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OCR for page 178
-
Crop Residues
INTRODUCTION
the potential for animal production through feeding crop residues is im-
pressive. The United States produces annually about 44 million tons of
wheat, 45 million tons of soybeans, and another 186 million tons of coarse
feed grains, dry basis (U.S. Department of Agriculture, 19791. The feed
grains consist primarily of corn, with lesser amounts of mile, barley, and
oats. Grain-producing plants normally produce an equal or greater weight
as vegetative material than as grain (Vetter and Boehlje, 19781. Therefore,
a total of at least 300 million tons of straws, stalks, and stubbles are
available in the United States each year (see Table 48) and another 40
million in Canada. Worldwide, over 1.5 billion tons of crop residues are
produced each year (for definitions of residues and other terms see the
glossary on p. 2101.
The 300 million tons of residues have sufficient energy to meet the
entire needs of the present beef cattle industry in the United States. How-
ever, the concentration of digestible energy is sufficiently low to prevent
the practical use of much of the residue without further treatment or
processing.
QUANTITY
Corn is the most widely produced grain crop in the United States. Nor-
mally, an amount of residue greater than the quantity of grain is produced
178
OCR for page 179
Crop Residues 179
above ground. Therefore, the production of 153 million tons of corn per
year yields at least 153 million tons of corn residue, which is over one-
half the total available residue supply (see Table 484.
Wheat residue constitutes 15 percent of the total crop residue because
grain production per land area is generally lower for wheat. Over 44 million
tons of wheat straw are produced per year.
Soybean residue accounts for another 15 percent of the crop residue
(45 million metric tons) and grain sorghum 5 percent (16 million metric
tons). Other small grains and crops account for the remaining residues
(see Table 484.
Crop residues are widely distributed. Corn residue is distributed throughout
the Corn Belt. Illinois, Iowa, Indiana, Kansas, Minnesota, and Nebraska
produce about 50 percent of the total crop residue supply. Wheat straw
is more widely distributed over the United States, but tends to be con-
centrated in the Great Plains States and the Northwest.
Soybean production has been centered in the Corn Belt, but is expanding
in the Southeast. Grain sorghum is produced primarily in the Great Plains
States, with 77 percent produced in Texas, Kansas, and Nebraska. Peanuts,
cotton, and rice are grown in the southern United States and California,
and sugarcane is produced in Louisiana, Florida, Hawaii, and Texas.
PHYSICAL CHARACTERISTICS
Crop residues can be collected from the field, but because of their bulky
characteristics and low market value per unit weight, transportation is
generally uneconomical. Because of differences in plant structure, grain
harvesting methods, and moisture content, residues vary concerning ease
of harvest. Straws from small grains are easily collected dry behind the
combine. Corn and especially grain sorghum residues often do not dry to
the extent needed for dry storage, but they can be stored as silage. Soybean
residue is difficult to harvest if allowed to drop on the ground behind the
combine. Soil contamination during harvest can be a problem with all
residues. Feeding of residues to livestock on the farm can be readily
accomplished. Most of the residues are produced in the summer and fall;
storage for extended periods may not be economical, but the greatest use
for livestock feed generally occurs in the winter.
Removal of crop residues from the soil may reduce soil filth (organic
matter) and increase the risk of wind and water erosion. Depending upon
soil type and topography, an average of one-half the total residue can be
removed (Larson et al., 19781. If the residue is used on the farm and the
resulting manure returned to the soil or if animals consume the residues
by grazing, there should be little detrimental effect on soil from crop
residue feeding.
OCR for page 180
180 UNDERUTILIZED RESOURCES AS ANIMAL FEEDSTUFFS
TABLE 48 Estimated Supply of Crop Residues
Dry Grain
(Product)
Crop Production ResidueDry Residue Percent of
Source (tons x 1 06)a Coefficients(tons x 1 o6) Total
Corn 153.0 1153.0 51.0
Soybean 45.2 145.2 15 .0
Wheat 44.2 144.2 14.7
Grain Sorghum 16.2 116.2 5.4
Barley 8.8 217.6 5.9
Oats 7.9 17.9 2.6
Cotton 2. 1 36.3 2. 1
Rice 5.6 15.6 1.9
Peanuts 1.6 1.52.4 0.8
Flax 0.3 30 9 0 3
Rye 0.6 10.6 0.2
Sugar Beets 4.3 0.140.6 0.2
Total 300.5
aFrom 1978 USDA Agricultural Statistics (1979).
From Vetter and Boehlje (1978); cotton, peanuts, sugar beets, and flax from Corkern et
al. (1979).
Some of the residues, such as cotton by-products, rice milling by-
products, and bagasse, that are produced at central locations have the
advantage of being collected and available for processing or treatment. In
fact, they may initially have a negative value because they present a
disposal problem.
NUTRITIVE VALUE
Without treatment, crop residues are low in nutritional value. Because
grain is harvested after the plant reaches physiological maturity, the veg-
etative portion is high in cell walls and lignin and low in protein and
digestible dry matter. It has been clearly shown that lignin inhibits diges-
tion of cellulose and hemicellulose, making about 1.4 times the weight
of the lignin in the matter indigestible (Van Soest, 19811. There is con-
siderable variation in digestibility both among and within residues. Con-
trolling and properly accounting for this variation may be the most important
key to efficient use of crop residues.
Corn
Corn residue consists of 54 percent stalks, 12 percent leaves, 21 percent
cobs, and 13 percent husks (Vetter, 19734. Husks and cobs are discharged
OCR for page 181
Crop Residues 181
from the rear of the combine and the mixture is referred to as husklage.
The husk is the most digestible part of the corn plant, with the digestibility
of the other parts being lower and more variable. Dry-matter digestibility
of the various parts of the corn plant ranges from 40 to 70 percent and
protein content from 2 to 7.5 percent (see Appendix Table 14. The corn
residues contain 70 to 80 percent cell walls, with nearly equal quantities
of cellulose and hemicellulose. Corn residue tends to be one of the richest
sources of hemicellulose found in nature.
The cornstalk decreases in digestibility and cell-soluble content with
time after physiological maturity of the corn plant (Berger et al., 1979;
McDonnell and Klopfenstein, 1980) (see Figure 11).
Digestibility of cornstalks is affected by moisture, variety, and tem-
perature, as well as by maturity (McDonnell and Klopfenstein, 19801.
Stalks left in the field for grazing also decrease in nutritional value with
time (Lamm and Ward, 19771. There is the possibility that the corn plant
might be changed genetically to improve stalk digestibility. The brown
midrib mutant is an example of such potential, but grain yields have been
lower than for normal corn (Colenbrander et al., 1973; Kahn and Hendrix,
19771.
.
70
65
60
> 50
~5
TO
O_
Y= -.193X + 63.22
R=.92 SE Y.X= 1.54
45
40
30 i
1 2
-
-
-
8
-
-
1 1 1
3 4 5 6 7
WEEKLY CORN STALKLAGE SAMPLI NG, 1976
9 10 (Weeks)
FIGURE 11 In vitro dry-matter disappearance (IVDMD) of cornstalks harvested over time.
SOURCE: Berger et al. ( 1979).
OCR for page 182
1 82 UNDERUTILIZED RESOURCES AS ANIMAL FEEDSTUFFS
Different harvesting systems produce corncobs, husklage, and corn-
stalks and stalklage; and stalk fields are available for grazing. Gestating
beef cows are able to more than maintain weight on these residues (see
Table 491. Growing calves gained weight (0.3 kg/day) on supplemented
corncobs (Koers et al., 19701. Berger et al. (1979) obtained gains of 0.65
kg/day with growing calves fed supplemented stalklage harvested the same
day as high-moisture (26 percent) grain. However, digestibilities as low
as 36.9 percent have been reported (Paterson et al., 1979J, which would
not support maintenance in calves.
Wheat and Other Small Grain and Grass Straws
Small grain straws are quite low in nutritional value; in addition to being
high in lignin content and, therefore, low in digestibility, they are also
very bulky. This tends to limit intake and adds to mechanical handling
problems. Wheat straw is probably the poorest quality straw, and barley
is only slightly better (see Table 494. Oat straw appears to have the highest
nutritional value (Anderson, 19781.
Acock (1978) has shown considerable variation in nutritional value of
wheat straw (protein and digestibility). Location of production, variety,
and time of straw harvest relative to grain harvest were all factors affecting
value. Jackson (1978) also reported these variations, as well as that due
to cultural practice.
Wheat straw with only a protein-vitamin-mineral supplement will not
maintain weight of gestating beef cows or calves. Acock et al. (1979) and
Dinusson (1969) have shown that feeding one-third alfalfa hay with wheat
straw can meet the protein needs of the gestating beef cow and give some
weight gain (0.2 kg/day). Coombe et al . ~ 1979a) and Lesoing et al . ~ 1980a)
have clearly demonstrated that chopped untreated wheat straw has little
value for growing calves. Similar conclusions can be drawn for barley
straw. Oat straw can probably meet the energy needs of the gestating beef
TABLE 49 Dry Cow Daily Weight Gain (kg) on Various Corn
Residue Systems (number of trials in parentheses)
Stacked
Source Grazing Stalks Stalklage Shucklage
Iowa 0.03 (5) 0.40 (4) 0.08 (1) 0.20 (3)
Nebraska 0.25 (6) 0.26 (2) 0.31 (1)
SOURCE: Ward (1978).
OCR for page 183
Crop Residues 183
cow but has little value for growing animals (Saxena et al., 1971) unless
treated to improve its nutritional value.
Rice straw is somewhat unique in that lignin and high silicon content
tend to limit digestibility. However, its feeding value would be similar to
wheat straw (Garrett et al., 19791. Grass straws available after grass seed
harvest have variable nutritive values. The variation is due to species
(Guggolz et al., 1971), variety (Early and Anderson, 1978), and time of
harvest (Durham and Hinman, 19791. Bluegrass straw supported small
weight gains and normal production in gestating beef cows (Early and
Anderson, 1978), but considerable amounts of supplemented grain were
needed to produce 0.5 kg/day gain in calves (Durham and Hinman, 1979~.
Rice and grass seed straws must often be removed from the field for
agronomic reasons. Therefore, these straws present disposal problems for
producers.
Soybean
Soybean residue is 30 to 35 percent pods and the remainder stalks (Vetter,
19731. Essentially no leaves are collectable. The pods are lower in cell
walls and lignin content than stalks and higher in protein and dry-matter
digestibility. Soybean stalks are very high in lignin content (20 to 23
percent) and therefore very low in digestibility. The pods may have some
use in beef cow maintenance diets, but probably have little value for
growing or lactating ruminants (Gupta et al., 19784.
Grain Sorghum
The grain sorghum plant is unique in that it does not die at physiological
until a killing frost (Smith,
19771. The residue following grain harvest is green and moist (60 to 70
percent H2O), and quality changes little with time (see Appendix Table
11. The moist residue harvested and stored as silage is a good beef cow
feed (McKee et al., 1977) and has potential in a diet for growing calves.
Both protein content and dry-matter digestibility may be higher than for
any residue except early harvested cornstalks or cornhusks.
Bolsen et al. (1977) obtained over 0.5 kg/day gain with growing calves
fed milo stover silage with protein supplement. They found an interesting
and consistent positive associative effect of feeding this residue with forage
sorghum silage (Bolsen et al., 19764. Ward et al. (1979) found that beef
cows could be maintained during gestation on milo stubble fields. The
cows gained about 0.3 kg/day, which is similar to the gain obtained with
corn stalk grazing.
maturity but continues to photosynthesize until a killing
OCR for page 184
184 UNDERUTILIZED RESOURCES AS ANIMAL FEEDSTUFFS
Other Residues
In the ginning of cotton, 50 to 75 percent of the harvested material is
residue, consisting of boll residues, leaves, stems, lint, and a small quan-
tity of cottonseeds. The residue has a low nutritional value, characterized
by its high lignin (14 percent) and low protein (5.6 percent) content. Use
of gin trash with supplemental cottonseed meal for growing steers produced
gains of 0.1 kg/day compared with 0.5 kg/day for steers fed sorghum
silage (Holloway et al., 19741. Finishing steers gained more rapidly when
the roughage portion of the diet consisted of 50 percent cottonseed hulls
than when it contained 50 percent cotton gin trash (Jones et al., 19571.
The estimated value of gin trash was 90 percent that of cottonseed hulls.
In another study, gin trash was substituted for 10, 30, and 50 percent of
alfalfa hay cubes in a diet consisting of 50 percent alfalfa and 50 percent
concentrate (Brown et al., 19791. Milk production of dairy cattle was
depressed slightly at the two higher levels. Efficiency of converting feed
energy to milk energy was decreased with increasing levels of gin trash.
Cottonseed hulls are a high-fiber, low-protein by-product of the cotton
industry. They have been used as a roughage source for beef and dairy
cattle. Cottonseed hulls substituted for alfalfa hay cubes at 10, 30, or 50
percent of the alfalfa resulted in no difference in milk production of dairy
cattle (Brown et al., 19771. However, as the percentage of cottonseed
hulls in the diet increased, the digestibilities of protein, energy, and fiber
decreased. Hunt et al. (1971) also observed no differences in milk pro-
duction when cottonseed hulls were included at 25, 35, and 45 percent
of the diet. A comparison of bluegrass straw, wheat screenings, and
pelleted and nonpelleted cottonseed hulls as roughage sources for yearling
steers showed cottonseed hulls to be inferior to the other roughage sources
(Heinemann, 19761. When each of the four sources constituted 13 percent
of the diet, average daily gains were 1.4, 1.4, 1.3 and 1.2 kg/day, re-
spectively. Feed conversion was least efficient for animals fed the cot-
tonseed hull diets.
Although high in fiber and lignin content, peanut hulls have a consid-
erable amount of protein (8 percent). This protein value may vary with
the quantity of peanut kernels that remain with the hulls during processing.
Utley and McCormick ( 1972) examined the use of peanut hulls in a feedlot
study with Hereford steers. The hulls were combined with concentrate at
0, 10, 20, and 30 percent of the diet and fed ad libitum for 84 days. The
highest average daily gains, when adjusted for body fill, were on diets
with 10 or 20 percent hulls, and the most efficient feed conversion was
with the 10 percent hull diet. A second feedlot study showed no significant
differences among diets. Dry-matter digestibility decreased with the ad
OCR for page 185
Crop Residues 185
dition of peanut hulls. Calhoun and Shelton (1973) also found that 10
percent peanut hulls was optimum for high-concentrate lamb diets. The
use of 30 percent peanut hulls for growing steers was found equivalent
to 30 percent cottonseed hulls (Burdick et al., 1975), and growth of
wintering calves was satisfactory with a 60 percent peanut hull diet.
Rice hulls are low in protein, high in fiber, and contain unusually large
amounts of lignin (1 1-17 percent) and silica (22 percent). At 40 percent
of the diet, scouring, with mucous and blood in the feces, has been
observed with cattle (White, 19664. At 20 percent of the diet these symp-
toms were not seen. McManus and Choung (1976) reported that raw rice
hulls were rejected by sheep. Wintering steers accepted rice hulls at 25
percent of the diet, the remainder being prairie hay (Noland and Ford,
19541. Daily feed intake was restricted to 5.4 kg, and average daily gain
was 0.8 kg, compared with 0.86 for an all prairie hay diet.
Sugarcane bagasse is the residue of the crushing and milling of sugar-
cane. It is very low in protein (~2 percent) and high in fiber. Randel
(1970a) was unable to show any differences in performance of male calves
initially weighing 114 to 454 kg fed a 20 or 30 percent bagasse diet at
either 12.5 or 16 percent crude protein. Milk production of dairy cattle
was not altered when a diet consisting of 22.5 percent bagasse, 20 percent
molasses, and 57.5 percent concentrate was substituted for a conventional
concentrate-sorghum silage diet (Randel, 1970b). Replacement of cotton-
seed hulls with bagasse in a 25 percent roughage diet for lactating dairy
cattle had no detrimental effect on milk production (Marshall and Van
Horn, 19751.
Clanton and Harris ( 1966) found that calves fed ensiled sugar beet tops
that had been field-wilted achieved higher daily gains than calves fed
unwilled ensiled beet tops or calves that were pastured on beet tops (0.61,
0.49, and 0.54 kg/day, respectively). In another study (Rush, 1977),
average daily gain decreased linearly as beet tops were substituted for
corn silage in a growing calf ration. Calves went from an average gain
of 0.88 kg/day with no beet tops to 0.59 kg/day when beet tops were
substituted for 60 percent of the corn silage. Levels of beet tops above
30 percent of the diet produced scouring. When pasturing cattle on beet
tops, one hectare can carry one animal unit for 36 days with animal gain
approximately 0.5 kg/day (Leonard et al., 19731. Sugar beet tops are best
utilized when combined with another residue (such as cornstalks) or forage.
Sugarcane tops are a fibrous feed that is normally discarded in the field
during the harvesting of sugarcane. Growing cattle fed fresh tops for 1 12
days maintained their weight, while those fed ensiled tops lost 0.27 kg/
day (Estima et al., 19671. The addition of molasses or cassava roots had
little effect on gain or feed consumption, but supplementing 1.5 kg/day
OCR for page 186
186 UNDERUTILIZED RESOURCES AS ANIMAL FEEDSTUFFS
of cottonseed meal stimulated both intake and daily gain. In another study
(Pate et al., 1971 J. growing steers full-fed on tops were unable to maintain
their weight, losing 0.1 kg/day. Subsequent supplementation with 0.9 kg/
day of cottonseed meal increased gains to 1.1 kg/day and increased dry-
matter intakes of cane top from 5.9 to 7.4 kg/day. Finishing cattle were
fed cane tops at 0, 17, 34, and 51 percent of the diet (Pate and Coleman,
19751. Steers fed the 17 percent level gained as well as those receiving
the control diet (0.9 kg/day), and feed efficiency was similar.
Residues from sunflower seeds and faba bean production appeared to
be quite high in digestibility (70.5 and 61.4 percent, respectively). Their
feeding value would be expected to be quite high on the basis of these
laboratory digestibilities, but animal growth data are unavailable (Kernan
et al., 19801.
Vegetable and fruit field residues consist of leaves, vines, culls? and
unharvested crops. Thus, unlike other crop residues, which are almost
universally low-quality roughages, these residues vary widely in their
nutritional value and in their availability. The University of California
summarized its previously unpublished research in the area of unusual
feedstuffs for livestock (Leonard et al., 1973), from which much of the
following information was taken.
Lettuce contains approximately 93 percent moisture. On a dry basis it
is comparable to some cereal grains, with a TDN of 70 percent and 7
percent digestible protein. Cattle prefer to consume the heads rather than
the leaves. Cattle consumed up to 16 kg carrots/day in addition to sup-
plement and gained about 0.1 kg/day. Fresh peaches can be fed at a rate
of 9-14 kg/day, with no evidence of scouring. When 2.7 kg dried peaches
were fed, scouring ensued, and shortly thereafter the animals refused the
fruit. One-half this level was consumed for 10 days with no ill effects.
Pears were consumed at a lower rate, and spoiled pears were more readily
refused than spoiled peaches. Scouring also occurred with fresh prunes at
levels over 6.8 kg/day. Dried prunes were fed at the level of 2.7 kg/day
with no detrimental effects. Grapes have been fed to cattle at levels up
to 16 kg/day and raisins at 2.7 kg/day with no ill effect. Consumption of
peaches created a slight off flavor in milk.
By-products from sweet corn production are available and of quite high
value. The dry-matter digestibility of the stalks remaining after harvest of
the ears is over 65 percent. Up to 20 percent of the ears are not harvested
because of weather and other factors. The whole-plant material is over
66 percent digestible. Cannery residue is over 70 percent digestible. All
of the products are high in moisture but also high in nutritive value, nearly
equal to field corn silage.
Pea vines are also high in nutritional value (63.4 percent TDN). They
are collected at central locations and present a disposal problem.
OCR for page 187
Crop Residues 187
Leaf waste from cauliflower, a product of the packing shed, was sep-
arated to provide a poultry meal fraction containing 375 to 620 mg/kg
xanthophyll and 26 to 31 percent protein, and a cattle meal fraction that
contained 17 to 21 percent protein (Livingston et al., 19721. The xantho-
phylls were equivalent to dehydrated alfalfa meal as a pigmenting agent
for broiler skin. Sweet potato vine meal has also been shown to be effective
as a pigmenting agent (Garlich et al., 19741.
Haines et al. (1959) fed celery tops to Hereford steers at 0, 10, 20, and
30 percent of a diet containing sorghum, soybean meal, citrus pulp, and
citrus molasses for 112 days. Diets were isonitrogenous, and dehydrated
Bermudagrass was fed ad libitum. Average daily gains were 1.01, 1.03,
0. 85, and 1 . 12 kg/day, respectively. Steers receiving the 20 percent celery
top ration were the least efficient converters of concentrate and roughage.
A digestion trial with four steers yielded a TDN of 79.5 percent. Crude
protein was 25.0 percent on a dry-matter basis.
Cassava, although not grown widely in the United States, is a major
food crop in many areas of the tropics and could assume importance as
both a human and animal food, since its yield of energy per unit land can
be quite high. Because of the presence of a toxic glucoside, cassava leaves
must be dried or boiled prior to feeding to reduce toxin levels. Cassava
leaves have a high protein content (25 percent), although they may be
deficient in methionine and tryptophan (Rogers and Milner, 19631. Use
of cassava leaves in poultry diets results in poor growth unless supple-
mented with methionine (Ross and Enriquez, 19691.
PROCESSING METHODS
If crop residues are to be used to meet the energy requirements of growing
and lactating ruminants, their feeding value must be increased. There
seem to be two possibilities for this at the present time. One is manipulation
of harvest time or genetics to obtain higher-quality residues, and the other
is to treat residues physically or chemically to increase digestibility and/
or intake.
Corn
Many chemicals have been screened in laboratory experiments for their
potential to enhance digestibility. However, only four are being routinely
used in experimentation with animals: sodium hydroxide, ammonia, cal-
cium hydroxide, and potassium hydroxide.
Chemical treatment breaks the ether linkages between lignin and cel-
lulose or hemicellulose. The saponified lignin is not soluble in acid and
OCR for page 188
188 UNDERUTILIZED RESOURCES AS ANIMAL FEEDSTUFFS
therefore may be measured by most methods (Lau and Van Soest, 1981~.
However, the resultant increase in digestibility is still obtained.
Modes of action for chemical treatment of crop residues have been
described by Wailer (19761. Chemical treatment solubilized some of the
hemicellulose while not changing the cellulose content. Extent of bacterial
digestion in vitro was increased for both cellulose and hemicellulose.
Chemical treatment, especially with sodium hydroxide, increased the rate
of digestion for both cellulose and hemicellulose. Therefore, one could
conclude that the modes of action of chemical treatment, especially treat-
ment with sodium hydroxide, include ( 1 ) solubilization of hemicellulose,
(2) increasing the extent of cellulose and hemicellulose digestion, and (3)
increasing the rate of cellulose and hemicellulose digestion, possibly by
swelling.
During the past several years two systems for application of chemical
treatments primarily with sodium hydroxide, have evolved (Jackson, 19771.
One system, described by Rexen and Thomsen (1976), involves appli-
cation of a concentrated sodium hydroxide solution prior to pelleting. Heat
produced in pelleting causes the chemical reaction to go rapidly to com-
pletion. The process involves collection and transportation of residue to
a central processing plant, followed by chopping or grinding and mixing
concentrated sodium hydroxide solution with the residue. Sodium hy-
droxide serves as a pellet binder in addition to its effect on nutrient
digestibility. A dense, hard pellet is then produced; excess moisture is
removed in the cooling process.
Response to pelleting of cornstalks is shown in Table 50. As indicated
by the in vitro digestibility values, the stalks were of very low value. Both
NaOH treatment and pelleting increased rate and efficiency of gains. The
combination of pelleting and NaOH treatment was slightly more than
additive. The diets contained one-half relatively low-quality alfalfa as well.
While animal performance was not especially good, feeding the treated
TABLE 50 Pelleted and Sodium Hydroxide-Treated Cornstalksa
Chopped Pelleted Chopped Pelleted
Performance Control Control NaOH Treated NaOH Treated
Daily gain (kg) 0.16 0.28 0.24 0.31
Daily feed (kg) 6.3 6.5 6.6 5.4
Feed/gain ratio 0.026 0.043 0.036 0.057
IVDMDb 37.0 38.0 59.0 61 .0
aTwenty-two calves/treatment, 205 kg initial weight, 91-day trial. Diets were 50 percent
alfalfa (50 percent IVDMD).
bin vitro dry-matter disappearance.
SOURCE: Klopfenstein, unpublished data.
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200 UNDERUTILIZED RESOURCES AS ANIMAL FEEDSTUFFS
problem is the period of time from the end of residue grazing until green
grass is available. This hiatus generally occurs during the calving period
when the nutrient requirements of the cow are rather high. A harvested
feed is necessary. There is an opportunity for increased use of crop residues
during this time period, but the nutritional value must be higher than that
of present material to meet the needs of the cow.
Another important problem with the grazing of stalks or stubble is the
weather. In higher-rainfall areas of the eastern United States the residues
deteriorate rapidly, and muddy conditions may prevent continual grazing.
In the western Corn Belt and Plains states, adequate grazing can usually
be obtained. Snow cover may prevent grazing, however, and some har-
vested forage is needed. Harvested crop residues can meet this need rather
economically. Ward ( 1978) reported an average of 88 days of crop residue
grazing in eastern Nebraska. An average of 250 kg/cow of supplemental
stacked residue was fed as well. Cows gained over 0.25 kg/day and were
supplied 1 ha corn or milo residue/cow.
Feeding straws to cows is of interest because of the availability of wheat
straw in many areas. Other residues (corn and grain sorghum) may not
be available in these areas.
Beef cow/calf production systems are illustrated in Table 57. These
systems range from extensive, using grass, to intensive, using only crop
residues. Any of these systems can be economical depending upon man-
agement and cost of grain and protein.
A system of growing and finishing beef calves is shown in Table 58.
The calves were allowed to graze cornstalks followed by harvested stalk-
lage feeding. Summer grazing of grass preceded a high-grain finishing
period. Less than 800 kg grain were needed to finish these animals, about
TABLE 57 Cow-Calf Production
Intensive Intensive
Condition Extensive Corn Residuea Strawa
Mid gestation Stalk grazing Stalklageb Treated straw
Late gestation Stalkageb.c Stalklageb C Treated straws
Early lactation Grass Treated stalklage ~Treated straws
and
concentrate
Mid and late lactation Grass Treated stalklage ~Treated straws
aRequires 4 metric tons residue/year and 170 kg protein.
bCould be replaced by treated straw.
CRequires .04 kg protein/kg residue.
Requires .06 kg protein/kg residue.
OCR for page 201
Crop Residues 201
TABLE 58 Beef Production Systems With Heifers
Utilizing Crop Residues
Cornstalk grazing, 56 daysa
Harvested stalklage, 75 daysb
Summer grass, 110 days'
High-grain finishing, 93 days
0.52 kg/day
0.02 kg/day
0.70 kg/day
1.34 kg/day
aEquivalent of 280 kg residue, 0.06 kg protein needed/kg crop residue.
b450 kg residue.
CEquivalent of 770 kg residue.
Equivalent of 1,600 kg residue.
SOURCE: Faulkner and Ward (1981).
1.7 kg/kg beef produced. Forages were emphasized, especially crop res-
idues, and compensatory gain was exploited.
Alfalfa, which is a good source of supplemental protein and minerals,
may be the logical choice to add to sodium hydroxide-treated rations in
an attempt to slow the rate of fiber passage, increase the extent of rumen
fiber digestion, and equilibrate mineral balance (Paterson et al., 1978a).
The additions of various levels of chopped alfalfa hay in sodium hydroxide-
treated corncob or cornstalk diets were evaluated in lamb digestion trials.
Dry-matter digestibility of the diets was improved from 50 percent for
the all-alfalfa diet to 63 percent for the 50:50 alfalfa:NaOH-treated cob
diet. However, when the sodium hydroxide-treated cobs composed more
than 50 percent of the diet, dry-matter digestibility decreased to approx-
imately 60 percent on the all-treated-cob diet. Lambs exhibited large
individual fluctuations in digestibility with diets of 100 percent sodium
hydroxide-treated cobs. This variation and the decreased digestibility may
be a function of sodium load and rate of fiber passage. In vitro dry-matter-
disappearance values compared well with the in vivo digestibilities in diets
of up to 50 percent treated cobs. The difference in digestibilities for the
two diets was approximately 20 percentage units at the all-treated-residue
diet. The failure of the in vivo values to correspond with the expected
potential digestibility of in vitro values seems to suggest the effects of
sodium on rate of passage and fiber digestion. Similar results were found
with cornstalks.
Hydroxide-treated corncobs were fed along with alfalfa hay to growing
steers to evaluate (1) response to chemical treatment and (2) associative
effects of alfalfa and hydroxide-treated cobs (Paterson et al., 1978a).
Treatment of corncobs with 3 g sodium hydroxide and 1 g calcium hy-
droxide/100 g dry matter increased gains of growing calves an equivalent
of 0.27 kg/day. Feeding 50 percent alfalfa with treated cobs increased the
OCR for page 202
202 UNDERUTILIZED RESOURCES AS ANIMAL FEEDSTUFFS
response to chemical treatment and showed positive associative effects
(see Figure 13~.
Jackson (1978), in an excellent review, has summarized the effects of
diluting sodium hydroxide-treated -straws with either concentrates or high-
quality forages. Concentrates dramatically reduced the digestibility of the
fiber, especially at higher levels. Below 15 percent of the diet, concentrates
seemed to have little effect on fiber digestion. High-quality forages, as
was shown here with alfalfa, did not reduce digestibility of crop-residue
fiber. Obviously, the formulation of the complete diet is very important
in realizing the full benefits of crop-residue treatment.
POTENTIAL UTILIZATION
Crop residues will likely play a very large role in future production of
meat and milk by ruminants. Low-cost extensive systems presently make
good use of some residues but meet the needs of only a small portion of
.70
.60 l
-
Z .50
-
~ .40
>
.30
~ 3 9 sodium hydroxide and 1 9
/ \ jcium hydroxide/100 9 cobs
/ \
Entreated \\
/\
1 1 1 .1
25 50 75 100
LEVEL OF ALFALFA REPLACING COB RATION
FIGURE 13 Average daily gains of steers fed corncob ration with 0,
50, or 100 percent alfalfa hay addition. SOURCE: Paterson (1979).
OCR for page 203
Crop Residues 203
the ruminant population. Utilization of crop residues can be increased by
cultural and management practices, such as stage of maturity at harvest.
The greatest increase in utilization of crop residues will likely come
from chemical treatment in combination with improved management prac-
tices. Sodium hydroxide has been widely studied as a chemical for crop-
residue treatment. While the treatment is effective, concerns about human
safety and sodium residues may limit its ultimate usefulness. Probably
treatments with ammonia and combinations of chemicals will prove more
useful.
In addition to feeding systems, systems of harvest, treatment, and stor-
age can be developed to optimize the use of residues.
ANIMAL AND HUMAN HEALTH PROBLEMS AND REGULATORY
ASPECTS
There are no special animal or human health problems involved with
feeding crop residues or treated residues to ruminants. Any residue stored
improperly will likely mold and can potentially produce aflatoxins that
can have devastating effects on animals.
Most crops that provide residues for feeding have had herbicides or
insecticides applied to them. These compounds present no health problems
to animals or people as long as label directions are adhered to strictly.
Compounds that are cleared for use on crops for silage will obviously be
suitable for use when crop residues are harvested. Herbicides are generally
not applied near harvest, but on some occasions insecticides might be
applied shortly before harvest. The insecticide label will indicate safety
for use on forage crops.
For some crops, such as cotton, the whole plant is never intended for
silage, and clearance for insecticides might not be as straightforward as
for forage crops. Herbicide and insecticide residues can present a very
real and serious problem for livestock producers. This does not need to
be a problem if the correct compounds are used and if they are used in
strict accordance with label directions.
Sodium hydroxide, calcium hydroxide, and ammonia do not leave any
toxic residues in treated feedstuffs. If these chemicals are sold for the
purpose of increasing the digestibility of feedstuffs, U.S. Food and Drug
Administration approval is probably necessary. Efficacy rather than safety
is the primary concern.
RESEARCH NEEDS
Considerable research has been conducted on crop residues, but much
remains to be done. The nutritional value of residues must be improved
OCR for page 204
204 UNDERUTILIZED RESOURCES AS ANIMAL FEEDSTUFFS
in many instances, and systems of collecting, storing, treating, and feeding
must be improved to make increased use economical.
Nutritional improvement seems to be possible by plant genetic im-
provement, harvest management, chemical treatment, physical treatment,
or biological treatment. All of these need further innovative research.
SUMMARY
The potential for increased use of crop residues in ruminant production
is quite impressive, but the extent of usage depends on two important
factors: the availability of grain for feeding to ruminants and the amount
of research progress made in improving the nutritional value of crop
residues.
Residues from the various crops vary in nutritional value, physical
characteristics, and response to treatment. It is risky to generalize from
one residue to another. Because of the low nutritional value of residues,
methods of increasing value are of interest. Calcium hydroxide and am-
monia treatments have the greatest long-term potential.
Livestock production systems can be developed to use large quantities
of residues. These systems would not presently replace all of the grains,
but would reduce the quantity used.
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2 10 UNDERUTILIZED RESOURCES AS ANIMAL FEEDSTUFFS
GLOSSARY TERMS
BAGASSE
CHAFF
CORN HUSK
CROP
RESIDUE
HULLS
HUSK
HUSKLAGE
IN VITRO
IN VIVO
POD
STALK
STALKLAGE
STOVER
STRAW
Solid residue remaining after extraction of juice.
Husks, hulls, joints, and small fragments of straw that are separated
from seed in threshing of small grains.
CORNCOBS Fibrous portion of the fruiting head (grain producing portion) of the corn
plant, excluding the husk.
Fibrous outside cover of the fruiting head (grain producing portion) of
the corn plant.
Fibrous residue remaining after harvest of the primary product (grain,
fruit, etc.).
Outer covering of seeds.
Outer covering of kernels or seeds, especially when fibrous.
Corncobs and husks.
Outside the living organism in an artificial environment.
Within the living organism.
Empty seed vessel.
Main stem of a herbaceous plant.
Moist, ensiled stalks.
Stalks and leaves of corn or sorghum after grain harvest.
Plant residue remaining after separation of the seeds by threshing of
small grains.
STUBBLE Lower parts of plant stems that remain standing in the field after harvest.
Representative terms from entire chapter:
sodium hydroxide
