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OCR for page 249
Carbohydrate
2 Chemistry and Feed
L) Processing
NONSTRUCTURAL CARBOHYDRATES
The more readily digestible carbohydrates in animal
feeds lack a satisfactory system of classification, even
though they represent the major energy yielding compo-
nents of feedstuffs. The lack of an adequate definition is
partly a function of the diversity of the chemical fraction
as well as lack of basic research into their specific nutritive
characteristics. The nonstructural carbohydrates are those
carbohydrates not included in the cell wall matrix and
they are not recovered in NDF. By this definition, the
nonstructural carbohydrates are comprised of sugars,
starches, organic acids, and other reserve carbohydrates
such as fructans.
Nonstructural carbohydrates can be classified as water-
soluble (including monosaccharides, disaccharides, oligo-
saccharides, and some polysaccharides) and larger polysac-
charides that are insoluble in water. Water soluble non-
structural carbohydrates, such as sugars (glucose and fruc-
tose) and disaccharides (sucrose and lactose) are rapidly
fermented in the rumen and comprise a significant fraction
of certain feeds (molasses, sugar beets, high sugar corn
grain, and whey). Sugar content of fresh grasses and
legumes is variable and may exceed 10 percent of the dry
matter (DM), but hay and silage have lower concentrations
because of losses from fermentation and respiration. Tem-
perate grasses store fructans in leaves and stems as water-
soluble levan. Fructosan is increased by cool weather and
may increase to as much as 30 percent of the DM for
cool season perennial ryegrass (Van Soest, 1983~. Although
water-soluble carbohydrates may be high in individual
feeds, concentrations are generally low in ruminant diets.
Galactans are the storage carbohydrate of leguminous
plants, and the B-glucan gums are found in the bran of
barley, oats, and rye, and the cell wall of grasses (Amen
and Hesselman, 1985~. Pectins are associated with the cell
wall but are not covalently linked to the lionized portions
and are almost completely digested (90 to 100 percent) in
the rumen. Pectin concentrations on a DM basis are high
in citrus and beet pulps, soybean hulls, and dicotyledonous
legume forages but are low in grasses (Allen and Knowlton,
1995~. Starch is the major storage carbohydrate in most
cereal grains. It is composed of two major molecules: amy-
lose and amylopectin. Amylose is a linear polymer of (x 1-4,
D-glucose units while amylopectin is a branched polymer
with linear chains of (x D-glucose that has a branch point
every 20 to 25 glucose units (French, 1973~. Most forages
contain little starch with the exception of small grain silage
(10 to 20 percent of DM), grain sorghum silage (25 to 35
percent), and corn silage (25 to 35 percent of DM). The
ruminal degradation of starch is variable ranging from 40
to over 90 percent depending on source, processing, and
other factors.
ANALYTIC PROCEDURES
Neutral Detergent Fiber
The accuracy of feed composition data and requirements
for NDF and NSC is compromised by the lack of standard
methods. The neutral detergent fraction includes cellulose,
hemicellulose, and lignin as the major components. There
are three major modifications of the NDF method, each
of which generates different values depending upon the
feed that is analyzed. The original NDF method (Van Soest
and Wine, 1967, Goering and Van Soest, 1970) used
sodium sulfite to remove contaminating proteins from
NDF by cleaving disulfide bonds and dissolving many
crosslinked proteins. It was discovered that the original
249
OCR for page 250
250 Nutrient Requirements of Dairy Cattle
method did not adequately remove starch from grains and
corn silage. The neutral detergent residue modification
was developed that included a heat-stable amylase in the
procedure to remove starch, however, sulfite was removed
from the procedure because of concerns about the possible
loss of lignin and phenolic compounds (Van Soest et al.,
19911. The amylase-treated NDF modification (aNDF)
was developed to measure NDF in all types of feeds and
uses both heat-stable amylase and sodium sulfite to obtain
NDF with minimum contamination by either starch or
protein. It has been adopted as the reference method for
NDF by the National Forage Testing Association (Under-
sander et al., 1993), and is being evaluated in a collaborative
study for AOAC approval as an official method. The use
of sodium sulfite is crucial for the removal of nitrogenous
contamination from heated feeds (Hintz et al., 19961. If
the objective is to accurately measure total fiber in feeds
with minimum contamination by digestible protein or
starch the aNDF method is preferred. Sodium sulfite
improves the filtration of fiber residues during the NDF
procedure and allows the method to be used on all types
of feeds and feed mixtures, including heated feeds and
protein supplements. The aNDF method cannot be used
to measure the slowly degraded protein (B3) fraction in
feeds in the Net Protein and Carbohydrate Model which
is defined as the difference between neutral detergent
insoluble crude protein (measured without the use of sul-
f~te) and acid detergent insoluble crude protein. When
NDF is measured without the use of sodium sulfite it
probably should be corrected for protein contamination.
However, for routine analysis the aNDF procedure will
provide an accurate estimate of NDF with minimum con-
tamination by protein or starch. The NDF concentrations
shown in Table 15-1 were determined using amylase
and sulfite.
Neutral Detergent Insoluble Nitrogen
The nitrogen associated with NDF is mostly cell wall-
bound protein plus other nitrogen compounds and includes
indigestible nitrogen found in the acid-detergent residue.
A major cell-wall associated protein is extensin that is cova-
lently linked to hemicellulosic carbohydrate (Fry, 19881.
The nitrogen insoluble in neutral detergent solution
(NDIN), but soluble in acid detergent, is digestible and
consists of slowly degraded protein (Licitra et al., 19961.
Pichard (1977) reported a positive correlation between the
slowly solubilized pool of nitrogen and NDIN in forage
samples. Krishnamoorthy et al. (1982) demonstrated that
over 30 percent of total nitrogen in forages and fermented
grains was NDIN (sulfite was not used).
Protein contamination of NDF for unheated forages is
not a major problem, but neutral detergent insoluble CP
(NDICP) is still in the range of 8 to 12 percent of the
NDF with sulfite. For certain concentrate feeds such as
distillers' and brewers' grains, CP contamination can
greatly inflate NDF values. The concentration of NDICP
(as a percentage of NDF) for brewers' and distillers' grains
can be as high as 40 percent (Weiss et al., 19891. Adding
sulfite to the NDF solution reduces CP contamination but
does not quantitatively remove all the contamination (Dong
and Rasco, 19871. Standardization of procedures for nitro-
gen fractionation of ruminant feeds has been reviewed by
Licitra et al. (19961.
Acid Detergent Fiber
The acid detergent fiber (ADF) fraction of foodstuffs
includes cellulose and lignin as primary components and
should be analyzed according to AOAC (19731. The residue
also contains variable amounts of ash and nitrogen
compounds.
Acid Detergent Insoluble Nitrogen
The concentration of acid detergent insoluble nitrogen
(ADIN) is used to determine protein availability in heated
feeds. Tannins, if present, are one possibility for increased
insoluble protein associated with the plant cell wall.
Another is the Maillard or nonenzymatic browning reaction
caused by heating and drying. The nitrogen in these frac-
tions has low biologic availability and tends to be recovered
in ADF (Van Soest, 1965b; Van Soest and Mason, 19911.
Heat drying of forages at temperatures above 60° C results
in significant increases in yields of lignin and fiber. The
increased yield of ADF can be accounted for largely by
the production of artifact lignin via nonezymatic Browning
Reaction (Van Soest, 1965b). The ADIN can be a sensitive
assay for nonenzymatic Browning Reaction due to over-
heating of certain feeds (Van Soest and Mason, 19911.
The ADIN concentration in forages has a strong negative
correlation to apparent protein digestibility (Thomas et al.,
19821. Nakamura et al. (1994), however, demonstrated a
weak correlation between ADIN concentrations in eight
different nonforage fiber sources and nitrogen digestibility.
Their results indicated that ADIN values in nonforage
sources of protein predicted more protein damage than
that measured by in viva nitrogen digestibility. The chemi-
cal composition of ADIN (Weiss et al., 1986) and the
relationship between ADIN concentrations and digestibil-
ity are different between concentrates and forages, there-
fore the use of a single equation to relate ADIN to nitrogen
digestibility for all feeds is not correct.
L. .
linen
Lignin is a noncarbohydrate, high molecular weight com-
pound that constitutes a diverse class of phenolic com-
OCR for page 251
Carbohydrate Chemistry and Feed Processing 251
pounds (Van Soest, 19831. The acid detergent lignin (ADL)
procedure of Van Soest (1965a) includes both hydrolytic
(sulfuric acid) and oxidative (potassium permanganate)
methods; the sulfuric acid variant of ADL is the most
popular (Jung et al., 19971. The Klason lignin is the residue
remaining after a two stage sulfuric acid hydrolysis that is
commonly used to determine the neutral sugar compo-
nents of cell wall polysaccharides (Theander and Wester-
lund, 19861. Differences in the ADL and Klason lignin
methods ~ i.e., order of acid strength use, detergent in the
ADF step, and addition of the filtration step to the ADL
procedure) account for the difference in lignin values as
measured by these two methods (Lowry et al., 19941. Kla-
son lignin values are typically two to four times greater for
grasses than the sulfuric ADL estimates and 30 percent
higher for legumes (Jung et al., 19971. Hatfield et al. (1994)
concluded that the Klason lignin is a more accurate esti-
mate of plant cell wall lignin content than is ADL. Other
evidence suggests that an acid soluble lignin fraction is lost
in the ADF step of the ADL procedure, thereby resulting
in underestimates of lignin content by the ADL method
(Lowry et al., 19941.
The Klason lignin procedure was approved by the AOAC
(1973) at the same time as ADF. Klason lignin is a better
marker for digestibility than permanganate lignin; however,
Klason lignin followed by treatment with permanganate
yields lignin by difference that is more recoverable in feces
(Van Soest et al., 19911. The fraction resistant to both 72
percent sulfuric acid detergent lignin and permanganate is
cutin, which is in many seed hulls. The correlation between
forage digestibility and concentrations of 72 percent sulfu-
ric acid detergent lignin and Klason lignin were compared
by Jung et al. (19971. Thirty-six forages, including C3
legumes and C3 and C4 grasses, were analyzed for sulfuric
acid detergent lignin, Klason lignin, and in vitro digestibili-
ties of DM and NDF. Twenty of these forages were also
fed to lambs at restricted intake for measurement of DM
and NDF digestibilities. Lignin concentrations determined
by the two lignin methods were positively correlated, and
the Klason lignin value was always greater than the acid
detergent lignin concentration. The largest differences
were observed for grass forages. In viva and in vitro digest-
ibilities of DM and NDF in forages were negatively corre-
lated with both lignin measurements. The degree of corre-
lation for the two lignin methods with digestibility was
generally similar across all forages and within forage classes.
Slopes of linear regressions of digestibility on lignin con-
centration did not differ between legumes and grasses.
Although the sulfuric acid detergent lignin and Klason
lignin procedures gave very different estimates of the lignin
concentration in forage, they were similarly correlated with
digestibility.
Total Nonstructural Carbohydrates
Total nonstructural carbohydrates (NSC) include starch,
sugar, and fructan measured using the procedure of Smith
(1981) when modified to use ferriccyanide as the colorimet-
ric indicator. The method of Salomonsson et al. (1984) as
modified by Herrera-Saldana et al. (1990) measures only
starch by an enzymatic method. Crude enzyme prepara-
tions such as taka-diastase (derived from Aspergillis oryzae)
represents more than 30 different enzymatic functions,
including amylolytic, proteolytic, and lipolytic (Nocek,
19911. Considerable variation may be associated with the
specificity and/or lack of specificity of enzymes used in the
starch and NSC analysis. In most cases the starch and
modified Smith (1981) procedure are synonymous. The
difference calculation usually accounts for more carbohy-
drate types (mainly pectin), especially for forages and
byproduct feeds. Table 4-1 provides a summary of several
common feed sources with measured values for NSC and
calculated NFC values as a percentage of DM.
Generally, wheat has the highest content of starch for
the grains (77 percent of the DM; ranging from 66 to 82
percent), followed by corn and sorghum (72 percent of
the DM; ranging from 65 to 80 percent) and then by barley
(57 percent of the DM; ranging from 55 to 75 percent),
and oats (58 percent of the DM; ranging from 45 to 69
percent); (Nocek and Tamminga, 1991; Huntington, 19941.
Starch content of corn silage (35 percent of the DM) is a
function of plant maturity and proportion of grain in the
whole plant. Corn silage with 32 percent grain should
contain about 22 percent starch. Alfalfa hay or silage con-
tains from 2.7 to 20 percent starch and protein supplements
such as soybean meal and cottonseed meal contain from
2.5 to 27 percent starch (Nocek and Tamminga, 19911.
EFFECTS OF PROCESSING ON ENERGY
IN FEED
Sources of Starch
BARLEY GRAIN
Cows digest whole barley poorly because of the cutinous
nature of the seed husk (Nordin and Campling, 19761.
Less than 10 percent of DM from whole barley is digested
after48 hours of in situ incubation in the rumen (McAllister
et al., 19901. When grains were broken into halves or quar-
ters, in situ DM digestibility was about 60 percent after
24 hour of incubation. Treatment of barley with an aqueous
solution of NaOH (30 to 40 g of NaOH/kg of barley) can
substitute for mechanical processing (0rskov and Green-
halgh,19771. Barley treated with NaOH has higher concen-
trations of ash (corresponding to the Na added); the con-
centrations of the other nutrients are reduced because of
OCR for page 252
252 Nutrient Requirements of Dairy CattIe
ash dilution (McNiven et al., 19951. Dry matter digestibility
of NaOH-treated barley in the total tract was similar,
digestibility of NDF was higher, and digestibility of starch
was lower than for rolled barley. Ruminal digestibility of
CP and DM was reduced about 30 percent by NaOH
treatment (McNiven et al., 19951. Cows fed NaOH-treated
barley or rolled barley produced similar amounts of milk
in a 10-week study (Bettenay, 1980), but fat and protein
concentrations in milk were reduced when NaOH-treated
barley was fed in a short-term study (McNiven et al., 19951.
Milk production and digestibility of DM were similar
when cows are fed rolled high-moisture barley or dry rolled
barley (Kennelly et al., 1988; Christen et al., 19961. Heat-
treatment of dry barley (exit temperatures of 135 or 175°
C) has little effect on its gross nutrient composition, energy
value, or milk production compared with dry rolled barley
(Robinson and McNiven, 1994; McNiven et al., 19951.
High producing cows fed twice daily produced more milk
when fed heat-treated barley than when fed rolled barley
but when cows were fed seven times per day no differences
were observed (Robinson and McNiven, 19941.
CORN GRAIN
Mechanical processing (grinding) significantly increases
the digestibility of dry corn. The digestibility of whole corn
was increased approximately 25 percent by either rolling
(Clark et al., 1975) or cracking (Moe et al., 19731. Ground
dry corn has 4 to 6 percent more digestible energy than
either rolled or coarsely cracked corn (Moe et al., 1973;
Knowlton et al., 1996; Wilkerson et al., 19971. Most of
the difference in digestibility between cracked and ground
corn is caused by a 7 to 10 percent improvement in digest-
ibility of starch (or nonfiber carbohydrate), but part of the
increase is offset by a reduction in digestibility of NDF
(Knowlton et al., 1996; Wilkerson et al., 19971. The site of
digestion of starch is affected more by grinding than is the
digestibility of starch in the total tract. Based on in situ
studies, approximately 44 percent of the starch in coarsely
cracked corn is digested in the rumen compared with 60 to
65 percent for finely ground corn (Cerneau and Michalet-
Doreau, 1991; LyLos et al., 19971.
Because of changes in the site of digestion, the difference
in measured NED concentrations between cracked and
ground corn should be less than the differences in digest-
ibility. The difference in measured NED concentrations
between cracked and ground dry corn is between 0 and 4
percent (Moe et al., 1973; Wilkerson et al., 19971. Milk
production increased 3.5 to 6 percent when high producing
(35 kg/d) cows were fed ground dry corn compared with
dry cracked corn (Mitzner et al., 1994; Knowlton et al.,
1996; Wilkerson et al., 19971. Milk composition was not
consistently affected by the fineness of the grind of dry
corn. Based on production and calorimetry data, average
dry ground corn should have about 6 percent more NED
than average cracked corn when fed at 3 X maintenance
(Table 15-11.
Dry matter digestibility of steam-flaked corn is not con-
sistently higher than that of rolled or ground dry corn when
fed to cows (Joy et al., 1997; Crocker et al., 1998; Yu et
al., 19981. Plascencia and Zinn (1996) however, reported
a 10 percentage unit increase (15 percent) in digestibility
of OM between steam-flaked and dry-rolled corn when
fed to lactating cows. In that study, digestibility of the dry-
rolled corn diet was much lower than would be expected.
Generally steam-flaking increases digestibility of starch by
10 to 20 percent but digestibility of NDF decreases by a
similar amount (Plascencia and Zinn, 1996; Joy et al., 1997;
Crocker et al., 1998; Yu et al., 1998; Dann et al., 19991.
Digestibility of starch in the total tract was consistently
increased as the density of the corn following steam-flaking
was reduced (Chen et al., 1994; Plascencia and Zinn, 1996;
Joy et al., 1997; Yu et al., 19981. However, variable
responses of flake density have been found for digestibility
of OM because digestibility of NDF usually decreases as
flake density is reduced. Steam-flaking generally increased
the proportion of starch digestion occurring in the rumen.
The optimal flake density based on milk production is
about 0.36 kg/L (28 lbs/bushel).
The average response in yield of fat-corrected milk was
4.5 percent when steam-flaked corn replaced dry ground
corn (Chen et al., 1994; Plascencia and Zinn, 1996; Joy et
al., 1997; Yu et al., 1998; Dann et al., 19991. Milk fat
percentage was either not affected or tended to decrease
and milk protein percentage was either not affected or
tended to increase when steam-flaked corn replaced dry
rolled corn. Based on milk production and changes in
digestibility, the NET value for average steam-flaked corn
is about 11 percent higher then that for average dry cracked
corn and about 4 percent higher than that for average dry
finely ground corn when fed at 3 X maintenance (Table
15-11. Theurer et al. (1999) calculated that steam-flaked
corn had 18 percent more NET than cracked corn. These
differences are highly related to DMI and differences
between cracked corn and other forms of corn should
increase as DMI increases.
The chemical composition of high-moisture corn is simi-
lar to that of dry corn except that high moisture corn
contains two to three times more soluble CP (Prigge et
al., 1976~. The concentration of NDF tends to be higher
in high moisture corn probably because of contamination
by the cob. On average, high-moisture corn was about 9
percent more digestible than dry corn when fed to lactating
cows (Tyrrell and Varga, 1987; Wilkerson et al., 1997~.
When similar diets were fed to nonlactating cows (at
approximately maintenance) the difference in digestibility
was <1 percent (McCaffree and Merrill, 1968; Tyrrell and
Varga, 1987~. Grinding high-moisture corn increased the
OCR for page 253
digestibility of energy or organic matter of diets about 5
percent compared with diets with rolled high moisture
corn (Ekinci and Broderick, 1997; Wilkerson et al., 19971.
Measured NED of diets containing rolled high-moisture
corn is about 5 percent higher than that of diets containing
rolled dry corn when fed to lactating cows (Tyrrell and
Varga, 1987; Wilkerson et al., 19971. If no associative effects
are assumed, the NED value of rolled high-moisture corn
was 12 to 13 percent higher than that for rolled dry corn.
When the corn was ground, diets with high-moisture corn
had 13 percent more NED than did diets with dry corn.
Assuming no associative effects, the NED of the ground
high-moisture corn was 32 percent higher than that for the
ground dry corn (Wilkerson et al., 19971. The difference in
NED values between high-moisture and dry corn was about
twice as large as the difference in digestibility. Ruminal
digestibility of starch is 15 to 25 percent higher when rolled
high-moisture corn is fed to high producing cows than
when rolled dry corn is fed (Aldrich et al., 1993; Knowlton
et al., 19981. Energetic losses should be higher when starch
is digested in the rumen rather than the small intestine;
NED values should differ less than digestibility.
Clark (1975) reviewed the early literature and found no
difference in dry matter intake (DMI) (ca. 17 kg/d) or
FCM production (ca. 20 kg/d) between cows fed high-
moisture or dry corn. In short term studies (LyLos et al.,
1997; Wilkerson et al., 1997), DMI was not affected, but
milk production increased about 5 percent when dry corn
was replaced with high-moisture corn in diets of high pro-
ducing cows. In a longer term study (Dhiman and Satter,
1995), with diets based on alfalfa and corn silage, cows
fed high-moisture corn (either rolled or finely ground)
produced 6 percent more 3.5 percent fat-corrected milk
(34.2 vs. 32.2 kg/d) than cows fed dry-rolled corn. Con-
versely, Knowlton et al. (1998) reported that DMI (23.5
kg/d), milk production (35 kg/d), and milk composition
were not different between cows fed high-moisture or dry
corn. Diets in that study were the same as those used in
the calorimetry study conducted by Wilkerson et al. ~ 19971.
Based on digestibility, measured NED values, and milk
production data, rolled high-moisture corn averages about
7 percent higher in NED than dry cracked corn at 3X
maintenance. Based on similar criteria, ground high-mois-
ture corn has about 11 percent more NED than cracked
dry corn at 3X maintenance (Table 15-11.
CORN SILAGE
Based on limited data, digestibility of starch from normal
corn silage (ca.35 percent DM) is similar to that of cracked
corn but digestibility of starch from mature corn silage is
about 10 percent less when fed to cows at approximately
3X maintenance (Harrison et al., 1996; Bal et al., 19971.
Mechanical rolling of corn silage (i.e., kernel processing)
Carbohydrate Chemistry and Feed Processing 253
increased digestibility of starch in the total diet by about
6 percent (Bal et al., 1998; Weiss and Wyatt, 2000; Bal et
al., 20001. Digestibility of energy in a diet with processed
mature corn silage (27 percent of DM) was about 7 percent
higher than for a diet with mature unprocessed corn silage,
but processing did not affect digestibility of energy in diets
with less mature corn silage (Johnson et al., 19981. In
another study, processing increased the TDN of one hybrid
of corn silage by about 8 percent but had essentially no
effect on another hybrid (Weiss and Wyatt, 20001. Milk
yield of high producing cows has not been consistently
affected by processing corn silage (Bal et al., 1998; Bal et
al., 2000; Weiss and Wyatt, 20001. Because of the paucity
of published data with lactating cows, an appropriate factor
to adjust the energy value of processed corn silage cannot
be developed at this time.
OAT GRAIN
More than 90 percent of the starch in oats is soluble
and almost 100 percent of the starch in ground oats disap-
peared in situ within 4 hour of incubation (Herrera-Saldana
et al., 19901. The DM digestibility of diets containing 25
percent whole or rolled oats was not different when fed
to lactating cows and milk production was similar (Moran,
19861. Current data do not support extensive processing
of oat grain for feeding to moderately producing dairy cows
or changing the NED value of processed oats.
SORGHUM GRAIN
Whole sorghum is poorly digested (Nordin and Cam-
pling, 19761. The digestibility of starch from dry rolled
sorghum is 7 to 18 percent less than that of ground or
steam-rolled corn (Oliveira et al., 1993), and barley (Her-
rera-Saldana and Huber, 1989) when fed to lactating cows.
In those studies, yield of solid or fat-corrected milk was
slightly (ca. 2 percent) lower when cows were fed dry-
rolled sorghum rather than when fed steam-flaked corn,
finely ground corn, or barley. Milk production was similar
for cows fed dry-rolled sorghum and rolled corn (Mitzner
et al., 19941.
Steam-flaked sorghum has consistently higher digestibil-
ity of starch than dry rolled sorghum when fed to lactating
cows. In three studies, digestibility of starch from diets
based on steam-flaked sorghum was 8 percent higher than
that for starch from diets based on dry-rolled sorghum
(Chen et al., 1994; Santos et al., 1997a; Simas et al., 19981.
Another study indicated a 27 percent increase in digestibil-
ity of starch when sorghum was steam-flaked (Moore et
al., 1992), but the digestibility of the starch in the dry-
rolled sorghum diet was very low. On average, digestibility
of starch for diets based on stream-flaked sorghum was 98
percent. The digestibility of DM or OM for diets with
OCR for page 254
254 Nutrient Requirements of Dairy Cattle
steam-flaked sorghum was about 8 percent higher than for
diets based on dry rolled sorghum (Moore et al., 1992;
Chen et al., 1994; Santos et al., 1997a; Simas et al., 19981.
The degree to which steam flaking increases the feeding
value of sorghum is primarily a function of flake density.
The optimal density of steam-flaked sorghum is about 0.36
kg/L (Chen et al., 1994; Plascencia and Zinn, 1996; Santos
et al., 1997a; Santos et al., 1997b). Extremely thin flakes
(density ~ 0.3 kg/L) often result in reduced DMI and
lower production (Moore et al., 1992; Santos et al., 1997a).
Milk production and gross efficiency of feed utilization
(FCM yield/DMI) when steam-flaked sorghum was fed
was about 10 percent higher than when dry-rolled sorghum
was fed (Moore et al., 1992; Chen et al., 1994; Santos et
al., 1997a; Simas et al., 19981. Based on milk production
and DM digestibility data, the NED value of steam-flaked
sorghum is about 13 percent higher than for dry-rolled
sorghum. Compared with cracked corn, dry rolled sorghum
contains about 4 percent less NED at 3X maintenance (a
function of less fat and lower starch digestibility). Steam-
flaked sorghum (mainly because of improved digestibility
of starch) has about 9 percent more NED than cracked
corn at 3X maintenance (Table 15-11. This difference is
less than the difference (16 percent) calculated by Theurer
et al. (19991.
WHEAT GRAIN
Data on the effects of processing wheat fed to dairy
cows are lacking. In situ DM disappearance of intact wheat
is low but once the kernel is broken, particle size does not
greatly affect extent or rate of DM disappearance (McAllis-
ter et al., 19901. In a study with nonlactating cows fed a
diet with 33 percent wheat, OM digestibility of the diet
was increased by 30 percent when the wheat was rolled
rather than when fed whole (Nordin and Campling, 19761.
The digestibility of OM was 88 percent for rolled wheat
and 41 percent for whole wheat grain. Based on that study,
wheat should undergo some mechanical processing prior
to feeding to dairy cows. Ground wheat to supply up to
33 percent of dietary DM has been fed to moderately
producing cows (ca. 30 kg/d) without negative effects (Fal-
det et al., 19891. The benefits, if any, of feeding; ground
wheat rather than rolled wheat to dairy cows are not known.
Oilseeds
COTTONSEED
The majority of cottonseed fed in the United States is
not processed; however, the effects of mechanical process-
ing and heat-treatment of cottonseeds have been investi-
gated (Arieli, 19981. The DM digestibility of diets with
15 percent intact, cracked, or ground Pima cottonseed
(naturally delinted) was not different when fed to lactating
cows although approximately 12 percent of the intact seeds
(weight basis) were excreted in the feces (Sullivan et al.,
1993a,b). Digestibility of fiber tended to be reduced and
digestibility of crude fat was increased by cracking or grind-
ing. Based on the digestibility data in those experiments,
the TDN of cracked and ground Pima seeds would be
about 7 percentage units higher (ca. 10 percent ~ than that
of intact Pima seeds. Milk production and gross efficiency
of feed utilization were not different when cows were fed
intact or cracked Pima cottonseed but gross efficiency was
9 percent higher for the diet with ground Pima seeds
compared with the diet that contained intact cottonseed
(Sullivan et al., 1993a,b). Similar to the data with Pima
cottonseed, 11 percent of the acid delinted cottonseeds
consumed by lactating cows were voided in the feces com-
pared with <1 percent of whole tinted cottonseed (Cop-
pock et al., 19851. Because of lack of dilution by lint,
delinted seeds generally have higher ether extract concen-
trations than tinted seeds; therefore differences in TDN
are less than differences in digestibiilty. However, based
on the data of Coppock et al. (1985) whole delinted cotton-
seeds have about 10 percent less TDN than whole tinted
seeds. When the delinted seeds were cracked TDN values
were slightly higher than those for whole tinted seeds (Cop-
pock et al., 19851. Grinding tinted cottonseeds had little
effect on extent and site of digestibility of most nutrients
or on milk production when fed to low producing cows
(fires et al., 19971.
The effect of heat-treatment of whole tinted cottonseed
on OM digestibility has been inconsistent. Heat-treatment
of cottonseeds has either not affected OM digestibility
(Pena et al., 1986) or decreased it (fires et al., 19971. In
the Pires et al. (1997) study, digestibility of NDF and CP
was reduced but digestibility of fatty acids was not affected
by heat-treatment. When heat-treated cottonseeds were
ground, digestibility of OM was similar to that for raw
cottonseeds (fires et al., 19971. Feed intake and milk pro-
duction were not different when low to moderate produc-
ing cows were fed raw or heat-treated cottonseed (Smith
and Vosloo, 1994; Pires et al., 19971. Pires et al. (1997)
reported increased milk protein when heat-treated cotton-
seed was fed.
Currently available data do not support adjusting the
NED value of tinted cottonseeds when they are ground or
cracked. Grinding significantly increases the energy value
of delinted cottonseeds. Even though chemical data sug-
gest that delinted cottonseeds would have more energy
than tinted seeds, based on digestibility, tinted seeds have
approximately 10 percent more available energy than delin-
ted seeds when intact seeds are fed.
SOYBEANS
Heat-treatment of soybeans generally consists of heating
the whole seed to 120 to 140° C and steeping for 30 to
OCR for page 255
Carbohydrate Chemistry and Feed Processing 255
120 minutes. Digestibility of diets with 10 to 18 percent
soybeans were not different when roasted or raw soybeans
were fed to dairy cows or steers (Bernard, 1990; Tice et
al., 1993; Aldrich et al., 1995), but one study (Scott et al.,
1991) found that OM digestibility of a diet that contained
16 percent soybeans was reduced (69 vs. 60 percent ~ when
roasted soybeans were fed compared with raw soybeans.
Roasting soybeans has not consistently altered crude fat
or fatty acid digestibility (Aldrich et al., 1995; Bernard,
1990; Scott et al., 1991; Tice et al., 19931.
Milk production was generally, but not always, increased
when cows were fed roasted soybeans compared with cows
fed raw soybeans. Two studies (Bernard, 1990; Scott et al.,
1991) with cows producing approximately 30 kg/d of milk
indicated no difference between raw and roasted soybeans.
Four other studies (Faldet and Satter, 1991; Tice et al.,
1993; Chouinard et al., 1997; Dhiman et al., 1997) indicated
that cows fed roasted soybeans produced 10 to 16 percent
more milk than did cows fed raw soybeans. Source of
forage did not seem to influence the results. Some of the
inconsistency could be caused by different heat-treatments.
Digestibility of OM from diets that contained whole,
cracked, or ground roasted soybeans was not different (Tice
et al., 19931. Milk production (38.5 vs.37.2 kg/d) was higher
for cows fed coarsely cracked roasted soybeans than for
cows fed ground roasted soybeans (Dhiman et al., 19971.
With low-producing cows (19 kg/d) mechanical processing
of roasted soybeans did not affect milk production (Tice
et al., 19931.
Data comparing the digestibility of diets that contained
extruded soybeans with diets that contained raw or roasted
soybeans are limited. Scott et al. (1991) reported similar
digestibility of diets that contained either 16 percent
extruded or roasted soybeans and both were lower than
the digestibility of the diet that contained raw soybeans.
Milk production by cows fed extruded soybeans was similar
or higher than that of cows fed raw or roasted soybeans
(Guillaume et al., 1991; Scott et al., 1991; Chouinard et
al., 19971. Digestibility data do not support adjusting NED
concentrations when soybeans are roasted, or extruded, or
when roasted soybeans are mechanically processed.
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Representative terms from entire chapter:
milk production
