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This is to certify that the

thesis entitled

~EFFECTS OF FINENESS OF GRINDING AND CONSERVATION
METHOD OF CORN GRAIN ON RUMINAL AND WHOLE TRACT
DIGESTIBILITY, RUMINAL MICROBIAL PROTEIN PRODUCTION,
AND FEEDING BEHAVIOR OF HOLSTEIN HEIFERS BEFORE AND

AFTER CALVING
presented by

YUN YING

has been accepted towards fulfillment
of the requirements for

M. S. degree in ANIMAL SCIENCE

 

 

or professor

Date 5/4/48

0-7639 MS U is an Affirmative Action/Equal Opportunity Institution

 

 

 

 

' LIBRARY

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Unlverslty

 

 

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EFFECTS OF FINENESS OF GRINDING AND CONSERVATION METHOD OF
CORN GRAIN ON RUMINAL AND WHOLE TRACT DIGESTIBILITY,
RUMINAL MICROBIAL PROTEIN PRODUCTION, AND FEEDING
BEHAVIOR OF HOLSTEIN HEIFERS BEFORE AND AFTER CALVING

By

Yun Ying

A THESIS

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

MASTER OF SCIENCE

Department of Animal Science

1997

ABSTRACT

EFFECTS OF F INENESS OF GRINDING AND CONSERVATION METHOD OF
CORN GRAIN ON RUMINAL AND WHOLE TRACT DIGESTIBILITY,
RUMINAL MICROBIAL PROTEIN PRODUCTION, AND FEEDING
BEHAVIOR OF HOLSTEIN HEIFERS BEFORE AND AFTER CALVING

By
Yun Ying

Eight ruminally and duodenally cannulated Holstein heifers were used in a
duplicated 4 x 4 Latin-square design with 21-d periods. Treatments were dry and high
moisture corn, ground finely or coarsely. Two experiments were conducted using the
same animals before and after calving. High moisture conservation and fine grinding
increased rate of starch digestion resulting in increased ruminal starch and OM
digestibility for both experiments. High moisture corn decreased ruminal pH and
increased pH variance without effect on DMI for both experiments. Fine grinding
increased total tract starch and OM digestibility to a greater extent than high moisture
conservation for early lactation cows. Fine grinding resulted in less daily BW loss, an
increase in 3.5% FCM and milk protein content, and a decrease in microbial efficiency
for the experiment after calving. Fine grinding might be more beneficial to animal

production than high moisture conservation for early lactation cows.

ACKNOWLEDGMENTS

First, I would like to thank my major professor, Dr. Michael S. Allen, for his enthusiasm,
help, and guidance throughout my research program. I am also grateful to the members
of my guidance committee, Dr. Kent Ames, Dr. David Beede and Dr. Michael
VandeHaar, for their helpful suggestions on my project and this thesis. I would
especially like to thank Dr. Ames who performed the ruminal and duodenal cannulation

surgeries and the Michigan Com Growers Association for funding this project.

I also would like to thank to Dave Main, Dave O’Daniel, and Dewey Longuski for

keeping me straight in the lab and all their help in the barn throughout this project.

I am especially grateful to Sara Scheurer, Jing Xu, and Masahito Oba for their friendship,

and their unselfish help and advice.

I appreciate the support of Pao Ku and Jean Link for atomic absorption analysis and

freeze drying of samples in the swine nutrition lab.

To Kui, Peng and my parents; Thank you for giving me support from long distance,

Thank you for everything.

I would like to make a special dedication to my grandmother who passed way while I was

writing the thesis.

iii

TABLE OF CONTENTS

 

 

 

 

 

LIST OF TABLES ------- - - ‘ vii
LIST OF ABBREVIATIONS AND SYMBOLS - ix
CHAPTER 1
REVIEW OF LITERATURE" -- -- -- -- ‘ - - 1
1.1 INTRODUCTION ................................................................................................. l
1.2 CHARACTERISTICS OF CORN STARCH ......................................................... 3
1.3 SITE OF STARCH DIGESTION .......................................................................... 6
1.4 RUMINAL STARCH DIGESTION ...................................................................... 7
1.5 INTESTINAL STARCH DIGESTION .................................................................. 10
1.6 EFFECT OF SITE OF STARCH DIGESTION ON ANIMAL
PERFORMANCE .............................................................................................. 12
1.7 CONCLUSIONS ................................................................................................... 15
TABLE ....................................................................................................................... 17
CHAPTER 2
EFFECTS OF FINENESS OF GRINDING AND CONSERVATION
NIETHOD OF CORN GRAIN ON RUMINAL AND WHOLE TRACT
DIGESTIBILITY, RUMINAL MICROBIAL PROTEIN PRODUCTION,
AND FEEDING BEHAVIOR OF HOLSTEIN HEIFERS BEFORE
CALVIN G - -- ....... - 18
ABSTRACT.-.= -- ...... - - - - - - -_ 18
2.1 INTRODUCTION ............................................................................................. 19
2.2 MATERIALS AND METHODS ....................................................................... 20
2.2.1 CORN GRAIN AND ALFALFA SILAGE HARVEST AND
PRESERVATION .............................................................................................. 20
2.2.2 EXPERIMENTAL DESIGN AND DATA COLLECTION ........................ 20
2.2.3 ANALYSIS OF SAMPLES ....................................................................... 25

iv

2.2.4 STATISTICAL ANALYSIS ..................................................................... 29
2.3 RESULTS AND DISCUSSION ........................................................................ 30
2.3.1 COMPOSITION OF DIETS AND PARTICLE SIZE OF CORN
GRAIN ............................................................................................................... 30
2.3.2 NUTRIENT DIGESTIBILITY ................................................................... 32
2.3.3 RUMEN POOL SIZE, PASSAGE OF INDIGESTIBLE NDF AND
STARCH, RUMINAL pH AND VOLATILE FATTY ACIDS ........................... 34
2.3.4 INTAKE AND FEEDING BEHAVIOR DATA ......................................... 36
2.3.5 MICROBIAL N PRODUCTION AND N FLOW TO THE

 

DUODENUM .................................................................................................... 37

2.4 CONCLUSIONS ............................................................................................... 38

TABLES - - 40
CHAPTER 3

EFFECTS OF FINENESS OF GRINDING AND CONSERVATION
METHOD OF CORN GRAIN ON RUMINAL AND WHOLE TRACT
DIGESTIBILITY, RUMINAL MICROBIAL PROTEIN PRODUCTION,
FEEDING BEHAVIOR, AND MILK YIELD OF PRIMIPAROUS

 

 

HOLSTEIN COWS AFTER CALVING -- -- - - - - 50
ABSTRACT - - -- - - -- -50
3.1 INTRODUCTION ............................................................................................. 51
3.2 MATERIALS AND METHODS ....................................................................... 52

3.2.1 CORN GRAIN AND ALFALFA SILAGE HARVEST AND

PRESERVATION .............................................................................................. 52
3.2.2 EXPERIMENTAL DESIGN AND DATA COLLECTION ....................... 53
3.2.3 ANALYSIS OF SAMPLES ....................................................................... 57
3.2.4 STATISTICAL ANALYSIS ...................................................................... 61

 

 

 

 

3.3 RESULTS AND DISCUSSION ........................................................................ 62
3.3.1 COMPOSITION OF DIETS AND PARTICLE SIZE OF CORN
GRAIN ............. 62
3.3.2 NUTRIENT DIGESTIBILITY ................................................. . ................. 64
3.3.3 RUMEN POOL SIZES, PASSAGE OF INDIGESTIBLE NDF AND
STARCH, RUMINAL pH AND VOLATILE FATTY ACIDS ........................... 66
3.3.4 INTAKE AND FEEDING BEHAVIOR DATA ......................................... 68
3.3.5 MILK PRODUCTION AND COMPOSITION .......................................... 69
3.3.6 MICROBIAL N PRODUCTION AND N FLOW TO THE
DUODENUM .................................................................................................... 70

3.4 CONCLUSIONS ............................................................................................... 71

TABLES- -- 72

CHAPTER 4

FINAL DISCUSSION AND CONCLUSIONS-...- ....... - 82

APPENDIX A. F ORMULAS USED.= - 94
95

 

LIST OF REFERENCES...---- .......

vi

LIST OF TABLES

CHAPTER 1
Table 1-1. Effect of increasing ruminal starch digestibility on DMI and FCM ....... 17
CHAPTER 2
Table 2-1. Chemical composition and particle size of corn grain ........................... 41
Table 2-2. Ingredient and chemical composition of diets. ...................................... 42
Table 23 Effect of treatment on intakes and digestibilities of DM, OM, and

starch. .................................................................................................. 43
Table 2-4. Effect of treatment on intakes and digestibilities of N DF and ADF ....... 44
Table 2-5. Effect of treatment on ruminal passage, digestion and pool sizes .......... 45
Table 2-6. Effect of treatment on ruminal pH and volatile fatty acids. ................... 46
Table 2-7. Effect of treatment on intake, body weight and body condition

score. ................................................................................................... 47
Table 2-8. Effect of treatment on feeding behavior. ............................................... 48
Table 2-9. Effect of treatment on N intakes and N metabolism of

gastrointestinal tract of pregnant heifers. .............................................. 49
CHAPTER 3
Table 3-1. Chemical composition and particle size of corn grain. .......................... 73
Table 3-2. Ingredient and chemical composition of diets. ...................................... 74
Table 3-3. Effect of treatment on intakes and digestibilities of DM, OM, and

starch. .................................................................................................. 75
Table 34. Effect of treatment on intakes and digestibilities of NDF and ADF ....... 76
Table 3-5. Effect of treatment on ruminal passage, digestion and pool sizes .......... 77
Table 3-6. Effect of treatment on ruminal pH and volatile fatty acids. ................... 78
Table 3-7. Effect of treatment on intake, milk yield, milk composition, body

weight and body condition score. ......................................................... 79

vii

Table 3-8. Effect of treatment on feeding behavior. ............................................... 80

Table 3-9. Effect of treatment on N intakes and N metabolism of
gastrointestinal tract of early lactation cows. ........................................ 81

viii

BCS

BW

CP

DM

DMI

FCM

HMC

INDF

DNDF

NAN

NANMN

NDF

OM

OMAD

OMTD

LIST OF ABBREVIATIONS AND SYMBOLS

acetate to propionate ratio

acid detergent fiber

apparently digested in the total gastrointestinal tract
body condition score

body weight

crude protein

dry matter

dry matter intake

fat correct milk

high moisture corn

indigestible NDF

digestible NDF

nonammonia nitrogen

nonammonia nonmicrobial nitrogen

neutral detergent fiber

organic matter

organic matter apparently digested in the rumen
organic matter truly digested in the rumen
volatile fatty acid

truly digested in the total gastrointestinal tract

ix

CHAPTER 1

REVIEW OF LITERATURE

1.1 INTRODUCTION

In the eastern and midwestem U. S. corn is the most important source of starch
for dairy cows. Digestibility and utilization of corn starch by dairy cattle varies widely
by processing and the physiological status of animals. Corn is harvested at 25% to 35%
moisture and ensiled or harvested at 5% to 20% moisture and artificially dried, if
necessary to approximately 15% moisture. Storage methods commonly used for high
moisture corn include packing upright silos, bags or bunkers after rolling or grinding, or
storing as whole corn in oxygen-limiting silos (Soderlund, 1997). Compared with dry
corn, high moisture corn allows for earlier harvest, resulting in decreased of dry matter
loss in the field and elimination of fuel costs incurred during artificial drying (forced
natural air system and forced heated air system). One disadvantage of utilizing high
moisture corn is the loss of marketing flexibility compared with dry corn. High moisture
corn must be fed to livestock and is not easily transported. Furthermore, spoilage losses
might be higher than for dry corn if high moisture corn is not properly ensiled (high pH,
high yeast and mold counts) or if the rate of removal from the silo is too slow to prevent

spoilage.

Many methods for physically processing grain have been used to improve starch
utilization. These methods usually consist of breaking, cracking, grinding, micronizing,
rolling, or pelleting dried grain (Theurer et al., 1986). Hale and Theurer (1972) listed a
complete description of different processing methods. Dry processing methods include
grinding, dry rolling, popping, extruding, micronizing, roasting, and pelleting. Wet
processing methods include soaking, steam-rolling, steam-flaking, exploding, pressure
cooking, high moisture fermentation of early harvested grains, and reconstituted grains.
These methods result in an increase in surface area and (or) gelatinization of starch. The
extruding, roasting, and pressure-cooking processes are no longer used extensively for
cereal grains. Likewise, popping, micronizing and exploding, developed during the
cheap fossil fuel prices of the 1960’s, are not commonly used currently. The flaking
system is an extension of the steam rolling process; the moisture content of the grain is
raised to approximately 18% while in the steam chamber, then the grains are run through
the rollers to produce a flake, thereby, expanding the corn and completely disrupting the
endosperm structure of the kernel. Theurer et a1. (1986) reported most processing
methods involving the application of heat and water; the degree of moisture and heat
application to grain, in addition to physically decreased particle size, resulted in greater
benefits than either process. Processing has different effects depending upon grain
source. Theurer et a1. (1986) reported that unprocessed grains with lower ruminal
digestibility such as corn and sorghum respond to processing to a greater extent than
barley.

Finally, starch utilization can be affected by animal factors such as level of intake,

body size, and pregnancy, because of their effects on rumen retention time and site of

starch digestion. For instance, Stanley et a1. (1993) reported that indigestible ADF
passage increased across the prepartum period (before calving 61 d to before calving 6 d)
and peaked just before calving. Postpartum indigestible ADF passage was slower than 6
d before calving, but still greater than 61 days before calving. Although differences were
found in ruminal capacity, DMI and indigestible ADF passage rate, there was no effect of
period on dry matter digestibility. Faichney et al. (1988) explained that despite decreased
ruminal retention time, retention of digesta in the small intestine increased just before
parturition. In addition, Colucci et al. (1982) found that retention time of digesta was
shorter in the gastrointestinal tract with increasing intake for Holstein dairy cows. To
understand starch utilization by dairy cows, the characteristics of corn starch and site of

starch digestion must be understood.

1.2 CHARACTERISTICS OF CORN STARCH

The major structures of the corn kernel consist of the pericarp, horny endosperm,
floury endosperm, gem and the tip cap. The pericarp, also called the hull, is the thin
outer layer of the kernel that protects it from deterioration. The pericarp is resistant to
water and water vapor. It also acts as a barrier to insects. The tip cap is the only area of
the kernel not covered by the pericarp, and is the attachment point of the kernel to the
cob. The germ (embryo) consists of essential genetic information, enzymes, vitamins and

minerals for the kernel to grow into a corn plant.

The endosperm which is 82-84% of the kemel’s dry weight, contains most of the
starch, essential enzymes and enzyme inhibitors, and is in addition to the source of
energy and protein for the germinating seed (Watson and Ramstad, 1987). Starch
granules are 5-30 pm in diameter and are embedded in a protein matrix. The starch
granule is composed of two main molecules: amylose and amylopectin. Amylose is a
linear polymer of alpha-1, 4 D-glucose units (French, 1984) and amylopectin is a
branched polymer with linear chains of alpha-1, 4 D-glucose, that contain alpha-1, 6
branch points every 20 to 25 glucose residues (Marshall and Whelan, 1974). Corn
hybrids vary in polysaccharide composition; corn starch varies from nearly 100%
amylose to nearly 100% amylopectin (Allen, 1991).

There are two types of endosperm: horny and floury. The floury endosperm
surrounds the central fissure and is opaque to transmitted light. Starch availability in
floury endosperm is more susceptible to grain processing (Huntington, 1997). Duvick
(1961) explained that the opacity of floury endosperm is due to light refraction from
minute air pockets around starch granules. These air pockets result from the tearing of
thin protein matrix as it shrinks during drying, so the matrix no longer completely
surrounds the starch granules, which assume a round shape. In the horny endosperm, the
protein matrix is thicker and remains intact after drying. When processed, the cell walls
of horny endosperm are broken but there is little release of free starch granules because
of strength of protein matrix. However, the cells of floury endosperm are completely
disrupted when processed, releasing free starch granules because the granules are not
completely surrounded by the protein matrix (Watson and Ramstad, 1987). Beauchemin

et a1. (1994) reported that damage to the corn kernels during eating was sufficient to

expose the endosperm so that both the rate and extent of digestion of masticated corn
were greater than half or quarter kernels.

Other factors such as corn maturity and moisture levels might affect endosperm
protein and starch fractions and thus affect starch digestibility. The endosperm of a
developing corn kernel is a population of cells of varying physiological ages. During
kernel development, the cells in the central crown region of the endosperm begin starch
accumulation first, the lower endosperm cells begin starch synthesis and accumulation
much later (Boyer et al., 1977). With maturity, the hard starch layer and milk line move
toward the cob and kernel sugar content declines while starch increases (Creech, 1965).
As corn matures, sugars are translocated from the stover to the ear and these sugars are
converted to starch. The accumulated starch is hard above the milk line but still soft
below the line, therefore, making it more difficult to fracture a mature kernel because of
hard starch accumulation.

The solubility of endosperm proteins can also affect starch digestion. Thornton
(197 6) and Stock et al. (1991) found that solubility of endosperm proteins was highly
correlated with moisture level in high moisture corn and solubility increased during the
length of storage. Length of storage (120, 195, 290, and 365 d after initial ensiling) was
correlated positively with in vitro rate of starch digestion, and lactic acid content, and was
negatively related to DM content. Their data suggested that increased fermentation and
protein solubility might increase availability of starch in the rumen, which might
contribute to greater acidosis problem when a large amount of high moisture corn was fed
to cattle. Variation in structure of starch can be affected by processing characteristics and

conservation method, which might affect starch digestibility.

1.3 SITE OF STARCH DIGESTION

Starch is fermented to volatile fatty acids in the rumen and the large intestine, or
digested and absorbed as glucose in the small intestine. The rumen is the major site of
starch digestion in ruminants, but with high grain diets, large quantities of dietary starch
may escape ruminal fermentation and be digested postruminally. Owens et a1. (1986)
observed that in 40 experiments with cattle, fed between 18 and 42 % dietary starch from
corn and sorghum, the range of starch digestion varied from 58% to 82% in the rumen,
from 47% to 88% in the small intestine, from 33% to 66% in the large intestine, and from
88% to 98% in the whole gastrointestinal tract.

Ruminal and small intestinal digestion of starch are not completely separable.
Pre-digestion in the rumen influences both the quantity and composition of starch
reaching the small intestine (Owens et al., 1986). Starch appearing in the small intestine
includes feed starch escaping ruminal digestion as well as microbial starch. Bacteria and
protozoa contain up to 26 and 38% starch respectively, although the typical range is from
6 to 10 % (Jouany and Thivend, 1972; Hespell and Bryant, 1979). Microbial starch can
account for all the starch flow to the small intestine with forage diets, but cattle fed high
concentrate diets, the percentage of starch in the duodenal digestion is more than 10%.
This indicates that some dietary starch must be escaping ruminal fermentation. To
determine the site and extent of starch digestion by dairy cows, it is important to discuss

factors affecting starch digestibility.

Ruminal starch digestibility is determined by the fractional rate constant of
digestion and the total fractional rate of disappearance of starch from the rumen (the rate
of digestion and passage of starch). It is important to note that digestibility is determined
not only by the rate of digestion but also the rate of passage. Processing methods that
increase rate of digestion such as grinding may or may not increase ruminal digestibility,
depending upon their effects on rate of passage from the rumen. It is this interaction of

rate of digestion and the rate of passage that determines the site of starch digestion.

1.4 RUMINAL STARCH DIGESTION

Ruminal starch degradation varies by source, moisture content, and particle size
of the starch, by the animal and other dietary factors. These factors will be discussed
individually, although interactions may exist. Nocek and Tamminga (1991) published
that rumen degradable corn starch (% of total starch intake) ranged widely from 51% to
94% depending upon different processing methods observed from 46 experiments. When
evaluated by in vitro or in situ methods, mean ruminal corn starch digestibility ranked
from smallest to greatest as rolled, ground, ensiled shelled, and steam-flaked, averaging
51, 58, 72, and 87%, respectively. When evaluated in vivo, the rank of mean ruminal
starch digestibility from lowest to highest was whole, cracked, ground, steam-flaked and
ensiled shelled, averaging 63, 65, 76, 86 and 86%, respectively. The reviewed data are

from different sources, animals, physiological status, and levels of intake.

Rate of starch digestion is related to moisture content. Aguirre et a1. (1988) fed 5
cannulated steers ensiled corn which was reconstituted from dry ground corn to 15, 20,
25, 30 and 35% moisture. Starch digestibility in the rumen increased from 86.7% to
95.7% (% of total starch intake) with increasing water content from 15% to 35%. As
moisture level increased, starch digestion in the small intestine also increased from 65.5%
to 88.8%, starch digested in large intestine increased from 47.2% to 53.4%, and total tract
starch digestibility increased from 96.7% to 99.7%.

Knowlton et al. (1996b) evaluated the effect of conservation method (high
moisture vs. dry) and the effect of grinding (fine or coarse) on starch digestibility of
lactating dairy cows. They reported that high moisture corn increased rumen starch
digestion compared to dry corn. Total tract starch digestibility was 18.3% greater for
high moisture corn than dry corn across both particle sizes, but there was a conservation
method by particle size interaction since the difference between fine corn and coarse corn
was greater for high moisture corn compared to dry corn. Total tract starch digestibility
was 7.5 units higher for ground than coarse corn, averaged across different moisture
levels, which is similar to differences for dry corn reported by Knowlton et al. (1996a).
These differences in total tract digestibility among corn processing methods are less than
the differences expected in ruminal starch digestibilities because of compensatory
digestion in the small intestine (Firkins, 1997).

Rate of passage is affected by the animal, diet characteristics and levels of intake.
Fine grinding may have less effect on rumen starch digestibility for animals with high
level of intake such as dairy cattle in early lactation than for growing or fattening

animals, dry cows or dairy cattle in late lactation with lower DMI (Allen and Knowlton,

1995). Allen (1997) reported that ruminal starch digestibility of ground corn was 92%
with DMI at 1.32% of BW (Galyean et al., 1979), 64% for steers with DMI at 1.65% of
BW (Goetsch et al., 1987), and a mean of 45% for data from four experiments with high
producing dairy cows with DMI at 3.8% of BW (Cameron et al., 1991; Christensen et al.,
1993; Lynch et al., 1991; McCarthy et al., 1989). Ground corn seems to be unique in its
range in ruminal starch digestibility; much less variation was found within grain type for
ruminal starch degradation of cracked, ensiled, steam-flaked, or whole grains (Nocek and
Tamminga, 1991). Allen (1997) proposed the possible explanation for this difference in
variation was fine particles of ground corn were more likely to flow from the rumen
suspended in the liquid fraction than are large particles. Large differences in liquid
passage rate are expected between steers at maintenance intake and dairy cattle at four
times maintenance intake.

Chemicals have also been added to cereal grain to influence starch flow and
digestibility. Oke et a1. ( 1991) treated ground corn with 50% formalin (37%
formaldehyde) and fed it to sheep at 50% or 75% of DMI, and found ruminal starch
digestion (% of intake) was reduced 38% for formaldehyde treated corn at both levels of
intake. Small intestinal starch digestibility (% of intake) was increased approximately
100% by formalin treatment. However the formalin treated corn had no effect on whole
tract starch digestibility, indicating that formaldehyde treatment was effective in shifting
the site of starch digestion from the rumen to the small intestine without decreasing total
gastrointestinal tract starch digestion. In general, dairy cows absorb only small amounts
of glucose directly from the gastrointestinal tract due to fermentation of dietary starch.

Therefore, cows rely on gluconeogenesis to meet metabolic requirements for glucose.

10

Propionic acid and glucogenic amino acids supply glucose synthesized via
gluconeogenesis. Formalin treated corn increased starch digestibility in the small
intestine and improved N retention possibly by sparing utilization of amino acids for
gluconeogenesis. Waldo et al. (1973) reported that formaldehyde was easy to overprotect
protein supplements from rumen degradation and reduced protein digestibility. Oke et a1.
(1991) found that formalin treatment of corn reduced ruminal degradability of protein and
increased N disappearance in the small intestine but had no effect on total tract N
digestibility. This led the authors to conclude that degradation of endosperm protein
affects ruminal digestibility of starch.

Diet characteristics might also affect ruminal starch digestibility. Ruminal starch
digestibility was decreased when com in diets was replaced by cottonseed hulls and corn
silage (Cole et al., 1976; Brink et al., 1986). However no effect was found when corn
was replaced by ground alfalfa hay (Kart et al., 1966; Tucker et al., 1968). The different
effects of roughage replacement of grain may be due to the effects of roughage physical

form on rate of passage.

1.5 INTESTINAL STARCH DIGESTION

Owens et al. (1986) reported that digestion of starch in the small intestine is
energetically favorable. Absorption and metabolism of glucose seemed to be more
efficient energetically than fermentation and absorption of organic acids because of loss

of fermentation gases and heat of fermentation. This would imply an advantage to

11

increasing escape of starch from the rumen. Increasing ruminal starch digestion to
maximize total tract digestibility and microbial protein production must be balanced with
acid accumulation in the rumen and the possible loss of energetic efficiency. However,
efficiency of post-ruminal digestion and absorption of starch decreases with increasing
starch passage to the small intestine, as starch disappearance as a percent of that
presented decreases (Nocek and Tamminga, 1991). Factors limiting starch digestion in
the small intestine are activity of amylase, maltase or isomaltase due to inadequate
production, non optimal enzyme activity or presence of enzyme inhibitors, absorption of
released glucose from the small intestine, time for digestion and absorption of starch, and
accessibility of starch in grains (Owens et al., 1986).

McCarthy et a1. (1989) reported significant quantities of starch could be digested
postruminally by dairy cattle in early lactation. Cows fed corn had significantly lower
ruminal starch digestibility than cows fed barley (49 vs. 77%), but because of increased
postruminal starch digestion for corn diet (44% vs. 19% for barley diets), whole tract
digestibility of starch in the corn diet was less than 4% lower than that for the barley diet.
Although many factors affect starch digestibility in the small intestine, there is evidence
that digestibility might be most limited by amylolytic activity.

Two primary sources of postruminal carbohydrase activity are the pancreas and
intestinal mucosa. Pancreatic amylase breaks down amylose to maltriose and maltose.
Maltase activity in the small intestine produces glucose. Complete hydrolysis of
amylopectin in the small intestine requires isomaltase because pancreatic amylase has no
a-1-6 glucosidic activity (Nocek and Tamminga, 1991). Harmon (1992) observed that

intestinal starch digestibility in steers or heifers ranged from 17 to 85% of starch entering

12

the duodenum. Kreikemeier et al. (1991) infused corn starch in the abomasum of steers
and recorded a decrease in disappearance from 86 to 55% as the amount of starch infused
increased from 480 to 1440 g/d. Owens et al. (1986) foundthe similar range in their
literature review. Nocek and Tamminga (1991) suggested that capacity for intestinal
starch digestion in the ruminant might be limited by enzymatic hydrolysis, in particular,
low amylase and inadequate isomaltose activity.

Kreikemeier et al. (1990) found that increasing feed intake increased pancreatic
amylase and glucoamylase activities, small intestine length, digesta weight, and alpha-
amylase activity of calves. Kreikemeier et al. (1991) also found that only about 35% of
corn starch disappearing in the steer’s small intestine resulted in net portal glucose
absorption and suggested that other routes of disappearance are microbial fermentation to

VFA and small intestine metabolism of glucose to lactate.

1.6 EFFECTS OF SITE OF STARCH DIEGSTION ON ANIMAL

PERFORMANCE

Glucose supplied to the mammary gland is the principal determinant of milk
yield. Kronfeld et a1. (1968) calculated that 72 g of glucose uptake by the mammary
gland were required to produce 1 kg of milk. Therefore, abundant supplies of glucose are
needed to support the requirements of mammary gland for milk lactose synthesis and also

support milk protein and fat synthesis and maintenance of the mammary gland.

13

Increasing plasma glucose is dependent upon glucose absorbed from the small intestine
or gluconeogenesis from substrates, such as propionic acid, in the liver.

Site of starch digestion might affect animal performance several ways.
Optimizing ruminal degradation of starch is important to maximize performance of dairy
cattle. Insufficient ruminal degradation of starch may reduce total tract starch
digestibility and impair microbial protein production. In addition, less fermentation acids
are available to the animal as an energy source. However, increased rumen-escape starch
decreases heat of fermentation possibly reducing heat stress in hot environments.
Excessive ruminally fermented starch results in too much VFA or lactate production in
the rumen and decreases ruminal pH and microbial efficiency (Hoover and Stokes, 1991),
digestibility of fiber, and DMI. Britton and Stock (1987) suggested that acidosis and rate
of starch digestion and intake are closely related in feedlot cattle and that it is critical to
maintain ruminal pH above 5.6 to aid in controlling subacute acidosis and maximize
intake. To maximize the amount of feed fermented in the rumen per day and to have
sufficient microbial efficiency, an Optimal pH must be considered (Allen and Beede,
1996).

Effect of ruminal fermentability of corn starch on DMI and milk yield of dairy
cows is variable. Data collected from papers from 1989 to 1997 (Table 1-1) with
ruminally and duodenally cannulated dairy cows show the effects of increasing ruminal
starch digestibility on DMI and FCM. Increasing ruminally degraded starch either
decreased or had no effect on DMI. Studies with early lactation cows fed high moisture
shelled corn or ear corn (Aldrich et al., 1993) and mid lactation cows fed barley or corn

(Overton et al., 1995) found that increased ruminal starch digestibility with barley or high

14

moisture shelled corn decreased DMI and slightly decreased FCM. McCarthy et al
(1989) reported that ruminal degraded starch increased when barley replaced corn for
early lactation cows, decreasing DMI with no effect on FCM.

Several studies (Peng et al., 1993; Plascencia and Zinn, 1996; Joy et al., 1997)
found that increased ruminally degraded starch had no effect on DMI but decreased
FCM. Other studies reported that increased ruminal starch digestibility had no effect on
DMI or FCM (Oliveira et al., 1995; Christensen et al., 1996; Knowlton et al., 1996b;
Yang et al., 1997; Crooker et al., 1997).

The degree to which DMI is affected by increased ruminal starch digestibility
might be due to the extent to which the increased fermentation acids are neutralized when
ruminal pH is reduced. Inadequate neutralization of fermentation acids might result in a
reduction in DMI which could decrease FCM production as in studies by Aldrich et al.
(1993) and Overton et al (1995). When increased fermentation acids can be neutralized
so that there is little or no effect on ruminal pH, FCM might not be affected as in the
study by McCarthy et al. (1989). In this instance, increased microbial protein production
for corn with greater available substrate might have affect decreased energy from lower
DMI.

However, if DMI is not regulated by the effects of fermentation acids, increased
ruminal degraded starch might depress milk fat decreasing FCM (Feng et al., 1993;
Plascencia and Zinn, 1996; Joy et al., 1997). When neither DMI nor FCM were affected
(Oliveira et al., 1995; Christensen et al., 1996; Knowlton et al., 1996b), fermentation

acids were probably not limiting DMI and had little or no effect on milk fat content.

15

Differences in ruminally fermented starch affect production of fermentation acids
and might affect ruminal pH, meal patterns and ultimately dry matter intake. Dry matter
intake is determined by meal size and meal frequency. There is little research on the
effects of corn grain processing and (or) conservation method on meal patterns, ruminal

pH and DMI of dairy cattle.

1.7 CONCLUSIONS

Processing might affect both rate of digestion and rate of passage of starch which
together determine ruminal digestibility. Conservation and processing methods that alter
site of starch digestion might affect microbial protein production, DMI, digestibility and
animal performance. Finally, increased ruminal starch digestibility might decrease DMI
and have variable effects on FCM.

Therefore, the objective of this thesis was to evaluate the effects of fineness of
grinding and conservation method of corn grain on ruminal and whole tract digestibility,
ruminal microbial protein production and feeding behavior of Holstein heifers before and
after calving. The experiment was conducted both before calving (mean DMI = 1.61% of
BW) and after calving (mean DMI = 3.33% of BW) because DMI might change the
relative passage rates and therefore the digestibility of the corn treatments. The
hypothesis was that high moisture corn and finely ground corn would increase levels of
ruminally degraded starch and total tract starch digestibility compared with field-dried

corn and coarsely ground corn, thereby, increasing ruminal microbial protein production,

16

decreasing ruminal pH, possibly decreasing DMI and performance of early lactation dairy

COWS.

17

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CHAPTER 2

EFFECTS OF FIN ENESS OF GRINDING AND CONSERVATION METHOD OF
CORN GRAIN ON RUMINAL AND WHOLE TRACT DIGESTIBILITY,
RUMINAL MICROBIAL PROTEIN PRODUCTION, AND FEEDING
BEHAVIOR OF HOLSTEIN HEIFERS BEFORE CALVING
ABSTRACT

The effects of fineness of grinding and conservation method of corn grain on
ruminal and whole tract digestibility, ruminal microbial protein production and feeding
behavior of pregnant Holstein heifers were examined. Eight ruminally and duodenally
cannulated heifers were utilized in a duplicated 4 x 4 Latin square design balanced for
carryover effects with 21-d periods. Corn treatments were dry corn, ground finely or
coarsely and high moisture corn, ground finely or coarsely, prior to feeding. Diets
contained 62% alfalfa silage and 36% com grain. High moisture conservation method
and fine grinding increased ruminal digestibility of starch and OM. However, mean
ruminal pH was reduced and pH variance was increased with high moisture conservation
only, probably because of increased ruminal VFA concentration. High moisture
conservation also reduced passage of total nitrogen to the duodenum and tended to
decrease microbial protein production per kg of OM fermented. Although there was no
effect of treatment on DMI, high moisture conservation decreased the daily number of
meals consumed. There was no effect of treatment on ruminal or total tract digestibility
of NDF or ADF. Fine grinding increased total tract starch digestibility, but had no effect
on total tract OM digestibility. Although both conservation method and fine grinding had

large effects on ruminal starch digestibility, only high moisture conservation decreased

ruminal pH, microbial efficiency, and number of meals per day for pregnant heifers.

18

19

2.1 INTRODUCTION

Corn is the most widely used cereal grain for dairy cattle diets in the eastern and
midwestem US. It is harvested at high moisture (25-35% moisture) and ensiled or
harvested after field drying to approximately 15% moisture. In both cases, some
processing (rolling, grinding) is necessary to rupture kernels and maximize whole tract
digestibility (Theurer, 1986). Site of starch digestion, which is affected by conservation
method and processing (Nocek and Tamminga, 1991), can affect animal performance by
altering energy available for microbial growth, forms of energy absorbed, efficiency of
DE utilization, ruminal fermentation, meal patterns and DM intake. Although there is
research in the literature which compares site of starch digestion across grain sources
such as barley, corn, and sorghum (Oliveira et al., 1993; Grings et al., 1992; Yang et al.,
1997), and processing such as grinding and steam-flaking, there are fewer data available
that evaluate effects of processing high moisture corn and dry corn from the same source
(Plascencia et al., 1997; Crooker et al., 1997; Joy et al., 1997). The objective of this
experiment was to evaluate the effect of the conservation method (high moisture ensiled
or field dry) and processing (finely or coarsely grinding) of corn on ruminal fermentation,
passage of nutrients to the duodenum, meal patterns and DM intake of pregnant Holstein

heifers.

20

2.2 MATERIALS AND METHODS

2.2.1 Corn Grain and Alfalfa Silage Harvest and Preservation

Corn grain (Great Lakes 450) was planted in one 7-acre loamy sand field at the
Michigan State University's campus farm (East Lansing) on May 14, 1994. The field was
divided into 12 subplots of 18 rows, 76 cm in width and 165 min length. Alternate
subplots were harvested with a 6-row combine as high moisture corn at 67.2% DM on
October 5, 1994. The remaining subplots were harvested as dry corn at 83% DM on
December 13, 1994 and artificially dried to 86% DM. High moisture corn was packed
(Porta-Packer, Fowlerville, MI) into a silage bag (UpNorth Plastics Inc., Cottage Grove,
MN) and ground finely or coarsely (Mighty Mac Chipper Shedder, Mackissic Inc., Parker
Ford, PA) prior to feeding. Corn population in the field was 28,000 plants per acre. Dry
corn was mixed and divided in half. One half of the dry corn was finely ground while the
other half was coarsely ground at the Michigan State University feed mill, bagged and
stored in a trailer throughout the experiment.

First-cutting alfalfa was ensiled in a 2.5-m diameter silage bag (50 tons; Ag
Bagger®, Ag Bag Corp., Blair, NE) to minimize variation and reduce spoilage at feed
out. Each load of alfalfa silage was sampled at filling and analyzed prior to the initiation

of the experiment to assess variation in nutrient composition.

2.2.2 Experimental Design and Data Collection

Eight ruminally and duodenally cannulated pregnant Holstein heifers (23 months

old at beginning of experiment, approximately 4 months before calving) were utilized in

21

a duplicated 4 x 4 Latin square design. Pregnant heifers were assigned to squares by
expected calving date. The squares were balanced for carryover effects so that each
treatment followed the other treatment an equal number of times. Within a square, each
cow was assigned randomly to one of four treatment combinations. A 2 x 2 factorial
arrangement of treatments was used in each square. Dietary treatments were com
conservation method (high moisture ensiled or field dried) and corn fineness of grinding
(finely or coarsely grinding). Experimental treatment periods were 21 days, including 11
days for diet adjustment followed by 10 days of data collection. The animal care protocol
was approved by All-University Committee on Animal Use and Care of Michigan State
University. The approved animal use form number was 06/95-088-00.

Heifers were ruminally and duodenally cannulated 45 days prior to the start of the
experiment. Duodenal cannulas were T-shaped and fabricated from a Teflon
fluorocarbon polymer (Ankom Technology Corporation, Fairport, NY). Surgical
placements of the cannulas were between ribs 10 and 11 as described by Robinson et a1.
(1985). The ruminal and duodenal cannulation surgeries were performed at the
Department of Large Animal Clinical Science, College of Veterinary Medicine, Michigan
State University. Cows were hospitalized until they recovered from the surgical
procedure.

Diets consisted of alfalfa silage, dry or high moisture corn, soybean meal,
minerals and vitamins for each treatment period (Table 2-1 and 2-2; values represent
mean ingredient and nutrient composition throughout the experiment). The diets were
balanced to 31% NDF, 39% starch and 15% crude protein. Minerals and vitamins were
included with soybean meal as a premix to meet requirements (NRC, 1989). High
moisture corn was ground prior to feeding through a mill without (coarse) or with (fine) a
1 cm screen (Mighty Mac Chipper Shedder, Mackissic Inc., Parker Ford, PA). Five

alfalfa silage samples from different sites of the silage bag were analyzed for DM, NDF

22

and crude protein, and the average values were used for diet formulation for the
experiment.

Alfalfa silage, corn treatments and protein-nfineral-vitamin premix were weighed
into individual polyethylene mangers for each cow and thoroughly mixed by hand. Cows
were fed once daily at 1400 h at 110% of expected intake. Ration offered was recorded
for each cow, and weights of orts were recorded prior to each feeding. Dry matter intake
was calculated as the average daily DMI from d 13 to d 21 of each period. Dietary
ingredients (0.5 kg) and individual cow orts (12.5% of orts as wet weight basis) were
collected daily during the collection period, frozen and composited within each collection
period. Alfalfa silage was analyzed weekly for DM content during the experiment and
diets were re-balanced accordingly.

Cows were housed in tie stalls bedded with chopped newspaper and were exposed
to continuous light throughout the experiment. Rumen empty body weights (BW) were
measured on the last 2 days of each period and on 2 days preceding the first period.

Body condition score (BCS) was evaluated to the quarter point on a five-point scale (1 =
thin to 5 = fat) on d 20 of each period and 2 days prior to beginning the first period.

Duodenal flow was estimated using a double marker system (Faichney, 1980)
with Cr-mordanted wheat straw N DF as a particulate phase marker and Co-EDTA as a
liquid phase marker. Chromium-mordanted NDF and Co-EDTA were prepared as
described by Udén et al. (1980). Chromium mordanted wheat straw was ground through
a Wiley mill (2 mm screen; Arthur H. Thomas, Philadelphia, PA) and the chromium-
mordanted NDF was provided at approximately 0.14% of DM intake (30 g/d per cow).
Chromium content of the fiber was approximately 5% of DM resulting in a Cr intake of
1.6 g/d per cow. Gelatin capsules (1.5 Oz, Tropac Inc., Airfield, NJ) filled with
chromium mordanted wheat straw were dosed into the rumen 2 times/d from d 11 until (1
19 at 0730 and 1930 h. Co-EDTA (0.43 g Co/d, 0.91 g Coll solution) was dosed at

approximately 0.04% of DMI by semi-continuous infusion into the rumen by a peristaltic

23

pump (FPUlOl, OmegaflexTM peristaltic pump, Omega Engineering Inc., Stamford, CT).
Pumps had a flow rate of 3.3 mllmin but were turned on intermittently for l min of every
10 min to achieve an average flow rate 0.33 mllmin over the 9 days (475 ml Co-EDTA
solution/d, 0.43 g Co/d). A priming dose of each marker was given on d 10 of the 21-d
period at 3 times the daily dose.

For determination of ruminal and total tract nutrient digestibility, duodenal
digesta and feces were taken every 3 h beginning at 1400 h on d 16 and continuing until
at 1300 h on d 19. The sampling time was adjusted ahead 1 h daily, so that 24 samples
representing each hour'in a day were collected. Two separate samples of duodenal
digesta were collected (300 ml and 40 ml). The 300 ml samples were frozen immediately
at ~20°C until analysis and the 40 ml samples were preserved with 3 ml of 6 N HCl and
frozen for later analysis of NH3. Fecal samples (400 g) were collected and frozen
immediately at —20°C until analysis.

Samples of ruminal fluid were collected every 3 h of a 24-h period starting at
1400 h on d 16 to account for diurnal effects on concentration of metabolites. Samples of
rumen fluid from five sites in the rumen were mixed and filtered through 4 layers of
cheesecloth to remove particulate matter. Three 40 ml subsamples of ruminal fluid were
taken from this sample for each period. One was preserved with 3 ml of 6 N HCl for
NH3 analysis, one was preserved with 3 ml 20% NaOH for volatile fatty acids (VFA) and
lactate analysis, and one was taken for purine analysis. All subsamples were frozen (at
-20°C) immediately following collection.

Rumen digesta were manually evacuated from each cow at 0800 h on d 20 (6 h
prefeeding) and 2000 h on d 21 of the experiment period (6 h postfeeding). A 10%
aliquot of digesta was separated during evacuation for ease of subsampling and
measuring liquid and solid phases. This aliquot was weighed, mixed by hand and
strained through four layers of cheesecloth to separate into solid and liquid phases. Solid

phase samples were weighed and subsampled, and a 400 g solid sample was frozen for

24

determination of DM and nutrient composition. Three separate subsamples (300 ml, 40
ml, and 40 ml) of rumen liquid were collected. The 300 ml samples were frozen (-20°C)
immediately for DM, NDF, ADF, acid detergent sulfuric acid-lignin, starch and
indigestible NDF analysis, while the 40 ml subsamples of ruminal fluid were preserved
with 3 ml of 6 N HCl and frozen (-20°C) for later NH3 analysis, and the 40 ml
subsamples of rumen fluid were preserved with 3 ml of 20% NaOH and frozen (-20°C)
for later VFA and lactate analysis. Rumen total digesta weights and volumes were
measured at each evacuation.

Feed disappearance, chewing behavior and ruminal pH were measured
continuously for 4 days from d 12 to d 15 of each experimental period using a
computerized data acquisition system described by Dado and Allen (1993). Data was
written to files every 5 seconds for each variable, for each cow. Chewing monitors were
fitted to cows 1 day prior to collection to allow for cow adaptation and remained in place
throughout the behavior collection period. There were no other cows present in the barn
during the study. Load cells for determination of feed consumption were calibrated prior
to each collection period. Electrodes for pH determination (described by Knowlton et al.,
1996a) were calibrated daily immediately before feeding. Electrodes generally held their
calibration within 0.05 pH units. Electrodes outside this range were recalibrated or
replaced. Occasional problems with jaw movement detectors, load cells and pH
electrodes were recorded. Additionally, the cows feeding behavior data for the entire day
were removed from the data file prior to analysis. Water intake was recorded daily from
water meters at each stall (Omega MKH 4465 5/8, Omega Engineering Inc., Stamford,
CT).

25

2.2.3 Analysis of Samples

Samples of each corn treatment were taken daily from d 13 until (1 21 of each
period for particle size analysis. A representative sample of each corn treatment was dry
sieved through 8 sieves (Sieve apertures: 4750, 2360, 1180, 600, 300, 150, 75 [.tm and
bottom pan), using a sieve shaker (Model RX-86, W.S. Tyler Inc., Gastonia, NC) for
approximately 15 min until the bottom pan weight was constant (ASAE, 1968). Mean
particle size of corn was calculated and variance was determined by fitting the data to a
gamma distribution (Allen et al., 1983).

Diet ingredient and orts samples were analyzed for DM, ash, NDF, ADF, acid
detergent sulfuric acid-lignin, starch, CP and indigestible NDF. The samples were dried
in a forced air oven at 55°C for 72 hours and analyzed for DM content. All samples were
ground with a Wiley mill (1 mm screen; Arthur H. Thomas, Philadelphia, PA). Ash was
determined following sample ignition at 500°C for 5 hours. Samples were analyzed
sequentially for NDF (procedure A, Van Soest et al., 1991), ADF (AOAC, 1984) and
acid detergent sulfuric acid-lignin (Goering and Van Soest, 1970). Crude protein was
analyzed according to Hach et al. (1987). Indigestible NDF was estimated as NDF
content of sample following in vitro fermentation in buffered rumen media for 120 hours
(Goering and Van Soest, 1970). Starch was analyzed by a one-stage enzymatic method
of glucoamylase (Diazyme L-200, Miles, Inc., Elkhart, IN) with a NaOH gelatinization
step (O'Neil et al., 1993). Following gelatinization the sample was centrifuged at 26,000
x g for 20 min. Concentration of glucose in the supernatant was analyzed by HPLC
using an Arninex fast carbohydrate column (100 x 7.8 mm, catalog number 125-0105;
Bio-Rad Laboratories, Richmond, CA). Column temperature was 85°C, and the solvent
was degassed deionized distilled H20 with a flow rate of 0.6 mllmin. Detection was by

refractive index (Waters 410, Millipore Corp., Milford, MA). Concentration of all

26

nutrients except DM was expressed as a percentage of DM determined from forced air
oven drying at 105°C.

Daily frozen duodenal samples (n = 8) were chopped and subsampled on an
equivalent wet weight basis, lyophilized and ground with a mortar and pestle. Duodenal
digesta was analyzed for DM, NDF, ADF, acid detergent sulfuric acid-lignin, ash, CP,
starch and indigestible NDF as previously described and purine analysis as described
later. Fecal samples were thawed, subsampled and composited on an equivalent wet
weight basis for each cow per day. Then, samples were dried in a forced air oven at 55°C
for 72 hours and analyzed for DM content. Fecal samples were ground with a Wiley mill
(1 mm screen) and analyzed for DM, NDF, ADF, acid detergent sulfuric acid-lignin, ash,
CP, starch and indigestible NDF as described previously.

For analysis of flow markers, daily frozen duodenal samples were chopped into
snow using a food processor (84142 Food cutter, Hobart Manufacturing Co., Troy, OH),
subsampled on an equal wet weight, thawed and partitioned into liquid and solid phases
by centrifuge (RCSC, Sorvall Instrument, E. I. du Pont de Memours & Co., Inc., Hoffman
Estates, IL) at 500 x g for 10 min at 4°C. Each phase of sample was dried in a 100°C
forced air oven for later chromium and cobalt analysis. Chromium and cobalt
concentration of feeds, duodenal liquid phase, duodenal solid phase and feces were
determined by atomic absorption spectrometry according to the manufacturers’
recommendations (Smith-Hieftje 4000, Thermo Jarrell Ash Co., Franklin, MA) following
digestion with a phosphoric acid-manganese sulfate solution (Williams et al., 1962).
Duodenal digesta flow was calculated as described by Armentano and Russell (1985).

Ruminal samples for purine analysis were prepared following the procedure of
Overton et a1 (1995). Purines were measured (Zinn and Owens, 1986), modified by
Overton et al. (1995) as a bacterial marker. Microbial protein production was calculated
by dividing purine to nitrogen ratio of ruminal microbes by purine percentage of

duodenal DM per day (Zinn and Owens, 1986).

27

Duodenal and ruminal samples for NH3 analysis were thawed and composited on
an equivalent volume basis for each cow per day. Ammonia was measured using the
general procedure of McCullough (1967), modified by Broderick and Kang (1980).
Absorbance was determined using a spectrophotometer (1 cm length path, DU-64
Spectrophotometer, Beckman Instruments, Inc., Fullerton, CA).

Ruminal fluid samples were thawed and composited on an equivalent volume
basis for each cow per day for VFA and lactate analysis. Composite rumen fluid samples
were centrifuged at 26,000 X g for 30 min. Concentrations of VFA and lactate of
supernatant were determined by HPLC as described by Dado and Allen (1995).

Ruminal solid and liquid subsamples from the evacuated rumen digesta were
dried in a 100°C forced air oven, and analyzed for DM, N DF, ADF, acid detergent
sulfuric acid-lignin, ash, starch, and indigestible NDF as described previously. Ruminal
liquid subsamples were analyzed for NH3 and VFA as described previously. Ruminal
pool sizes (kg) of DM, liquid, NDF, starch and indigestible NDF were calculated by
multiplying the concentrations of each by the ruminal digesta weight (kg).

Ruminal starch and NDF turnover time were determined by dividing the pool size
of starch or NDF by hourly starch or NDF intake. Rates of starch, indigestible NDF
(INDF) and potentially digestible NDF (DNDF) passage from the rumen were
determined by dividing starch or INDF or DNDF daily outflow to duodenum
(OUTFLUX, dual markers system) by the pool size of starch, or indigestible NDF or
digestible NDF. Rate of digestion of starch or DNDF was calculated by the reciprocal of
the turnover time (equal to rate of digestion and rate of passage) minus rate of passage of
starch or DNDF. Rate of IN DF passage from the rumen (INFLUX, internal marker
system) was determined by the method of Dado and Allen (1995) by dividing the rumen
pool size of INDF into hourly intake of INDF. Estimated rate of water passage from the

rumen was calculated, as duodenal flux of water divided by the pool size of water in the

28

rumen. This calculation assumes no net water absorption prior to the duodenum and that
Co—EDTA passes at the same rate as water.

Mean ruminal pH, hours below pH 5.5 and 6.0, and the areas of the pH x time
curve under pH 5.5 and 6.0 (Mackie and Gilchrist, 1979) were calculated. The area of
the pH x time curve below a critical pH gives a weighted average of the deviation from
this pH which is more meaningful to optimal ruminal pH (Allen and Beede, 1996).

For feeding behavior data analysis, means were calculated for number of meals
per day, meal size (kg per meal), minutes between meals, eating time in minutes per meal
and per day, eating chews per meal and per day, eating chew rate (chews per minute),
number of ruminating bouts per day, minutes between ruminating bouts, ruminating time
in minutes per bout and per day, ruminating chews per bout and per day, ruminating
chew rate and total chewing per day (eating chews and ruminating chews) using a
program written in SAS programming language (Version 6.1, SAS Institute Inc., Cary,
NC).

29

2.2.4 Statistical Analysis

Data were analyzed using the fit model procedure of JMP (Version 3.2, SAS
Institute Inc., Cary, NC) as duplicated (n = 2) 4 x 4 Latin squares using the following
model:

Yijkl = u + Si + ij + Pk + T1 + STil + SPik + Eijkl
where

u = overall mean,

Si = random effect of square (i = 1 to 2),

Cm) = random effect of cow within square (j = l to 4),

Pk = random effect of period (k = l to 4),

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

STil = interaction of square and treatment,

SP“, = interaction of square and period, and

Em,l = residual, assumed to be normally distributed.

A reduced model without square x treatment or square x period interactions was
used when these effects were not significant (P > 0.10). Preplanned orthogonal contrasts
were used to determine significance of the main treatment effects of the conservation

method, fineness of grinding and their interaction. Main effects and interactions were

declared significant at P < 0.05, and P < 0.10, respectively.

30

2.3 RESULTS AND DISCUSSION

2.3.1 Composition of Diets and Particle Size of Corn Grain

Chemical composition of the corn treatments appears in Table 2-1. Except for the
expected effect of conservation method on DM content, only slight differences in
composition were detected among treatments. High moisture conservation method had a
very slight effect on percentage of organic matter percent for corn by increasing OM
percentage by 0.15 units of DM. Dry corn had higher NDF content than high moisture
corn ( 10.7 vs. 8.1% of DM). Finely ground corn tended to have higher starch content
than coarse corn (P = 0.07). Diets contained 62% alfalfa silage and 36% com grain
(Table 2-2). Diets containing high moisture corn had lower DM (47.1 vs. 50.7%) and
NDF (30.8 vs. 31.7 % of DM) than diets containing dry corn. Remaining nutrients
measured in diets did not differ by treatment.

Mean particle size of dry fine corn, dry coarse corn, high moisture fine corn and
high moisture coarse corn was 771 :l: 56 um, 4524 i 170 pm, 1933 i 157 um and 5526 i
461 pm, respectively. Field dried conservation and fine grinding decreased particle size
of corn (P < 0.01, Table 2-1). Because moisture contents for field dried conservation and
high moisture conservation were different, they were processed with different mills.
There were similar reductions in particle size by fine grinding dry corn and high moisture

corn (Figure 2-1).

31

6000_

5000_

4000_

3000_

2000_

Particle szie (um)

1000_

 

 

Figure 2-1 Particle size mean and standard deviation for four corn grains

DF: dry fine, MF: high moisture fine, DC: dry coarse, MC: high moisture coarse.

32

2.3.2 Nutrient Digestibility

Apparent ruminal starch digestibility was higher for fine grinding and for high
moisture conservation (Table 2-3). Grinding corn finely increased ruminal starch
digestibility an average of 46% compared to coarsely ground corn diets and high
moisture conservation increased rurrrinal starch digestibility an average of 36% compared
to field dried corn diets. An interaction among treatments was observed for post-ruminal
apparent starch digestibility as a percentage of starch entering the duodenum. Apparent
digestibility of starch entering the duodenum was higher for high moisture coarsely
ground corn compared to with finely ground corn, but opposite effects were observed for
dry corn which had higher apparent digestibility of starch entering the duodenum for
finely ground compared to coarsely ground corn. Fine grinding increased apparent
digestibility of starch in the total tract from 93.4% to 96.8% (P < 0.01, Table 2-3).
Conservation method had no effect on apparent total tract starch digestibility.
Additionally, the increased rurrrinal starch digestibility with corn grain processing and
high moisture conservation agrees with a previous study with lactating cows (Knowlton
et al., 1996b). Grinding breaks floury and horny endosperm of corn kernels to release
starch granules thereby increasing rate of starch degradation. The ratio of starch
apparently digested in the rumen to that digested post ruminally was over 4-fold higher
for the finely ground high moisture corn, and 2—fold higher for the finely ground dry corn
diets compared with their respective coarse corn diets. There was a significant
interaction, which was due to the greater difference between finely and coarsely grinding
for the high moisture corn diets compared to dry corn treatment (Table 2-3).

Ruminal and total tract digestibilities of NDF and ADF were not affected by
treatment (Table 2-4). Fine grinding decreased post-ruminal NDF digestibility by 25%

compared to coarse corn diets, although the difference had no effect on total tract NDF

33

digestibility. This might have been due to increased substrate available for microbial
growth in the large intestine, resulting in increased NDF digestibility for coarse corn diets
compared with finely ground corn treatment. However, Grant and Mertens (1992)
reported that addition of starch decreased in vitro NDF digestibility because of decreased
rate of digestion and increased lag time by additional starch.

There were no treatment differences observed for apparent total tract DM or OM
digestibility in spite of large treatment differences for OM digestibility in the rumen
(Table 2-3). Apparent digestibility of OM in the rumen increased from 37.4% in dry com
diets to 46.1% for high moisture corn diets (P < 0.01). Apparent digestibility of OM in
the rumen increased from 37.3% for coarse corn diets to 46.1% for fine corn diets (P <
0.01). High moisture conservation and fine grinding increased the true ruminal
digestibility of OM, but a significant interaction was detected indicating that fine
grinding increased true OM digestibility to a greater extent for high moisture corn
correlated to dry corn. The amount of OM passage to duodenum and postruminal OM
digestibility, expressed as a percentage of OM intake were decreased 24.4% and 26.5%
lower, respectively, as high moisture corn compared to dry corn and finely ground corn
compared to coarsely ground corn. High moisture conservation and fine grinding also
decreased postruminal OM digestibility expressed as a percentage of OM entering the
duodenum, but a significant interaction indicated that the decrease was much greater for
cows fed high moisture corn diets. Greater postruminal OM digestibility compensated
for lower ruminal OM digestibility for dry and coarse treatments resulting in no effect of

treatment on whole tract OM digestibility.

34

2.3.3 Rumen Pool Size, Passage of Indigestible NDF and Starch, Ruminal pH and

Volatile Fatty Acids

There was no effect of treatment on ruminal pool size of liquid, DM, digesta
volume, digesta weight or digesta density (Table 2-5). However, significant interactions
of treatment were detected for pool sizes of NDF, indigestible NDF and starch, as well as
NDF and starch turnover time, indigestible NDF rate of passage, and rate of digestion of
potentially digestible NDF. Ruminal turnover time and pool size of starch increased for
coarsely ground corn for both conservation methods, but a significant interaction
indicated that the increase was much greater for dry corn. The increase in turnover time
and pool size was due to a slower rate of digestion. Field dry conservation decreased
starch rate of digestion an average of 38% lower compared with high moisture
conservation. Grinding corn coarsely decreased starch rate of digestion an average of
34% lower compared to finely ground corn diets. Cows fed high moisture fine corn diets
had fastest rate of digestion and lowest rate of passage compared with the other three
treatments. Rate of digestion was much lower for the dry coarse corn diet, probably
because of the lower surface area available for enzymatic attack and lower solubility of
endosperm proteins, reducing access of microbes to starch granules (Oke et al., 1991).

Ruminal turnover time and pool sizes of NDF and indigestible NDF increased for
coarsely ground corn that was field dried compared to finely ground dry corn, but
decreased for coarsely ground corn conserved as high moisture corn compared with
finely ground high moisture com. This might be due to decreased rate of passage of

INDF (outflux) for coarse dry corn compared with finely ground dry corn. Moreover,

35

coarse grinding increased rate of passage of IN DF (outflux) compared to fine grinding for
high moisture corn. Although there was no effect of treatment on rate of passage of
INDF (influx), the numerical differences were similar to the effects of treatment on rate
of passage of INDF (outflux). An interaction was observed for rate of digestion of
digestible NDF with a faster rate of digestion for fine dry corn compared to coarse dry
corn, but slower rate of digestion for fine high moisture corn compared with coarse high
moisture corn. There is no obvious explanation for this. Meanwhile, there was no effect
of diet on water passage calculated with this method.

High moisture conservation decreased daily mean pH in the rumen and increased
pH variance but had no effect on pH range, hours below pH 6.0 or 5.5, or area below pH
6.0 or 5.5 (Table 2-6). Furthermore, particle size processing had no effect on ruminal pH.
For finely ground corn diets, the assumed increase in fermentation acid production from
greater ruminal OM digestibility apparently was buffered adequately in the rumen to
prevent a decrease in ruminal pH. Fine grinding tended to decrease the ammonia N
concentration in the rumen an averaging 12.1% less than coarsely ground corn treatments
(P = 0.10, Table 2-6).

High moisture conservation increased total volatile fatty acids (VFA)
concentration in the rumen an average of 5% higher compared with dry corn diets (Table
2-6), which coresponded to a decreased of daily mean ruminal pH by 0.10 units. High
moisture conservation decreased the molar proportion of propionate of VFA an average
of 6.6% lower and increased the ratio of acetate to propionate an average of 9.1% higher
compared with dry corn treatments. The decreased in the proportion of propionate and

the increased in the ratio of acetate to propionate was larger for the finely ground corn as

36

indicated by significant interactions of treatments. An interaction was observed for
acetate as a percentage of VFA with a higher percentage of acetate for dry fine corn
compared to dry coarse corn and a lower percentage of acetate for high moisture fine
corn compared with high moisture coarse corn. There is no effect of fine grinding on
total VFA concentration and individual acid proportions. A significant interaction of
treatments was found for formate as a percentage of VFA with a greater percentage for
dry coarse corn compared with dry fine corn and a lower formate as a percentage of VFA
for high moisture coarse corn compared to high moisture fine corn. Lactate in the rumen

was not detected.

2.3.4 Intake and Feeding Behavior Data

Treatment differences were not detected for DMI, DMI as a percentage of BW, or
change in BW or BCS (Table 2-7). DMI as a percent of BW averaged 1.63% for
pregnant heifers. Although no effect of treatment was observed for DMI, dry corn
treatment resulted in an increase in the number of meals consumed per day (Table 2-8).
There was no effect of treatment on meal size or length, eating time or intermeal interval.
However, there was an interaction of treatment for eating rate with a faster eating rate for
fine dry corn compared to coarse dry corn and a slower eating rate for fine high moisture
corn compared to coarse high moisture corn. An interaction was observed for the number
of chews per meal and per day with a greater number of chews for coarse dry corn

compared to fine dry corn and fewer chews for coarse high moisture corn compared with

37

fine high moisture corn. The reasons for these two interactions are not apparent.
Chewing rate during eating tended (P = 0.07) to be lower for the high moisture corn
treatments compared to field dried corn treatments, which might be because of softer
kernel for high moisture corn. There was no effect of treatment on rumination activity,

total chewing activity or daily water intake.

2.3.5 Microbial N Production “and N Flow to the Duodenum

Intake of N averaged 194 g/d and was not affected by treatment (Table 2-9), but
the amount and proportion of total N, nonammonia nitrogen (NAN) and nonammonia
nonmicrobial nitrogen (N AN MN ) passed to the duodenum were significantly lower for
high moisture corn diets than dry corn diets (P < 0.05). Postruminal N digestibility (% of
intake) was an average of 9.4% lower for high moisture corn diets compared with dry
corn diets (P: 0.03). However, apparent total tract digestibility of N was not affected by
high moisture conservation. Fine grinding tended to decrease total tract N digestibility
and decreased passage of NANMN compared to coarsely ground corn treatment.
Additonally, there was no effect of fine grinding on passage of total N, NAN
(nonammonia nitrogen), microbial N and postruminal N digestibility. NANMN includes
by-pass protein, peptides, anrino acids from feed and endogenous protein. High moisture
conservation method and fineness of grinding reduced the amount and proportion of
passage of NANMN, and also there was an interaction observed because of a larger

decrease for fine grinding when cows fed high moisture corn diets, indicating that high

38

fermentation diets (high moisture corn) had more protein degraded in the rumen.
Although the amount of microbial N was not affected by treatment, the percentage of
microbial N in the NAN was higher for high moisture corn compared with dry corn and
finely ground corn compared to coarsely ground com. A significant interaction of
treatments indicated that the increase was much greater for high moisture corn diets.
Efficiency of microbial protein synthesis expressed as grams of microbial N per kilogram
of OM either apparently or truly digested in the rumen tended to decrease by high
moisture conservation method. McCarthy et a1 (1989) reported the amount of microbial
N passed to duodenum was not affected by quickly fermented barley compared to corn,
which agrees with this data that quickly fermented ground or high moisture corn had no
effect on the amount of microbial N passed to duodenum. High moisture conservation
decreased microbial efficiency an average of 16% (Table 2-9) but increased true ruminal
digestibility of OM an average of 15% higher (Table 2—3), which resulted in no effect of

high moisture conservation on total tract digestibility of OM.

2.4 CONCLUSIONS

High moisture conservation and fine grinding increased both apparent and true
ruminal OM and starch digestibility, but had no effect on total tract OM digestibility.
Total tract starch digestibility was reduced by fine grinding, only. The higher ruminal
starch digestibility for high moisture corn and finely ground corn was due to increased
rate of starch digestion. High moisture corn decreased mean daily ruminal pH and

increased variance in ruminal pH, and although decreased the daily number of meals

39

consumed, it had no effect on DMI. Additionally, high moisture conservation reduced
passage of total nitrogen to the duodenum and tended to decrease microbial protein
production per kg of OM fermented. There was no effect of treatment on ruminal or
total tract digestibility of NDF or ADF.

Although high moisture conservation method and fine grinding had similar
positive effects on ruminal digestibilities of starch and OM with negative effects on
postruminal digestibilities of OM and starch, only high moisture conservation method
decreased ruminal pH, microbial efficiency, and number of meals per day for pregnant
heifers. Fine grinding might be more advantageous than high moisture conservation to

increase ruminal starch digestibility of corn grain fed to heifers.

40

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48

 

 

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CHAPTER 3

EFFECTS OF F INENESS OF GRINDING AND CONSERVATION METHOD OF
CORN GRAIN ON RUMINAL AND WHOLE TRACT DIGESTIBILITY,
RUMINAL MICROBIAL PROTEIN PRODUCTION, FEEDING BEHAVIOR,
AND MILK YIELD OF PRIMIPAROUS HOLSTEIN COWS AFTER CALVING

ABSTRACT

The effects of fineness of grinding and conservation method of corn grain on
ruminal and whole tract digestibility, ruminal microbial protein production, feeding
behavior and milk yield of primiparous Holstein cows were examined. Eight ruminally
and duodenally fistulated Holstein cows (39 i 11 DIM) were utilized in a duplicated 4 x
4 Latin square design balanced for carryover effects with 21-d periods. Corn treatments
were dry corn, ground finely or coarsely and high moisture corn, ground finely or
coarsely prior to feeding. Diets contained 49% alfalfa silage and 38% com grain. High
moisture conservation and fine grinding increased rate of starch digestion in the rumen
which resulted in increased ruminal and whole tract digestibility. However, only high
moisture corn decreased mean ruminal pH and increased variance in ruminal pH. High
moisture conservation decreased ruminal digestibility of NDF and ADF but increased
NDF and ADF digestion postruminally resulting in reduced whole tract digestibility for
ADF only. High moisture conservation decreased the daily number of meals consumed
and tended to increase meal size with no effect of treatment on DMI. Fine grinding
decreased rumen pool sizes of liquid, DM, NDF, indigestible NDF and starch. High
moisture conservation and fine grinding had greater gain (or less loss) of BW per day, but
had no effect on BCS. Fine grinding decreased microbial N efficiency and microbial N
yield was not affected by treatment. Fine grinding seems more beneficial to maxmize

FCM production than high moisture conservation for early lactation dairy cows.

50

51

3.1 INTRODUCTION

Corn is the most important source of starch for dairy cows in the eastern and
midwestem US. Starch utilization by dairy cattle varies widely by processing and
physiological status of animals (Nocek and Tamminga, 1991). These differences might
be due to effects of processing, corn genetics, maturity at harvest and conservation
method, animal factors such as level of intake, body size, pregnancy and many other
factors. Corn grain is harvested at high moisture content (ZS-35% moisture) and ensiled
or field dried to approximately 15% moisture. Physical processing of whole grain such
as grinding and rolling increased total tract starch digestibility (Theurer et al., 1986). Site
of starch digestion, which is also affected by conservation method and processing (Nocek
and Tamminga, 1991), can affect animal performance such as altering energy available
for microbial growth, forms of energy absorbed, efficiency of DE utilization, ruminal
fermentation and production, meal patterns and DM intake. Level of intake affects
residence time in the rumen and might affect site of starch digestion. Stanley et al.
(1993) reported that indigestible ADF passage increased across the prepartum period
(before calving 61 days to before calving 6 days) and peaked just before calving.
Postpartum indigestible ADF passage was slower than 6 days before calving but still
greater than 61 days before calving. Colucci et al. (1982) also found that retention time
of digesta was shorter in the gastrointestinal tract with increasing intake for Holstein
dairy cows. Nocek and Tamminga (1991) reported that maximum milk production was

associated with maximum intake of both ruminally and intestinally digested starch.

52

Although there is research in the literature which compares site of starch digestion across
grain sources such as barley, corn and sorghum (Oliveira, 1993; Grings, 1992; Knowlton
et al., 1996b; Yang, 1997) and processing such as grinding and steam-flaking (Knowlton
et al., 1996a; Plascencia, 1997), there is no published research on the effects of
processing high moisture corn and dry corn from the same source for early lactation dairy
cattle. The objective of this experiment was to evaluate the effects of processing (fine or
coarse) and conservation method (high moisture ensiled or field dry) of corn on
performance, ruminal and whole tract digestibility, ruminal microbial protein production

and feeding behavior of early lactation Holstein cows.

3.2 MATERIALS AND METHODS
3.2.1 Corn Grain and Alfalfa Silage Harvest and Preservation

The same corn grain and alfalfa silage were used for this experiment as were used
in the experiment described in Chapter 2. High moisture corn grain was harvested at
67.2% DM from one half of a 7-acre loamy sand field in Michigan State University
campus on October 5, 1994. Dry corn was harvested from the remaining 7-acre field at
83% DM on December 13, 1994 and artificially dried to 86% DM. High moisture corn
was ensiled in a silage bag (UpNorth Plastics Inc., Cottage Grove, MN) and ground
finely or coarsely prior to feeding. Corn population in the field was 28,000 plants per
acre. Dry corn was mixed and divided in half. Half of the dry corn was finely ground,

and half was coarsely ground and was stored in sealed bags in a trailer. First -cutting

53

alfalfa was ensiled in a 2.5-m diameter silage bags (50 tons; Ag Bagger®, Ag Bag Corp.,

Blair, NE) to minimize variation and reduce spoilage at feed out.

3.2.1 Experimental Design and Data Collection

The same cows were used for this experiment as were used in the experiment
described in Chapter 2. Eight ruminally and duodenally cannulated early lactation
Holstein primiparous cows (29 months old, 39 :t 11 DIM; X :1: SD) were utilized in a
duplicated 4 x 4 Latin square design. Cows were assigned to square by expected calving
date and squares were balanced for carryover effects so that each treatment followed the
other treatment an equal number of times. Within a square, each cow was assigned
randomly to one of four treatment combinations. Cows were arranged in the same order
as before calving. A 2 x 2 factorial arrangement of treatments was used in each square.
Dietary treatments were com particle size (fine or coarse) and corn conservation method
(high moisture or field dried). Experimental treatment periods were 21—d, including 10
days for diet adjustment followed by 11 days of data collection. The animal care protocol
was approved by All-University Committee on Animal Use and Care of Michigan State
University. The approved animal use form number was 06/95-088-00. Eight cows were
ruminally and duodenally cannulated at 21 months old. Duodenal cannula surgery was as
described in Chapter 2.

Diets consisted of alfalfa silage, dry or high moisture corn, soybean meal,
minerals and vitamins for each treatment period (Table 3-1 and 3-2; values represent
mean ingredient and nutrient composition throughout the experiment). The diets were
balanced to 27% NDF, 41% starch and 16.5% crude protein. Minerals and vitamins were
supplemented to meet requirements (NRC, 1989). High moisture corn was ground prior

to feeding through a mill without (coarse) or with (fine) a 1 cm screen (Mighty Mac

54

Chipper Shedder, Mackissic Inc., Parker Ford, PA). Five alfalfa silage samples from
different sites of the silage bag were analyzed for DM, NDF and crude protein, and the
average values were used for diet formulation for the experiment.

Alfalfa silage, corn treatments, soybean meal and mineral-vitamin mix were
weighed in individual polyethylene mangers for each cow and mixed by hand. Cows
were fed once daily at 1200 h at 110% of expected intake. Ration offered was recorded
for each cow daily, and weights of orts were recorded prior to each feeding. Dry matter
intake was calculated as the average daily DMI from d 12 to d 21 of each period.

Dietary ingredients (0.5 kg) and individual cow orts ( 12.5% of orts as wet weight basis)
were collected daily during the collection period, frozen and composited within each
collection period. Alfalfa silage was analyzed weekly for DM content during the
experiment and diets were re-balanced accordingly.

Cows were milked twice daily in their stalls at 0600 and 1700 h. Milk weight was
recorded for each cow every milking. Milk samples were taken at each milking on d 11,
12, 13, and 14 of each period and analyzed for fat, protein, lactose, and SCC with
infrared spectroscopy by Michigan DHIA (East Lansing). Fat corrected milk wase
calculated assuming 0.7% ash (NRC, 1989).

Cows were housed in tie stalls bedded with chopped newspaper and were exposed
to continuous light throughout the experiment. Cows were allowed to exercise for
approximately 30 min in a dry lot following milking except during collection of
behavioral data. Rumen empty body weights were measured on the last 2 days of the
each period and on 2 days preceding the first period. Body condition score was evaluated
to the quarter point on a five-point scale (1 = thin to 5 = fat) on d 20 of each period and 2
days prior to beginning the first period.

Duodenal flow was estimated using a double marker system (Faichney, 1980)
with Cr-mordanted wheat straw NDF as a particulate phase marker and Co—EDTA as a

liquid phase marker. Chromium-mordanted NDF and Co-EDTA were prepared as

55

described by Udén et al. (1980). Chromium mordanted wheat straw was ground through
a Wiley mill (2 mm screen; Arthur H. Thomas, Philadelphia, PA) and was provided at
approximately 0.07% of DM intake (30 g/d/cow). Chromium content of the fiber was
approximately 5% of DM resulting in a Cr intake of 1.6 g/d/cow. Gelatin capsules (1.5
Oz, Tropac Inc., Airfield, NJ) filled with chromium mordanted wheat straw were dosed
into the rumen 2 times/d from d 10 until (1 18 at 0730 and 1930 h. Co-EDTA was dosed
at approximately 0.04% of DM intake (0.43 g Cold, 0.91 Col 1 solution) by semi-
continuous infusion into the rumen by a peristaltic pump (FPUlOl, OmegaflexTM
peristaltic pump, Omega Engineering Inc., Stamford, CT). Pumps had a flow rate of 3.3
mllmin but were turned on intermittently for 1 minute out of every 10 minutes to achieve
an average flow rate of 0.33 mllmin over the 9 days (475 ml Co-EDTA solution/d, 0.43 g
Cold). A priming dose of each marker was given on d 9 of the 21-d period at 3 times the
daily dose.

For determination of ruminal and total tract nutrient digestibility, duodenal
digesta and feces were sampled every three hours beginning at 1200 h on d 15 and
continuing until 1100 h on d 18. The sampling time was adjusted ahead 1 h daily so that
24 samples representing each hour in a day would be collected. Two separate samples of
duodenal digesta were collected (400 ml and 75 ml). The 400 ml samples were frozen
immediately at -20°C until analysis and the 75 ml samples were preserved with 5 ml of 6
N HCl and frozen for later analysis of NH3. Fecal samples (400 g) were collected and
frozen immediately at —20°C until analysis.

Samples of ruminal fluid were collected every 3 h of a 24-h period starting at
1200 h on d 19 to account for diurnal effects on concentration of metabolites. Samples of
rumen fluid from five sites in the rumen were mixed and filtered through 4 layers of
cheesecloth to remove particulate matter. Three 75 ml subsamples of ruminal fluid were
taken from this sample for each time period. One was preserved with 5 ml of 6 N HCl
for NH3 analysis, one was preserved with 5 ml of 20% NaOH for VFA and lactate

56

analysis and one was taken for purine analysis. All subsamples were frozen (at -20°C)
immediately following collection.

Ruminal digesta was evacuated manually from each cow at 0630 h on d 20 (5.5 h
prefeeding) and 1730 h on d 21 of the experiment period (5.5 h postfeeding). A 10%
aliquot of digesta was separated during evacuation for ease of subsampling and
measuring liquid and solid phases. This aliquot was weighed, mixed by hand and
strained through four layers of cheesecloth to separate it into solid and liquid phases.
Solid phase samples were weighed and subsampled a 400 g solid sample was frozen for
determination of DM and nutrient composition. Three separate subsamples (400 ml, 75
ml, and 75 ml) of rumen liquid were collected. The 400 ml samples were frozen (-20°C)
immediately for DM, N DF, ADF, acid detergent sulfuric acid-lignin, starch and
indigestible NDF analysis, while the 75 ml subsample of ruminal fluid was preserved
with 5 ml of 6 N HCl and frozen (-20°C) for later NH3 analysis, and 75 ml subsample of
ruminal fluid was preserved with 5 ml of 20% NaOH, and frozen (-20°C) for later VFA
and lactate analysis. Rumen total digesta weight and volume were measured at each
evacuation.

Feed disappearance, chewing behavior and ruminal pH were measured
continuously for 4 days from d 11 to d 14 of each experiment period using a
computerized data acquisition system described by Dado and Allen (1993). Data were
written to files every 5 seconds for each variable, for each cow. Chewing monitors were
fitted to cows 1 (1 prior to collection to allow for cow adaptation, and remained in place
for the throughout the behavior collection period. No other cows were present in the barn
during the study. Load cells for determination of feed consumption were calibrated prior
to each collection period. Electrodes for pH determination (described by Knowlton et al.,
1996a) were calibrated daily immediately before feeding. Electrodes generally held their
calibration within 0.05 pH units. Electrodes outside this range were recalibrated or

replaced. Occasional problems with jaw movement detectors, load cells, and pH

57

electrodes were recorded, and feeding behavior data from that cow for the entire day was
removed from the data file prior to analysis. Water intake was recorded daily from water

meters at each stall (Omega MKH 4465 5/8, Omega Engineering Inc., Stamford, CT).

3.2.3 Analysis of Samples

Samples of each corn treatment were taken daily from d 12 until (1 21 of each
period for particle size analysis. A representative sample of each corn treatment was dry
sieved through 8 sieves (Sieve apertures: 4750, 2360, 1180, 600, 300, 150, 75 um and
bottom pan), using a sieve shaker (Model RX-86, W.S. Tyler Inc., Gastonia, NC) for
approximately 15 min until the bottom pan weight was constant (ASAE, 1968). Mean
particle size of corn was calculated and variance was determined by fitting the data to a
gamma distribution (Allen et al., 1983).

Diet ingredient and orts samples were analyzed for DM, ash, NDF, ADF, acid
detergent sulfuric acid-lignin, starch, CP and indigestible NDF. The samples were dried
in a forced air oven at 55°C for 72 hours and analde for DM content. All samples were
ground with a Wiley mill (l-mm screen Arthur H. Thomas, Philadelphia, PA). Ash was
determined following sample ignition at 500°C for 5 hours. Samples were analyzed
sequentially for NDF (procedure A, Van Soest et al., 1991), ADF (AOAC, 1984) and
acid detergent sulfuric acid-lignin (Goering and Van Soest, 1970). Crude protein was
analyzed according to Hach et al. (1987). Indigestible NDF was estimated as N DF
content of sample following in vitro fermentation in buffered rumen media for 120 hours
(Goering and Van Soest, 1970). Starch was analyzed by a one-stage enzymatic method
of glucoamylase (Diazyme L-200, Miles, Inc., Elkhart, IN) with a NaOH gelatinization
step (O'Neil et al., 1993). Following gelatiniztion the sample was centrifuged at 26,000 x

g for 20 min, and concentration of glucose in the supernatant was analyzed by HPLC

58

using an Aminex fast carbohydrate column (100 x 7.8 mm, catalog number 125-0105;
Bio-Rad Laboratories, Richmond, CA). Column temperature was 85°C, and the solvent
was degassed deionized distilled H20 with a flow rate of 0.6 mllmin. Detection was by
refractive index (Waters 410, Millipore Corp., Milford, MA). Concentration of all
nutrients except DM was expressed as a percentage of the DM determined from forced
air oven drying at 105°C.

Daily frozen duodenal samples (n = 8) were chopped and subsampled on an
equivalent wet weight basis, lyophilized and ground with a mortar and pestle. Duodenal
digesta were analyzed for DM, NDF, ADF, acid detergent sulfuric acid-lignin, ash, CP,
starch and indigestible NDF as described previously. Ruminal samples for purine
analysis were measured as described later. Fecal samples were thawed, subsampled and
composited on an equivalent wet weight basis for each cow per day and dried in a forced
air oven at 55°C for 72 hours and analyzed for DM content. Fecal samples were ground
with a Wiley mill (1 mm screen) and analyzed for DM, NDF, ADF, acid detergent
sulfuric acid-lignin, ash, CP, starch and indigestible NDF as described previously.

For analysis of flow markers, daily frozen duodenal samples were chopped into
snow using a food processor (84142 Food cutter, Hobart Manufacturing Co., Troy, OH),
subsampled on an equal wet weight, thawed, and partitioned into liquid and solid phases
by centrifuge (RCSC, Sorvall Instrument, E. I. du Pont de Memours & Co., Inc., Hoffman
Estates, IL) at 500 x g for 10 min at 4°C. Each phase of sample was dried in a 100°C
forced air oven for later chromium and cobalt analysis. Chromium and cobalt
concentration of feeds, duodenal liquid phase, duodenal solid phase and feces were
determined by atomic absorption spectrometry according to the manufacturers’
recommendations (Smith-Hieftje 4000, Thermo J arrell Ash Co., Franklin, MA) following
digestion using phosphoric acid-manganese sulfate solution (Williams et al., 1962).

Duodenal digesta flow was calculated as described by Ar'rnentano and Russell (1985).

59

Ruminal samples for purine analysis were prepared following the procedure of
Overton et al. (1995). Purines were measured (Zinn and Owens, 1986), modified by
Overton et al. (1995), as a bacterial marker. Microbial protein production was calculated
by dividing purine and nitrogen ratio of rumen microbes by purine percentage of
duodenal DM per day (Zinn and Owens, 1986).

Duodenal and ruminal samples for NH3 analysis were thawed and composited on
an equivalent volume basis for each cow per day. Ammonia was measured using the
general procedure of McCullough (1967), modified by Broderick and Kang (1980).
Absorbance was determined using a spectrophotometer (1 cm length path, DU-64
Spectrophotometer, Beckman Instruments, Inc., Fullerton, CA).

Ruminal fluid samples were thawed and composited on an equivalent volume
basis for each cow per day for VFA and lactate analysis. Composite ruminal fluid
samples were centrifuged at 26,000 x g for 30 min. Concentrations of VFA and lactate of
supernatant were determined by HPLC as described by Dado and Allen (1995).

Ruminal solid and liquid subsamples from the evacuated rumen digesta were
dried in a 100°C forced air oven, and analyzed for DM, NDF, ADF, acid detergent
sulfuric acid—lignin, ash, starch, and indigestible NDF as described previously. Rumen
liquid subsamples were analyzed for NH3 and VFA as described previously. Rumen pool
sizes (kg) of DM, liquid, NDF, starch and indigestible NDF were calculated by
multiplying the concentrations of each by the rumen digesta weight (kg).

Ruminal starch and NDF turnover time were determined by dividing the pool size
of starch or NDF by hourly starch or NDF intake. Rates of starch, indigestible NDF
(INDF) and potentially digestible NDF (DNDF) passage from the rumen were
determined by dividing starch or INDF or DNDF daily out flow to duodenum
(OUTFLUX, dual markers system) by the pool size of starch, or indigestible NDF or
digestible NDF. Rate of digestion of starch or DNDF was calculated by the reciprocal of

the turnover time (equal to rate of digestion and rate of passage) minus rate of passage of

6O

starch or DNDF. Rate of INDF passage from the rumen (INFLUX, internal marker
system) was determined by the method of Dado and Allen (1995) by dividing the rumen
pool size of INDF into hourly intake of INDF. Estimated rate of water passage from the
rumen was calculated as duodenal flux of water divided by the pool size of water in the
rumen. This calculation assumes no net water absorption prior to the duodenum and that
Co—EDTA passes at the same rate as water.

Mean ruminal pH, hours below pH 5 .5 and 6.0, and the areas of the pH X time
curve under pH 5.5 and 6.0 (Mackie and Gilchrist, 1979) were calculated. The area of
the pH x time curve below a critical pH gives a weighted average of the deviation from
this pH which is more meaningful to optimal ruminal pH (Allen and Beede, 1996).

For feeding behavior data analysis, means were calculated for number of meals
per day, meal size (kg per meal), minutes between meals, eating time in minutes per meal
and per day, eating chews per meal and per day, eating chew rate (chews per minute),
number of ruminating bouts per day, minutes between ruminating bouts, ruminating time
in minutes per bout and per day, ruminating chews per bout and per day, ruminating
chew rate and total chewing per day (eating chews and ruminating chews) using a
program written in SAS programming language (Version 6.1, SAS Institute Inc., Cary,
NC).

61

3.2.4 Statistical Analysis

Data were analyzed using the fit model procedure of JMP (Version 3.2, SAS
Institute Inc., Cary, NC) as duplicated (n = 2) 4 x 4 Latin squares using the following
model:

Yijkl = u + Si + ij + Pk + Tl + STi1 + SPik + Eijkl
where

p = overall mean,

Si = random effect of square (i = 1 to 2),

C50) = random effect of cow within square 0 = 1 to 4),

Pk = random effect of period (k = 1 to 4),

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

STil = interaction of square and treatment,

SPik = interaction of square and period, and

Eijkl = residual, assumed to be normally distributed.

A reduced model without square x treatment or square x period interactions was
used when these effects were not significant (P > 0.10). Preplanned orthogonal contrasts
were used to determine significance of the main treatment effects of conservation

method, fineness of grinding and their interaction. Main effects and interactions were

declared significant at P < 0.05, and P < 0.10, respectively.

62

3.3 RESULTS AND DISCUSSION

3.3.1 Composition of Diets and Particle Size

Chemical composition of the corn treatments appears in Table 3-1. Except for the
expected effect of conservation method on DM content, only slight differences in
composition were detected among treatments. Dry corn had an average of 1.5 units more
NDF and an average of 0.14 units more lignin than high moisture corn. Indigestible NDF
was higher for dry corn but the difference was greater for coarse corn than for finely
ground corn. Starch content in the corn was higher for finely ground compared to
coarsely ground for high moisture corn, but it was lower for finely ground in relation to
coarsely ground for dry corn.

Diets contained 49% alfalfa silage, 38% com grain and 9.7% soybean meal (Table
3-2). Dry matter of dry corn and high moisture diets were 52.1% and 48.2%. Diets
containing high moisture corn had lower NDF, ADF and acid detergent sulfuric acid-
lignin content compared to dry corn diets. Indigestible NDF was also lower for high
moisture corn diet but the differences greater for coarsely ground than for finely ground
corn diets. Starch content of high moisture corn diet was higher for finely ground corn
diet related to coarsely ground corn diet, but starch content of dry corn diet was lower for
coarsely ground corn diet compared to finely ground corn diet. These differences in
chemical composition, although significant, were slight.

Mean particle size of dry fine corn, dry coarse corn, high moisture fine corn and
high moisture coarse corn was 850 :t 124 pm, 4360 :1: 250 mm, 2058 :t 293 [.tm, and 5739
i 286 m, respectively. Field dried conservation and fine grinding decreased particle

size of corn grain (P < 0.01, Table 3-1). Because moisture contents for field dried

63

conservation and high moisture conservation were different, they were processed with
different mills. There were similar reductions in particle size by fine grinding dry corn

and high moisture corn (Figure 3-1).

Particle size (um)

 

 

Figure 3-1 Particle size mean and standard deviation for four corn grains

DF: dry fine, MF: high moisture fine, DC: dry coarse, MC: high moisture coarse.

3.3.2 Nutrient Digestibility

Apparent ruminal starch digestibility was higher for fine grinding and for high
moisture conservation (Table 3-3). Grinding corn finely increased ruminal starch
digestibility an average of 65% compared to coarsely ground corn diets. High moisture
conservation increased ruminal starch digestibility an average of 24% higher compared to
dry corn diets. High moisture conservation and fine grinding decreased post-ruminal
apparent starch digestibility as a percentage of starch intake. However, only high
moisture conservation increased post-ruminal starch digestibility as a percentage of starch
entering the duodenum. Fine grinding increased and high moisture conservation tended
(P = 0.07) to increase apparent digestibility of starch in the total tract by 4.2% and 1.2%
higher, respectively. The increased total tract starch digestibility with fine grinding and
high moisture conservation, agrees with a previous study by Knowlton et al. (1996b). In
the experiment conducted before calving (results reported in Chapter 2), high moisture
conservation had no effect on starch apparently digested in the total gastrointestinal tract.
In this experiment, the ratio of starch apparently digested in the rumen to that digested
post ruminally was over 3-fold higher for the finely ground corn compared to coarsely
ground corn. The significant interaction was due to the greater difference between fine
and coarse grinding for the high moisture corn diets compared with the dry corn diets
(Table 3-3).

High moisture conservation resulted in lower NDF and ADF intake for finely

ground corn but not for coarsely ground corn (Table 3-4). High moisture conservation

65

also decreased the amount of NDF and ADF digested in the rumen and the ruminal
digestibility of NDF and ADF but the reduction was greater for finely ground corn. Post-
ruminal digestion of NDF was higher for high moisture corn than dry corn as amount per
day, digestibility as a percentage of NDF intake, or as a percentage of NDF entering the
duodenum, but the difference was greater for the finely ground treatment. The increased
postruminal digestion of NDF for the high moisture corn diet compensated for the
decreased ruminal NDF digestibility, resulting in no effect of treatment on total tract
NDF digestibility. Fine grinding resulted in a greater amount of ADF digested post-
ruminally, and both high moisture conservation and fine grinding increased postruminal
ADF digestibility as a percentage of ADF intake but not as a percentage of ADF entering
the duodenum. There was a trend towards reduced total tract ADF digestibility for high
moisture conservation and for fine grinding. The reduction in ruminal NDF and ADF
digestibility for the high moisture treatments compared to a reduction in ruminal pH for
these treatments (Table 3-6). Increased digestibility of starch has been reported to
decrease NDF digestion by decreasing rate of digestion and increasing lag time (Grant
and Mertens, 1992).

High moisture conservation and fine grinding increased the apparent total tract
digestibility of DM (P < 0.05, Table 3-3), by 0.9 units and 1.3 units, respectively. The
apparent total tract digestibility of OM was higher for the high moisture and finely
ground corn treatments averaging 1.3% and 1.7%, respectively (Table 3-3). Apparent
OM digestibility in the rumen increased an average of 27.8% higher for finely ground
corn compared to coarsely ground corn and an average of 9.2% higher for high moisture

corn treatment compared with to dry corn diet. The proportion of OM truly digested in

66

the rumen also increased with high moisture conservation or fine grinding an average of
5.8% or 16.9% higher, respectively, con totalto dry corn diet or coarsely ground corn
diet. High moisture conservation and fine grinding increased whole tract OM
digestibility, which differed from the experiment conducted before calving in which there
was no effect of treatment on total tract OM digestibility. The amount of OM passage to
the duodenum, expressed as a percentage of OM intake decreased as high moisture corn
compared to dry corn and finely ground corn compared to coarsely ground corn.
Postruminal OM digestibility decreased an average of 40% lower by finely ground corn
compared to coarsely ground corn. However, postruminal OM digestibility was not
affected by high moisture conservation, which differed from the experiment conducted
before calving in which there was decreased postruminal OM digestibility by high

moisture conservation.

3.3.3 Rumen Pool Size, Passage of Indigestible NDF and Starch, Ruminal pH and

Volatile Fatty Acids

Fine grinding decreased rumen digesta volume and weight and decreased rumen
pool sizes of liquid, DM, NDF and indigestible N DF (Table 3-5), which differed from the
experiment conducted before calving. There was no effect of fine grinding on rumen
digesta volume and weight or rumen pool sizes of liquid, DM, NDF and indiges VFAa
NDF for before calving. However, significant interactions of treatment were observed

for rumen pool sizes of NDF and indigestible NDF, with larger rumen pool sizes of NDF

67

and indigestible NDF for coarse dry corn compared to fine dry corn, smaller rumen pool
sizes of NDF and indigestible NDF for coarse high moisture corn compared with fine
high moisture corn for the experiment conducted before calving. Conservation method
had no effect on rumen digesta volume and weight or rumen pool sizes of liquid, DM,
NDF, and indigestible NDF. There was no effect of treatment on density of digesta in the
rumen. High moisture conservation and fine grinding increased rate of starch digestion
in the rumen by an average of 63.8% and 138.4% higher, respectively, resulting in
deceased ruminal turnover time and rumen pool size for starch for both treatments. The
higher rate of digestion might be due to increased surface area available for enzymatic
attack for the finely ground corn and increased solubility of endosperm protein increasing
access of microbes to starch granules for the high moisture corn (Oke, et al., 1991).
Finely ground corn increased rate of passage of IN DF from the rumen calculated with
both the INFLUX and OUTFLUX methods. In addition, fine grinding increased rate of
digestion of potentially digestible NDF, with a greater increase for dry corn compared to
high moisture corn. The increased rate of NDF digestion and passage resulted in
decreased turnover time of NDF in the rumen for the fine corn treatments with a greater
decrease for the dry corn than high moisture corn treatment and a decrease in NDF pool
size for the finely ground treatments. There was no effect of treatments on water passage
calculated with this method.

High moisture conservation decreased daily mean pH, increased pH variance and
increased hours below pH 6.0 or 5.5 and area below pH 6.0 or 5.5 (Table 3-6). Fine
grinding had no effect on ruminal pH but increased pH variance compared to coarsely

ground corn. The assumed increase in fermentation acid production from greater ruminal

68

OM digestibility for the finely ground corn diets apparently was buffered adequately in
the rumen to prevent a decrease in ruminal pH. This is similar to the effect by high
moisture conservation observed in the experiment conducted before calving (Table 2-6).
Fine grinding decreased the concentration of ammonia N in the rumen an average of
12.4% lower compared with coarsely ground corn.

High moisture conservation tended to decrease acetate as a percentage of VFA
averaging 3.6% compared to dry corn (P = 0.11, Table 3-6). High moisture conservation
increased valerate as a percentage of VFA and decreased isovalerate as a percentage of
VFA. Although there was no effect of treatment on total VFA, the numerical differences
were similar to the effects of treatment on ruminal digestibility of OM and starch, with a
greater value for fine corn replaced coarse corn and a higher for high moisture coarse
corn compared to dry coarse corn treatment. Fine grinding decreased isovalerate as a
percentage of VFA by an average of 10.8% lower. High moisture conservation and fine

grinding had no effect on lactate concentration in the rumen.

3.3.4 Intake and Feeding Behavior Data

High moisture conservation and fine grinding resulted in greater gain (or less loss)
of BW per day (Table 3-7), but only fine grinding increased body weight of early
lactation dairy cows. Conservation method and fine grinding had no effect on daily DMI
or DMI as a percentage of BW, which agrees with the experiment conducted before

calving and the study by Knowlton et al (1996a). DMI as a percentage of BW averaged

69

3.35% for early lactation dairy cows. Although no effect of treatment was observed for
DMI, high moisture treatment resulted in fewer meals per day (P = 0.01, Table 3-8). The
animals consumed approximately 10.2 and 11.2 meals per day for high moisture corn and
dry corn, respectively. High moisture corn tended to increase meal size (P = 0.08) but
did not affect DMI. Eating rate was faster for the high moisture treatment averaging 21%
than the dry corn diets. Eating time per day was shorter for high moisture corn than dry
corn, which might have increased ruminal pH variance. A treatment interaction was
observed for the number of chews per meal with greater number of chews per meal for
high moisture fine corn in relation to dry fine corn but fewer number of chews per meal
for high moisture coarse corn compared to dry coarse corn. Fine grinding tended to
increase the number of chews per day (P = 0.10) compared to coarse corn, but the
difference was greater for dry corn. There was no effect of treatment on rumination
activity or total chewing activity. Water intake increased 7.7% for finely ground corn and
4.3% for dry corn treatment (Table 3-8), which agrees with a previous study (Knowlton
et al., 1996a). Conservation method might have a greater effect on feeding behavior and

ruminal pH than processing for corn grain.

3.3.5 Milk Production and Composition

Finely ground corn increased 4% fat correct milk (FCM) yield per day 1.4 kg
compared to coarse corn (P = 0.04, Table 3-7), and dry corn tended to increase 4% FCM

(P = 0.10, Table 3-7). Fine grinding increased milk protein 0.07 units compared to

70

coarse corn. Solids not fat as a percentage or as daily yield increased for the finely
ground corn diets. Fine grinding and conservation method had no effect on percentage

and yield of milk fat and milk lactose.

3.3.6 Microbial N Production and N Flow to the Duodenum

A significant interaction of treatment was detected for N intake which was higher
for dry fine corn compared with dry coarse corn, and lower N intake for high moisture
fine corn compared to high moisture coarse corn (Table 3-9).

Efficiency of microbial protein production per kg of OM apparently or truly
fermented was lower for finely ground corn than coarsely ground corn averaging 22% or
19% lower, respectively. High moisture treatment tended to decrease efficiency of
microbial protein production per kg of OM apparently fermented (P = 0.10, Table 3-9).

Compared to literature values for lactating cowsN intake and N passage to the
duodenum seem low (Clark et al., 1992). However, this might be because the cows used
in this experiment were primiparous. High moisture conservation and fine grinding had
no effect on the amount and proportion of total N, NAN, NAMN and microbial N passed
to the duodenum. However, significant interactions of treatments were observed with
greater total N and NAN passage to the duodenum as a percentage of N intake for dry
coarse corn compared to dry fine corn, and lower total N and NAN passed to the
duodenum as a percentage of N intake for high moisture coarse corn compared with high

moisture fine corn.

71

Conservation method and fineness grinding had no effect on the amount of
postruminal N flow per day, but high moisture conservation increased postruminal N
digestibility as a percentage of N passage to the duodenum an averaging of 4.5% higher.
Postruminal N digestibility as a percent of N intake increased with fine grinding for high
moisture corn and decreased with fine grinding for corn. High moisture conservation
increased post-ruminal digestibility of N as a percentage of N entering the duodenum
which resulted in increased apparent total tract digestibility of N (P < 0.01). There was
an interaction of treatment for the amount of total tract N disappearance per day with
higher N digested in the total tract for dry fine corn compared with dry coarse corn, but
lower N digested in the total tract for high moisture fine corn compared to high moisture

coarse corn was detected (P = 0.06).

3.4 CONCLUSIONS

Fine grinding increased ruminal and total tract starch digestibility as well as OM
digestibility to a greater extent than high moisture conservation and had no effect on
ruminal pH. Fine grinding also resulted in a greater gain (or less loss) of BW per day,
increased 4% fat-correct milk yield, and increased milk protein content. Although high
moisture conservation decreased the daily number of meals consumed and tended to
increase meal size, it had no effect on DMI. Fine grinding might be more beneficial to

increase ruminal starch digestion for lactating cows than high moisture conservation.

72

TABLES

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CHAPTER 4

FINAL DISCUSSION AND CONCLUSIONS

Experiments were conducted both before and after calving because DMI might
affect the relative rates of passage, thereby affecting the digestibility of treatments.
Stanley et al. (1993) reported that indigestible ADF passage increased across the
prepartum period (before calving 61 days to before calving 6 days) and peaked just
before calving. Postpartum indigestible ADF passage was slower than 6 days before
calving but still was greater than 61 days before calving. Although differences were
found in ruminal capacity, DMI, and indigestible ADF passage rate, there were no effects
of period on whole tract DM digestibility in the two studies in this thesis. Faichney et al.
(1988) observed a decreased ruminal retention time, and retention of digesta in the small
intestine increased just before parturition. In addition, Colucci et a1. (1982) found that
retention time of digesta was shorter in the gastrointestinal tract with increasing intake of
Holstein dairy cows.

In this study, diet differences between the experiment conducted before (4 months
before calving) and after calving (1.5 months after calving) were forage percentage of the
diet, NDF, protein and starch percent of the diets. The forage percentages in the diets for
experiments conducted before and after calving were 62.2% and 48.7%, respectively, and
were due to the higher energy and protein requirements for the cows after calving. NDF
percentage of the diets was higher for the experiment conducted before calving in
comparison to the experiment conducted after calving (31% vs. 27%), and starch

percentage in the diets was lower before calving (38% vs. 41%).

82

83

DMI was almost twice as high for early lactation Holstein dairy cows compared
with the pregnant heifers (14.9 kg/d vs. 7.7 kg/d). Rumen digesta weight and volume for
early lactation cows were 1.42 fold higher than the pregnant heifers (63.2 kg vs. 44.4 kg,
and 78.4 1 vs. 52.2 1). Starch passage in the rumen was similar for both experiments
conducted before and after calving, averaging 13%lh and 12%/h, respectively.
Indigestible NDF passage was similar for both experiments averaging 2.2 %/h and 2.3
%fh, respectively. Rate of passage of potentially digestible NDF was also similar for the
experiment conducted before and after calving (2.1%/h vs. 2.3%/h). Water passage was
slightly higher for the experiment conducted after calving compared to the experiment
conducted before calving (8%lh vs. 5%lh). The relative rates of passage were not as high
as expected for the early lactation experiment compared to the experiment with pregnant
heifers, possibly due to increased passage rate from fetal pressure in the rumen.

Faster rate of starch digestion and shorter retention time of starch in the rumen for
the high moisture and finely ground treatments were found in both experiments.
However, high moisture conservation reduced starch passage rate for the experiment
conducted before calving only. High moisture conservation and fine grinding increased
both apparent and true ruminal digestibility of OM and ruminal digestibility of starch
digestion for both experiments (Figure 4-1 and Figure 4-3). The higher ruminal starch
digestibility was due to faster starch digestion rate. The higher rate of digestion might be
due to increased surface area available for enzymatic attack for the finely ground corn
and increased solubility of endosperm protein increasing access of microbes to starch
granule for the high moisture corn (Oke, etal., 1991). High moisture conservation
decreased ruminal NDF digestibility only for early lactation dairy cows and a significant
interaction of treatment was observed indicating that the reduction was much greater for
the finely ground corn diets. This might be because high moisture conservation
decreased ruminal digestibility of NDF by increasing rate of passage of indigestible NDF
(OUTFLUX). Grant and Mertens (1992) reported that additional starch decreased in

84

vitro NDF digestibility due to a decreased rate of digestion and increased lag time, and
some rumen microbes had greater preferences and affinities for some carbohydrates
(glucose, maltose, and surcose) than others (xylose and cellobiose). Fine grinding had no
effect on ruminal NDF digestibility for both experiments.

Postruminal starch digestibility as a percent of starch intake was lower for high
moisture and finely ground treatments for both experiments (Figure 4-1). Postruminal
starch digestibility as a percentage of starch entering the duodenum was lower for high
moisture corn diet and finely ground corn diet for pregnant heifers. However, high
moisture treatment increased post ruminal starch digestion as a percentage of starch
entering the duodenum and fine grinding had no effect on post ruminal starch digestion as
a percentage of starch entering the duodenum for the experiment conducted after calving.
The reason for this opposite effect of high moisture conservation on postruminal starch
digestibility for the experiment conducted before and after calving is not apparent. Total
tract digestibility of starch was higher for finely ground corn diet compared to coarsely

ground corn for both experiments and high moisture conservation increased total tract

starch digestibility for early lactation cows only.

 

85

 

 

A
I Post ruminal
Rtu‘mna]
100_
g 80_
g
:5; 60
'33
g
‘5 40
.c
2
(U
5 20 ‘
0
BF DC MF MC
B
I Post ruminal
100- Ruminal
g 80 .
§
;§ 60 -
‘6
3
=5 40 _ .
.c
2
(U
a 20 _
0 _

 

 

Figure 4-1 Ruminal, postruminal and total tract digestibility of starch for before
calving (A) and after calving (B)
DF: dry fine, DC: dry coarse, MF: high moisture fine, MC: high moisture coarse

86

Fine grinding decreased postruminal OM digestibility as a percentage of OM
intake and as a percentage of OM entering the duodenum in both experiments. However,
high moisture conservation reduced postruminal OM digestibility as a percentage of OM
intake and as a percentage of OM entering the duodenum only for the experiment
conducted before calving. High moisture conservation and fine grinding increased total
tract OM digestibility for the early lactation cows but had no effect on the pregnant

heifers (Figure 4-2).

87

A
I Post ruminal

80- Ruminal

OM apparent digestibility (%)

 

 

J ‘ MF MC

B
I Post ruminal

100. I Ruminal

OM apparent digestibility (%)

 

 

DC MF MC

Figure 4-2 Ruminal, postruminal and total tract digestibility of OM for before calving
(A) and after calving (B)
DF: dry fine, DC: dry coarse, MF: high moisture fine, MC: high moisture coarse.

88

Postruminal NDF digestibility as a percentage of NDF intake deceased for fine
grinding for the experiment with pregnant heifers; but was not affected by fine grinding
for early lactation cows. High moisture conservation increased postruminal NDF
digestibility as a percentage of N DF intake or as a percentage of NDF entering the
duodenum for early lactation dairy cows only. Total tract digestibility of NDF did not
alter by high moisture conservation method or fine grinding for the experiment conducted

before or after calving (Figure 4-3).

A

I Post ruminal
R u mm!

50

NDF Digestibility (%)

 

 

DF DC MF MC

I Post ruminal
Ruminal

010)
CO

.5
O

NDF Digestibility (%)
N (.0
O O

.1;
O

 

 

0 .

DF DC MF MC

Figure 4-3 Ruminal, postruminal and total tract digestibility of NDF for before

calving (A) and after calving (B)
DF: dry fine, DC: dry coarse, MF: high moisture fine, MC: high moisture coarse.

90

Although total tract digestibility of total N was increased by high moisture
conservation for the experiment conducted after calving, total N, NAN, NANMN,
microbial N passed to the duodenum and N digested postruminally tract were not affected
by high moisture conservation (Figure 4-4). The increase was due to increased
postruminal N digestibility as a percentage of N passage to the duodenum, which differed
from the experiment before calving. In the experiment conducted before calving, there
was no effect of high moisture conservation on total N digestibility, in spite of decreased
postruminal N digestibility as a percentage of N intake, the passage to duodenum of total
N, NAN and N ANMN by the high moisture treatment.

Fine grinding decreased and high moisture conservation tended to decrease
microbial protein per kg of OM apparently or truly fermented for the experiment
conducted after calving. However, only high moisture conservation reduced efficiency of
microbial protein production per kg of OM apparently or truly fermented for the
experiment conducted before calving. Additionally, high moisture conservation reduced
passage of total nitrogen to the duodenum for the experiment conducted before calving.
Finally, fine grinding and high moisture conservation increased ruminal starch
digestibility but did not increase microbial protein production for both experiments.

(Figure 4—4).

91

N passage to duodenum (%)

 

 

B
Ammonia

N passage to duodenum (%)

 

 

Figure 4—4 N passage to duodenum for before calving (A) and after calving (B)
DF: dry fine, DC: dry coarse, MF: high moisture fine, MC: high moisture coarse.

92

High moisture corn decreased mean ruminal pH and increased variance in ruminal
pH for both experiments. However, there was no effect of treatment on DMI even
though high moisture conservation decreased the daily number of meals consumed for
both experiments conducted before and after calving. High moisture corn tended to
increase meal size for early lactation cows only. The reason of increased number of
meals by dried corn is not apparent. Particle size had no effect on ruminal pH. The
assumed increase in fermentation acid production from greater ruminal OM digestibility
for the finely ground corn diets apparently was buffered adequately in the rumen to
prevent a decrease in ruminal pH. Mean daily ruminal pH was 0.5 units lower for high
moisture corn diet for after calving experiment compared to before calving experiment
(Table 2-6 and Table 3-6).

In summary, high moisture conservation method and fine grinding increased
ruminal digestibility of starch and OM for both experiments. The higher ruminal starch
digestibility was due to faster rate of starch digestion in the rumen. Fineness of grinding
had a greater effect on total tract starch digestibility for both experiments. Although both
conservation method and fineness of grinding had large effects on ruminal starch
digestibility only high moisture conservation decreased ruminal pH, and number of meals
per day for both experiments. Fine grinding resulted a greater gain (or less loss) of BW
per day, an increase in 4% fat-correct milk yield, and an increase in milk protein content
for the experimental after calving. Ruminal starch digestibility can be increased by fine
grinding for both dry and high moisture levels. Although fine grinding and high moisture

conservation increased substrate available for microbial protein production, the fineness

93

of grinding and conservation method used depends upon the animals abilities to

neutralize fermentation acids and maintain ruminal pH.

FUTURE WORK

Research is needed to confirm the effects of high moisture conservation method
and fine grinding on ruminal starch and OM digestibility at different concentrations of
starch and NDF in the diets from the same source. Future work is also needed to
understand the mechanism by which dry corn resulted in an additional meal per day and
why fine grinding increased ruminal and total tract starch digestibility with no effect on

ruminal pH.

APPENDIX A. F ORMULAS USED

% solids not fat (% SNF)
= % milk protein + % milk lactose + % milk ash
-assumed .71 % for % milk ash
Source: Tyrrell and Reid (1965) JDS 48: 1215.

average % fat for test week (similar for %protein, %lactose and SCC)
= (total lb. fat produced for six sampled milkings) + (total lb. of milk
produced for six sampled milkings)
= ((lb. of milk from first milking)(first milking % fat/ 100) + (fat lb. from

second milking) + .................. + (fat lb. from sixth milking» + ((lb. of milk
from first milking) + (lb. of milk from second milking) + .................... + (lb.
of milk from sixth milking»

4.0% FCM (source: NRC, 1989)
= milk kg (.4 + (.15)(% milk fat))

3.5% FCM (source: NRC, 1989)
= milk kg (.43 + (.162)(% milk fat))

94

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