GRAIN PROCESSING EFFECTS ON STARCH U T I L I Z A T I O N
BY R U M I N A N T S 1'2
C. Brent Theurer 3
University of Arizona, Tucson
ABSTRACT
Starch utilization may be markedly enhanced by proper grain processing; however, extent of
improvement is primarily dependent upon the ruminant species, grain source and method of processing. Grain processing has less impact on starch digestion by sheep than cattle. The magnitude
of improvement is inverse to the starch digestion values for nonprocessed (or minimally processed)
grains. Utilization of sorghum grain starch is improved most by extensive processing, and then
corn, with little improvement in barley starch digestion. Studies comparing processing effects on
barley or wheat starch utilization by cattle were not found. Steam-flaking consistently improves
digestibility of starch by cattle fed corn- or sorghum grain-based diets over whole, ground or dryrolled processes. Other extensive processing methods appear to enhance starch digestibility of corn
and sorghum grain to a similar extent as steam-fiaking, but comparative data are too limited to
quantitate adequately effects of these methods. This improvement in starch utilization appears to
be the primary reason for enhanced feed conversion of cattle fed diets high in these processed
grains. The major site of cereal grain starch digestion is usually the rumen. Processing increases
microbial degradation of starch in the rumen and decreases amounts of starch digested postruminally. Rates of in vitro amylolytic attack of starch in cereal grains by both ruminal microbial
and pancreatic enzyme sources are improved by processing methods employing proper combinations of moisture, heat and pressure. In vitro and in situ studies suggest that much of the increase
in ruminal starch fermentation with steam-flaking is due to changes in starch granular structure,
which produces additive effects beyond those of decreasing particle size. Thus, efficiency of
rurninal starch fermentation by cattle appears to be improved by proper processing of corn and
sorghum grain. Processing and grain source studies both suggest that maximal total tract starch
digestibility is positively related to the extent of digestion in the rumen.
(Key Words: Starch Digestion, Processing, Ruminants, Barley, Maize, Sorghum.)
I ntroduction
Starch is the primary nutrient of those
r u m i n a n t diets used to p r o m o t e high levels of
production. Thus, o p t i m a l starch utilization is
f u n d a m e n t a l to improving efficiency o f production of animal products. The principal sources
of starch in these diets are the cereal grains,
m o s t c o m m o n l y barley, corn and sorghum
grain. E n h a n c e m e n t o f starch utilization by
grain processing is d e p e n d e n t u p o n the m e t h o d s
o f processing, r u m i n a n t species and grain
source.
1Presented at a symposium entitled "Starch Utilization by Ruminants" at the 77th Annu. Meet. of the
Amer. Soc. of Anim. Sci., August 15, 1985, Univ. of
Georgia, Athens.
2Arizona Agr. Exp. Sta. Journal Article 4092.
3 Dept. Anim. Sci.
Received October 14, 1985.
Accepted May 9, 1986.
Many m e t h o d s of processing grain have been
used in an a t t e m p t to i m p r o v e their feed utilization by ruminants. A c o m p l e t e description o f
these various processes are described b y Hale
and T h e u r e r (1972) and Hale (1980). In this
manuscript the t e r m " p r o c e s s e d " grains applies
to extensive m e t h o d s of preparing grains for
feeding: steam-flaking, reconstituting, early
harvest ensiling (high moisture), popping,
exploding, roasting or micronizing; whereas the
t e r m " n o n p r o c e s s e d " grains refers to w h o l e
grains or those minimally processed: cracked,
ground, dry-rolled or raw.
As n o t e d in recent reviews (Hale, 1973;
~rskov, 1976), processing m e t h o d s do not
appear to be as i m p o r t a n t with sheep and goats
(as with cattle), due to their ability to utilize
effectively whole grains.
In an excellent review, Hale ( 1 9 7 3 ) s t a t e s
that the effect of processing t r e a t m e n t on
starch utilization by ruminants should be
evaluated in the intact grain rather than with
isolated starches, because the relationship of
1649
J. Anim. Sci. 1986. 63:1649-1662
1650
THEURER
starch with other grain components may be
altered with grain processing.
The magnitude of the processing effect on
starch utilization is greater with corn and sorghum grain than with barley. This u n d o u b t e d l y
relates to inherent differences among these
grains in starch and protein digestibility. Direct
comparisons of starch digestibilities among feed
grains are limited. Saba et al. (1964) and
Keating et al. (1965) found that total starch
digestibilities were higher in barley diets than in
sorghum grain diets when fed to cattle. Table 1
summarizes starch and protein digestibilities for
barley, corn and sorghum grain from values
(mostly single grain studies) cited in the literature, and from the only comparison trial among
these three grains reported in recent years
(Spicer et al., 1986). Apparent digestibilities of
both starch and protein are lowest for sorghum grain, followed b y corn and then barley.
Protein and starch digestibilities appear to be
directly related.
TABLE 1. DIGESTIBILITY AMONG
FEED GRAINS
Item
Sorghum
grain
It is also interesting to note that grains providing extensive ruminal degradation appear to
exhibit higher overall starch digestibilities (table
1). Thus, the lower the ruminal escape, the
higher the total starch utilization. Theurer
(1984) concluded that the amount of starch
escaping ruminal fermentation appears to be an
important factor for explaining differences in
both total starch and total protein digestibility
among feed grains. Only minimal data (Kay et
al., 1972; Spicer et al., 1986) are available
directly comparing the extent of in vivo ruminal digestibilities of starch in feed grains. Kay
et al. (1972) noted ruminal starch digestibility
for barley to be greater than that for corn (81
vs 61%).
Studies concerned with processing effects
on alteration of cereal grain starch and its utilization can be classified into three categories:
1) performance and efficiency of feed utilization, 2) in vitro measurements of starch structural changes and rates of ruminal microbial
fermentation or enzymatic degradation and
3) in vivo determinations of total, ruminal and
postruminal digestion.
Performance and Efficiency
of Feed Utilization
Corn
Barley
%
Proteina
Total tract digestion
55
68
72
Starch a
Total tract digestion
Ruminal digestion
Ruminal escape
Intestinal digestionb
92
66
34
79
96
73
27
82
99
93
7
78
Proteinc
Total tract digestion
61
66
68
Starch c
Total tract digestion
Ruminal digestion
Ruminal escape
Intestinal digestiond
97
75
25
87
99
84
16
94
99
88
12
93
asummarized without regard to processing effects
from individual values (or recalculations) presented
in reviews by Waldo (1973), Sowe (1982), Theurer
(1984) and data presented in tables 5 through 10.
bBased on amounts apparently presented to small
intestine.
CAdapted from comparison trial data among the
three minimally processed grains (Spicer et al., 1986).
dBased on amounts in abomasal digesta.
The influence of various processing methods
on performance and feed conversion by beef
cattle has. been reviewed by Hale (1980). The
studies clearly demonstrate the efficacy of
steam-flaking, reconstituting, early harvesting,
popping, exploding or micronizing as methods
for improving utilization of corn- or sorghum
grain-based diets (table 2). Each of these processing methods appears to be about equally
effective in improving feed conversion, if
quality control is carefully practiced. Average
feed conversions and daily gains for whole shell
and dry rolled corn were similar in these summary comparisons. Hale (1980) also notes that
extensive processing of wheat or barley does
not improve feed utilization, but may enhance
feed intake and gain.
In Vitro Degradation
and Starch Granule Alteration
Starch structure may be altered and in vitro
or in situ rates of amylolytic attack by both
ruminal microbial and pancreatic enzyme
sources may be markedly improyed by extensive processing of barley, corn and sorghum
grain. In vitro starch digestion by ruminal
GRAIN PROCESSING AND STARCH UTILIZATION
1651
TABLE 2. COMPARISON OF CORN AND SORGHUM GRAIN PROCESSING SYSTEMS
ON FEED CONVERSION AND DAILY GAIN IN BEEF CATTLE
FINISHING TRIALSa
Feed/kg gain
Processing method
Corn
Dry-rolled
Flaked
Reconstitutedb
Micronized, exploded, popped
6.9
6.3
6.4
Sorghum
grain
7.3
6.5
6.3
6.5
Daily gain (kg)
Sorghum
Corn
grain
1.2
1.2
1.3
1.2
1.2
1.2
1.2
aAdapted from Hale (1980).
bAlso includes early harvested processing system for corn comparisons.
microorganisms (Trei et al., 1970) or by pancreatic enzymes (Osman et al., 1970) may be
increased approximately threefold by steamflaking or pressure-cooking *s dry-grinding of
sorghum grain (table 3). Similar improvements
in barley, sorghum grain and corn starch utilization, using in vitro amylase techniques, have
been reported b y Frederick et al. (1973) and
McNeill et al. (1975). In situ ruminal incubation of steam-flaked or high moisture ensiled
corn also resulted in greater starch utilization
than incubation of dry-ground corn (Galyean et
al., 1981).
Osman et al. (1970) showed that with moistheat treatment of grains (steam-flaking or
pressure-cooking), the degree of flaking (flake
flatness) is the principal factor in improving
availability of barley and sorghum grain starch
tO in vitro enzymatic degradation. Proper interaction of heat, pressure and moisture seems to
be involved in altering susceptibility of cereal
starches to enzymatic attack. The data of
Frederick et al. (1973) suggest that there is a
critical pressure at which enzymatic degradation of cereal starches will be improved. This
critical pressure appears to be altered by moisture content of the grain and temperature of
the contact surfaces used to flake the grain.
Moist-heat processing of barley or sorghum
grain also markedly increases in vitro volatile
fatty acid (VFA) production (#M/g of dry
matter incubated) by ruminal microorganisms
(Theurer et al., 1967; Trei et al., 1970). Results
from the latter study indicate that in vitro V F A
production and starch digestion are closely correlated. This apparent increase in efficiency of
TABLE 3. IN VITRO SORGHUM GRAIN STARCH DIGESTION BY RUMINAL
MICROORGANISMS OR PANCREATIC ENZYMESa
Enzyme source
Processing method
Starch
digestion, %
Ruminal microbial suspension b
Dry-ground
Pressure-cooked and flaked
18
53
Bovine pancreas homogenate
Dry-ground
Steam-flaked
13
37
Porcine pancreatin
Dry-ground
Steam-flaked
17
49
aAdapted from Osman et al. (1970) and Trei et ai. (1970).
bMicrobial fraction was separated by continuous flow centrifugation at 39,000 • g from ruminal ingesta of
steers fed 65% grain diet.
1652
THEURER
starch fermentation is in agreement with the
nylon bag studies of Galyean et al. (1981), who
demonstrated that processing corn by steamflaking or high moisture ensiling produces
additive effects beyond those of reduction in
particle size alone (table 4). In situ starch disappearance within each particle size was higher
for processed (steam-flaked or high moisture
ensiled) than for nonprocessed (dry-ground)
corn, in nearly every comparison.
Hale (1973) hypothesized from histological
studies on reconstituted grain (Sullins et al.,
1971) that disrupting the protein matrix
around starch may be essential in improving
digestion of processed grains. McNeill et al.
(1975) suggest that the effect of processing
upon the solubility (or integrity) of the protein
matrix encapsulating starch granules is the
primary factor affecting efficiency of starch
utilization. Using scanning electron microscopy, Harbers (1975) concluded that processing sorghum grain clearly alters starch so it
is more susceptible to amylolytic attack. He
studied starch granule structural changes in
steam-flaked, micronized and popped sorghum
grain and amylolysis of that starch by purified
pancreatic amylase and ruminal microorganisms. His studies with sorghum grain clearly
demonstrated that 1) steam-flaking or micronizing alters starch granules and produces small
conglomerates of non-descript starch, 2) popping grain expands individual starch granules
into thin lattices of interconnecting sheets and
3) for each of the processes, protein bodies
(kafrin) seem to remain intact, but protein surrounding and between individual starch granules is disrupted.
Total, Ruminal
and Post-ruminal Digestion
Many studies have used abomasally or duodenally cannulated animals to determine the
effect of grain processing on in vivo starch utilization by ruminants. Several researchers have
concluded that cannulation has no major negative effect on digestive functions of sheep and
cattle recovered from surgery (Harris and
Phillipson, 1962; Hayes et al., 1964; MacRae
and Wilson, 1977). It has been generally
accepted that flow of duodenal digesta is
depressed as a result of continuous collection
procedures in the first 24 h with a possible
compensatory increase during subsequent days.
However, with long-term total collections,
several researchers (Thompson and Lamming,
1972; Oldham and Ling, 1977; Wanderley et
al., 1985) found no consistent evidence of flow
inhibition. Thus, the use of cannulated animals,
well-trained to the collection procedures,
appears to be satisfactory for partitioning
starch utilization in the digestive tract. Collection procedures and marker methods for estimating duodenal flow appear to be important
factors altering flow and digestibility estimates
(Drennen et al., 1970; Theurer, 1979; Wanderley et al., 1985), and should be carefully considered in making comparative evaluations of
ruminal and post-ruminal starch utilizations
among grains.
Due to incomplete recovery of markers at
the duodenum (Tamminga, 1975; Zinn et al.,
1980; Wanderley et al., 1985), ruminal disappearance of starch may be underestimated in
studies employing marker ratio techniques. In
the studies of Wanderley et al. (1985), con-
TABLE 4. PERCENTAGE IN SITU RUMINAL CORN STARCH DISAPPEARANCE
AS INFLUENCED BY PARTICLE SIZE AND PROCESSINGab
Comparison
1
Mean particle size, gm
1,500
Processing method
3,000
750
Dry-ground
Steam-flaked
12
31
12
37
19
41
Dry-ground
High-moisture ensiled
19
12
17
24
27
44
aAdapted from Galyean et al. (1981).
bDisappearance values are averaged over all incubation times (2, 4, 6, 8 h) with 16 observations per mean.
GRAIN PROCESSING AND STARCH UTILIZATION
ducted with steers fed a high grain diet, apparent ruminal dry matter disappearance estimated
by chromium oxide and lignin ratio techniques
were 12 and 29% lower, respectively, than
those determined by automated, continuous
total collection of duodenal digesta.
The major site of cereal grain starch digestion is usually the tureen. As expected from the
relative starch digestion values for nonprocessed
grains, in vivo ruminal and total starch utilization of sorghum grain is improved most by
processing, followed by corn, with little or no
improvement in ruminal or total starch digestion for barley. Tables 5, 6 and 7 summarize
studies comparing the effect of processing
methods on total and ruminal starch digestion
of barley, corn or sorghum grain diets fed to
sheep and cattle. Values for sheep (table 5) are
averaged over all grains, due to limited comparisons within grains, whereas total and ruminal
digestibilities for cattle are summarized separately for corn (table 6) and sorghum grain
(table 7). Studies comparing processing effects
on barley or wheat starch utilization by cattle
were not found.
With sheep, only small increases in total and
ruminal starch utilization were observed by
rolling or flaking, reconstituting, high moisture
ensiling or roasting as compared to feeding the
grain whole, ground, cracked or raw (table 5).
Data are not consistent within or among grains
and essentially no improvements occurred due
to processing barley. This minimal impact of
processing might be expected because total
digestibilities for nonprocessed grains averaged
several percentage units higher for sheep than
cattle (96 vs 91%; table 5 vs 6 and 7), and
average percentage of starch escaping ruminal
fermentation in sheep is markedly lower than
that for cattle (11 vs 30 and 43%; table 5 vs 6
and 7).
Steam-flaking consistently improves ruminal
degradation by microorganisms, as well as total
starch digestibilities, by cattle fed corn-based
diets over whole, dry-rolled or steamed-whole
processes (averages of 86 and 99 vs 70 and 91%,
respectively; table 6). Grinding or cracking
apparently improves total starch digestibilities
over whole corn (Galyean et al., 1979; Turgeon
et al., 1983). In one study (Galyean et al.,
1976), corn processed by high moisture harvesting (ground before ensiling) improved starch
utilization to the same extent as steam-flaking.
It is interesting to note that all of the comparisons of corn processing systems cited with
1653
cattle have been published since 1976.
As with corn, ruminal escape of extensively
processed sorghum grain fed to cattle is decreased to about one-half that of dry-rolled or
ground grain (table 7). Total starch digestion
averages 98% for sorghum grain processed by
steam-flaking, micronizing or reconstitution
compared with 91% for dry-rolled or ground
grain. Total tract digestibility of extensively
processed sorghum grain and corn appears to be
similar (98 vs 99%), whereas ruminal escape
appears to be somewhat lower for corn than for
sorghum grain (14 vs 24%; table 6 vs 7).
Daily starch intakes are generally low in the
cattle studies reported herein, averaging only
3,300 g. Typical intakes for finishing feedlot
cattle in the United States will usually exceed
5,000 g daily. Only four studies approached or
exceeded this level. Limited data (Kartchner,
1972; Garcia et al., 1981b) suggest that increasing intake has little effect on total digestibility coefficients or percentage ruminal escape
of starch from steam-flaked sorghum grain.
Despite the low starch intakes, the studies summarized may be fairly representative of the
effects of processing on starch utilization by
cattle with greater daily intakes; however, sufficient data are lacking to substantiate processing
effects with various grains fed at high levels of
intake.
~lrskov (1976) concluded that the extent of
processing of cereals for cattle should be sufficient to avoid large reductions in digestibility,
but further processing to increase the extent
and rate of ruminal fermentation would be of
doubtful value or even undesirable. In contrast,
from the experimental results summarized
herein, increasing the extent or rate of ruminal
microbial degradation of starch by processing is
advantageous to the animal in terms of total
starch utilization (and usually efficiency of
feed utilization). The data of Rahnema (1977),
Theurer (1979) and Spicer et al. (1986)suggest
that factors (i.e., processing or grain source)
decreasing escape of feed starch from ruminal
fermentation also may alter feed protein
escape, as well as amounts of microbial N presented to the intestines.
Alterations in escape of starch from ruminal
fermentation will affect amounts of starch presented to the intestines for subsequent digestive
action. Tables 8, 9 and 10 summarize processing comparison studies on post-ruminal
digestion by sheep and cattle. Published data
for sheep are too limited to establish the effect
1654
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of processing on post-ruminal digestion of
starch.
The marked decrease in amounts of starch
entering, the intestines of cattle due to processing is clearly documented in the corn and
sorghum grain comparison studies summarized
in tables 9 and 10. Amounts of starch digested
post-ruminally by cattle are also markedly less
for steam-flaked, reconstituted or micronized
grains compared with whole, ground or dryrolled grains (345 vs 591 for corn; 885 vs 1,425
g for sorghum grain). Percentage of starch
digested in the intestines (of that presented)
was consistently greater for the processed vs
nonprocessed grains (92 vs 76% averaged over
both grains). A major effect of proper grain
processing is to shift the site of starch digestion
from the intestines to the rumen, with concomitant increases in percentage digested
within both sites. When intestinal capacity to
digest starch is limiting for nonprocessed grains,
it appears that processing minimizes intestinal
limitations by decreasing the amounts of starch
presented to the intestines, as well as increasing
percentage starch digested post-ruminally.
The effect of processing on starch digestion
in the small intestine is not well documented;
however, in two of three studies (Kartchner,
1972; Hibberd et al., 1983; Aguirre et al.,
1984) steam-flaking or reeonstitution of corn
or sorghum grain enhanced starch digestion in
the small intestine of cattle. Although the percentages of corn and sorghum grain starch fermented in the ceacum and large intestine (of
that presented) in their studies appear to be
increased by steam-flaking or reconstituting vs
dry-rolling (or whole) grain, the amounts of
starch escaping digestion in the small intestine
are markedly decreased by one-third or more.
Thus, the amounts of processed starch fermented post-ileally are somewhat lower than
that for nonprocessed starch. Post-ileal starch
digestion in the preceding studies ranges from
1 to 13% of the total starch ingested, but most
values were 2 to 3% of ingested. These limited
data suggest that most studies underestimate
the value of processing on starch utilization
because of the apparent compensating digestibility in the large intestine for incomplete digestion of starch in the rumen and small intestine
for poorly processed (or nonprocessed) grains.
In these three studies, starch digestibilities
through the ileum averaged 89% for dry rolled
or whole grains compared with 96% for the
steam-flaked or reconstituted grains. This
1656
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GRAIN PROCESSING AND STARCH UTILIZATION
1659
TABLE 9. PROCESSING EFFECTS ON POST-RUMINALDIGESTION BY CATTLE
OF CORN STARCH PRESENTED TO THE INTESTINESa
Starch
Reference
Grain
processing
method
Entering
intestines, g
Digested in
intestines b
g
%
Cole et al. (1976)
Dry-rolled
Steam-flaked
710
222
540
195
76
88
Galyean et al. (1976)
Dry-rolled
Ground, high moisture
(GHM)
GHM + propionic acid
Steam-flaked
673
572
85
359
1,095
477
327
964
448
91
88
94
Lee et al. (1982)
Whole
Steam-flaked
1,420
450
667
400
47
89
Turgeon et al. (1983)
Whole
Cracked
2,472
1,935
1,953
1,601
79
82
Aguirre et al. (1984)
Whole
Dry-rolled
Steam-flaked
550
500
350
400
400
335
73
8O
96
Processing comparison avg
Whole or dry-rolled
Steam-flaked
832
375
591
345
71
92
Digested
in small
intestine, %
67
71
88
aAdapted from data in references cited.
bBased on amount entering the intestines and appearing in the feces.
represents an 8% improvement over the nonprocessed grains, which is greater than the
improvement based on total digestibility for
these three studies (93 vs 98%). It is possible
that with higher starch intakes that these ileal
differences may be even greater than those
noted by Kartchner (1972), Hibberd et al.
(1983) and Aguirre et al. (1984).
In conclusion, proper processing of corn or
sorghum grain for cattle fed high grain diets
improves in vitro, in situ and in vivo starch
utilization. This improvement appears to be due
largely to a marked increase in ruminal fermentation of the processed starch, as well as increased digestion in the small intestine, while
decreasing fermentation losses in the ceacum
and large intestine. Processing also probably
enhances energy and N economy for the animal
by minimizing starch fermentation and microbial protein synthesis in the lower gut (Orskov
et al., 1970; Spicer et al., 1986). In the corn-
parison studies reported herein, only about 10
to 25% of the starch from steam-flaked corn or
sorghum grain escapes digestion in the rumen,
whereas 30 to 45% of the starch from dryrolled grains escapes ruminal fermentation.
Although data are limited, similar differences
in ruminal escape of starch are noted for other
processing methods when compared with nonprocessed grains. Thus, a m o u n t s of processed
starch digested i n t h e intestines a r e decreased
by one-third or more of that of p0st-ruminal
digestion of nonprocessed c o r n or Sorghum
grain starch.
For sorghum grain, processing appears to
improve starch utilization by disruption of the
protein matrix surrounding the starch granules.
Proper processing of corn or sorghum grain includes quality control to ensure optimal conditions for adequate application o f moisture,
heat and pressure (or early harvest ensiling or
r e c o n s t i t u t i o n ) . Processing and grain Source
THEURER
1660
TABLE 10. PROCESSING EFFECTS ON POST-RUMINAL DIGESTION BY" CATTLE
OF SORGHUM GRAIN ~TARCH PRESENTED TO THE INTESTINES a
Starch
Reference
Holmes et al. (1970)
Grain
processrng
method
Steamed and rolled c
Pressure-steamed and
and rolled d
Entering
intestines, g
Digested in
intestinesb
g
%
360
266
74
150
101
67
McNeill et al. (1971)
Ground
Micronized
Reconstituted
Steam-flaked
1,200
1,220
760
380
1,128
1,159
745
372
94
95
98
98
Kartchner (1972)
Dry-rolled
Steam-flaked
Dry-rolled
Steam-flaked
1,747
1,229
2,866
1,341
1,563
1,145
2,534
1,136
88
95
93
94
Hinrnan and Johnson (1974a)
Ground
Dry-rolled
Micronized
Steam-flaked
368
875
534
699
335
595
518
664
91
68
97
95
Hinrnan and Johnson (1974b)
Dry-rolled
Micronized-low
Micronized-rnedium
Micronized-high
1,394
1,481
1,405
1,202
711
1,407
1,349
1,118
51
95
96
93
Garcia et al. (1981a)
Dry-rolled
Steam-flaked
2,715
848
2,362
789
87
93
Hibberd et al. (1983)
Dry-rolled
Reconstituted
1,923
482
1,290
407
67
84
Processing comparison avg
Dry-rolled or ground
Steam-flaked,
reconstituted
or micronized
1,781
1,425
80
952
885
93
Digested
in small
intestine, g
89
93
88
85
33
71
aAdapted from data in references cited.
bBased on amount entering the intestines and appearing in the feces.
CSteamed 8 rain before rolling (steaming time less than one-half of that recommended for steam-flaking).
dsteamed at 3.5 kg/cm 2 for 1.5 min before rolling (usually referred to as pressure-cooked).
studies b o t h suggest t h a t grains w h i c h are
e x t e n s i v e l y d e g r a d e d in t h e r u m e n also have t h e
highest overall s t a r c h digestibilities.
C o m p a r a t i v e studies o n s t a r c h utilization o f
p r o c e s s e d f e e d grains are lacking and s h o u l d be
c o n d u c t e d t o establish m o r e clearly t h e i r c o m parative value f o r providing e n e r g y t o high producing r u m i n a n t animals. Clearly, additional
i n f o r m a t i o n is n e e d e d o n t h e i m p a c t o f grain
processing o n pre- and post-ileal starch utiliza-
t i o n a n d its relationship t o energy and N utilizat i o n in r u m i n a n t s .
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