1999)
found that carbohydrate source had no effect on bacterial N ﬂow or g bacterial N
per kg truly digested DM.

When beet pulp was substituted for corn grain at 20% of diet DM for
lactating cows, daily mean concentration Of ammonia was not affected (O’Mara
et al., 1997). Ruminal ammonia concentration is the combined result of ammonia

production, ammonia absorption, and microbial ammonia utilization, so the failure

30

to detect differences in ammonia concentration does not rule out differences in
the effect Of N availability on microbial protein production. Microbial efﬁciency
has not been compared for diets containing beet pulp or corn grain in lactating

dairy cattle.

Effects of Beet Pulp on Milk Production

Three of the four experiments in which corn was replaced with beet pulp
(Mansﬁeld et al., 1994; Swain and Armentano, 1994; Clark and Armentano,
1997) reported no effect of treatment on milk yield (MY), and those that reported
fat-corrected milk (FCM) yield found no effect Of diet (Mansﬁeld et al., 1994;
Clark and Armentano, 1997). Among eleven other experiments in which beet
pulp replaced corn under various feeding systems, only two reported increased
MY or FCM yield for beet pulp diets; beet pulp decreased MY in one experiment
and had no effect in others.

Only one experiment in which beet pulp was substituted for corn in a TMR
(O’Mara et al., 1997) found a 1.4-kg/d decrease in raw milk yield when beet pulp
was substituted for com. This was despite a 1.5 kg/d increase in DMI. There
were no effects Of diet on whole-tract DM or OM digestibility. Ruminal
fermentation Of the added corn could lead to greater propionate absorption from
the rumen. Propionate is a precursor to glucose, which is used to produce
lactose, a primary determinant Of milk volume (Linzell and Peaker, 1971 ).
Propionate concentration in the rumen was not different between treatments

(O'Mara et al., 1997), but quantities Of propionate produced and absorbed could

31

have been greater on the corn diet if the rate of propionate absorption or
passage also increased. Finally, the cows used in this experiment were
producing only about 20 kg of milk per day (O’Mara et al., 1997). Individual
production potential affects response to changes in diet (Voelker et al., 2002), SO
the effects Of replacement of corn with beet pulp in these cows may be different
than in high-producing cows.

Milk fat yield or content might Often be expected to be greater when cows
are fed diets with beet pulp substituted for corn, though multiple, and separate,
mechanisms likely exist for the Often-Observed “milk fat depression.” Some diet
carbohydrate characteristics that are associated with milk fat depression are
small forage particle size, insufﬁcient ﬁber content, and high grain content
(Emery, 1988). When Armentano and Pereira (1997) summarized several
studies involving various NFFS, increasing dietary NDF concentration by adding
NFFS increased milk fat content, although NFFS NDF contributed less to the
prediction Of milk percent than did forage NDF in a separate data set. However,
the increase in milk fat percent with added NFFS might have been due to
decreased milk yield and unchanged milk fat yield with added NFFS (Armentano
and Pereira, 1997).

When substituting beet pulp for corn resulted in lower milk yield (O’Mara et
al., 1997), cows fed beet pulp also produced 0.07 kg/d less milk fat, so the milk
fat percent was not affected by diet. Therefore, the lower milk fat yield was the
result Of lower milk yield, not the result of greater fat content; nor was there

evidence of “milk fat depression” for cows fed the corn treatment. Effects of diet

32

on milk fat in two other experiments were in the opposite direction. The studies
Of Swain and Armentano (1994) and Clark and Armentano (1997) were
speciﬁcally designed to determine the effects Of substituting beet pulp for corn
grain on milk fat. Swain and Armentano (1994) reported 0.10 kg/d more milk fat
and an increase of 0.32 percentage units for milk fat concentration in cows fed
the beet pulp treatment compared to the corn treatment. Clark and Armentano
(1997), feeding diets with slightly more forage and 11-13 percentage units less
corn than Swain and Armentano (1994), reported no treatment effects on milk fat.
Mansﬁeld and coworkers (1994), feeding diets with more moderate amounts of
corn, reported a 0.18 percentage-unit increase in milk fat content when beet pulp
was substituted for half Of the corn. Among the ten non-TMR studies that
reported milk fat content, three measured greater milk fat content for beet pulp
treatments, one for grain treatment, and Six reported no effect. Therefore, the
response Of milk fat synthesis to substitution of beet pulp for corn grain is not
consistent, even taking into account other diet characteristics.

Interestingly, milk protein yield or percent was affected by diet in three Of
the four TMR experiments, though the results vary by experiment. Swain and
Armentano (1994), who reported no effect on milk yield and greater milk fat
synthesis on the beet pulp diet, also reported no effect Of diet on milk protein.
O’Mara and coworkers (1997) measured 0.12 percentage units greater protein
content in milk from cows fed the beet pulp diet. This may have been caused by
differences in milk volume, since milk protein yield was similar and cows fed corn

produced 1.4 kg/d more milk, possibly due to greater propionate availability and

33

lactose synthesis (Linzell and Peaker, 1971). A tendency (P = 0.07) for slightly
greater milk protein content (0.06 percentage units) on the high-corn diet was the
only milk production response reported by Clark and Armentano (1997) between
the corn and whole beet pulp diets. Finally, Mansﬁeld and coworkers (1994),
who found no difference in milk yield and a greater milk fat content when beet
pulp replaced half the corn, reported greater protein content (0.11 percentage
units) and yield (0.05 kg/d) for the com diet.

When higher milk protein concentration occurred in cows fed diets
containing greater amounts Of com, the response may have been the result Of
increased insulin secretion (McGuire et al., 1995) due to greater ruminal
propionate production and absorption with added dietary starch. A
hyperinsulinemic—euglycemic clamp (McGuire et al., 1995) or Simple insulin
infusion (Molento et al., 2002) caused a modest increase in milk protein yield and
content. This might be a direct effect of insulin on amino acid uptake and an
effect Of increased supply of amino acids from nonmammary tissues, and it might
also be an indirect effect mediated through IGF-I (Mackle et al., 1999).

Diet differences across the experiments, such as forage concentration,
type, and quality, and protein source, as well as differences in milk yield and
stage of lactation, probably contributed tO the variation in milk protein responses
to treatments. However, It is clear from these experiments that substituting a
highly digestible ﬁber source for a rapidly-fermentable starch source can affect

milk protein content and yield.

34

Effects of Beet Pulp on Energy Partitioning

O’Mara et al. (1997) reported that blood glucose was not affected by
substituting beet pulp for corn, which suggests that cows were in Similar energy
status across treatments, although DMI was numerically greater for BP. Authors
did not discuss energy partitioning repsonses. However, cows fed the beet pulp
diet had positive body weight change, while cows fed the corn diet had slightly
negative body weight change. Body weight could have been affected by gut ﬁll,
or feeding beet pulp may have shifted the partitioning of energy away from milk
production and into body reserves, Since cows fed beet pulp also had lower
average milk yield. Plasma insulin concentration was not measured. Plasma (3-
hydroxybutyrate was 10.5 mg/L lower on the beet pulp diet than on the corn diet,
consistent with lower metabolism Of adipose tissue for the beet pulp diet.
However, plasma concentration Of non-esteriﬁed fatty acids, which are created
by adipose mobilization, was not affected by treatment. Regardless Of the
mechanism, replacing corn with beet pulp probably altered energy partitioning,
reducing milk yield and possibly increasing body tissue gain. Again, it should be
noted that milk yield for these cows averaged ~20 kg/d, so their response to

added beet pulp might differ from the responses of high-producing cows.

Summary
Beet pulp in diets for dairy cattle can supply soluble and insoluble ﬁber
that is fermented more rapidly than forage NDF but less rapidly than starch.

Substituting beet pulp for corn grain in a high-concentrate diet can yield a slight

35

 

increase in intake, while substituting beet pulp for corn grain in a diet with a
moderate proportion of concentrate Often reduces intake. This is likely a result Of
greater ﬁlling effects of beet pulp for high-forage diets; for a low-forage diet with
low rates Of beet pulp inclusion, metabolic fuel absorption probably limits DMI
more than ruminal distention. Metabolic fuel absorption would be determined by
effects Of beet pulp on site of starch digestion, and those effects are unknown.

Adding beet pulp to a diet with a low forage-to-concentrate ratio might
stimulate additional chewing under some circumstances, but beet pulp is not a
reliable source Of “effective” ﬁber by the deﬁnition of increasing chewing time or
milk fat synthesis. Very little is known about the effect Of beet pulp on ruminal
pH, especially in vivo, but removing starch and adding NDF and pectin might
increase ruminal pH. Due to the rapid rate Of digestion of beet pulp NDF, and
perhaps due to effects on pH, beet pulp should improve total dietary NDF
digestion when substituted for corn grain. Effects of beet pulp on microbial
protein efﬁciency have not been studied in lactating cows; the response is not
likely to depend on ruminal pH or N availability but would probably be affected by
particle passage rate response and might be affected by liquid passage rate
response.

Beet pulp substituted for grain has not had a consistent effect on milk
yield; because it is highly dependent on DMI, milk yield might be increased with
added beet pulp if the dilution of starch permitted greater intake. Adding beet
pulp to high-grain diets has increased milk fat concentration on several

occasions, but not in the majority of experiments comparing beet pulp and grain.

36

 

Finally, beet pulp may alter the partitioning Of energy when substituted for grain,
although that response has not been previously studied.

Further study of the effects Of substituting beet pulp for grain would
provide valuable information for using grain and a common non-forage ﬁber
source to improve the efﬁciency of feed utilization in diets for dairy cattle. It
would also provide a large pool of data, collected under identical conditions,

which could help Clarify basic principles of feed intake, milk production, digestion,

 

and microbial efﬁciency in ruminants.

37

Table 1. Chemical composition of dried, unmolassed beet pulp.a

 

 

Component Mean SD N
DM, % 90.5 2.0 7
--- % Of DM --
OM 93.4 2.9 9
Ash 6.0 2.4 8
ADF 23.6 3.8 9
NDF 46.0 9.4 10
CP 11.7 3.8 14
EE 1.5 1.2 9
Lignin 4.5 1.1 6

 

3 Sources: Bhattacharya and Sleiman, 1971; Welch and Smith, 1971; Mansﬁeld
et al., 1994; Ramanzin et al., 1994; Swain and Armentano, 1994; Torrent et al.,
1994; Petit and Tremblay, 1995a; Petit and Tremblay, 1995b; Clark and

Armentano, 1997; O'Mara et al., 1997; Witt et al., 1999; Bhatti and Firkins, 1995.

38

CHAPTER 2

Pelleted beet pulp substituted for high-moisture corn: Effects on feed

intake, chewing behavior, and milk production of lactating dairy cows

ABSTRACT

The effects of increasing concentrations Of dried, pelleted beet pulp
substituted for high-moisture corn on intake, milk production, and chewing
behavior were evaluated using 8 ruminally and duodenally cannulated
multiparous Holstein cows in a duplicated 4 x 4 Latin square design with 21-d
periods. Cows were 79 :t 17 (mean :1: SD) DIM at the beginning of the
experiment. Experimental diets with 40% forage (corn silage and alfalfa silage)
and 60% concentrate contained 0%, 6.1%, 12.1%, or 24.3% beet pulp
substituted for high-moisture corn on a DM basis. Diet concentrations of NDF
and starch were 24.3% and 34.6% (0% beet pulp), 26.2% and 30.5% (6% beet
pulp), 28.0% and 26.5% (12% beet pulp), and 31.6% and 18.4% (24% beet
pulp), respectively. Increasing beet pulp in the diet caused a linear decrease in
DMI (P < 0.05). Time Spent eating per day (P < 0.05) and per kg DMI (P < 0.01)
increased, and sorting against NDF tended to increase (P = 0.07), with added
beet pulp. Substituting beet pulp for corn caused a quadratic response in milk fat
yield (P = 0.03), with the highest yield for the 6% beet pulp treatment. A

tendency was detected for a similar quadratic response in 3.5% FCM yield (P =

39

 

0.07). Greater plasma insulin concentration (P < 0.01) may have resulted in
greater gain Of body condition (P = 0.06) for cows fed diets with higher starch
concentration. Partial substitution Of pelleted beet pulp for high-moisture corn

decreased intake but also may have permitted greater fat-corrected milk yield.

INTRODUCTION

Grain is Often substituted for forage in diets for high-producing cows in an
effort to increase intake and milk yield. Reducing dietary neutral detergent ﬁber
(NDF) concentration by decreasing the forage to concentrate ratio usually
increases dry matter intake (DMI), probably by reducing the ﬁlling effect Of the
diet (Allen, 2000). However, increasing dietary starch can also negatively affect
feed intake and milk production. Feeding less forage NDF reduces chewing
(Allen, 1997), which can reduce ﬂow of saliva and its buffers into the rumen. This
could possibly reduce ruminal pH, ﬁber digestion and milk fat concentration.
Propionate production increases with greater dietary starch content and probably
depresses dry matter intake (Anil and Forbes, 1980), which can limit milk
synthesis.

Adding non-forage NDF to low-forage diets might reduce the negative
effects of increased starch fermentation without increasing the ﬁlling effect of the
diet to the same extent as forage NDF. The responses of DMI to various non-
forage ﬁber sources substituted for grain are not consistent (Allen, 2000). Beet

pulp contains approximately 40% NDF and is unique in its high concentration of

40

 

neutral-detergent soluble ﬁber, especially pectic substances. Previous
experiments have reported a variety of responses in DMI tO the substitution Of
dried beet pulp for corn grain. Of four experiments which substituted beet pulp
for grain in a total-mixed ration, two reported increased DMI (Clark and
Armentano, 1997; O’Mara et al., 1997), one reported decreased DMI (Mansﬁeld
et al., 1994), and one measured no effect of beet pulp on DMI (Swain and
Armentano, 1994). Among the same experiments, three reported no effects Of
treatment on milk yield (Mansﬁeld et al., 1994; Swain and Armentano, 1994;
Clark and Armentano, 1997), and one reported decreased milk yield when beet
pulp was substituted for corn grain (O’Mara et al., 1997). Fat-corrected milk
yield, when reported, was not affected by treatment. In these experiments, beet
pulp comprised at least 15% of diet DM. However, the effects of rate of
substitution and the mechanisms of intake regulation for diets containing beet
pulp have not previously been investigated.

Substituting beet pulp for high-moisture corn in a diet with a low forage
content should maximize dry matter intake and 3.5% FCM yield at one or more
rates Of inclusion. Therefore, this experiment investigated the responses to four
concentrations Of beet pulp substituted for high-moisture corn (0, 6, 12, and 24%
of diet DM) for feed intake, meal patterns, chewing behavior, ruminal nutrient

pools, and milk yield and composition.

41

 

MATERIALS AND METHODS

Cows and Treatments

Eight multiparous Holstein cows (79:17 DIM; mean 1 SD) from the
Michigan State University Dairy Cattle Teaching and Research Center were
assigned randomly to a duplicated 4 x 4 Latin square balanced for carryover
effects in a dose-response arrangement of treatments. Treatments were diets
containing dried, pelleted beet pulp (BP) at 0%, 6%, 12%, and 24% substituted
for high-moisture corn (HMC) on a DM basis. Treatment periods were 21 d with
the ﬁnal 10 d used to collect samples and data. Cows were cannulated ruminally
and duodenally prior to calving and assigned randomly to treatment sequence.
Surgery was performed at the Department Of Large Animal Clinical Science,
College Of Veterinary Medicine, Michigan State University. At the beginning of
the experiment, empty body weight (ruminal digesta removed) of cows was 515.9

:I: 63.5 kg (mean :I: SD).

Nutrient composition for HMC and BP are shown in Table 1. Experimental
diets contained 40% forage (50:50 corn silage: alfalfa silage), high-moisture corn,
beet pulp at 0% (OBP), 6% (GBP), 12% (1ZBP), and 24% (24BP) of diet DM, a
premixed protein supplement (soybean meal, corn distiller’s grains, and blood
meal), and a mineral and vitamin mix (Table 2). All diets were formulated for

18% dietary CP and fed as total mixed rations.

42

 

Data and Sample Collection

Throughout the experiment, cows were housed in tie-stalls and fed once
daily (1100 h) at 110% Of expected intake. Amounts Of feed Offered and orts
were weighed for each cow daily during the collection period. Samples Of all diet
ingredients (0.5 kg) and orts from each cow (12.5%) were collected daily on d 12-
19 and combined into one sample per period. Cows were milked twice daily in
their stalls during the feeding behavior monitoring phase (CI 16-19) and in a
milking parlor during the rest of each period. Milk yield was measured, and milk
was sampled, at each milking on CI 16-19. Empty body weight was measured
after evacuation of ruminal digesta on two consecutive days immediately prior to
the start of the ﬁrst period, and on d 20 and d 21 Of each period. Body condition
score (BCS) was determined immediately prior to the start of the ﬁrst period and
on d 21 Of each period by three trained investigators blinded to treatments
(Wildman et al., 1982; ﬁve-point scale where 1 = thin and 5 = fat).

Feeding behavior was monitored from d 16 through d 19 (96 h) of each
period by a computerized data acquisition system (Dado and Allen, 1993). Data
Of chewing activities, feed disappearance, and water consumption were recorded
for each cow every 5 sec. When chewing equipment malfunctioned for an
individual cow during a 24-h period (1100h to 1100h), chewing behavior was
deleted for that cow during that 24-h period. The system successfully collected
83.1% of the total chewing behavior data (average 3.4 d per cow per period).
Daily means were calculated for number Of meal bouts per day, interval between

meals, meal size, eating time, ruminating time, and total chewing time. These

43

 

response variables were calculated as daily means then averaged over the four
days for each period.

Blood was collected from the coccygeal vein into tubes containing sodium
heparin every 9 hours from d 12 - 14, starting at 1400 h on d 12, SO that samples
represented 3-h intervals of a 24-hour period in order to account for diurnal
variation. Blood was centrifuged at 2,000 x g for 15 min immediately after
sample collection, and plasma was harvested and frozen at -20°C until analysis.

Ruminal contents were evacuated manually through the ruminal cannula
at 1500 h (4 h after feeding) on d 20 and at 0900 h (2 h before feeding) on d 21
of each period. Total ruminal content mass and volume were determined.
During evacuation, 10% aliquots of digesta were separated to allow accurate
sampling. Aliquots were squeezed through a nylon screen (1 mm pore size) to
separate into primarily solid and liquid phases. Samples were taken from both
phases for determination of nutrient pool Size, and additional liquid samples were
taken to measure VFA concentration and rumen ﬂuid consistency. All samples

except the consistency sample were frozen immediately at —20°C.

Sample and Statistical Analysis

Diet ingredients and orts were dried in a 55°C forced-air oven for 72 h and
analyzed for DM concentration. All samples were ground with a Wiley mill (1 mm
screen; Authur H. Thomas, Philadelphia, PA). Rumen liquid and solid sub—
samples were lyophilized (Tri-Philizer'“ MP, FTS Systems, Stone Ridge, NY),

ground, and recombined according to the original ratio Of solid and liquid DM.

44

Samples were analyzed for ash, NDF, indigestible NDF (INDF), CP, and starch.
Ash concentration was determined after 5 h oxidation at 500° C in a mufﬂe
furnace. Concentrations of NDF were determined according to Van Soest et al.
(1991, method A). lndigestible NDF was estimated as NDF residue after 120-h
in vitro fermentation (Goering and Van Soest, 1970). Rumen ﬂuid for the in vitro

incubations was collected from a non-pregnant dry cow fed alfalfa hay only.

Fraction of potentially digestible NDF (pdNDF) was calculated by difference (1.00

— INDF). Forage samples were analyzed for ADF and sulfuric acid lignin content
(Van Soest et al., 1991). Crude protein was analyzed according to Hach et al.
(1987). Starch was measured by an enzymatic method (Karkalas, 1985) after
samples were gelatinized with sodium hydroxide. Glucose concentration was
measured using a glucose oxidase method (Glucose kit #510; Sigma Chemical
CO., St. Louis, MO), and absorbance was determined with a micro-plate reader
(SpectraMax 190, Molecular Devices Corp., Sunnyvale, CA). Concentrations Of
all nutrients except DM were expressed as percentages of DM determined by
drying at 105° C in a forced-air oven for more than 8 h.

A commercial kit was used to determine plasma concentration of insulin
(Coat-A-Count, Diagnostic Products Corporation, Los Angeles, CA). Milk
samples were analyzed for fat, true protein, and lactose with infrared
spectroscopy by Michigan DHIA (East Lansing).

Energy values were calculated as follows:

NEL intake = DMI (kg) x (0.0245 x TDN(%)) (NRC, 1989)

(DM digestibility for calculation Of TDN was measured as reported in Chapter 3.)

45

Milk NEL (Mcal/kg) = 0.0929 x (Fat %) + 0.0563 x (True Protein%) +
0.0395 x (Lactose%) (NRC, 2001)

Milk NEL (Mcal/d) = MY (kg) x [0.0929 x (Fat %) + 0.0563 x (True
Protein%) + 0.0395 x (Lactose%)] (NRC, 2001)

NEM = 0.030 x Bw “5 (NRC, 2001); and

NE balance = NEL intake — NEM - NEL (Mcal/d).

Ruminal pool Sizes (kg) Of OM, NDF, indigestible NDF, and starch were
determined by multiplying the concentration of each component in DM by the
ruminal digesta DM weight (kg).

Hunger and satiety ratios were calculated as follows (Forbes, 1995):

Hunger ratio = meal kg DM/ premeal interval

Satiety ratio = meal kg DM/ postmeal interval.

Ratios were calculated for individual meals and averaged for the four days of
feeding behavior data collection.

All data were analyzed using the ﬁt model procedure of JMP® according
tO the following model:

Yijk=u+Ci+Pj+Tk+eijk
where

l1 = overall mean,

C; = random effect of cow (i = 1 to 8),

Pj = ﬁxed effect Of period (j = 1 to 4),

TI, = ﬁxed effect of treatment (k = 1 to 4),

9in = residual, assumed to be normally distributed.

46

 

Period by treatment interaction was originally evaluated, but it was removed from
the statistical model because it was not Signiﬁcant for response variables of
primary interest. Linear and quadratic dose-response effects were evaluated
using the same model with diet percent beet pulp (1, 6, 12, and 24%) in place of
the ﬁxed effect of treatment. Pearson correlation coefﬁcients were determined
between cow-period observations for some parameters. Treatment effects,
linear and quadratic responses, and correlations were declared signiﬁcant at P <
0.05, and tendencies were declared at P < 0.10.

Data from two cow-periods were excluded from statistical analysis. One
cow developed a cecal torsion requiring surgery early in period 3; data and
samples were not collected from this cow during period 3, but she recovered
sufﬁciently for her period 4 data to be used. Period 4 data from a second cow
were excluded after she showed signs of estrus because her intake and milk
yield were outliers (outside the 95% conﬁdence interval for cow-period

Observations).

RESULTS AND DISCUSSION
Feed Intake
As beet pulp was increasingly substituted for high-moisture corn, dry
matter intake decreased (P < 0.05; Table 3). Although the relationship detected
was linear, DMI was similar for OBP, 6BP and 12BP, and DMI was numerically

lower by approximately 2 kg/d for 24BP. Others have reported varied responses

47

 

in DMI to substitution of beet pulp for corn grain. Swain and Armentano (1994)
reported no DMI effect. O’Mara and coworkers (1997) did not statistically
evaluate DMI but reported a numerical increase in DMI for beet pulp over corn in
a high-forage diet. Substituting beet pulp at 16% Of DM into a high-corn diet
(Clark and Armentano, 1997) increased intake by only 0.4 kg/d, while replacing
half of the corn with beet pulp in a higher-forage diet (Mansﬁeld et al., 1994)
reduced intake by 1.3 kg/d. The diets fed in the latter experiment are the most
Similar to diets in the present study and had a DMI response similar to the

numerical difference between 24BP and the other three treatments.

Regulation of Feed Intake

Intake can be affected by innumerable variables, such as ruminal ﬁll, meal
patterns, metabolic fuels, and ruminal patterns of fermentation and pH.
Substituting a high-ﬁber byproduct for grain may have resulted in the limitation of
intake by physical ﬁlling effects Of the diet, but “ﬁll” is likely a composite Of several
physical and chemical characteristics of the diet that affect volume and mass Of
digesta over time (Forbes, 1995). Because volume and mass Of wet ruminal
contents did not decrease when DMI decreased with increasing dietary BP
(Table 3), stimulation of stretch receptors in the rumen wall probably was a
predominant factor Signaling satiety and reducing DMI with added BP. Water
content of ruminal digesta increased linearly as BP was substituted for corn (P =
0.01 ), probably because beet pulp has a higher water-holding capacity than

grains and other byproducts, and similar to alfalfa and grass (Ramanzin et al.,

48

 

1994; Bailoni et al., 1998). The substitution Of beet pulp for high-moisture corn
probably increased the water-holding capacity Of the digesta and contributed to
the tendency for increased digesta wet weight (P = 0.11). Neither ruminal DM
pool nor ruminal NDF pool was limiting to intake, because DM pool decreased
linearly (P = 0.04), and NDF pool tended to decrease linearly (P = 0.11), as
added BP reduced DMI. Therefore, ruminal digesta volume, weight, and water-
holding capacity contributed to the limitation of intake by distension when high-
moisture corn was replaced with beet pulp.

Feed intake can be increased by reducing intermeal interval or by
increasing meal size. lntermeal interval was not affected by treatment, nor was
the amount of DM consumed per meal (Table 4). However, the response of
hunger ratio (meal size/premeal interval) to beet pulp concentration was
quadratic (P < 0.01), and was greatest for 12BP and lowest for 24BP, suggesting
that hunger had the greatest effect on intake for 1ZBP and the least effect for
24BP. The quadratic response suggests that hunger eventually was
counteracted by other factors limiting intake; cows might eat to minimize total
discomfort resulting from both hunger and satiety Signals (Forbes, 2000). Satiety
ratio was unaffected by treatment (P > 0.15), but since hunger and satiety Signals
are integrated to regulate feed intake (Forbes, 1995), response of hunger ratio or
satiety ratio alone cannot describe the mechanisms Of intake regulation.

Across cow-period Observations, DMI was not related to the number of
meals per day, meal length, intermeal interval, or NDF consumed per meal

(Table 7); but as meal size increased, DMI also increased (Figure 1a; R = 0.39, P

49

= 0.04). Therefore, the ability to consume a larger amount Of feed at one meal,
before satiety Signals such as absorption of metabolic fuels or ruminal ﬁll
overcame hunger, increased the amount of feed consumed in the entire day.
Average consumption of NDF per meal increased (P < 0.001) with added beet
pulp (Table 4), SO increasing NDF consumption per meal may have slowed feed
intake. However, as will be discussed further, eating rate and time probably did
not actually limit daily DMI. While dried, pelleted beet pulp might be expected to
physically affect eating behavior, eating Chew rate was unaffected by treatment
(Table 4).

Eating time per day and per kg DMI increased linearly with added BP (P =
0.04, P < 0.01, respectively), so rate of feed intake was Slowed (Table 5). Others
have reported no effect of beet pulp substitution for corn on time eating per day
or per kg DMI (Clark and Armentano, 1997). Across cow-period observations,
greater time spent in total chewing per kg DMI was associated with decreased
DMI (Table 7). AS diet NDF intake increased with added BP in the present
experiment, time eating per kg NDF decreased (P < 0.01). Since forage content
was equal across treatments, physical or Chemical effects of the ﬁber in beet pulp
apparently had a negative effect on rate Of feed intake.

Due to the physical form Of pelleted beet pulp, it is easily sorted. While
sorting against beet pulp was not measured, cows tended to increasingly sort
against dietary NDF (P = 0.07) as the concentration of BP increased in the diet
(Table 5). In addition, sorting behavior (orts %NDF - feed %NDF) displayed a

quadratic relationship to FCM yield (Figure 2; R = 0.51, P < 0.05), with the

50

 

greatest sorting occurring at ~40 kg/d FCM, slightly above the median of 37 kg/d.
Therefore, sorting against NDF may have slowed intake; and while sorting
behavior increased with production up to 40 kg/d, the highest milk yield was not
associated with the highest degree Of sorting.

Although replacing high-moisture com with beet pulp tended to increase
sorting and Slowed rate Of feed intake, time Spent eating and in total Chewing
behavior did not limit DMI. If eating time or total chewing time were limiting to
DMI, then those responses should demonstrate a quadratic increase as DMI was
reduced with increasing dietary beet pulp concentration, eventually reaching a
plateau. However, no quadratic responses were detected for time Spent eating,
ruminating, or in total chewing (Table 5), and time Spent eating or in total
chewing was not related to DMI across cow-period observations (Table 7).
Therefore, eating and chewing time were not primary factors limiting feed intake.

Intake might be regulated by the metabolism of propionate in the liver
(Allen, 2000), and ruminal propionate production is usually increased by greater
starch fermentation. The amount of starch truly digested in the rumen decreased
from 3.8 kg/d to 0.7 kg/d (Chapter 3), and ruminal molar percent of propionate in
total VFA decreased quadratically (Chapter 4) as starch intake was reduced by
approximately half (Table 3) and as true ruminal starch digestibility decreased
from 46.5% to only 16.9% (Chapter 3) with added BP. Therefore, it is not likely
that propionate metabolism in the liver caused the reduction in DMI with added
BP, because propionate metabolism probably decreased with added BP. In

addition, across cow-period Observations, DMI was not related to total valerate

51

concentration, molar percent of propionate in total VFA, or acetatezpropionate
(Table 8), and intake tended to be positively correlated with VFA absorption rate
(R = 0.31, P < 0.10). Therefore, ruminal VFA concentration and absorption rate
did not negatively affect intake.

Ruminal pH might be implicated in the control Of feed intake, particularly in
satiety. Ruminal pH was measured over 96 h and is reported in Chapter 4.
Substituting BP for HMC decreased DMI and resulted in a range of individual
mean daily pH values from 5.58 to 6.56, but pH was not related to treatment
(Chapter 4), and mean pH and DMI were not correlated (Figure 1b). Intake was
not correlated with daily range, maximum, or minimum pH, but DMI was
negatively related to daily standard deviation (Figure 1c; R = -0.41, P = 0.03) and
variance (R = -0.42, P = 0.03) Of ruminal pH. The direction of cause and effect is
not established by these results. Increased intake might be associated with
reduced pH variation if cows consumed more frequent, smaller meals and thus
increased intake while reducing ruminal pH variation. However, increased DMI
was associated with greater meal size, not smaller meal size (Figure 1a), and
DMI was not related to intermeal interval, so it is unlikely that the consumption of
more frequent, smaller meals resulted in increased DMI and decreased ruminal
pH variation. Rather, it is more likely that increased pH ﬂuctuations resulted in
feed intake depression. Increases in both DMI and daily pH range were
associated with the higher-starch diets (Table 3; and in Chapter 4), so the
negative correlation between DMI and ruminal pH variation is independent of the

treatment effects.

52

The limitation of intake by ruminal distention was closely related to effects
detected among treatment means as beet pulp was substituted for high-moisture
corn. By contrast, the relationships between pH variation or VFA absorption and

DMI occurred independently from treatment effects for the individual variables.

Milk Production and Nutrient Partitioning

Milk yield was not affected by diet (P > 0.50; Table 9), but increasing BP
tended to have a quadratic effect (P = 0.07) on 3.5% FCM yield and had a
quadratic effect on milk fat yield (P = 0.03). Yields Of FCM and milk fat were
highest for 6BP and lowest for 24BP. These effects correspond with non-
signiﬁcant quadratic patterns Of raw milk yield and milk fat content in response tO
increasing BP and decreasing HMC, and they may reﬂect a slight response in
milk lactose and fat synthesis to added beet pulp at the lower concentrations.
Lower milk yield for 24BP is likely because Of decreased DMI. Three of four
other experiments comparing corn grain with beet pulp in TMRS reported no
effect of treatment on raw milk yield (Mansﬁeld et al., 1994; Swain and
Armentano, 1994; Clark and Armentano, 1997), and those that reported fat-
corrected milk yield found no effect Of diet (Mansﬁeld et al., 1994; Clark and
Armentano, 1997). Only one experiment (O’Mara et al., 1997) found a 1.4-kgld
decrease in raw milk yield when beet pulp was substituted for corn in a grass-
silage-based diet. Milk protein and lactose yields and concentrations were not
affected in the present experiment by substituting beet pulp for corn in the

present experiment (Table 9). The reduction in DMI with increasing BP was

53

greater than the decrease in milk yield, so the efﬁciency Of milk production (kg
FCM/kg DMI) tended to increase (P = 0.07) as HMC decreased and BP
increased in the diet.

Beginning with a diet containing 36% HMC and 35% starch, then
substituting BP containing 40% NDF for the HMC not only served to test the
treatment effects of two common feed ingredients; it also provided a large pool of
data including variables such as intake, production, energy status, and feeding
behavior, with reasonably wide ranges, under identical conditions. Relationships
among these variables across cow-period means help both to interpret treatment
effects and to clarify basic scientiﬁc principles of intake, milk production, and
feeding behavior in ruminants. Among cow-period Observations, increasing
ruminal pH (Chapter 4) was associated with greater yield Of FCM (R = 0.43, P =
0.03) and tended to be associated with greater fat yield, but pH did not affect milk
fat content (Figure 3).

Although intake and milk production were inﬂuenced by diet, measures of
energy intake, energy partitioning to milk and output in milk, and energy balance
were not affected (Table 10); nor were changes in body weight different among
treatments (P > 0.45). While partitioning Of absorbed energy to milk (milk NEL as
a percent of NE intake) was not affected by adding beet pulp, a tendency (P =
0.06) was detected for a slightly more negative Change in body condition score;
as BP replaced corn in the diets, cows likely mobilized nutrients from body
reserves for milk production, rather than adding condition as they did for OBP and

6BP.

54

 

Plasma Insulin

Plasma insulin responds to energy intake, especially glucose and its
precursors, and it both regulates and is regulated by energy utilization in various
tissues, including liver, muscle, adipose, and mammary tissue. AS cows
consumed more BP and less HMC, both plasma insulin concentration and the
standard deviation of insulin concentration over 24 h decreased (Table 10).
Differences were detected between treatments for both mean (P < 0.01) and
standard deviation (P = 0.02), and the effects were linear and negative as BP
increased (P < 0.001, P < 0.01, respectively). Plasma insulin was not related to
change in BCS or to percent Of NEL intake partitioned to milk (Table 11).

Insulin secretion can be affected by intake, ruminal fermentation products,
and absorption of metabolites in the whole tract. Because both DMI and plasma
insulin decreased with added BP, lower feed intake might have resulted in lower
insulin, although NEL intake was not affected by treatment (Table 10). Insulin
concentration and DMI were correlated across treatments as well (Table 11; R =
0.41, P = 0.03). Starch consumed per meal decreased (Table 3) as BP
increased, so a smaller amount of starch from high-moisture com was
undergoing rapid fermentation during and immediately after each meal. This
could have resulted in lower plasma insulin concentrations and less ﬂuctuation in
insulin concentrations (Table 10), with the resulting decrease in energy

partitioned to adipose tissue indicated by the tendency for decreased BCS.

55

Site Of starch digestion can affect insulin secretion by altering the form of
absorbed fuels. In ruminants, propionate reaching the liver stimulates insulin
secretion (Reynolds, 1995). AS will be reported in Chapter 4, decreasing the
amount of starch in the diet resulted in decreased propionate concentration and
increased acetatezpropionate in rumen ﬂuid. Thus, lower insulin secretion for the
higher beet pulp diets could be a result Of lower propionate production. However,
insulin concentration was not correlated with rumen ﬂuid propionate
concentration or molar percent Of total VFA (data not shown). Although absolute
rates of production and removal were not measured, the amount and proportion
Of starch truly digested in the rumen was not related to insulin concentration,
either (data not shown), so the insulin response probably cannot be explained by
increased propionate absorption alone.

Insulin secretion is also stimulated by increased plasma glucose
concentration; although there is little net glucose absorption across the portal-
drained viscera in cattle (Reynolds, 1995), plasma glucose concentration may be
increased by greater gluconeogenesis, by increased glucose absorption and
utilization in small intestine cells, and by greater availability of glucose-sparing
fuels such as acetate, B-hydroxybutyrate, and lactate. Most Of the glucose
absorbed in the ruminant small intestine probably is either utilized within
intestinal cells, thus sparing Circulating glucose, or absorbed into blood as
lactate, which the liver can convert to glucose. Although plasma insulin
concentration decreased with added BP, amount of starch digested postruminally

(kg/d) was not different among treatments (Chapter 3); and among cow-period

56

Observations, amount or proportion of starch digested postruminally was not
related to insulin concentration, so intestinal glucose or lactate absorption alone
probably did not contribute to the insulin effect. Only the amount Of starch
consumed or digested in the whole tract was related to plasma insulin (R = 0.51,
P < 0.01; and R = 0.52, P < 0.01, respectively), and adding ruminal digestibility of
starch to the model did not improve the prediction Of insulin concentration from
starch intake. Therefore, although replacing HMC with BP shifted starch
digestion from the rumen to the intestines, the reduced plasma insulin
concentration with added BP probably was caused by the reduction in the total
amount of starch consumed and digested, regardless of the form in which it was

absorbed.

SUMMARY

Substitution Of beet pulp for high-moisture corn resulted in decreased DMI,
and ruminal distention probably limited DMI with added beet pulp. Mean and
minimum ruminal pH did not affect DMI, but, independent of treatment effects,
increased variation in pH might have decreased DMI. Replacing high-moisture
corn with beet pulp caused a quadratic response for milk fat yield and the
tendency for a quadratic response for FCM yield. Partial substitution Of pelleted
beet pulp for high-moisture corn decreased intake due to ﬁlling effects but also

permitted similar or greater fat-corrected milk yield.

57

Table 1. Nutrient composition of high-moisture corn and dried, pelleted beet

 

 

 

pulp.

Nutrient High-moisture corn Beet pulp
DM, % as fed 71.5 84.9

-----% of DM -----

NDF 10.0 39.9
CP 8.3 8.9
lndigestible NDF 3.8 8.0
Starch 70.5 3.9
Ether extract 4.7 0.7
Ash 1.0 7.8

 

Table 2. Ingredient and nutrient composition of experimental diets.

 

 

0% BP 6% BP 12% BP 24% BP
Ingredients ----% Of DM-----
Corn silage 20.1 20.1 20.1 20.1
Alfalfa Silage 19.9 19.9 19.9 19.9
Protein mix 19.5 19.5 19.5 19.5
Mineral vitamin mix 4.8 4.8 4.8 4.8
Dried, pelleted beet pulp 0 6.1 12.1 24.3
High-moisture corn 35.6 29.5 23.5 11.4
Nutrient
DM 50.2 50.5 50.8 51.6
Starch 34.6 30.5 26.5 18.4
NDF 24.3 26.2 28.0 31.6
lndigestible NDF 9.4 9.6 9.8 10.2
Forage NDF 17.1 17.1 17.1 17.1
CF 18.0 18.0 18.0 18.1
% Starch from
high-moisture corn 72.7 68.3 62.6 43.7
% NDF from forage 70.2 65.3 61.1 54.1
% NDF from beet pulp 0.0 9.3 17.3 30.7

 

58

Table 3. Effects Of substitution Of pelleted beet pulp for high-moisture corn on
nutrient intake and ruminal pool.

Intake, kg/d
OM
OM
NDF

Starch
Ruminal wet
contents, kg
Ruminal contents
volume, L
Ruminal contents,
%DM
Ruminal pool, kg
OM
OM

NDF
Potentially
digestible NDF

lndigestible NDF
Starch

 

 

Treatment LS Means P

0% 6% 12% 24%

BP BP BP BP SE Trt L O
23.7 23.8 23.9 21.8 0.7 0.11 <0.05 0.15
22.3 22.4 22.4 20.2 0.7 0.06 0.50 0.15

5.7 6.2 6.6 6.9 0.2 <0.01 0.01 0.15

8.2 7.3 6.4 4.0 0.2 <0.01 <0.01 0.21
77.7 76.7 78.9 80.7 2.2 0.36 0.11 0.58
96.1 92.8 95.5 96.0 3.0 0.64 0.49 0.43
14.2 13.9 13.4 13.2 0.4 0.12 0.01 0.57
11.0 10.4 10.6 9.9 0.5 0.19 0.04 0.74
10.1 9.5 9.7 9.0 0.5 0.14 0.03 0.85
5.5 5.0 5.2 4.9 0.3 0.19 0.11 0.62
2.4 2.1 2.3 2.1 0.2 0.30 0.17 0.61
3.1 2.9 2.8 2.8 0.2 0.42 0.13 0.21
1.24 1.03 0.87 0.63 0.08 <0.01 <0.01 0.36

 

59

Table 4. Effects of substitution of pelleted beet pulp for high-moisture corn on
meal patterns and water consumption.

 

Meals/d
Meal length,
min/meal

Meal size, kg
DM
NDF
INDF
pdNDF
Starch

lntermeal interval,
min

Eating Chew rate,
chews/min

Hunger ratio‘,
kg/min

Satiety ratio‘,

kg/min

Ruminating bouts
/d

Ruminating bout
length, min

Interval between
ruminating bouts,
min

Ruminating chew
rate, chews/min

Drinking time,
min/d
Water drunk, L/d

Drinking bouts Id

 

 

Treatment LS Means P

0% 6% 12% 24%

BP BP BP BP SE Trt L O
9.7 9.5 9.3 9.0 0.4 0.55 0.13 0.93
37.9 36.6 37.6 40.3 2.9 0.66 0.64 0.45
2.5 2.3 2.4 2.5 0.1 0.70 0.44 0.35
0.61 0.61 0.68 0.79 0.04 <0.01 <0.01 0.38
0.26 0.26 0.27 0.29 0.02 0.22 0.06 0.38
0.34 0.36 0.41 0.50 0.02 <0.01 <0.01 0.39
0.87 0.72 0.63 0.47 0.04 <0.01 <0.01 0.25
100 100 103 106 4 0.56 0.16 0.94
73.4 73.5 74.6 74.7 2.8 0.65 0.63 0.86
0.16 0.19 0.20 0.14 0.02 0.03 0.01 <0.01
0.27 0.21 0.25 0.23 0.04 0.17 0.22 0.30
12.6 12.6 12.6 12.6 0.5 1.00 1.00 0.97
36.6 37.6 38.9 38.6 2.4 0.66 0.33 0.48
70.4 71.2 67.6 67.5 2.7 0.45 0.18 0.95
60.9 62.3 62.7 60.9 1.9 0.39 0.11 0.09

17 17 18 17 2 0.72 0.30 0.26

91 98 92 90 4 0.19 0.52 0.32

11 12 11 11 1 0.14 0.35 0.24

 

1 Hunger ratio = meal kg DM/ premeal interval;
Satiety ratio = meal kg DMI postmeal interval (Forbes, 1995).

60

Table 5. Effects of substitution of pelleted beet pulp for high-moisture corn on

Chewing time.

 

Eating time, min
Id

lbout

lkg of DMI

lkg Of NDF intake

lkg Of pdNDF intake
/kg of forage NDF
intake
Feed NDF%

- orts NDF%

Ruminating time, min
/d

lbout

lkg Of DMI

lkg Of NDF intake

lkg of pdNDF intake
lkg Of forage NDF
intake

lkg ruminal DM pool
lkg ruminal NDF
pool

 

 

Total chewing time, min

/d

lbout

lkg Of DMI

lkg Of NDF intake

lkg of pdNDF intake
lkg of forage NDF
intake

lkg ruminal DM pOOl
lkg ruminal NDF
pOOl

Treatment LS Means P

0% 6% 12% 24%

BP BP BP BP SE Trt L Q
298 297 302 318 13 0.21 0.04 0.44
34.0 33.0 33.7 36.6 2.7 0.65 0.65 0.45
12.6 12.9 12.9 14.2 0.6 0.05 <0.01 0.38
52.1 49.6 47.1 46.4 2.4 0.04 <0.01 0.27
93.1 83.6 78.8 74.0 4.0 <0.01 <0.01 0.07
74.1 73.2 74.7 83.1 3.0 0.02 <0.01 0.11

1.0 1.6 3.8 2.2 2.0 0.15 0.07 0.12
472 467 483 499 24 0.61 0.15 0.73
35.9 37.1 38.4 38.1 2.5 0.65 0.31 0.45
21.0 19.6 20.3 22.4 1.0 0.05 0.07 0.02
82.7 75.8 73.6 74.6 4.6 0.18 0.05 0.12
148 130 124 119 8 0.01 0.01 0.10
123 115 119 132 6 0.04 0.07 0.02
44.4 46.0 46.8 51.3 3.4 0.31 0.05 0.78
89.2 98.0 93.3 104 8 0.28 0.13 0.94
784 792 805 833 25 0.50 0.12 0.89
35.1 35.3 36.0 38.0 1.8 0.64 0.06 0.77
33.6 32.5 34.0 37.4 1.1 0.01 0.29 0.04
135 125 123 124 6 0.22 0.07 0.15
242 211 206 196 10 <0.01 <0.01 0.05
192 190 199 220 8 0.07 0.01 0.22
73.5 74.5 77.6 83.0 4.7 0.30 0.04 0.78
148 159 154 168 11 0.36 0.12 0.87

 

61

Table 6. Effects of substitution of pelleted beet pulp for high-moisture corn on

chewing activity.

 

 

Treatment LS Means P
00/0 60/0 120/0 240/0
BP BP BP BP SE Trt L Q

Eating chews

Id 22344 23068 23156 24054 1607 0.40 0.09 0.85
lbout 2543 2510 2556 2783 248 0.68 0.81 0.58
lkg Of DMI 945 964 980 1118 63 0.01 <0.01 0.29
lkg of NDF

intake 3899 3714 3553 3544 232 0.12 0.03 0.26
lkg of pdNDF

intake 6962 6395 5992 5627 397 <0.01 <0.01 0.19
lkg Of forage

NDF intake 5544 5645 5710 6357 348 0.03 <0.01 0.34
Ruminating Chews

Id 28177 28190 28425 31144 1548 0.44 0.13 0.44
lbout 2242 2331 2420 2387 210 0.75 0.28 0.30
lkg Of DMI 1225 1188 1200 1313 86 0.61 0.44 0.26
lkg of NDF

intake 5053 4606 4418 4731 309 0.30 0.06 0.08
lkg of pdNDF

intake 8291 7382 6892 7241 464 0.08 0.02 0.07
lkg Of forage

NDF intake 9035 7913 7448 7512 534 0.06 0.06 0.03
lkg ruminal DM

pool 2627 2765 2757 3156 245 0.34 0.07 0.69
lkg ruminal

NDF pool 5456 6141 5644 6431 591 0.37 0.69 0.96
Total chews

Id 50695 50426 49642 5701 1 2389 0.19 0.05 0.27
lkg of DMI 2155 2132 2200 2712 136 0.01 0.49 0.08
/kg Of NDF

intake 8934 8207 8033 8558 481 0.31 0.07 0.08
lkg of pdNDF

intake 15985 14124 13592 13548 837 0.05 0.02 0.07
lkg of forage

NDF intake 12559 12412 12820 15442 776 0.03 0.53 0.10
lkg ruminal DM

pool 4720 4869 5039 5677 410 0.18 0.02 0.68
/kg ruminal

NDF pool 9752 10766 10423 11457 950 0.31 0.09 0.72

 

62

Table 7. Pearson correlation coefﬁcients between DMI and eating or chewing
behavior.

 

 

DMI, kg/d
Meals/d 0.07
Meal length, min 0.09
lntermeal interval, min -0.31
Meal DM, kg/meal 0.391
Meal NDF, kg/meal -0.01
Hunger ratio , kg/min 0.36
Time eating, min/d 0.20
Time eating lkg DMI -0.19
Time eating lkg forage NDF intake -0.391
Total chewing time (TCT), min/d -0.01
TCT / kg DMI -0.581
TCT l kg forage NDF intake -0.70‘

 

1 Correlation is signiﬁcant (P < 0.05).
2 Calculated for each meal: kg DMI / premeal interval (Forbes, 1995).

Table 8. Pearson correlation coefﬁcients between DMI and characteristics of
ruminal fermentation and pH.

 

 

DMI, kg/d
Total ruminal [VFA], mM -0.23
% propionate, mOl / 100mol VFA -0.22
Acetate: Propionate 0.18
Valerate absorption rate, %/h 0.31 2
Ruminal pH mean 0.06
Ruminal pH standard deviation -0.41 I
Ruminal pH minimum 0.27
Ruminal pH range -0.30
Ruminal pH variance 0.421

 

1 Correlation is signiﬁcant (P < 0.05).
2 Tendency for signiﬁcant correlation (P < 0.10).

63

Table 9. Effects of substitution of pelleted beet pulp for high-moisture corn on

milk production.

 

 

Treatment LS Means P
0% 6% 12% 24%
BP BP BP BP SE Trt L Q
Yield, kg/d
Milk 36.4 36.6 35.9 35.4 1.2 0.58 0.95 0.74
3.5% FCM1 37.4 38.4 38.0 36.8 1.2 0.20 0.14 0.07
Milk fat 1.34 1.40 1.39 1.33 0.07 0.14 0.04 0.03
Milk protein 1.13 1.15 1.15 1.09 0.03 0.18 0.29 0.11
Milk lactose 1.80 1.82 1.78 1.75 0.07 0.57 0.99 0.71
Milk composition, %
Fat 3.72 3.84 3.90 3.81 0.22 0.46 0.12 0.16
Protein 3.21 3.21 3.22 3.10 0.11 0.41 0.59 0.32
Lactose 4.95 4.96 4.95 4.94 0.02 0.75 0.66 0.53
kg 3.5%FCM/kg DMI 1.59 1.62 1.60 1.70 0.05 0.26 0.07 0.52

 

I 3.5% fat-corrected milk.

64

Table 10. Effects Of substitution Of pelleted beet pulp for high-moisture corn on

energy balance and plasma insulin.

 

 

 

Treatment LS Means P

0% 6% 12% 24%

BP BP BP BP SE Trt L Q
NEL intake‘, Mcal/d 38.9 38.2 40.0 36.5 1.2 0.21 0.43 0.24
Milk NELz, Mcal/kg 0.72 0.73 0.74 0.72 0.02 0.50 0.13 0.13
Milk NEL, %NEL intake 67.4 69.0 66.5 70.7 1.8 0.27 0.67 0.42
BW change, kg /21d -8.0 6.7 -11.6 -1.5 15.8 0.49 0.50 0.45
BCS change, /21d 0.06 0.11 -0.04 -0.05 0.06 0.15 0.06 0.93
NEL balance3, Mcal/d 3.2 1.8 4.1 1.1 1.1 0.16 0.59 0.39
NEW“, %NEL intake 24.0 25.1 23.6 26.2 0.8 0.03 0.06 0.30
Mean plasma insulin“,
ulU/ml 13.0 13.2 11.6 8.9 1.2 <0.01 <0.01 0.26
Plasma insulin standard deviation“,
plU/ml 4.9 4.7 3.8 2.9 0.5 0.02 <0.01 0.96

 

‘ New...) = DMI (kg) x (0.0245 x TDN(%)) (NRC 1989).
2 NEL(milk) (McaI/d) = MY (kg) x (0.0929 x fat% + 0.0563 x true protein% + 0.0395
x lactose%) (NRC, 2001).
3 NEL(intake) " NEL(maintenance)""NEL(milk). Where NEL(maintenance) = 0080 X BWO'75 (NRC

2001).

4 Calculated using 8 samples collected over 3 d, representing 3-hr intervals Of a

24-hr day.

Table 11. Pearson correlation coefﬁcients between plasma insulin and

characteristics of intake, production, and energy balance.

DMI, kg/d

Total tract starch digestion, kg/d
Milk NEL, Mcal/kg

Milk NEL, %NEL intake

Plasma [insulin], mM

 

0.41 T

0.52 I
0.51 I

-0.23

 

1 Correlation is signiﬁcant (P < 0.05).

65

Figure 1. Relationship between DMI (kg/d) and (a) average kg
DMI/meal (DMI = 16.3 + 2.8 x meal DMI; R = 0.40; P < 0.04); (b)
mean ruminal pH (R = 0.05; P > 0.70); and (c) pH standard
deviation (DMI = 27.1 - 11.5 x pH standard deviation; R = -0.41;
P < 0.03). 0 denotes 0% beet pulp, + denotes 6% beet pulp, I
denotes 12% beet pulp, and C denotes 24% beet pulp (%diet
DM) substituted for high-moisture corn.

(a) 28.0 .I
27.0
26.0 ‘
25.0 _
24.0 T
23.0 T
22.0 ‘
21.0 ‘
20.0 ‘

19.0 I l I I I
1.75 2.00 2.25 2.50 2.75 3.00 3.25

 

DMI (kg/d)

 

 

 

 

Meal DM (kg)

(b) 28.0
27.0- 0
26.0— - .
25.0-
24.0- - .
23.0: 0. :0- 0 . O
22.0-
21.0-
20.0- 0
19.0

 

DMI (kg/d)

 

 

 

l I I

l I
5.4 5.6 5.8 6.0 6.2 6.4 6.6

Ruminal pH mean

66

DMI (kg/d)

 

28.0
27.04
26.0"
25.0‘
24.0"
23.0“
22.0‘
21.0“
20.0‘

 

 

 

 

19.0

I
0.20 0.25 0.30 0.35 0.40 0.45 0.50

I I T l

Ruminal pH standard deviation

67

Figure 2. Relationship between sorting against NDF(%NDF in
orts - %NDF in feed) and 3.5% FCM yield. Sorting = -29.6 + 0.9
x FCM - 0.2 x (FCM - 37.8)2; (R = 0.54; P < 0.03). 0 denotes
0% beet pulp, + denotes 6% beet pulp, I denotes 12% beet
pulp, and C denotes 24% beet pulp (%diet DM) substituted for
high-moisture corn.

 

15

 

 

 

 

Sorting (%NDFin orts - %NDF in feed)

-151I\IIrIIII|IIIIII
35 40 45

3.5% fat-corrected milk (kg/d)

68

Figure 3. Relationship between milk fat concentration and mean

ruminal pH (R = 0.10; P > 0.50). O denotes 0% beet pulp, +

denotes 6% beet pulp, I denotes 12% beet pulp, and C denotes

24% beet pulp (%diet DM) substituted for high-moisture corn.

Milk fat concentration (%)

5.0

4.5

 

 

 

 

I
- O
I .
. . IO
I
-1 O
J I
O O 0
_ . l
. O
0 O O "
—I O . "
I I I I I
5.4 5.6 5 8 6.0 6 2 6.4 6.6

Ruminal pH mean

69

CHAPTER 3

Pelleted beet pulp substituted for high-moisture corn: Effects on digestion

and ruminal digestion kinetics in lactating dairy cows

ABSTRACT

The effects of increasing concentrations Of dried, pelleted beet pulp
substituted for high-moisture corn on digestion and ruminal digestion kinetics
were evaluated using 8 ruminally and duodenally cannulated multiparous
Holstein cows in a duplicated 4 x 4 Latin square design with 21-d periods. Cows
were 79 :I: 17 (mean :I: SD) DIM at the beginning of the experiment. Experimental
diets with 40% forage (corn silage and alfalfa Silage) and 60% concentrate
contained 0%, 6.1%, 12.1%, or 24.3% beet pulp substituted for high-moisture
corn on a DM basis. Diet concentrations Of NDF and starch were 24.3% and
34.6% (0% beet pulp), 26.2% and 30.5% (6% beet pulp), 28.0% and 26.5% (12%
beet pulp), and 31.6% and 18.4% (24% beet pulp), respectively. Ruminal DM
pool decreased (P < 0.05), and NDF turnover rate increased (P < 0.01) as beet
pulp increased. Potentially digestible NDF was digested more extensively (P <
0.01) and at a faster rate (P < 0.01) in the rumen with increasing beet pulp,
resulting in increased total tract NDF digestibility (P < 0.01). Passage rates of
potentially digestible NDF and of indigestible NDF were not affected by treatment
(P > 0.20, P > 0.10, respectively). True ruminal digestibility of starch decreased

with increasing BP substitution (P < 0.01). This was caused by a linear increase

70

in starch passage rate (P = 0.01), possibly because of increasing ruminal ﬁll, and
a linear decrease in digestion rate (P < 0.01) Of starch in the rumen, possibly the
result of reduced amylolytic enzyme activity for lower-starch diets. Although true
ruminal starch digestibility decreased when more beet pulp was fed (P < 0.01),
whole tract starch digestibility was not affected (P > 0.40) because Of
compensatory digestion of starch in the intestines. Due to more thorough
digestion Of ﬁber in diets containing more beet pulp, total tract digestibility of DM
increased (P < 0.10), and intake Of digestible DM was not affected (P > 0.40).
Partially replacing high-moisture corn with beet pulp increased ﬁber digestibility

without reducing total tract starch digestibility.

INTRODUCTION

Because starch is usually more completely digested than NDF, replacing
forage with grain can increase diet digestibility. However, nutrient digestion can
also be reduced if passage rate is drastically increased or if ﬁber digestibility is
severely reduced by increased starch concentration. Depressed ﬁber digestibility
can be caused by several factors: decreased mastication and slower particle
size reduction; a reduction in ruminal pH resulting from increased volatile fatty
acid (VFA) production and decreased ﬂow of saliva buffers (Strobel and Russell,
1986); and inhibition Of ﬁber digestion independent Of effects of mastication or pH

(Grant and Mertens, 1992).

71

When low-forage, high-grain diets are fed, adding carbohydrate sources
that are more rapidly and extensively fermented than forage neutral detergent
ﬁber (NDF) and mimic some of its beneﬁcial effects, but that do not bring the
same negative effects as starch fermentation, can improve the overall digestion
and absorption of nutrients. Beet pulp contains approximately 40% NDF and is
unique in its high concentration of neutral-detergent soluble ﬁber, especially
pectic substances (~25% Of DM). The NDF in beet pulp can be digested more
quickly than forage NDF (Bhatti and Firkins, 1995), and pectin is fermented more
rapidly than cellulose and hemicellulose (Marounek et al., 1985). Unlike starch,
pectin fermentation does not inhibit cellulose and hemicellulose digestion,
primarily because pectinolytic bacteria are also inhibited at low pH (Marounek et
aL,1985)

Therefore, substituting beet pulp for high-moisture corn grain in a diet with
a low forage content should, at some rate of inclusion, improve NDF digestion
and therefore increase overall nutrient digestion in the whole tract. Starch
digestion kinetics Should also be altered, changing the proportion Of starch
digested in the rumen and intestines, although the direction of that shift cannot
be predicted. The Objective Of this experiment was to measure the effects of
substituting beet pulp for high-moisture corn at four concentrations (0, 6, 12, and
24% Of diet DM) on ruminal, postruminal, and whole tract digestion Of NDF,

starch, dry matter and organic matter.

72

MATERIALS AND METHODS

Treatments and Cows

Experimental procedures were approved by the All University Committee
on Animal Use and Care at Michigan State University. Eight multiparous
Holstein cows (79 :1: 17 DIM; mean x SD) from the Michigan State University
Dairy Cattle Teaching and Research Center were assigned randomly to a
duplicated 4 x 4 Latin square balanced for carry over effects in a dose-response
arrangement of treatments. Treatment periods were 21 d with the ﬁnal 10 (I used
to collect samples and data. Treatments were diets containing dried, pelleted
beet pulp substituted for high-moisture corn at 0% (OBP), 6% (GBP), 12%
(1ZBP), and 24% (24BP) Of diet DM. Cows were cannulated ruminally and
duodenally prior to calving. Duodenal cannulas were soft gutter type made of
tygon and vinyl tubing (Crocker et al., 1998). The duodenum was ﬁstulated
proximal to the pylorus region and prior to the pancreatic duct and the cannulas
were placed between 10th and 11th ribs as described by Robinson et al. (1985).
Both ruminal and duodenal surgeries were performed at the Department of Large
Animal Clinical Science, College of Veterinary Medicine, Michigan State
University. At the beginning Of the experiment, empty body weight (ruminal
digesta removed) of cows was 515.9 a: 63.5 kg (mean 3: SD).

Nutrient composition for high-moisture corn and pelleted beet pulp are
Shown in Table 1. Experimental diets contained 40% forage (50:50 corn silage:
alfalfa silage), high-moisture corn, beet pulp at 0-24% of diet DM, a premixed

protein supplement (soybean meal, corn distiller’s grains, and blood meal), and a

73

mineral and vitamin mix (Table 2). All diets were formulated for 18% dietary CP

concentration and fed as total mixed rations.

Data and Sample Collection

Throughout the experiment, cows were housed in tie-stalls, and fed once
daily (1100 h) at 110% of expected intake. Amounts Of feed Offered and refused
were weighed for each cow daily during collection periods. Samples of all dietary
ingredients (0.5 kg) and orts from each cow (12.5%) were collected daily on d 12-
19 and combined into one sample per period (or per cow-period) before drying.

Chromic oxide was used as a marker to estimate nutrient digestibility in
the rumen and in the total tract. Gelatin capsules (1.5 oz., Tropac lnc., Airﬁeld,
NJ) containing 5 g of Chromic oxide and spelt hulls (Wiley mill, 2 mm screen;
Authur H. Thomas, Philadelphia, PA) were dosed through the ruminal cannula at
0300, 1100, and 1900 h (total Of 15 g Cr203 Id) from 7 to 14 d with a priming dose
Of 3X on d 7. Duodenal samples (1,000 g), fecal samples (500 g), and rumen
ﬂuid samples (100 mL) were collected every 9 h from d 12 to d 14 SO that 8
samples were taken for each cow each period, representing every 3 h Of a 24-
hour period to account for diurnal variation. Rumen ﬂuid samples were taken by
sampling contents from ﬁve different Sites in the rumen which were then
combined and strained. Fluid pH was immediately recorded. Samples were
immediately frozen at -20°C.

Effect of treatment on rate Of liquid passage was measured on d 15 using

a pulse dose of cobalt EDTA (Allen et al., 2000). Cobalt EDTA was closed two

74

hours after feeding on d 19. Rumen ﬂuid was sampled before dosing and at 0.5,
1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, and 8 h after dosing. Samples
were immediately frozen.

Ruminal contents were evacuated manually through the ruminal cannula
at 1500 h (4 h after feeding) on d 20 and at 0900 h (2 h before feeding) on d 21
of each period. Total ruminal content mass and volume were determined.
During evacuation, 10% aliquots of digesta were separated to allow accurate
sampling. Aliquots were squeezed through a nylon screen (1 mm pore size) to
separate into primarily solid and liquid phases. Samples were taken from both
phases for determination of nutrient pool Size, and additional liquid samples were

taken to measure VFA concentrations.

Sample and Statistical Analysis

Diet ingredients, orts, and feces were dried in a 55°C forced-air oven for
72 h and analyzed for DM concentration. All dried samples were ground with a
Wiley mill (1 mm screen; Authur H. Thomas, Philadelphia, PA). Dried, ground
fecal samples were combined on an equal DM basis into one sample per cow per
period. Ruminal digesta samples were lyophilized (Tri-Philizer'“ MP, FTS
Systems, Stone Ridge, NY). Dudodenal samples were thawed, combined and
ﬁltered into primarily solid and liquid phases using nylon mesh (1 mm pore size)
to minimize sampling errors due to segregation of samples into solid and liquid

phases. Both phases were weighed, and sub-samples were taken from each

75

phase. Liquid and solid sub-samples were lyophilized, ground, and recombined
by weight according to the original ratio Of solid and liquid DM.

All dried samples were analyzed for ash, NDF, indigestible NDF (INDF),
CP, and starch. Ash concentration was determined after 5 h oxidation at 500°C
in a mufﬂe furnace. Concentrations of NDF were determined according to Van
Soest et al. (1991, method A). Forage samples were analyzed for ADF and
sulfuric acid lignin content (Van Soest et al., 1991). lndigestible NDF was
estimated as NDF residue after 120-h in vitro fermentation (Goering and Van
Soest, 1990). Crude protein was analyzed according to Hach et al. (1985).
Starch was hydrolyzed enzymatically (Karkalas, 1985) after samples were
gelatinized with sodium hydroxide. Glucose concentration was then measured
using glucose oxidase (Glucose kit #510; Sigma Chemical Co., St. Louis, MO),
and absorbance was determined with a micro-plate reader (SpectraMax 190,
Molecular Devices Corp., Sunnyvale, CA). Concentrations Of all nutrients except
for DM were expressed as percentages Of DM determined by drying at 105°C in
a forced-air oven.

Rumen ﬂuid samples taken to measure rate Of liquid passage were
analyzed for cobalt concentration by ﬂame atomic absorption spectrophotometry
(SpectrAA 220/FS, Varian Australia Pty. Ltd., Mulgrave, Victoria, Australia). Rate
Of cobalt disappearance was determined by non-linear regression Of its decline in
concentration in rumen ﬂuid over time after dosing, accounting for background

(Allen et al., 2000).

76

Feeds, duodenal digesta, and feces were analyzed for concentrations of
chromium. Samples were digested with phosphoric acid (Williams et al., 1962),
and chromium was quantiﬁed by ﬂame atomic absorption spectrometry
(SpectraAA 220, Varian, Victoria, Australia) according to manufacturer's
recommendation. Nutrient intake was calculated using the composition of feed
Offered and refused. Duodenal ﬂow Of microbial OM was determined as
described by Oba and Allen (2002b), and true ruminally degraded OM (T RDOM)
was calculated by subtracting duodenal ﬂow Of non-microbial OM from OM
intake. Ruminal pool sizes (kg) Of OM, NDF, indigestible NDF, and starch were
determined by multiplying the concentration of each component by the ruminal
digesta DM weight (kg). Turnover rate in the rumen, passage rate from the
rumen, and ruminal digestion rate of each component (%lh) were calculated by
the following equations:

Turnover rate in the rumen (%lh) =

(Intake of component / Ruminal pool of component) / 24 x 100
Passage rate from the rumen (%lh) =

(Duodenal ﬂow Of component / Ruminal pool Of component) / 24 x 100;

and
Digestion rate in the rumen (%lh) =

Turnover rate in the rumen (%lh) — Passage rate from the rumen (%lh).

TO determine differences between treatments, all data were analyzed
using the ﬁt model procedure of JMP® according to the following model:

Yijk=u+Ci+Pj+Tk+eijk

77

where

l1 = overall mean,

Ci = random effect Of cow ( i = 1 to 8),

P; = ﬁxed effect Of period (j = 1 to 4),

Tk = ﬁxed effect of treatment (k = 1 to 4), and

em, = residual, assumed to be normally distributed.

Period by treatment interaction was originally evaluated, but it was removed from
the statistical model because it was not signiﬁcant. Linear and quadratic dose-
response effects were evaluated using the same model with diet percent beet
pulp (0, 6, 12, and 24) in place of the ﬁxed effect Of treatment. Pearson
correlation coefﬁcients were determined between cow-period Observations for
some parameters. Treatment effects, linear and quadratic responses, and
correlations were declared signiﬁcant at P < 0.05, and tendencies were declared
at P < 0.10.

Data from two cow-periods were excluded from statistical analysis. One
cow developed a cecal torsion requiring surgery early in period 3; data and
samples were not collected from this cow during period 3, but she recovered
sufﬁciently for her data to be used in period 4. Period 4 data from a second cow
were excluded after she showed signs of estrus because her intake and milk
yield were outliers (outside the 95% conﬁdence interval for cow-period

Observations).

78

RESULTS AND DISCUSSION
Ruminal NDF Digestion

Turnover rate of NDF (Table 3) increased linearly with added beet pulp (P
< 0.01). A faster turnover rate can result from increased passage rate, increased
digestion rate, or both. Passage rates of potentially digestible NDF (pdNDF) and
indigestible NDF were not affected by treatment (Table 3). However, digestion
rate Of pdNDF more than doubled, from 2.71% to 5.86%lh (P < 0.0001 ), from
0BP to 24BP.

As BP was substituted for HMC as up to 24% Of diet DM, the proportion Of
NDF from forage decreased from approximately 70 to 54% of total NDF, and the
proportion of NDF from BP increased from 0 to approximately 31% of total NDF
(Table 2). Beet pulp NDF has a Shorter lag time and more rapid fermentation
rate than most other sources Of ﬁber (Bhatti and Firkins, 1995) partly because it
has been previously soaked in hot water (Bichsel, 1988). Therefore, increasing
the contribution of beet pulp NDF to total NDF can increase the overall rate of
NDF digestion independent of any associative effects of beet pulp NDF on the
digestion NDF from other sources.

Substituting the readily-fermented pectin and NDF Of beet pulp for corn
may also increase the rate Of digestion of other dietary ﬁber through associative
effects of both ﬁber and starch. Adding BP likely increased the population of
ﬁbrOlytic bacteria by providing excess available substrate for ﬁber fermenters and
increasing ﬁbrolytic enzyme activity in the rumen. Dilution of the concentration Of

dietary starch would also reduce the negative affects Of starch fermentation on

79

cellulolytic bacteria. Measurements Of ruminal pH over 96 h in this study are
reported in Chapter 4. As mean and minimum daily pH were not different among
treatments, the improvement in ﬁber digestion with added BP was not caused by
increased mean pH. However, reduction of NDF digestion by the addition of

starch can occur even when pH is held constant (Grant and Mertens, 1992).

Ruminal pH and NDF Digestion

Increased rate of NDF digestion with added beet pulp was not the result of
increased mean pH among treatments. However, correlations among cow-
period Observations between ruminal pH Characteristics and rate Of ruminal ﬁber
digestion show that greater daily mean pH resulted in more rapid digestion Of
potentially digestible NDF (Figure 1; R = 0.41 P < 0.05), as did greater minimum
ruminal pH (R = 0.55, P < 0.01). Lower mean or minimum ruminal pH and
greater variability in pH probably Slowed fermentation Of NDF because low pH
(especially below 6.0) slows growth of ﬁbrolytic bacteria, perhaps due to
intracellular accumulation of VFA and anion toxicity (Russell and Wilson, 1996).
Although higher pH mean and minimum were associated with more rapid ﬁber
fermentation, it did not improve ruminal ﬁber digestibility (P > 0.30), because
higher pH also increased passage rates of pdNDF and INDF from the rumen
(Table 4). Slower ﬁber fermentation at low ruminal pH was independent of
treatment effects; Slower ﬁber fermentation when ruminal pH variation increased

corresponds with treatment effects on pH and ﬁber digestion kinetics.

80

Whole Tract NDF Digestion

As NDF intake and the rate of ruminal NDF digestion increased with beet
pulp replacing corn grain, the amount Of NDF digested in the rumen also
increased (P < 0.01; Table 5). Ruminal digestibility Of total NDF was not affected
(P > 0.10), but potentially digestible NDF was more completely digested with
added beet pulp (P < 0.01). There was no compensatory postruminal NDF
digestion, so the diets with the greatest ruminal NDF digestibility also had the

greatest total tract NDF digestibility (P < 0.001 ).

Ruminal Starch Digestion Kinetics

Corresponding to diet composition and DMI, starch intake decreased from
8.2 kg/d for 0BP to 4.0 kg/d for 24 BP (Table 6; P < 0.0001). Starch turnover rate
was not affected by treatment (Table 3; P > 0.40) due to opposing changes in
ruminal rates Of both passage and digestion Of starch. AS HMC was replaced by
BP, passage rate of starch increased linearly (P = 0.01) and ruminal starch
digestion rate decreased from 11.3%lh for 0BP to 1.9%lh for 24BP (P < 0.01).
As the dietary concentration of HMC decreased, the proportion of starch from
HMC decreased (Table 2), and starch from other sources (such as corn silage)
was probably fermented less rapidly due to differences in processing and
preservation. Rate Of starch fermentation also might have been reduced by
lower amylase activity in rumen ﬂuid, because Of a smaller population Of
amylolytic microbes and possibly because of depressed enzyme activity of the

population.

81

 

Site of Starch Digestion

Large differences in starch intake, rapid passage of starch from the rumen
for the high-beet pulp diets, and a sharp decrease in ruminal starch digestion rate
resulted in much lower true ruminal starch digestibility (P < 0.01; Table 6).
Reducing dietary starch content by 14 percentage units (0% BP to 6% BP)
resulted in a 31% decrease in true ruminal starch digestion (from 46.5% to
32.3%). From 0BP to 24BP, dietary starch content was reduced by 48%, the
amount Of starch truly digested in the rumen decreased 82 % (3.8 kg to 0.7 kg),
and the percentage of starch truly digested in the rumen decreased 64 percent
(46.5% to 16.9%).

Treatment effects on ruminal digestibility of starch were compensated for
by intestinal digestion; the percent of starch consumed that was digested
postruminally increased from 45.7% to 77.5% (P = 0.02) as dietary starch content
decreased from 34.6% to 18.4%, and digestibility of starch passing into the
duodenum increased from 78.0% to 85.0% (P = 0.02). Because postruminal
digestion of starch results in the absorption Of glucose, which is more
energetically efﬁcient than starch fermentation to VFA (Owens et al., 1986), cows
may have Obtained energy from starch more efﬁciently when fed diets containing
less starch. Because these cows were not ileally cannulated, the proportions of
starch digested and absorbed as glucose in the small intestine or fermented and
absorbed as VFA in the large intestine could not be measured. AS a result of

increased postruminal starch digestion, total tract digestibility of starch was the

82

same across beet pulp treatments (P > 0.40) even though the amount of starch
digested in the total tract decreased from 7.2 kgld to 3.5 kg/d (P < 0.0001) as
starch intake decreased.

Source of starch can affect ruminal and intestinal starch digestion. The
rate and extent of starch digestion might be expected to be greater for rolled
HMC than for kernels in corn silage, the second most signiﬁcant starch source in
these diets, because of greater surface areazweight in the rolled HMC. AS HMC
was increasingly replaced by beet pulp, the percent Of dietary starch coming from
HMC decreased from 73% to 44% (Table 2). It would be possible that ruminal
rate of starch digestion (%lh) decreased as BP increased because corn silage
grain was digested more Slowly than the rolled HMC, and corn silage kernels
comprised a greater proportion of total starch as BP increased in the diets.
However, total tract digestibility Of starch was Similar among treatments (Table
7), so starch reaching the duodenum was as digestible, if not more digestible, for
diets in which HMC starch comprised a smaller percentage Of total dietary starch.
Unfermented corn silage kernels would be more resistant to intestinal digestion
than unfermented HMC, so it is not likely that a greater proportion of corn-silage
grain was resisting ruminal degradation for high-beet-pulp diets (thus reducing
ruminal starch digestion rate) and then being digested in the intestines to the
same extent as the starch in low-BP diets. While the ruminal digestion Of silage
kernels was probably affected by dietary starch concentration, the treatment
effects detected were not only the result Of changing proportions Of starch

sources.

83

If the amount of duodenal enzyme activity limits the amount Of starch
digested in the small intestine, then extent of digestion should decrease as starch
ﬂow increases (Owens et al., 1986). However, across cow-period observations,
amount of starch digested in the intestines (kg/d) increased linearly with greater
duodenal starch ﬂow (R = 0.98, P < 0.0001; Figure 2a). Intestinal starch
digestibility (% of duodenal ﬂow) also tended to increase as duodenal starch ﬂow
increased (R = 0.34, P = 0.07; Figure 2b). Similar responses in intestinal starch
digestion were reported in a study in which treatments were dietary starch
concentration and fermentability of corn grain (Oba and Allen, 2002a). Since
greater ﬂow was not associated with lower intestinal digestibility, starch digestion
in the small intestine was probably limited by physical or chemical characteristics
of starch escaping ruminal digestion, rather than by enzyme activity (Oba and
Allen, 2002a). However, amylase secretion responds to dietary starch
concentration (Owens, 1986), so enzyme quantity could possibly limit starch

digestion.

Digestion of DM and OM

Substituting highly fermentable ﬁber for rapidly fermentable starch
radically altered ruminal digestion and passage of starch and ﬁber, probably
through both physical and microbial changes in the rumen environment. This
resulted in a tendency for decreased DM apparent ruminal digestion (P = 0.10)
but did not affect apparent or true OM digestion in the rumen (Table 7). Among

cow-period Observations, ruminal OM digestibility increased with faster ruminal

84

starch digestion (R = 0.71, P < 0.0001) and decreased with faster starch passage
from the rumen (R = -0.69, P < 0.0001). Greater true ruminal starch digestibility
also increased true ruminal OM digestibility (R = 0.83, P < 0.0001). Ruminal ﬁber
digestibility and digestion kinetics were not related to TRDOM (P > 0.20).
Therefore, ruminal starch digestion, but not NDF digestion, affected digestibility
Of OM in the rumen.

The tendency for a quadratic effect of dietary beet pulp content on ﬂow of
DM to the duodenum was detected, with the highest value for 12% beet pulp; OM
ﬂow followed a similar pattern but with the highest value for 6% beet pulp (Table
7). However, because compensatory postruminal starch digestion took place as
the concentration of beet pulp increased, quantities Of DM and OM apparently
digested in the whole tract were not affected by treatment. Because DMI
decreased linearly with added beet pulp while the amount of DM disappearance
did not change, apparent total tract OM digestibility increased, and DM
digestibility tended to increase. Therefore, substituting highly digestible NDF for
rapidly fermented starch in a high-concentrate diet did not reduce the amount of
apparently absorbed DM, but increased total diet digestibility by increasing NDF

digestion.

SUMMARY
Increasing the substitution rate Of pelleted beet pulp for high-moisture corn
decreased the rate Of ruminal starch digestion and increased starch passage

rate, shifting the Site of starch digestion increasingly to the intestines. Added

85

beet pulp greatly increased the rate at which potentially digestible NDF was
digested in the rumen and also increased total tract NDF digestibility. Partially
replacing a highly fermentable starch source with beet pulp was accomplished
without reducing apparent nutrient digestibility because adding beet pulp

increased ﬁber digestibility without reducing total tract starch digestibility.

86

Table 1. Nutrient composition of high-moisture corn and dried, pelleted beet

 

 

 

pulp.

Nutrient HkLh-moisture corn Beet pulp
DM, % as fed 71.5 84.9

----% of DM-----

NDF 10.0 39.9
CF 8.3 8.9
lndigestible NDF 3.8 8.0
Starch 70.5 3.9
Ether extract 4.7 0.7
Ash 1.0 7.8

 

Table 2. Ingredient and nutrient composition of experimental diets.

 

0% BP 6% BP 12% BP 24% BP
Ingredients ----- % of DM-—----
Corn Silage 20.1 20.1 20.1 20.1
Alfalfa silage 19.9 19.9 19.9 19.9
Protein mix 19.5 19.5 19.5 19.5
Mineral vitamin mix 4.8 4.8 4.8 4.8
Dried, pelleted beet pulp 0 6.1 12.1 24.3
High-moisture corn 35.6 29.5 23.5 11.4
Nutrient
DM 50.2 50.5 50.8 51.6
Starch 34.6 30.5 26.5 18.4
NDF 24.3 26.2 28.0 31.6
lndigestible NDF 9.4 9.6 9.8 10.2
Forage NDF 17.1 17.1 17.1 17.1
CP 18.0 18.0 18.0 18.1
% Starch from
high-moisture corn 72.7 68.3 62.6 43.7
% NDF from forage 70.2 65.3 61.1 54.1
% NDF from beet pulp 0.0 9.3 17.3 30.7

 

87

Table 3. Effects Of substitution of pelleted beet pulp for high-moisture corn on

ruminal digestion kinetics.

Treatment LS Means

 

 

 

 

 

0% 6% 12% 24%
BP BP BP BP SE Trt L Q
Ruminal turnover
rate, %lhr
DM 9.1 9.8 9.4 9.3 0.6 0.34 0.20 0.20
OM 9.4 10.2 9.6 9.6 0.6 0.25 0.24 0.24
NDF 4.5 5.5 5.2 5.9 0.4 <0.01 <0.01 0.24
pdNDF 5.9 7.6 7.2 8.6 0.6 <0.01 <0.01 0.38
Starch 29.0 29.6 28.3 25.4 2.3 0.49 0.87 0.56
Ruminal passage
rate, %lh
Potentially
digestible NDF 3.16 3.29 2.74 2.89 0.36 0.49 0.29 0.76
INDF 3.09 3.78 3.44 3.67 0.28 0.11 0.16 0.26
Starch 15.90 19.31 18.33 23.50 2.99 0.07 0.01 0.96
Liquid1 18.6 17.5 16.7 16.6 1.0 0.13 0.03 0.21
Ruminal digestion
rate, %lh
pdNDF 2.71 4.29 4.43 5.86 0.47 <0.01 <0.01 0.23
Starch 11.30 10.36 9.45 1.91 3.06 0.02 <0.01 0.27
1 Measured using CO-EDTA.
Table 4. Correlation coefﬁcients for ﬁber digestion kinetics and ruminal pH.
pdNDF pdNDF INDF
digestion rate passage rate passage rate
Mean ruminal pH 0.4Tr 0.343 0.372
Minimum ruminal pH 0.551 0.40 2 0.441

 

1 Correlation is signiﬁcant (P < 0.05).

2 Tendency for signiﬁcant correlation (P < 0.10).

3P<0.12

88

Table 5. Effects of substitution Of pelleted beet pulp for high-moisture corn on
digestion Of total NDF and potentially digestible NDF (pdNDF).

 

 

Treatment LS Means P
0% 6% 12% 24%
BP BP BP BP SE Trt L Q
NDF
Intake, kgld 5.7 6.2 6.6 6.9 0.2 <0.01 0.01 0.15
Ruminally digested
kgld 2.1 2.1 2.3 2.9 0.2 0.04 <0.01 0.39
% 35.9 34.5 34.5 42.5 3.5 0.32 0.14 0.23
Passage to
duodenum, kg/d 3.7 4.1 4.3 4.0 0.3 0.37 0.08 0.11
Postruminally digested
kgld 0.68 0.72 0.99 0.88 0.18 0.56 0.33 0.47
% of intake 12.0 11.7 15.3 12.7 3.0 0.81 0.54 0.59
% of duodenal
passage 16.7 17.6 24.3 22.7 3.8 0.40 0.17 0.50
Total tract digested
kg/d 2.5 2.9 3.5 3.9 0.22 <0.01 <0.01 0.13
% Of intake 43.4 47.3 53.4 57.2 2.1 <0.01 <0.01 0.31
pdNDF
Intake, kgld 3.2 3.6 4.0 4.3 0.1 <0.01 <0.01 0.17
Ruminally digested
kg/d 1.6 2.0 2.3 2.8 0.1 <0.01 <0.01 0.37
% 46.1 56.8 60.3 67.3 3.4 <0.01 0.02 0.20
Passage to
duodenum, kgld 1.6 1.6 1.6 1.4 0.1 0.51 0.81 0.86
Postruminally digested
kgld 0.36 0.45 0.49 0.35 0.11 0.77 0.34 0.30
% of intake 10.9 12.6 12.1 8.0 2.9 0.70 0.57 0.40
% Of duodenal
passage 22.3 17.6 26.7 24.9 7.6 0.82 0.90 0.99
Total tract digested
kgld 1.9 2.4 2.8 3.2 0.1 <0.01 <0.01 0.03
% Of intake 60.2 67.0 71.6 75.4 1.7 <0.01 <0.01 0.03

 

89

Table 6. Effects of substitution Of pelleted beet pulp for high-moisture corn on

digestion Of starch.

 

 

 

Treatment LS Means P
0% 6% 12% 24%
BP BP BP BP SE Trt L Q

Intake, kg/d 8.2 7.3 6.4 4.0 0.2 <0.01 <0.01 0.21
Apparently ruminally digested

kgld 3.5 2.1 1.6 0.4 0.6 <0.01 <0.01 0.32

% 42.2 27.9 26.1 9.7 10.0 0.03 <0.01 0.74
Truly ruminally digested

kgld 3.8 2.4 1.9 0.7 0.6 <0.01 <0.01 0.32

% 46.5 32.3 31.2 16.9 9.8 0.05 <0.01 0.68
Passage to

duodenum, kgld 4.7 5.2 4.8 3.7 0.6 0.11 0.40 0.14
Apparent postruminal digested

kgld 3.7 4.1 4.0 3.1 0.6 0.32 0.27 0.14

% Of intake 45.7 57.2 62.6 77.5 9.5 0.02 <0.01 0.77

% of duodenal

passage 78.0 77.4 83.2 85.0 2.6 0.02 <0.01 0.96

Apparent total tract digested

kg/d 7.2 6.2 5.7 3.5 0.2 <0.01 <0.01 0.30

% 88.0 86.2 88.6 87.5 1.6 0.49 0.99 0.97

 

90

Table 7. Effects of substitution of pelleted beet pulp for high-moisture corn on

digestion of DM and OM.

 

 

Treatment LS Means P
0% 6% 12% 24%
BP BP BP BP SE Trt L Q

DM
lntake,kg/d 23.7 23.8 23.9 21.8 0.7 0.11 <0.05 0.15
Apparently ruminally digested

kgld 6.4 5.3 3.7 4.7 1.1 0.29 0.09 0.16
% 27.4 22.2 16.2 21.9 4.8 0.38 0.10 0.15
Passage to duodenum,

kgld 17.2 18.6 20.2 17.1 1.5 0.35 <0.10 0.08
Apparent total tract digested

kgld 16.1 15.9 16.7 15.4 0.5 0.28 0.35 0.22
% 68.4 66.9 70.6 70.8 1.3 <0.10 0.07 0.87
OM
Intake, kg/d 22.3 22.4 22.4 20.2 0.7 0.06 0.50 0.15
Apparently ruminally digested

kgld 7.0 5.4 5.9 5.7 0.8 0.30 0.21 0.32
% 31.2 23.8 26.7 27.9 3.5 0.34 0.22 0.27
Truly ruminally digested

kgld 11.4 9.7 10.2 9.4 0.8 0.15 0.85 0.95
% 50.7 42.9 45.9 46.4 3.6 0.34 0.69 0.60
Passage to

duodenum, kgld 16.2 17.0 16.4 14.5 1.0 0.21 0.16 0.12
Apparent postruminal digested

kgld 9.5 9.7 10.0 8.6 0.9 0.69 0.50 0.36
% Of intake 38.9 43.8 45.0 42.9 3.8 0.67 0.24 0.29
%Of duodenal

passage 57.8 58.0 60.7 59.7 2.6 0.77 0.51 0.64
Apparent total tract digested

kgld 15.6 15.4 16.0 14.6 0.4 0.19 0.37 0.19
% 69.9 68.7 72.2 72.5 1.3 0.09 0.05 0.90

 

91

Figure 1. Relationship between rate of digestion of potentially
digestible NDF (%lh) and mean ruminal pH. pdNDF rate of
digestiond= -11.1 + 2.5 mean pH (R = 0.41; P < 0-.05). 0
denotes 0% beet pulp, + denotes 6% beet pulp, I denotes 12%

beet pulp, and O denotes 24% beet pulp (%diet DM) substituted
for high-moisture corn.

 

8.0 '1

.e P- 9’ >1
O O O O
I I I L

digestible NDF (%lh)
9°
C
L

 

Rate of digestion of potentially

N
3’
O
O

.3
O
I

 

 

 

P
o

T I I
5.6 5.8 6.0 6.2 6.4 6.6

Ruminal pH mean

9‘
.5

92

Figure 2. Relationship between (a) starch digested (kg/d) and
duodenal starch ﬂow (Starch digested postruminally = -0.28 +
0.88 duodenal starch ﬂow; R = 0.97, P < 0.01), and (b) starch
digestibility (% duodenal ﬂow) and duodenal starch ﬂow [Starch
digested postruminally (%duodenal ﬂow) = 74.1 + 1.4 duodenal
starch ﬂow; R = 0.35, P < 0.07] . 0 denotes 0% beet pulp, +
denotes 6% beet pulp, I denotes 12% beet pulp, and C denotes
24% beet pulp (%diet DM) substituted for high-moisture com.

(a)

 

 

 

 

 

 

 

 

 

7. I.
goo ’0.
8 3’ 01 _
3;; V5.
O >.
a: O
:5 g 4.0“ 0
S '- I
§ 53.0“ ' O
5 a
32.0“
1.0" l I l I l l
1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
Duodenal starch ﬂow (kgld)
lb)
2. 95
To
E 90‘
3
E O 35*
*- I:
3 a
9- : 80‘
U Q)
9- 8 a
a: 75
2 E 70'
0
5 65 I I r I I
fl)

I
1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
Duodenal starch ﬂow (kgld)

93

CHAPTER 4
Pelleted beet pulp substituted for high-moisture corn: Effects on ruminal

fermentation, pH, and microbial protein efficiency in lactating dairy cows.

ABSTRACT

The effects of increasing concentrations of dried, pelleted beet pulp
substituted for high-moisture corn on ruminal fermentation, pH, and microbial
efﬁciency were evaluated using 8 ruminally and duodenally cannulated
multiparous Holstein cows in a duplicated 4 x 4 Latin square design with 21-d
periods. Cows were 79 :t 17 (mean 1 SD) DIM at the beginning Of the
experiment. Experimental diets with 40% forage (corn Silage and alfalfa silage)
and 60% concentrate contained 0%, 6.1%, 12.1%, or 24.3% beet pulp
substituted for high-moisture corn on a DM basis. Diet concentrations of NDF
and starch were 24.3% and 34.6% (0% beet pulp), 26.2% and 30.5% (6% beet
pulp), 28.0% and 26.5% (12% beet pulp), and 31.6% and 18.4% (24% beet
pulp), respectively. Substituting beet pulp for corn did not affect daily mean or
minimum ruminal pH (P > 0.15), but it tended to reduce pH range (P = 0.07).
Ruminal acetatezpropionate responded in a positive exponential (quadratic)
relationship to added beet pulp. Rate of valerate absorption from the rumen was
not affected by treatment (P > 0.50). Substituting beet pulp for corn up to 24% Of
diet DM did not affect efﬁciency of ruminal microbial protein production,
expressed as microbial N ﬂow to the duodenum as a percent Of OM truly
digested in the rumen (P > 0.25). Microbial efﬁciency was not correlated to mean

pH (P > 0.90) or daily minimum pH (P > 0.90). While microbial efﬁciency was

94

not directly related to concentration of beet pulp fed, it was positively correlated
with passage rate of particulate matter, as represented by starch (R = 0.65, P <
0.01) and INDF (R = 0.51, P = 0.02), probably due to reduced protein turnover in

the rumen.

INTRODUCTION

Achieving optimal temporal patterns of ruminal carbohydrate fermentation is
necessary to maximize milk yield and efﬁciency in dairy cattle, because their
primary sources Of energy and protein are fermentation products, especially
volatile fatty acids (VFA) and microbial protein. Dietary starch concentration is
often increased in order to increase diet fermentability, but increasing rate, or
even extent, of ruminal fermentation does not necessarily result in Optimal
fermentation.

Replacing feed ingredients high in cellulose and hemicellulose with
ingredients high in starch usually increases ruminal production of VFA and alters
the proportions of individual VFA produced. Ruminal infusion of propionate
reduces feed intake (Anil and Forbes, 1980) and alters nutrient partitioning and
milk production (Reynolds, 1995). Greater VFA production can lead to reduced
ruminal pH, which might increase the rate Of VFA absorption from the rumen
(Dijkstra et al., 1993). Low ruminal pH reduces ﬁber digestion (Orskov and
Fraser, 1975) and decreases microbial efﬁciency because Of increased energy

spilling (Strobel and Russell, 1986). Therefore, Optimal ruminal fermentation for

95

high-concentrate diets can probably be achieved by diluting starch with a non-
forage carbohydrate source that is less rapidly fermented, produces less
propionate, and does not reduce ruminal pH.

The NDF in beet pulp can be digested more quickly than forage NDF (Bhatti
and Firkins, 1995), and pectin is fermented more rapidly than cellulose and
hemicellulose, but pectinolytic bacteria are also inhibited at low pH (Marounek et
al., 1985). Substituting beet pulp for high-moisture corn in a diet with a
moderately low forage content Should alter ruminal fermentation and might
increase mean or minimum ruminal pH. If beet pulp improves microbial
utilization of energy or reduces microbial protein turnover in the rumen, microbial
protein efﬁciency may be improved. The Objective Of this experiment was to
characterize the responses of ruminal fermentation, pH, and microbial protein
efﬁciency to beet pulp substituted for high-moisture corn at 0%, 6%, 12%, and

24% of diet DM.

MATERIALS AND METHODS
Treatments and Cows
Experimental procedures were approved by the All University Committee
on Animal Use and Care at Michigan State University. Eight multiparous
Holstein cows (79 a 17 DIM; mean 1 SD) from the Michigan State University
Dairy Cattle Teaching and Research Center were assigned randomly to a

duplicated 4 x 4 Latin square balanced for carry over effects in a dose-response

96

arrangement Of treatments. Treatments were diets containing dried, pelleted

beet pulp (BP) substituted for high-moisture corn (HMC) at 0% (OBP), 6% (GBP),

12% (1ZBP), and 24% (24BP) Of diet DM. Treatment periods were 21 d with the

ﬁnal 10 d used tO collect samples and data. Cows were cannulated ruminally and

duodenally prior to calving. Duodenal cannulas were soft gutter type made Of

tygon and vinyl tubing (Crocker et al., 1998). The duodenum was ﬁstulated ﬂ

proximal to the pylorus region and prior to the pancreatic duct and the cannulas

were placed between 10th and 11th ribs as described by Robinson et al. (1985). I-

 

Both ruminal and duodenal surgeries were performed at the Department of Large
Animal Clinical Science, College of Veterinary Medicine, Michigan State
University. At the beginning of the experiment, empty body weight (ruminal
digesta removed) Of cows was 515.9 a: 63.5 kg (mean x SD).

Nutrient composition for high-moisture com and pelleted beet pulp are
shown in Table 1. Experimental diets contained 40% forage (50:50 corn silage:
alfalfa silage), high-moisture corn, beet pulp at 0 - 24% of diet DM, a premixed
protein supplement (soybean meal, corn distiller’s grains, and blood meal), and a
mineral and vitamin mix (Table 2). All diets were formulated for 18% dietary CP

concentration and fed as total mixed rations.

Data and Sample Collection
Throughout the experiment, cows were housed in tie-stalls, fed once daily
(1100 h) at 110% of expected intake, and milked twice daily. Amounts Of feed

Offered and refused were weighed for each cow daily during the collection period.

97

Samples of all dietary ingredients (0.5 kg) and orts from each cow (12.5%) were
collected daily and combined into one sample per period.

Chromic oxide was used as a marker to estimate nutrient digestibility in
the rumen and in the total tract. Gelatin capsules (1.5 oz. Tropac lnc., Airﬁeld,
NJ) containing 5 g of Chromic oxide and Spelt hulls (Wiley mill, 2 mm screen;
Authur H. Thomas, Philadelphia, PA) were dosed through the ruminal cannula at
0300, 1100, and 1900 h (total of 15 g Cr203 Id) from 7 to 14 d with a priming dose
of 3X on d 7. Duodenal samples (1,000 g per a cow) and fecal samples (500 g),
and rumen ﬂuid samples for VFA (100 mL) and microbial pellet (350 mL) were
collected every 9 h from 12 to 14 d, so that 8 samples were taken for each cow,
representing every 3 h of a 24-hour period to account for diurnal variation.
Rumen ﬂuid for the microbial pellet was taken from the reticulum, near the
reticular-omasal oriﬁce, and strained through a layer Of nylon mesh
(approximately 1 mm pore size). Rumen ﬂuid samples for VFA were taken by
sampling contents from ﬁve different sites in the rumen and were then combined
and strained. Fluid pH was immediately recorded. Duodenal, fecal, and rumen
ﬂuid VFA and microbial pellet samples were immediately frozen at -20°C.

Effect of treatment on rate Of liquid passage and relative rate of valerate
absorption was measured on d 15 using a pulse dose of valeric acid and cobalt
EDTA (Allen et al., 2000). Valeric acid and cobalt EDTA was dosed two hours
after feeding on d 19. Rumen ﬂuid was sampled before dosing and at 0.5, 1, 1.5,
2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, and 8 h after dosing. Samples were

immediately frozen.

98

Ruminal pH was monitored from d 16 through d 19 (96 h) Of each period
by a computerized data acquisition system (Dado and Allen, 1993). Ruminal pH
data were recorded for each cow every 5 sec. Electrodes for ruminal pH
determination were Checked daily and calibrated as needed, and ruminal pH data
were deleted for the previous 24 h if readings had changed more than 0.05 unit
at pH 7 or pH 4. The system successfully collected 66.1% Of the total ruminal pH
data (average 2.7 d per cow per period). Daily mean, minimum, maximum,
variation range, time below pH 6.0, 5.8, and 5.5, and area below the pH 6.0, 5.8,
and 5.5 were calculated. Response variables were averaged over four days for
each period.

Ruminal contents were evacuated manually through the ruminal cannula
at 1500 h (4 h after feeding) on d 20 and at 0900 h (2 h before feeding) on d 21
of each period. Total ruminal content mass and volume were determined.

During evacuation, 10% aliquots of digesta were separated to allow accurate
sub-sampling. Aliquots were squeezed through a nylon screen (pore size: 1 mm)
to separate into primarily solid and liquid phases. Samples were taken from both
phases for determination Of nutrient pool size, and additional liquid samples were
taken to measure VFA content and rumen ﬂuid consistency. All samples except
the consistency sample were frozen immediately at -20°C.

After rumen evacuation, 20 ml of rumen ﬂuid (maintained at 37°C in a
water bath) were used to measured consistency in a clean, dry Bostwick

consistometer (CSC Scientiﬁc CO., Fairfax, Virginia). Distance traveled by the

99

liquid front (cm) was recorded every 30 s for 300 s, and samples were run in

duplicate. Data reported are the distance traveled after 300 3.

Sample and Statistical Analysis

Diet ingredients, orts, and feces were dried in a 55°C forced-air oven for
72 h and analyzed for DM concentration. Duodenal samples for each cow were
thawed, combined by period, and separated into solid and liquid phases for
drying. Microbial pellets were obtained from combined rumen ﬂuid samples for
each cow by differential centrifugation (Overton et al., 1995). Ruminal digesta,
duodenal digesta, and microbial pellets were lyophilized (Tri-Philizer'“ MP, FTS
Systems, Stone Ridge, NY). All samples were ground with a Wiley mill (1mm
screen; Authur H. Thomas, Philadelphia, PA). Dried, ground ruminal digesta and
duodenal digesta were recombined according to the ratios of solid and liquid DM
in the original whole sample. Samples were analyzed for ash, NDF, indigestible
NDF (INDF), CP, and starch. Ash concentration was determined after 5 h
oxidation at 500°C in a mufﬂe furnace. Concentrations of NDF were determined
according to Van Soest et al. (1991, method A). lndigestible NDF was estimated
as NDF residue after 120-h in vitro fermentation (Goering and Van Soest, 1990).
Forage samples were analyzed for ADF and sulfuric acid lignin content (Van
Soest et al., 1991). Crude protein was analyzed according to Hach et al. (1985).
Starch was hydrolyzed enzymatically (Karkalas, 1985) after samples were
gelatinized with sodium hydroxide. Glucose concentration was then measured

using glucose oxidase (Glucose kit #510; Sigma Chemical CO., St. Louis, MO),

100

and absorbance was determined with micro-plate reader (SpectraMax 190,
Molecular Devices Corp., Sunnyvale, CA). Concentrations Of all nutrients except
for DM were expressed as percentages of DM determined by drying at 105°C in
a forced-air oven.

Feed samples, duodenal digesta, and fecal samples were analyzed for
concentrations of Cr. Samples were digested with phosphoric acid (Williams,
1962), and quantiﬁed by ﬂame atomic absorption spectrometry (SpectraAA 220,
Varian, Victoria, Australia) according to manufacturer's recommendation.
Ruminal pool sizes (kg) of OM, NDF, INDF, and starch were determined by
multiplying the concentration of each component by the ruminal digesta DM
weight (kg). Turnover rate in the rumen, passage rate from the rumen, and
ruminal digestion rate Of each component (%lh) were calculated (Oba and Allen,
2002).

Rumen ﬂuid was analyzed for concentration of major VFA and lactate by
HPLC (Waters Corp., Milford, MA). Duodenal digesta were analyzed for purines
and ammonia to estimate microbial nitrogen ﬂow and non-ammonia non-
microbial nitrogen ﬂow to the duodenum. Purine concentration was used as a
microbial marker, and purine to microbial N ratio was estimated by analysis of
microbial pellets. Total purines were measured by spectrophotometer (Beckman
Instruments, Inc., Fullerton, CA) at 260 nm (Zinn and Owens, 1986). Ammonia
concentration was determined for centrifuged duodenal and rumen ﬂuid samples

according to Broderick and Kang (1980).

101

Rumen ﬂuid samples taken to measure rate Of valerate absorption were
analyzed for valerate concentration by HPLC (Waters Corp., Milford, MA) and
cobalt concentration by atomic absorption spectrophotometry (SpectrAA 220/FS,
Varian Australia Pty. Ltd., Mulgrave, Victoria, Australia). Rates of valerate and
cobalt disappearance were determined by non-linear regression Of the decline in
their respective concentrations in rumen ﬂuid over time after dosing, accounting
for background (Allen et al., 2000).

All data were analyzed using the ﬁt model procedure of JMP® according
to the following model:

Yijkl = l1 + Ci + Pj 'I' Tk 1‘ eijk
where

u = overall mean,

C, = random effect Of cow (i = 1 to 8),

Pj = ﬁxed effect of period (j = 1 to 4),

Ti, = ﬁxed effect of treatment (k = 1 to 4), and

9ij = residual, assumed to be normally distributed.

Period by treatment interaction was originally evaluated, but it was removed from
the statistical model because it was not Signiﬁcant for response variables of
primary interest. Linear and quadratic dose-response effects were evaluated
using the same model with diet percent beet pulp in place of the ﬁxed effect of
treatment. Pearson correlation coefﬁcients were determined between cow-period

Observations for some parameters. Treatment effects, linear and quadratic

102

 

responses, and correlations were declared signiﬁcant at P < 0.05, and
tendencies were declared at P < 0.10.

Data from two cow-periods were excluded from statistical analysis. One
cow developed a cecal torsion requiring surgery early in period 3; data and
samples were not collected from this cow during period 3, but she recovered
sufﬁciently for her period 4 data to be used. Period 4 data from a second cow
were excluded after she showed Signs Of estrus because her intake and milk
yield were outliers (outside the 95% conﬁdence interval for cow-period

observations).

RESULTS AND DISCUSSION

Ruminal pH

A primary hypothesis regarding the substitution of ﬁbrous beet pulp for
high-moisture corn was that feeding diets containing high concentrations of
rapidly-fermentable grain would result in lower average and nadir ruminal pH
values, and that the pectin and insoluble ﬁber in beet pulp would attenuate this
decrease. Diets ranged from 35% starch and 24% NDF in 0BP to 18% starch
and 32% NDF in 24BP, but when pH was averaged from continuous collection
over four days, no difference existed between treatments (Table 3). Daily
minimum pH was not affected by treatment, but daily maximum pH decreased
linearly as BP increased (P = 0.05), reducing the range of pH (P = 0.07).
Decreasing range and maximum pH suggest that substituting BP for HMC might

have reduced diurnal variation in ruminal pH, but variance and standard deviation

103

did not decrease. Measures Of time and area (time x pH) below pH 6.0, 5.8, and
5.5 were not affected by treatment.

Mean pH was near the pKa Of bicarbonate for all treatments. It is possible
that the remaining buffering capacity Of the rumen ﬂuid, especially the
bicarbonate system, was different between treatments while ruminal pH was
similar across treatments (Allen, 1997). Therefore, measurement of rumen ﬂuid
buffering capacity would be useful in future studies of effects of carbohydrate

source on the rumen environment.

Ruminal Volatile Fatty Acid Concentration and Removal

Total VFA concentration in rumen ﬂuid was similar across treatments
(Table 4), but the response Of ruminal VFA pool (mol) to increasing BP was
quadratic (P < 0.05) with the largest VFA pool for cows fed 12BP. Rate Of
valerate absorption from the rumen, an estimate Of VFA absorption, was similar
(approximately 40%/h) for all treatments. Ruminal liquid dilution rate was
reduced by the substitution Of BP for HMC (P = 0.03), so VFA escaped more
slowly in liquid for diets containing more beet pulp, and a larger proportion of
VFA produced may have been absorbed across the rumen wall. Because beet
pulp contains high concentrations of pectin, which gelatinizes under the
appropriate conditions, rumen ﬂuid consistency was also measured. Rumen ﬂuid
consistency was not different among treatments (P > 0.40). However, across
cow-period measurements, there was a quadratic relationship between liquid

passage rate and consistency [passage rate = 0.163 + 0.00128 x consistency —

104

0.000946 x (consistency — 14.4)2; R = 0.52, P = 0.02]. This suggests that
consistency and at least one other factor affected liquid passage rate.

Despite large differences in starch content among diets, lactate
concentration was similar for 0BP, 6BP, and 12BP (P > 0.25). Another study
comparing beet pulp and corn grain also reported no difference in lactate
concentration (O’Mara et al., 1997).

As expected, substituting beet pulp for high-moisture corn increased the
molar proportion Of acetate (P < 0.0001) and butyrate (P < 0.05) and decreased
the molar proportion of propionate (P < 0.001). Branched-chain VFAS were lower
for 24BP than for the other diets (P < 0.001), suggesting that proteolysis was
reduced and (or) that incorporation of branched-chain amino acids into microbial
protein was increased. Fermentation results of other in vivo studies comparing
beet pulp and corn in TMRS have varied; the only study detecting fermentation
acid effects (Clark and Armentano, 1997) reported results similar to those in this
experiment for acetate, propionate, and butyrate. VFA concentrations resulting
from comparisons Of beet pulp and grain in continuous culture differ from in vivo
results. Two studies (Mansﬁeld et al., 1994; Chester-Jones et al., 1991) reported
greater acetate and lower butyrate concentrations with beet pulp added to corn,
and these two and another (Bach et al., 1999) reported no effect on propionate
concentration. Differences between in vitro and in vivo responses may be due to
the effect in vivo of differential rates Of VFA absorption from the rumen (Dijkstra

etaL,1993)

105

Ruminal pH and Volatile Fatty Acids

Across treatments, both slower absorption of VFA and slower liquid
passage from the rumen led to higher VFA concentrations in the rumen (Figure
1a,b); VFA concentration was negatively correlated with rate Of valerate
absorption (R = -0.70, P < 0.0001) and with liquid passage rate (R = -0.54, P <
0.01). As VFA concentration increased, ruminal pH decreased (R = -0.47, P =
0.03) due to greater acid load (Figure 1C). Rate of valerate absorption was
unexpectedly Slower under lower pH (R = 0.48, P = 0.04); because VFAS are
primarily absorbed in the undissociated state, VFA absorption usually increases
under more acidic conditions because a larger proportion of VFA exist in that
form (Dijkstra et al., 1993). However, in this case, lower ruminal pH might have
decreased rumen motility, resulting in less thorough mixing of ruminal contents
and thus a slower rate of VFA absorption. Although rumen motility was not
measured, valerate absorption rate increased with greater passage rate of
indigestible NDF (Table 5; R = 0.43, P = 0.02) and tended to increase with
greater liquid passage rate (Table 5; R = 0.33, P = 0.08), which might be
indicators Of rumen motility. However, passage rate and thus VFA absorption
might have been affected by DMI along with or instead Of pH, as rate Of valerate
absorption tended to increase with increasing DMI (R = 0.31, P < 0.10). Finally,
greater utilization Of metabolic fuels with higher milk yield might have created a
steeper gradient of VFA across the rumen wall, demonstrated by an increase in

valerate absorption rate with greater FCM yield (R = 0.49, P < 0.01).

106

Ruminal Nitrogen Digestion

Ruminal ammonia concentration responded in a quadratic relationship to
dietary BP concentration (P = 0.04), with the maximum concentration for 1ZBP
and the lowest concentration for 24BP. Across treatments, ruminal ammonia
concentration was not correlated with ruminal pH (Table 7). Ammonia availability
probably did not limit microbial protein synthesis for any Of the diets, because
maximum microbial N production occurs at 5 mg/dl, far below the values in this
study, and does not increase at higher ammonia concentrations (Satter and
Slyter, 1974). Some amylolytic microbes exhibit extensive proteolysis (Russell et
al., 1981), and the additional ammonia N can be used for protein synthesis,
absorbed across the rumen wall, or may pass to the duodenum. Microbes which
primarily degrade nonstructural carbohydrates Obtain approximately two-thirds Of
their N from amino acids and peptides, not ammonia (Russell et al., 1983), while
ﬁbrolytic microbes Obtain all N for protein synthesis from ammonia (Bryant,
1973). The rate of incorporation of ammonia into protein for 1ZBP may not have
been sufﬁcient to utilize the ammonia made available by deamination, resulting in

a higher ammonia concentration.

Microbial Nitrogen Efﬁciency

Flow Of microbial N in the duodenum decreased linearly (P = 0.04) as beet
pulp was substituted for corn (Table 6). Mean efﬁciency of conversion Of truly
ruminally degraded OM (TRDOM) tO microbial N (MNE) ranged from 36.4 to 41.4

g/kg TRDOM, and these values are within the range of previously published

107

values Of approximately 10 tO 50 g/kg TRDOM (Clark et al., 1992). However,
MNE was not different among treatments (P > 0.25), even though diets varied
widely in starch and NDF content. While microbial N ﬂow decreased with added
BP, kg TRDOM decreased numerically (not statistically; Chapter 3), so the
absence Of a MNE treatment effect might have been caused by concurrent

decrease in both microbial ﬂow and kg digested.

 

 

I
Ruminal concentrations Of amino acids and peptides were not measured I
in the present study, but their availability could have limited the rate of growth for .4
amylolytic bacteria (Van Kessel and Russell, 1996). However, diets in this

experiment were formulated for sufﬁcient RDP; animals were fed 18% dietary
crude protein (% of DM) with observed RDP ranging from 55 to 60% (NANMN
ranged from 44.6 to 40.2% of N intake). Soybean meal was the primary protein
supplement (32-36% of total dietary CP), and soybean meal increases microbial
N ﬂow compared to other protein supplements (Clark et al., 1992). Therefore, it
is unlikely that amino acid or peptide availability limited microbial growth for the
high-starch diets.

Cows absorbed less NAN in the intestines (P = 0.03) as NAN ﬂow to the
duodenum decreased with increasing BP (P = 0.02), but total N absorbed (kg/d)

and total tract digestibility of N were not affected by treatment.

Microbial Nitrogen Efﬁciency and Fermentation

AS described above, efﬁciency of microbial protein production was not

affected by drastically altering the carbohydrate source and thus the pattern Of

108

fermentation. Strobel and Russell (1986) suggested that low ruminal pH causes
energy spilling and decreases the efficiency with which microbes convert feed
energy and nitrogen into protein. However, when data from all cow-periods in
this study were pooled, MNE was not associated with mean ruminal pH (Table 7;
Figure 2a) or with any other measure of ruminal pH (data not shown). The range
of cow-period mean pH values was 5.58 to 6.56, and treatment mean pH was
near 6.0 for all treatments. While MNE was not associated with pH for this
experiment, such a relationship might exist for a range of pH values below 6.0.
Microbial efﬁciency was not related to ruminal ammonia concentration (Figure 2b;
P > 0.30) or with VFA concentration (Figure 2c; P > 0.30).

Microbial efﬁciency decreased as ruminal starch digestion rate increased
(Figure 2d; R = -0.61, P < 0.01), suggesting that bacteria spilled energy instead
of using the additional energy for greater protein synthesis. Microbial efﬁciency
also decreased as ruminal digestibility of OM increased (R = -O.70, P < 0.0001);
more extensive digestion of OM in the rumen might have been the result of
longer retention time, which would increase the opportunity for microbial turnover
and therefore reduce MNE. MNE was not related to the rate or extent of ruminal

NDF digestion (data not shown).

Microbial Nitrogen Efficiency and Ruminal Passage Kinetics
The dominant factor determining efﬁciency of microbial protein synthesis
was the rate at which microbes escaped the rumen, presumably attached to feed

particles. The responses most strongly and positively correlated with MNE

109

 

(Table 7) were the ruminal passage rates of particles: starch (Figure 2e; R =
0.63, P < 0.001), indigestible NDF (R = 0.45, P = 0.02), and potentially digestible
NDF (R = 0.36, P = 0.07). Microbes associated with particulate digesta may
have escaped the rumen more rapidly, reducing microbial protein turnover by
reducing both autolysis (Wells and Russell, 1996) and protozoal predation
(Wallace and McPherson, 1987). Although microbial N ﬂow increased with
greater DMI (R = 0.51, P < 0.01), microbial efﬁciency was not related to DMI (P >
0.60), so DMI probably did not cause the increased passage rate and
subsequent increased microbial efﬁciency.

Obaand Allen (2002b) have reported similar responses of MNE, or failures
of MNE to respond, to pH, fermentation characteristics, and digestion kinetics in
the rumen when lactating cows were fed diets quite different from diets in the
present study; diets contained ground high-moisture corn or dry ground corn at
two dietary starch concentrations. They also found no relationship between MNE
and ruminal pH or ammonia concentration, and they reported that MNE
decreased as rate of ruminal starch increased. A positive relationship between
ruminal starch passage rate and MNE was also demonstrated (Oba and Allen
2002b). The similar responses of MNE in two experiments with very different
treatments suggest that, among high-producing cows, the efﬁciency of microbial
protein production is not always affected by ruminal pH or ammonia
concentration, that it is reduced at high rates of starch fermentation, and that it is

improved by increased particulate passage rate from the rumen.

110

Although passage rate of particulate digesta affected MNE, liquid passage
rate was unrelated to MNE (Table 7; Figure 2f). Previous experiments have
manipulated passage rate in vitro and in sheep, especially by increasing liquid
dilution rate, and have reported responses in microbial protein ﬂow and
production that suggest that increased dilution rate results in greater MNE
(lsaacson et al., 1975; Harrison et al., 1976; Kennedy and Milligan, 1978).

However, response to liquid passage rate was not separated from the potential

concurrent response in particulate passage rate. In addition, the range of dilution
rates measured in the present experiment are generally higher than the ranges of
rates reported in these other studies. Because liquid passage rate and rumen
ﬂuid consistency demonstrated a quadratic relationship, as described earlier, and
because ﬂuid consistency was not affected by treatment (Table 4), more than
one factor (including consistency) likely affected liquid passage and may have
caused particulate and liquid passage to be uncoupled.

Wells and Russell (1996) proposed that the rate of microbial turnover
(%lh) decreases geometrically and asymptotically as dilution rate (h'1) increases,
and that the extent of the effect depends upon microbial lysis rate. The range of
individual dilution rates measured in the present study (10.6-22.9%lh) would fall
among and above the top half of dilution rates in the proposed model. Lysis rate
was not measured, but assuming that lysis did not occur at the highest rate used
in the model (10%/h), an increase of 12%/h in dilution rate would lead to no more
than a 5% decrease in microbial turnover, and, it follows, only a small increase in

microbial efﬁciency. More rapid particle passage rate was therefore much more

111

important than ﬂuid passage rate in improving microbial efﬁciency. Increasing
particulate passage rate removed bacteria from the rumen more quickly, which
increased the rate at which microbes escaped the rumen and reduced the extent

of microbial lysis, thus increasing microbial efﬁciency.

SUMMARY
Substituting dried, pelleted beet pulp for high-moisture corn from 0 to 24%
of diet DM altered ruminal fermentation but did not affect daily mean or minimum
ruminal pH, nor rate of VFA absorption. Among individual observations, ruminal
VFA concentration was associated negatively with pH, rate of valerate
absorption, and liquid passage rate. Microbial N efﬁciency was not related to
ruminal pH and was not affected by replacing high-moisture corn with beet pulp,

but was increased by greater particulate passage rate.

112

Table 1. Nutrient composition of high-moisture corn and dried, pelleted beet
pulp.

 

 

 

Nutrient High-moisture corn Beet pulp
DM, % as fed 71.5 84.9
-----°/o of DM -----
NDF 10.0 39.9
OF 8.3 8.9
Indigestbile NDF 3.8 8.0
Starch 70.5 3.9
Ether extract 4.7 0.7
Ash 1.0 7.8

 

Table 2. lnmedient and nutrient composition of experimental diets.

Ingredients
Corn silage
Alfalfa silage
Protein mix
Mineral vitamin mix
Dried, pelleted beet pulp
High-moisture corn
Nutrient
DM
Starch
NDF
lndigestible NDF
Forage NDF

CP
% Starch from
high—moisture corn

°/o NDF from forage
°/o NDF from beet pulp

 

0% BP 6% BP 12% BP 24% BP
----°/o Of DM-----

20.1 20.1 20.1 20.1
19.9 19.9 19.9 19.9
19.5 19.5 19.5 19.5
4.8 4.8 4.8 4.8

O 6.1 12.1 24.3
35.6 29.5 23.5 11.4
50.2 50.5 50.8 51.6
34.6 30.5 26.5 18.4
24.3 26.2 28.0 31.6
9.4 9.6 9.8 10.2
17.1 17.1 17.1 17.1
18.0 18.0 18.0 18.1
72.7 68.3 62.6 43.7
70.2 65.3 61.1 54.1
0.0 9.3 17.3 30.7

 

113

 

Table 3. Effects of substitution of pelleted beet pulp for high-moisture corn on
ruminal pH.

 

 

 

 

 

Treatment LS Means P
0% 6% 12% 24%

Daily ruminal pH BP BP BP BP SE Trt L Q
Mean 5.93 5.97 6.02 5.94 0.10 0.53 0.16 0.17
Minimum 5.36 5.39 5.40 5.47 0.12 0.59 0.16 0.95
Maximum 6.56 6.55 6.55 6.43 0.08 0.17 0.05 0.28
Range 1.23 1.19 1.06 1.07 0.09 0.24 0.07 0.50
Variance 0.14 0.12 0.11 0.11 0.02 0.42 0.17 0.34
Standard

deviation 0.36 0.34 0.32 0.33 0.03 0.40 0.14 0.26
Time < 6.0 12.9 12.0 12.1 13.8 2.2 0.43 0.26 0.15
Time < 5.8 9.3 8.1 7.4 9.6 2.0 0.43 0.13 0.10
Time < 5.5 4.8 4.1 2.7 3.6 1.4 0.40 0.15 0.24
Area below 6.0 634 565 481 591 149 0.65 0.22 0.24
Area below 5.8 369 325 249 310 102 0.63 0.25 0.32

Area below 5.5 118 109 75 79 42 0.70 0.47 0.66

 

114

Table 4. Effects of substitution of pelleted beet pulp for high-moisture corn on
ruminal fermentation and VFA removal.

 

Treatment LS Means P
0% 6% 12% 24%
BP BP BP BP SE Trt L Q

Total VFA, mM 138 141 142 142 3 0.35 0.14 0.26
Total ruminal VFA

pool, mol 3.99 4.10 4.63 3.83 0.32 0.12 0.07 <0.05
Rate of valerate

absorption, %/h 41.3 43.2 37.3 40.0 4.0 0.51 0.57 0.69
Liquid passage

rate, %/h 18.6 17.5 16.7 16.6 1.0 0.13 0.03 0.21
Rumen ﬂuid

consistencya 14.6 14.2 14.0 15.1 1.3 0.84 0.51 0.42
Lactate, mM 0.30 0.31 0.26 0.08 0.16 0.72 0.27 0.64
VFA, mol/100 mol

Acetate 56.9 59.1 60.2 61.6 1.1 <0.01 <0.01 0.04

Propionate 27.0 24.9 23.0 22.4 1.1 <0.01 <0.01 0.04

Butyrate 11.3 11.5 12.2 12.3 0.4 0.19 0.04 0.60

Branched-chain

VFA 2.33 2.34 2.31 1.85 0.09 <0.01 0.28 0.01

AcetatezPropionate 2.19 2.45 2.69 2.80 0.16 <0.01 <0.01 0.04

 

 

 

aDistance traveled (cm) by front edge of 20 ml rumen liquid in 300 s in Bostwick’s

consistometer.

Table 5. Pearson correlation coefﬁcients for ruminal VFA concentration and

related variables.

(1) Ruminal [VFA], mM

(2) pH, daily mean

(3) Valerate absorption rate, %lh

4 Li uid assa erate, %lh
( ) q p 9

1Correlation is signiﬁcant (P < 0.05).

(1)

p.471
-o.7o‘
-o.541

115

(2)

0:481
0.15

(3)

0.54

(4)

Table 6. Effects of substitution of pelleted beet pulp for high-moisture corn on N

 

 

 

digestion.
Treatment LS Means P
0% 6% 12% 24%
BP BP BP BP SE Trt L Q

Nintake,g/d 678 692 697 641 21 0.18 0.23 0.09
Ruminal ammonia,

mg/dl 19.6 19.3 21.4 17.8 0.9 0.02 0.09 0.04
Flow to duodenum

Ammonia N, g/d 19.8 20.6 21.5 19.2 1.5 0.34 0.14 0.10
NAN‘

g/d 693 707 691 610 32 0.09 0.02 0.19
%ofNintake 102.0 102.5 97.4 95.2 4.2 0.43 0.11 0.92
NANMN2

g/d 278 306 287 255 34 0.66 0.42 0.39
%ofNintake 40.8 44.6 40.5 40.2 5.1 0.85 0.74 0.69
%duodenal NAN 39.7 43.0 40.9 42.1 4.4 0.90 0.74 0.74
MicrobialN

g/d 415 401 404 352 27 0.22 0.04 0.55
% duodenal NAN 60.3 57.0 59.0 57.9 4.0 0.90 0.73 0.74
g/kg TRDOM3 36.4 41.4 40.8 39.5 3.3 0.71 0.29 0.33
NAN digested postruminally

g/d 492 492 485 428 25 0.13 0.03 0.32
%of intake 72.5 71.6 68.7 67.3 3.5 0.58 0.16 0.87
%ofduodenal

passage 71.2 69.5 70.3 70.2 1.6 0.68 0.64 0.41
N apparently digested in total tract

g/d 476 477 498 458 15 0.32 0.23 0.15
% 70.5 69.1 71.7 71.5 1.6 0.40 0.31 0.84

 

1 Non-ammonia N.

2 Non-ammonia non-microbial N.
3 Truly ruminally digested CM.

116

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117

Figure 1. Relationship between VFA concentration in rumen ﬂuid
and (a) rate of valerate absorption ([VFA] = 162 - 52 x rate of
valerate absorption; R = -0.69; P < 0.01); (b) liquid passage
rate([VFA] = 162 - 1233 x liquid passage rate; R = -0.49; P <
0.01) and (0) mean ruminal pH ([VFA] = 221 - 14 x mean pH; R =
-0.44; P < 0.03). 0 denotes 0% beet pulp, + denotes 6% beet
pulp, I denotes 12% beet pulp, and 0 denotes 24% beet pulp
(%diet DM) substituted for high-moisture com.

A
N
V

 

 

 

 

 

125 rm 1 I l Ii q
2025 30 35 4045 50 55 60 65

Rate of valerate absorption (%lh)

Total VFAconcentration (mM)

 

a .5
# 0|
(II C
l l

140 "
135 "

Total ruminal VFA
concentration (mM)

 

130 -'

 

 

 

125 llTlllllllllgl
10 15 20 25

Liquid passage rate (%lh)

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155
150i

145+
1407
135 -
130 .

125 - - - - $
5.4 5.6 5.8 6.0 6.2 6.4 6.6

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(mM)

 

 

 

Total VFAconcentration

 

119

Figure 2. Relationship between microbial N efﬁciency (9
microbial N / kg TRDOM) and (a) 24-h mean ruminal pH (R =
0.00; P > 0.95); (b) concentration of ammonia in rumen ﬂuid (R
= 0.17; P > 0.30); (0) concentration of VFA in rumen ﬂuid (R =
0.20; P > 0.30); (d) ruminal starch digestion rate (MNE = 4.35 -
0.05 x starch digestion rate; R = -0.52; P < 0.01); (e) starch
passage rate (MNE = 2.65 + 0.06 x starch passage rate; R =
0.63; P < 0.01); and (f) liquid passage rate (R = 0.10; P > 0.50).
0 denotes 0% beet pulp, + denotes 6% beet pulp, I denotes
12% beet pulp, and 0 denotes 24% beet pulp (%diet DM)
substituted for high-moisture com.

(a)

(b)

O
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0'!

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130 135 140 145 150 155
Ruminal VFA concentration (mM)

 

 

 

 

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122

CHAPTER 5

CONCLUSIONS AND IMPLICATIONS

Substituting dried, pelleted beet pulp for part of the grain in a high-
concentrate diet can improve nutrient utilization. Even though substituting beet
pulp for high-moisture corn decreased dry matter intake due to greater ruminal ﬁll
and increased the amount of time required to consume the diet, energy intake
was not reduced. Therefore, milk yield was unaffected, and yield of fat-corrected

milk was slightly improved by lower rates of beet pulp substitution.

 

Rates of fermentation and passage for starch and ﬁber were affected
drastically by diet composition. Substituting rapidly-fermented ﬁber for rapidly-
fermented starch improved the rate and extent of NDF digestion without
negatively affecting milk yield. Although this diet change also increased the
passage rate of starch from the rumen and reduced ruminal starch digestion,
postruminal starch digestion compensated for the decreased ruminal digestion.
Because compensatory starch digestion did take place and there was no
signiﬁcant compensatory ﬁber digestion in the intestines when diets contained
more com, adding a highly digestible ﬁber source to a high grain diet could
potentially result in even greater energy intake. Increasing diet digestibility can
also reduce the volume of waste per unit milk produced.

The use of nitrogen sources in feed for microbial protein synthesis was
neither improved nor made more efﬁcient by adding beet pulp to a highly
fermentable diet. However, the relationship between ruminal particulate passage

rate and microbial efﬁciency was conﬁrmed; and since beet pulp did increase

123

starch passage rate, it might also improve microbial efﬁciency in some feeding
situations. Increasing the efﬁciency of nitrogen use might reduce the amount of
nitrogen required to maximize absorbable protein and subsequent milk yield.
This could reduce the cost of feed because protein supplements are one of the
most expensive components of dairy rations, and it may also aid in the reduction
of waste nitrogen entering the environment.

Maintaining a “normal” ruminal pH is one of the primary goals in dairy
nutrition, yet much study is still required to clarify the factors affecting pH and the
mechanisms by which pH affects digestion, health, and production. In this study,
ruminal pH did not differ between cows fed a diet containing 24.3% NDF with no
beet pulp and cows fed a diet containing 31.6% NDF with the maximum beet
pulp inclusion rate (24%). The absence of a pH change could be attributed to
equal dietary forage NDF contents, except that adding beet pulp increased
chewing, which probably induced greater inﬂux of salivary buffers. Despite
abundant support in the literature for a link between pH and microbial efﬁciency
(Strobel and Russell, 1986), we failed to detect a relationship between any
measure of daily mean pH or variation in pH and microbial efﬁciency. Similarly,
although increasing ﬂuid pH has previously reduced ruminal VFA absorption rate
(Dijkstra et al., 1993), greater daily mean pH was related to greater valerate
absorption rate in the present experiment. Therefore, our concepts of the
association of pH with measures of digestion and production need to be

reevaluated.

124

 

 

In addition to the causes and effects of altered ruminal pH, other questions
are raised by the results of this experiment. Beet pulp was added to a diet with
one of the lowest possible forage contents and one of the highest possible corn
grain contents advisable for the grain, forage, and feeding conditions. However,
it is not clear how beet pulp would affect digestion and production at lower or
higher dietary contents of forage NDF, nor for grains differing in rate or extent of
digestion. The effects on particulate and liquid passage, as well as the
relationships between passage rates and other ruminal measurements, suggest
that rumen motility was affected by adding beet pulp. Therefore, measurement
of the effects of beet pulp on rumen motility would help clarify the relative
usefulness of beet pulp as an effective ﬁber source and would help explain the
effects of beet pulp on volatile fatty acid absorption and on particulate and liquid
passage rate. Finally, the different effects of particulate and liquid passage rates
on microbial efﬁciency suggest that there might be several strategies for
improving microbial efﬁciency through increased passage rate without reducing
the digestibility of the diet.

Even though forage NDF was low (17% of DM) for all treatments and
starch concentration was 35% of DM for the diet containing no beet pulp, ruminal
pH was not extremely low and milk fat concentrations for all treatments were
above 3.70%, indicating that the diets fed in this experiment were not
exceptionally highly fermentable. Beet pulp probably would be of greater beneﬁt,
especially in moderating ruminal pH, when more highly fermentable diets are fed,

or when a similar diet is fed under less controlled conditions. While the results of

125

the present experiment suggest that beet pulp can be included as up to 12
percent of diet dry matter without reducing fat-corrected milk yield, the optimal
rate of substitution in individual situations should be selected based on nutritional
management practices and characteristics of diet, including diet forage-to-
concentrate ratio, grain type and fermentability, and forage type, particle size,

and quality.

126

REFERENCES

Allen, M. S. 1996. Physical constraints on voluntary intake of forages by
ruminants. J. Anim. Sci. 74:3063-3075.

Allen, M. S. 1997. Relationship between fermentation acid production in the
rumen and the requirement for physically effective ﬁber. J. Dairy Sci. 80:1447-
1462.

Allen, M. S. 2000. Effects of diet on short-term regulation of feed intake by
lactating dairy cattle. J. Dairy Sci. 83:1598-1624.

Allen, M. S., L. E. Armentano, M. N. Pereira, Y. Ying, and J. Xu. 2000.
Method to measure fractional rate of volatile fatty acid absorption from the
rumen. Proc. 2000 Rumen Function Conference, Chicago. 25:24.

Anil, M. H., and J. M. Forbes. 1980. Feeding in sheep during intraportal
infusions of short-chain fatty acids and the effect of liver denervation. J. Physiol.
298:407-414.

Armentano, L., and M. Periera. 1997. Measuring the effectiveness of ﬁber by
animal response trials. J. Dairy Sci. 80:1416-1425.

Aspinall, G. O. 1970. Polysaccharides. Pergamon Press, Oxford, England.

Bach, A., I. K. Yoon, M. D. Stern, H. G. Jung, and H. Chester-Jones. 1999.
Effects of type of carbohydrate supplementation to lush pasture on microbial
fermentation in continuous culture. J. Dairy Sci. 82:153-160.

Bailoni, L., M. Ramanzin, A. Simonetto, N. Oblakov, S. Schiavon, and G.
Bittante. 1998. The effect of in vitro fermentation on speciﬁc gravity and
sedimentation measurements of forage particles. J. Anim. Sci. 76:3095-3103.

Beauchemin, K. A., B. l. Farr, and L. M. Rode. 1991. Enhancement of the

effective ﬁber content of barley-based concentrates fed to dairy cows. J. Dairy
Sci. 74:3128-3139.

Bhattacharya, A. N., and F. T. Sleiman. 1971. Beet pulp as a grain replacement
for dairy cows and sheep. J. Dairy Sci. 54:89-94.

Bhattacharya, A. N., and W. F. Lubbadah. 1971. Feeding high levels of beet
pulp in high concentrate dairy rations. J. Dairy Sci. 54:95-99.

Bhatti, S. A., and J. L. Firkins. 1995. Kinetics of hydration and functional speciﬁc
gravity of ﬁbrous feed by-products. J. Anim. Sci. 73:1449-1458.

127

 

Bichsel, S. E. 1988. An overview of the U. S. beet sugar industry. Pp. 1-8 in M.
A. Clarke and M. A. Godshall, eds. Chemistry and Processing of Sugarbeet and
Sugarcane. Elsevier, New York.

Broderick, G. A., and J. H. Kang. 1980. Automated simultaneous determination
of ammonia and total amino acids in rumen ﬂuid and in vitro media. J. Dairy Sci.
63:64-75.

Bryant, M. P. 1973. Nutritional requirements of the predominant rumen
cellulolytic bacteria. Fed. Proc. 32:1809-1813.

Bryant, M. P., and R. N. Doetsch. 1954. A study of actively celluloytic rod-
shaped bacteria of the bovine rumen. J. Dairy Sci. 37:1176-1183.

Bryant, M. P., and N. Small. 1956a. The anaerobic monotrichous butyric acid-
producing curved rod-shaped bacteria of the rumen. J. Bacteriol. 72:16-21.

Bryant, M. P. and N. Small. 1956b. Characteristics of two new genera of
anaerobic fuved rods isolated from the rumen of cattle. J. bacterial. 72:22-26.

Bryant, M. P., N. Small, C. Bouma, and H. Chu. 1958. Bacteroides ruminicola n.
sp. And Succinimonas amylolytica the new genus and species. Species of
succinic acid-producing anaerobic bacteria of the bovine rumen. J. Bacteriol.
76:15-23.

Bywater, A. C. 1984. A generalised model of feed intake and digestion in
lactating cows. Agric. Syst. 13:167-186.

Callison, S. L., J. L. Firkins, M. L. Eastridge, and B. L. Hull. 2001. Site of
nutrient digestion by dairy cows fed corn of different particle size or steam-rolled.
J. Dairy Sci. 84:1458-1467.

Calsamiglia, S., A. Ferret, and M. Devant 2002. Effects of pH and pH
ﬂuctuations on microbial fermentation and nutrient ﬂow from a dual-ﬂow
continuous culture system. J. Dairy Sci. 85:574-579.

Campling, R. C. 1970. Physical regulation of voluntary intake. Pp. 226-234 in
A. T. Phillipson, ed. Physiology of Digesiton and Metabolism in the Ruminant.
Oriel Press, Ltd., Newcastle-upon-Tyne, England.

Chester-Jones, H., M. D. Stern, H. M. Metwally, J. G. Linn, and D. M. Ziegler.
1991. Effects of dietary protein-energy interrelationships on holstein steer

performance and ruminal bacterial fermentation in continuous culture. J. Anim.
Sci. 69:4956-4966.

128

 

 

 

Choi, B. R., and M. S. Allen. 1999. Intake regulation by volatile fatty acids and
physical ﬁll. S. Afr. J. Anim. Sci 29(lSRP):40—41 (Abstr.).

Clark, J. H., and C. L. Davis. 1983. Future improvement fo milk production:
potential for nutritional improvement. J. Anim. Sci. 57:750-764.

Clark, J. H., T. H. Klusmeyer, and M. R. Cameron. 1992. Microbial protein
synthesis and ﬂows of nitrogen fractions to the duodenum of dairy cows. J. Dairy
Sci. 75:2304-2323.

Clark, P. W., and L. E. Armentano. 1997. Inﬂuence of particle size on the
effectiveness of beet pulp ﬁber. J. Dairy Sci. 80:898-904.

Crocker, L. M., E. J. DePeters, J. G. Fadel, H. Prez-Monti, S. J. Taylor, J. A.
Wyckoff, and R. A. Zinn. 1998. Inﬂuence of processed corn grain in diets of

dairy cows on digestion of nutrients and milk composition. J. Dairy Sci. 81 :2394-
2407.

Dado, R. G., and M. S. Allen. 1993. Continuous computer acquisition of feed
and water intake, chewing reticular motility, and ruminal pH of cattle. J. Dairy
Sci. 76:1589-1600.

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.

Dehority, B. A. 1969. Pectin-fermenting bacteria isolated from the bovine
rumen. J. Bacteriol. 99:189-196.

De Visser, H., P. L. van der Togt, H. Huisert, and S. Tamminga. 1992.

Structural and non-structural carbohydrates in concentrate supplements of
silage-based dairy cow rations. 2. Rumen degradation, fermentation and kinetics.
Netherlands J. Agric. Sci. 40: 431-445.

De Visser, H., H. Huisert, and R. S. Ketelaar. 1991. Dried beet pulp, pressed
beet pulp and maize silage as substitutes for concentrates in dairy cow rations. 2.
Feed intake, fermentation pattern and ruminal degradation characteristics.
Netherlands J. Agric. Sci. 39: 21-30.

Dewhurst, R. J., K. Aston, W. J. Fisher, R. T. Evans, M. S. Dhanoa, and A. B.
McAllan. 1999. Comparison of energy and protein sources offered at low levels
in grass-silage-based diets for dairy cows. Anim. Sci. 68:789-799.

Dijkstra, J., H. Boer, J. Van Bruchem, M. Bruining, and S. Tamminga. 1993.
Absorption of volatile fatty acids from the rumen of lactating dairy cows as

129

inﬂuenced by volatile fatty acid concentration, pH and rumen liquid volume. Br.
J. Nutr. 69:385-396.

Emery, R. S. 1988. Milk fat depression and the inﬂuence of diet on milk
composition. Pp. 289-306 in T. H. Herdt, ed. Metabolic Diseases of Ruminant
Livestock. Vol. 4, no. 2. Vet. Clin. North Amer. Food Anim. Pract. W. B.
Saunders Company, Philadelphia.

Fahey, G. C., Jr., and L. L. Berger. 1988. Carbohydrate nutrition of ruminants.
Pp. 269-297 In D. C. Church, ed. The Ruminant Animal: digestive physiology
and nutrition. Waveland Press, Inc., Prospect Heights, Illinois.

Firkins, J. L. 1996. Maximizing microbial protein synthesis in the rumen. J. Nutr.
126:13478-13548.

Firkins, J. L. 1997. Effects of feeding nonforage ﬁber sources on site of ﬁber
digestion. J. Dairy Sci. 80:1426—1437.

Forbes, J. M. 1995. Voluntary Food Intake and Diet Selection in Farm Animals.
CAB International, New York.

Forbes, J. M., and F. D. Provenza. 2000. Integration of Ieaming and metabolic
signals into a theory of dietary choice and food intake. Pp. 3-19 in P. B. Cronjé,
ed. Ruminant Physiology: Digestion, Metabolism, Growth and Reproduction.
CAB International, New York.

Friggens, N., G. C. Emmans, S. Roberston, D. G. Chamberlain, C. T.
Whittemeore, and J. D. Oldham. 1995. The lactational responses of dairy cows

to amount of feed and to the source of carbohydrate energy. J. Dairy Sci.
78:1734-1744.

Gaillard, B. D. E. 1962. The relationship between cell wall constituents of
roughages and the digestibility of the organic matter. J. Agric. Sci. 59:369-373.

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.

Gordon, G. L. R., and M. W. Phillips. 1992. Extracellular pectin Iyase produced
by Neocallimastix sp. LM1, a rumen anaerobic fungus. Letters in Appl. Microbiol.
15:1 13-1 15.

Grant, R. J. 1997. Interactions among forages and nonforage ﬁber sources. J.
Dairy Sci. 80:1438-1446.

130

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

Grant, R. J., V. F. Colenbrander, and D. R. Mertens. 1990. Milk fat depression
in dairy cows: role of particle size of alfalfa hay. J. Dairy Sci. 73:1823-1833.

Griinari, J. M., M. A. McGuire, D. A. Dwyer, D. E. Bauman, and D. L. Palmquist.
1997. Role of insulin in the regulation of milk fat synthesis in dairy cows. J.
Dairy Sci. 80:1076-1084.

Grovum, W. L. 1995. Mechanisms explaining the effects of short chain fatty
acids on feed intake in ruminants -osmotic pressure, insulin and glucagons. Pp.
173-198 in W. v. Engelhardt, S. Leonhard-Marek, G. Breves, D. Giesecke, eds.
Ruminant Physiology: Digestion, Metabolism, Growth and Reproduction.
Ferdinand Enke Verlag, Stuttgart.

Hach, C. C., B. K. Bowden, A. B. Lopelove, and S. V. Brayton. 1987. More
powerful peroxide Kjeldahl digestion method. J. AOAC 70:783-787.

Harrison, D. G., D. E. Beever, D. J. Thomson, and D. F. Osbourn. 1976.
Manipulation of fermentation in the rumen. J. Sci. Fd Agric. 26:617-620.

Hespell, R. B., and P. J. O'Bryan-Shah. 1988. Esterase activities in Butyrivibrio
ﬁbrisolvens strains. Appl. Environ. Microbiol. 54:1917-1922.

Hoover, W. H. 1986. Chemical factors involved in ruminal ﬁber digestion. J.
Dairy Sci. 69:2755-2766.

Hoover, W. H., and S. R. Stokes. 1991. Balancing carbohydrates and proteins
for optimum rumen microbial yield. J. Dairy Sci. 74:3630-3644.

Huhtanen, P. 1987. The effect of dietary inclusion of barley, unmolassed sugar
beet pulp and molasses on milk production, digestibility and digesta passage in
dairy cows given silage based diet. J. Agric. Sci. Finland. 59:101-120.

lsaacson, H. R., F. C. Hinds, M. P. Bryant, and F. N. Owens. 1975. Efﬁciency of

energy utilization by mixed rumen bacteria in continuous culture. J. Dairy Sci.
58:1645—1659.

JMP® Version 3.2. 1997. SAS Institute Inc., Cary, North Carolina.

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

Keady, T. W. J., C. S. Mayne, D. A. Fitzpatrick, and M. Marsden. 1999. The
effects of energy source and level of digestible undegradable protein in

131

concentrates in silage intake and performance of lactating dairy cows offered a
range of grass silages. Anim. Sci. 68:763-777.

Kennedy, P. M., and L. P. Milligan. 1978. Effects of cold exposure on digestion,
microbial synthesis and nitrogen transformations in sheep. Br. J. Nutr. 39:105-
1 17.

Kertesz, Z. I. 1951. The Pectic Substances. lnterscience Publishers, Inc. New
York.

Kyriazakis, l., and G. C. Emmans. 1995. The voluntary feed intake of pigs given
feeds based on wheat bran, dried citrus pulp and grass meal, in relation to
measurements of feed bulk. Br. J. Nutr. 73:191-207.

Lechner-Doss, M., M. Kaske, and W. V. Engelhardt. 1991. Factors affecting the
mean retention time of particles in the forestomach of ruminants and camelids.
Pp. 455-482 in T. Tsuda, Y. Sasaki, and R. Kawashima, eds. Physiological
Aspects of Digestion and Metabolism in Ruminants. Academic Press, Inc. New
York.

Leedle, J. A. Z., M. P. Bryant, and R. B. Hespell. 1982. Diurnal variations in
bacterial numbers and ﬂuid parameters in ruminal contents of animals fed Iow- or
high-forage diets. Appl. Environ. Microbiol. 44:402-412.

Lehman, F. 1941. Die Iehre vom ballast. Z. Tierphysiol. Tierernaehr.
Futtermittelkd. 5:155-173.

Leng, R. A. 1970. Formation and production of volatile fatty acids in the rumen.
Pp. 406-421 In Phillipson, A. T., ed. Physiology of Digestion and Metabolism in
the Ruminant. Oriel Press, Newcastle upon Tyne, England.

Linzell, J. L., and M. Peaker. 1971. Mechanism of milk secretion. Physiol. Rev.
51:564-597.

Mackle, T. R., D. A. Dwyer, K. L. lngvartsen, P. Y. Chouinard, J. M. Lynch, D. M.
Barband, and D. E. Bauman. 1999. Effects of insulin and amino acids on milk
protein concentration and yield from dairy cows. J. Dairy Sci. 82:1512-1524.

Mansﬁeld, H. R., M. D. Stern, and E. E. Otterby. 1994. Effects of beet pulp and
animal by-products on milk yield and in vitro fermentation by rumen
microorganisms. J. Dairy Sci. 77:205-216.

Marounek, M. S. Bartos, and P. Brezina. 1985. Factors inﬂuencing the
production of volatile fatty acids from hemicellulose, pectin and starch by mixed
culture of rumen microorganisms. Zeitschrift fiir tierphysiologie, tierernahrung
und futtermittelkunde 53:50-58.

132

Marounek, M., and D. Duskova. 1999. Metabolism of pectin in rumen bacteria
Butyrivibrio ﬁbrisolvens and Prevotella ruminicola. Letters in Appl. Microbiol.
29:429-433.

Mauseth, J. D. 1988. Plant Anatomy. The Benjamin/Cummings Publishing
Company, Inc. Reading, Massachusetts.

Mbanya, J. N., M. H. Anil, and J. M. Forbes. 1993. The voluntary intake of hay
and silage by lactating cows in response to ruminal infusion of acetate or

propionate, or both, with or without distension of the rumen by a balloon. Br. J.
Nutr. 69:713-720.

McDowell, G. H., and E. F. Annison. 1991. Hormonal control of energy and
protein metabolism. In T. Tsuda, Y. Sasaki, and R. Kawashima, eds.
Physiological aspects of digestion and metabolism in ruminants. Academic
Press, Inc., New York.

McGuire, M. A., J. M. Griinari, D. A. Dwyer, and D. E. Bauman. 1995. Role of
insulin in the regulation of mammary synthesis of fat and protein. J. Dairy Sci.
78:816-824.

Mertens, D. R. 1994. Regulation of forage intake. Pp. 450-493 in G. C. Fahey,
Jr., M. Collins, D. R. Mertens, and L. E. Moser, ed. Forage Quality, Evaluation,
and Utilization. American Society of Agronomy, Cop Science Society of America,
and Soil Science Society of America, Madison, WI.

Mertens, D. R. 1997. Creating a system for meeting the ﬁber requirements of
dairy cows. J. Dairy Sci. 80:1463-1481.

Mertens, D. R., and L. O. Ely. 1979. A dynamic model of ﬁber digestion and
passage in the ruminant for evaluating forage quality. J. Anim. Sci. 4921085-
1095.

Michigan Department of Agriculture. 2002. News releases: Michigan Agricultural
Commodities Map. www.mda.state.mi.us/market/commodity/ sugar.html

Molento, C. F. M., E. Block, R. I. Cue, and D. Petitclerc. 2002. Effects of insulin,
recombinant bovine somatotropin, and their interaction on insulin-like growth
factor-I secretion and milk protein production in dairy cows. J. Dairy Sci. 85:738-
747.

Moorby, J. M., R. J. Dewhurst, C. Thomas, and S. Marsden. 1996. The

inﬂuence of dietary energy source and dietary protein level on milk protein
concentration from dairy cows. Anim. Sci. 63:1-10.

133

National Research Council. 1989. Nutrient Requirements of Dairy Cattle, sixth
revised edition. National Academy Press, Washington, D. C.

National Research Council. 2001. Nutrient Requirements of Dairy Cattle,
seventh revised edition. National Academy Press, Washington, D. C.

Neel, J. P. S., E. C. Prigge, and E. C. Townsend. 1995. Inﬂuence of moisture
content of forage on ruminal functional speciﬁc gravity and passage of digesta.
J. Anim. Sci. 73:3094-3102.

Nocek, J. E., and J. B. Russell. 1988. Protein and energy as an integrated
system. Relationship of ruminal protein and carbohydrate availability to microbial
synthesis and milk production. J. Dairy Sci. 71 :2070-2107.

Oba, M., and M. S. Allen. 1999. Evaluation of the importance of the digestibility
of neutral detergen ﬁber from forage: effects on dry matter intake and m ilk yield
of dairy cows. J. Dairy Sci. 82:589-596.

Oba, M., and M. S. Allen. 2000. Effect of brown midrib 3 mutation in corn silage
on productivity of dairy cows fed two levels of dietary NDF: 33. Digestibility and
microbial efﬁciency. J. Dairy Sci. 83:1350-1358.

Oba, M. 2002. Effects of propionate infusion on feeding behavior of lactating
dairy cows. PhD Diss., Michigan State University.

Oba, M., and M. S. Allen. 2002a. Effects of corn grain conservation method on
ruminal digestion kinetics for lactating dairy cows at two dietary starch
concentrations. J. Dairy Sci. (in press).

Oba, M., and M. S. Allen. 2002b. Effects of diet fermentability on efﬁciency of
microbial nitrogen production in lactating dairy cows. J. Dairy Sci. (in press).

O’Connor, J. D., C. J. Sniffen, D. G. Fox, and W. Chalupa. 1993. A net
carbohydrate and protein system for evaluating cattle diets: IV. Predicting amino
acid adequacy. J. Anim. Sci. 71:1298-1311.

O’Mara, F. P., J. J. Murphy, and M. Rath. 1997. The effect of replacing dietary
beet pulp with wheat treated with sodium hydroxide, ground wheat, or ground
corn in lactating cows. J. Dairy Sci. 80:530-540.

Orskov, E. R., and C. Fraser. 1975. The effects of processing of barley-based

supplements on rumen pH, rate of digestion, and voluntary intake of dried grass
in sheep. Br. J. Nutr. 34:493-500.

134

Osborne, J. M., and B. A. Dehority. 1989. Synergism in degradation and
utilization of intact forage cellulose, hemicellulose, and pectin by three pure
cultures of ruminal bacteria. Appl. Environ. Microbiol. 55:2247-2250.

Overton, T. R., M. R. Cameron, J. P. Elliott, and J. H. Clark, and D. R. Nelson.
1995. Ruminal fermentation and passage of nutrients to the duodenum of
lactating cows fed mixtures of corn and barley. J. Dairy Sci. 78:1981-1998.

Owens, F. N., and Goetsch, A. L. 1986. Digesta passage and microbial protein
synthesis. Pp. 196 - 223 in LR Milligan, W.L. Grovum, and A. Dobson, eds.
Control of digestion and metabolism in ruminants : proceedings of the Sixth
International Symposium on Ruminant Physiology. Prentice-Hall, Englewood
Cliffs, NJ.

Owens, F. N., R. A. Zinn, and Y. K. Kim. 1986. Limits to starch digestion in the
ruminant small intestine. J. Anim. Sci. 63:1634-1348

Petit, H. V., and G. F. Tremblay. 1995a. Ruminal fermentation and digestion in

lactating cows fed grass silage with protein and energy supplements. J. Dairy
Sci. 78:342-352.

Petit, H. V., and G. F. Tremblay. 1995b. Milk production and intake of lactating

cows fed grass silage with protein and energy supplements. J. Dairy Sci.
78:353-361.

Plascencia, A., and R. A. Zinn. 1996. Inﬂuence of ﬂake density on the feeding

value of steam-processed corn in diets for lactating dairy cows. J. Anim. Sci.
74:310-316.

Ramanzin, M., L. Bailoni, and G. Bittante. 1994. Solubility, water-holding
capacity, and speciﬁc gravity of different concentrates. J. Dairy Sci. 77:774-781.

Reynolds, C. K. 1995. Quantitative aspects of liver metabolism in ruminants.
Pages 351-372 in Ruminant Physiology: Digestion, Metabolism, Growth and

Reproduction, W. v. Englehardt, S. Leonhard-Marek, G. Breves, D. Geisecke, ed.
Ferdinand Enke Verlag, Stuttgart, Germany.

Robinson, P. H. Cl. J. Sniffen, and D. F. Smith. 1985. Development of a one-
piece reentrant cannula for the proximal duodenum of dairy cows. J. Dairy Sci.
68:986-995.

Robinson, P. H., P. L. Burgess, and R. E. McQueen. 1990. Inﬂuence of

moisture content of mixed rations on feed intake and milk production of dairy
cows. J. Dairy Sci. 73:2916-2921.

135

Rogers, J. A., B. C. Marks, C. L. Davis, J. H. Clark. 1979. Alteration of rumen
fermentation in steers by increasing rumen ﬂuid dilution rate with mineral salts.
J. Dairy Sci. 62:1599-1605.

Roubouts, F. M., and W. Pilnik. 1980. Pectic enzymes. pp. 227-282 in Microbial
Enzymes and Bioconversions, A. H. Rose, ed. Academic Press, London.

Russell, J. B., W. G. Bottje, and M. A. Cotta. 1981. Degradation of protein by
mixed cultures of rumen bacteria: identiﬁcation of Streptococcus bovis as an
actively proteolytic rumen bacterium. J. Anim. Sci. 53:242-252.

Russell, J. B., C. J. Sniffen, and P. J. Van Soest. 1983. Effect of carbohydrate
limitation on degradation and utilization of casein by mixed rumen bacteria. J.
Dairy Sci. 66:763-775.

Russell, J. B., and D. B. Wilson. 1996. Why are ruminal celluloytic bacteria
unable to digest cellulose at low pH? J. Dairy Sci. 79:1503-1509.

Sanson, D. W. 1993. Effects of increasing levels of corn or beet pulp on utilizatin
of low-quality crested wheatgrass hay by lambs and in vitro dry matter
disappearance of forages. J. Anim. Sci. 71 :1615-1622.

Satter, L. D., and L. L. Slyter. 1974. Effect of ammonia concentration on rumen
microbial protein production in vitro. Brit. J. Nutr. 32:199-208.

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.

Shaw, J. C., and W. L. Ensor. 1959. Effect of feeding cod lover oil and
unsaturated fatty acids on rumen volatile fatty acids and milk fat content. J. Dairy
Sci. 42: 1 238-1 240.

Sievert, S. J., and R. D. Shaver. 1993. Carbohydrate and Aspergillus oryzae
effects on intake, digestion, and milk production by dairy cows. J. Dairy Sci.
76:245-254.

Stouthamer, A. H., and C. Bettenhaussen. Utilization of energy for growth and
maintenance in continuous and batch cultures of microorganisms. Biochim.
Biophys. Acta, 301 :53-70.

Strobel, H. J., and J. B. Russell. 1986. Effect of pH and energy spilling on
bacterial protein synthesis by carbohydrate-limited cultures of mixed rumen
bacteria. J. Dairy Sci. 69: 2941-2947.

136

Sunvold, G. D., H. S. Hussein, G. C. Fahey, Jr., N. R. Merchen, and G. A.
Reinhart. 1995. In vitro fermentation of cellulose, beet pulp, citrus pulp, and

citrus pectin using fecal inoculum from cats, dogs, horses, humans, and pigs and
rumen ﬂuid from cattle. J. Anim. Sci. 73:3639-3648.

Sutton, J. D., J. A. Bines, S. V. Morant, and D. J. Napper. 1987. A comparison
of starchy and ﬁbrous concentrates for milk production, energy utilization and hay
intake by Friesian cows. J. Agric. Sci., Camb. 109:375—386.

Swain, S. M., and L. E. Armentano. 1994. Quantitative evaluation of ﬁber from
nonforage sources used to replace alfalfa silage. J. Dairy Sci. 77:2318-2331.

Thibault, J. F., F. Guillon, and F. M. Rombouts. 1991. Gelation of sugar beet
pectin by oxidative coupling. In R. H.Walter, ed. The Chemistry and Technology
of Pectin, p. 119-133 . Academic Press, Inc., New York.

Tjebbes, J. 1988. Utilization of ﬁber and other non-sugar products from
sugarbeet. pp. 139-145 in M. A. Clarke and M. A. Godshall, eds. Chemistry and
Processing of Sugarbeet and Sugarcane. Elsevier Science Publishers B. V.,
Amsterdam, the Netherlands.

Torrent, J., D. E. Johnson, and M. A. Kujawa. 1994. Co-product ﬁber
digestibility: kinetic and in vivo assessment. J. Anim. Sci. 72:790-795.

Van Buren, J. P. 1991. Function of pectin in plant tissue structure and ﬁrmness.
In The chemistry and technology of pectin, R. H. Walter, ed., pp. 1-22. Academic
Press, New York.

Van Kessel, J. S., and J. B. Russell. 1996. The effect of amino nitrogen on the
energetics of ruminal bacteria and its impact on energy spilling. J. Dairy Sci.
79:1237-1243.

Van Soest, P. J. 1994. Nutritional Ecology of the Ruminant, 2"d ed. Cornell
University Press, Ithaca.

Van Soest, P. J., J. B. Robertson, and B. A. Lewis. 1991. Methods for dietary
ﬁber, neutral detergent ﬁber and nonstarch polysaccharides in relation to animal
nutrition. J. Dairy Sci. 74:3583-3597.

Van Vuuren, A. M. C. J. van der Koelen, and J. Vroons-de Bruin. 1993.
Ryegrass versus corn starch or beet pulp ﬁber diet effects on digestion and
intestinal amino acids in dairy cows. J. Dairy Sci. 76:2692-2700.

Voelker, J. A., G. M. Burato, and M. S. Allen. 2002. Effects of pretrial milk yield

on responses of feed intake, digestion, and production to dietary forage
concentration. J. Dairy Sci. 85: (in press).

137

Waite, R., and A. R. N. Gorrod. 1959. The comprehensive analysis of grasses.
J. Sci. Food Agric. 10:317-326.

Wallace, R. J., and C. A. McPherson. 1987. Factors affecting the rate of
breakdown of bacterial protein in rumen ﬂuid. Br. J. Nutr. 58:313-323.

Weekes, T. E. C. 1991. Hormonal control of glucose metabolism. Pp. 183-200
in T. Tsuda, Y. Sasaki, and R. Kawashima, eds. Physiological Aspects of
Digestion and Metabolism in Ruminants. Proc. Seventh international symposium
on ruminant physiology. Academic Press, Inc., New York.

Weimer, P. J., G. C. Waghom, C. L. Odt, and D. R. Mertens. 1999. Effect of diet
on populations of three species of ruminal cellulolytic bacteria in lactating dairy
cows. J. Dairy Sci. 82:122-134.

Welch, J. G., and A. M. Smith. 1971. Effect of beet pulp and citrus pulp on
rumination activity. J. Anim. Sci. 33:472-475.

Wells, J. E., and J. B. Russell. 1996. Why do so many ruminal bacteria die and
Iyse so quickly? J. Dairy Sci. 79:1487-1495.

Wildman, E.E., G.M. Jones, RE. Wagner, R.L. Boman, H.F. Troutt, Jr., and TN.
Lesch. 1982. A dairy cow body condition scoring system and its relationship to
selected production characteristics. J. Dairy Sci. 65:495-501.

Williams, C. H., D. J. David, and O. lismaa. 1962. The determination of chromic
oxide in feces samples by atomic absorption spectrophotometry. J. Agric. Sci.
59:381-385.

Winner, C. 1993. History of the crop. Pp. 1-36 In D. A. Cooke and R. K. Scott,
eds. The Sugar Beet Crop. Chapman and Hall, New York.

Witt, M. W., L. A. Sinclair, R. G. Wilkinson, and P. J. Buttery. 1999. The effects
of synchronizing the rate of dietary energy and nitrogen supply to the rumen on
the production and metabolism of sheep: food characterization and growth and
metabolism of ewe lambs given food ad libitum. Anim. Sci. 69:223-235.

Zinn, R. A. and F. N. Owens. 1986. A rapid procedure for purine measurement

and its use for estimating net ruminal protein synthesis. Can. J. Anim. Sci.
66:157-166.

138

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