Alternative Fiber Sources for Dairy Cattle:

Uses and Limitations

Rick Grant

Department of Animal Science, University of Nebraska,
Lincoln, NE 68583-0908 U.S.A.
E-mail: ansc801@unlvm.uml.edu

Take Home Messages

• Fibrous co-products can be used to successfully replace either dietary concentrate or forage.
• Fibrous co-products reduce the incidence of ruminal acidosis when they replace starchy concentrates.
• When fibrous coproducts replace dietary forage, the effective fiber content of the total ration must remain adequate to prevent acidosis-related problems that may reduce performance.
• Guidelines are suggested for optimal feeding of alternative fiber sources for lactating dairy cows.

Introduction

Fibrous co-products are a major feed resource for the dairy industry. Commonly used co-products which supply fiber and energy to the diet include soybean hulls, corn gluten feed, dried distillers grains, brewers grains, beet pulp, wheat midds, and wheat bran. Some of these co-products, such as dried distillers grains, are commonly considered excellent sources of crude and escape protein as well. Alternative feeds such as whole cottonseed provides fiber, lipid, and protein. When feeding co-products, potential objectives include: increasing milk yield, decreasing feed costs, extending limited supplies of forage, and/or reducing the incidence of ruminal acidosis. Important considerations when incorporating these co-products into a feeding system include:

• economics of using co-products in different feeding systems,
• proper handling and storage facilities,
• potential variations in nutrient content,
• energy values at high levels of feed intake typical of lactating dairy cows,
• effectiveness of fiber in finely ground co-product feeds, and
• whether the byproduct will replace starch or forage fiber in the ration.

This paper will focus on the energy and fiber value of co-product feeds as a function of whether the feed is replacing starch or forage fiber in the ration. An understanding of both the practical and fundamental nutritional aspects of feeding fibrous co-products is necessary to successfully incorporate them into diets for high-producing dairy cows.

Replacement of Dietary Starch with Fibrous Co-products

When feeding high levels of grain, the composition of the grain should be adjusted to include greater percentages of alternative fiber sources such as soybean hulls, ear corn, corn gluten feed, beet pulp, and hominy. Inclusion of these fibrous feeds helps to minimize ruminal acidosis and related herd health problems associated with feeding low-fiber diets.

Soybean Hulls

Soybean hulls are high in fiber (Table 1), but the fiber is so highly digestible that the hulls are essentially equal to corn in energy value when fed to beef or dairy cattle. The typical composition of several common co-products is given in Table 1. For extensive information on chemical composition of co-product feeds, see Belyea (5). The typical neutral detergent fiber (NDF) digestion rate for many forages is approximately 4 to 5%/h, so the NDF in soybean hulls and beet pulp is obviously very rapidly digested.

Table 1. Chemical composition and fiber digestion of fibrous co-products.

Item	Byproduct
	Soyhullsa	Brewers grains	Beet pulp	Cottonseed hulls
	(% of DM)
CP	11.3	25.4	9.7	4.1
NDF	70.3	46.0	54.0	90.0
Lignin	2.0	6.0	2.0	24.0
NDF Kd, h-1	0.070b	0.043	0.116	0.035
NDF Lag, h	0.4	0.5	0.8	2.7

^a Data for soyhulls from Shain et al. (20). Data for other co-products from Belyea (5).

^b NDF digestion data from Torrent et al. (23) and Shain et al. (20).

Dairy cattle, as ruminants, evolved as utilizers of forage and other roughage sources. However, grain feeding is often the most economical means to increase energy intake. Overconsumption of starchy grain results in two problems of immense concern to dairy producers: ruminal acidosis and negative associative effects of starch on fiber digestion. Ruminal acidosis is associated with feed intake fluctuations, off-feed problems, milk fat depression, laminitis, poor body condition, and reduced milk yield.

Anderson et al. (3) fed beef steers diets containing stalklage (control), and either 50% corn or 50% soybean hulls in place of stalklage. At this level, steers consuming the corn diet showed a rapid drop in ruminal pH to below 5.65, followed by a rapid return to prefeeding levels (Figure 1). Steers fed the 50% soybean hull diet showed a more gradual decline in pH to 6.2, then a slow decline to 6.0 by 12 h postfeeding. The decrease in ruminal pH from 6.2 to 6.0 for this diet was due to soybean hull NDF fermentation because cell solubles would not account for the prolonged, lower ruminal pH. It would be ideal if ruminal pH did not decrease with soybean hull supplementation, but because the hull is as digestible as corn, a similar amount of volatile fatty acids (VFA) is produced. However, because soybean hulls contain high NDF and low lignin concentrations (Table 1), they result in a ruminal VFA profile more closely resembling that of forages than mixed diets with comparable energy content (2, 8).

Figure 1. Changes in ruminal pH following feeding for cattle fed a control, 50% corn, or 50% soybean hull diet (2,3).

Similar research has not been conducted with dairy cows, although one would expect a similar effect on ruminal pH when adding soybean hulls or other fibrous co-products are added to the diet. The typical diet for high-producing cows is often half grain or more on a dry basis. This type of ration leads to substantial negative associative effects of starch on fiber digestion, presumably mediated by reductions in ruminal pH. To enhance the ruminal fibrolytic activity, the best substitute for starchy concentrates is highly digestible fiber, such as that found in soybean hulls and other common co-products such as beet pulp or gluten feeds.

Nakamura and Owen (17) fed diets to lactating dairy cattle in which the pelleted concentrate contained 100% corn, 50% corn:50% soybean hulls, or 100% soybean hulls, plus 5 to 10% soybean meal, minerals, and vitamins. All diets contained equal crude protein levels (16%) and were fed as total mixed rations. The results of this study are shown in Table 2. Addition of soybean hulls did not improve milk yield; however, they minimized the depression of milk fat percentage often associated with feeding pelleted grains, and so 3.5% fat-corrected milk yield was maintained at normal levels. This study clearly indicated that addition of fibrous co-products minimizes the milk fat depressing effect of pelleted grain diets, and that soybean hulls in particular have an energy value at least equal to corn when fed to lactating dairy cattle.

Table 2. Performance of dairy cows fed diets containing soybean hulls in place of corn in the concentrate mix¹.

Item	Diets
	Corn	Corn-Soyhulls	Soyhulls
DMI, % of BW	4.32	4.36	4.38
Milk, kg/d	29.8a	28.9ab	27.3b
3.5% FCM, kg/d	27.8	28.1	27.1
FCM/DMI, kg/kg	1.20	1.18	1.15
Milk fat, %	3.13a	3.33ab	3.49b
Milk protein, %	3.08a	3.00a	2.84b
Milk lactose, %	5.06	4.85	5.11

^a,b Means within a row with unlike superscripts differ (P<0.05).

¹ Data from Nakamura and Owen (17).

More recent research (11, 15, 20) has verified that soybean hulls are an effective replacement for concentrate or forage in lactation diets. On a more fundamental level, intake and flow of NDF to the duodenum was 42 to 43% greater for cows fed soybean hulls in place of corn in the concentrate mix (15). Flow of total amino acids and total essential amino acids to the duodenum was not altered when soybean hulls replaced either 25 or 50% of the forage or concentrate dry matter (11).

Corn Gluten Feed, Beet Pulp, and Fibrous Co-product

Combinations

Although soybean hulls have been most intensively investigated, other fibrous co-products and co-product combinations will provide highly digestible fiber and consequently reduce the negative performance and metabolic effects associated with feeding large quantities of starch.

Bernard et al. (6) found that corn gluten feed can replace 27% of the dietary dry matter without altering milk yield, whether fed dry or wet, but these researchers pointed out that new feed deliveries should be sampled regularly and amounts fed adjusted to compensate for varying nutrient concentrations. Indeed, variability in nutrient composition of co-product feeds can be substantial. Likewise, Hutjens (14) reviewed the feeding of wet and dry corn gluten feed and found that corn gluten feed can be fed at up to 20 to 30% of the dietary dry matter. Interestingly, it appears that primiparous cows respond more favorably to wet corn gluten feed than do older cows.

Several researchers have examined various amounts of soybean hulls, corn gluten feed, wheat midds, and beet pulp as replacements for dietary concentrates (7, 10, 16). Generally levels of up to 22 to 31% of the ration dry matter have no negative effect on milk yield. Bernard and McNeill (7) concluded that although high-fiber energy supplements supported milk production equally, significant differences existed among co-products in their effect on dry matter intake and milk composition (Table 3).

Research at the University of Nebraska (1) evaluated the effectiveness of either whole cottonseed or a combination of soybeans, soybean hulls, and sodium bicarbonate at replacing forage fiber. The combination of whole soybeans and soybean hulls resulted in the same chemical composition as the whole cottonseed. Both the cottonseed and the soybean and hull combination were fed at 15% of the ration dry matter. Although rumination time was substantially reduced for the soybean and hull combination, the added bicarbonate compensated for this reduction in chewing and saliva production. Therefore, milk fat percentage and efficiency of fat-corrected milk production was the same as for the whole cottonseed diet. These results illustrate the potential to feed varying combinations of different co-products to achieve the same production results most economically. Specifically, the combination of soybeans and soybean hulls is usually substantially less expensive than cottonseed in the midwestern US.

Table 3. Corn gluten feed, soybean hulls, and wheat midds in lactation diets¹.

Item	Diet
	Control	Corn gluten feed	Soyhulls	Wheat midds
Ingredients
Corn silage	46.2	40.4	48.0	41.1
Corn gluten feed	--	22.4	--	--
Soyhulls	--	--	22.6	--
Wheat midds	--	--	--	22.4
Corn, shelled	34.5	25.5	10.8	22.4
SBM, 49% CP	16.5	8.9	15.5	11.5
Composition
CP, % of DM	15.8	16.0	15.7	15.6
NDF, % of DM	33.0	35.9	42.6	36.6
NEL, Mcal/kg	1.68	1.69	1.65	1.68
Performance
DMI, kg/d	21.3ab	22.0ab	22.5a	21.2b
Milk, kg/d	27.7	28.6	27.7	27.9
Milk fat, %	3.50	3.50	3.67	3.47
Milk protein, %	3.39ab	3.44a	3.32b	3.38ab

^a,b Means within a row with unlike superscripts differ (P<0.01).

¹ Data from Bernard and McNeill (7).

Fibrous Co-product and Lipid Mixtures

Shain et al. (20) fed lactating dairy cows four diets of equal protein and energy content that contained either no added fat, 1% ruminally inert fat (Ca salt of long-chain fatty acid), a 6% level of soybean hull:soy lecithin:soapstock (SLS), or a 12% level of SLS. Soapstock and soy lecithin are commonly available lipid co-products of the soybean oil processing industry. Efficiency of 4% fat-corrected milk production was greatest for cows fed SLS at 6% of dietary dry matter (Table 4). The SLS mixture was an excellent source of fiber and vegetable fat, comparable in feeding value to corn, for inclusion in the diets of beef calves and lactating dairy cows. Use of soybean hulls and other fibrous co-products as a carrier for dietary lipids holds considerable promise as high-energy co-product feeds. Subsequent research at the University of Nebraska indicates that at least a portion of the SLS product escapes ruminal fermentation and can alter milk fatty acid profiles to create a more consumer-friendly product (less C16:0 and more C18 series fatty acids).

Table 4. Performance of dairy cows fed mixtures of soybean hulls:soy lecithin:soapstock¹.

Item	Diet
	Control	6% SLS	12% SLS	Ca-FA
Milk, kg/d	30.95a	35.42b	32.33a	31.48a
Fat, %	3.74	3.58	3.61	3.69
Protein, %	3.18ab	3.09b	3.23a	3.13a
Lactose, %	5.11a	5.16a	5.06b	5.02b
4% FCM, kg/d	29.47b	32.97a	30.41b	29.96b
FCM/DMI, kg/kg	1.24a	1.25a	1.12b	1.24a

^a,b Means within a row with unlike superscripts differ (P<0.05).

¹ Data from Shain et al. (20).

Replacing Forage Fiber with Fibrous Co-products

When replacing forage fiber with significant amounts of fibrous co-products, adequate effective fiber in the ration must be maintained. A complete consideration of fiber nutrition of the dairy cow includes:

ADF = 19 to 21% of dry matter (minimum),

NDF = 26 to 29% (minimum),

NDF from coarse roughage = at least 65% of NDF from coarse roughage, and

Particle size = 1 cm theoretical length of cut.

Adequate fiber level of proper particle length assures normal chewing activity and ruminal function. Effective fiber is a measure of the feed's ability to stimulate chewing and includes fiber content and texture (particle size). Symptoms of insufficient effective fiber include:

• decreased rumination,
• decreased salivation,
• decreased ruminal pH and acetate:propionate ratios,
• decreased milk fat,
• intake fluctuations and off-feed problems,
• laminitis, and
• low body condition score.

Dietary NDF from forage can be reduced to 60% or less, well below the National Research Council (18) recommendation of 75%, and still provide sufficient effective fiber for fat-corrected milk production that is similar to or superior to high forage diets (Table 6). In fact, the NDF from forage has been reduced to as little as 39.6% with no significant effect on NDF intake or fat-corrected milk production (11). All diets summarized in Table 6 contained combinations of alfalfa hay or silage and corn silage that were replaced by fibrous co-product feeds. Whether similar results would be obtained using other forages has not been investigated. Most research has been conducted with soybean hulls; and, averaged over all experiments, the NDF intake was 11.9% and fat-corrected milk production was 2.8% greater than control, high forage diets (Table 6).

The maximal, or optimal, amount of fibrous co-product feed that can safely replace dietary forage for a complete lactation is not known with certainty. Studies designed to determine the effectiveness of fibrous co-products (as judged by milk fat percentage) when replacing forage fiber (4, 21) have utilized midlactation cows. Early lactation cows may not tolerate greater amounts of fibrous co-products compared with later lactation cows because of greater tendencies toward lameness, abomasal displacement, and other metabolic disorders (4, 9). Of the 10 trials summarized in Table 6, only 5 were continuous trials that lasted longer than 10 wk, and none lasted for a complete lactation. Consequently, appropriate amounts of fibrous co-products as replacements for dietary forage are unclear.

Figure 2 illustrates a potential decision support aid, based on the limited data in Table 6, regarding the optimal feeding of soybean hulls as dietary forage replacements. If an economically sound decision has been made to replace forage with soybean hulls, stage of lactation and dietary forage concentration should be considered. The source, amount, and physical form of the forage affects the use of fibrous co-products (26, 27). For the trials in Table 6, cows averaged 30 days in milk at the beginning of the experiments. Consequently, no definitive data exist for the dairy cow during the critical transitional weeks of lactation. Perhaps fibrous co-products may be safely fed prior to 30 days in milk, but more data are needed to support or refute this idea. The data in Table 6 demonstrate that soybean hulls and some other common fibrous co-products can be fed successfully after 28 days in milk, and that dry matter intake and fat-corrected milk yield are a function of forage level and physical form. Keep in mind that the scheme in Figure 2 is tentative, conservative, and probably will be modified as more research is conducted. However, it does provide dairy producers and nutritionists with information when making decisions about whether and how to feed fibrous co-products.

A series of trials at Ohio State University have examined the replacement of forage fiber with co-products. Firkins et al. (13) fed a diet containing 15% alfalfa silage, 20% corn silage, 36% corn, 7% soybean meal, and 20% dry corn gluten feed (dry basis). This diet was fed with or without 1% sodium bicarbonate. The combination of 1% buffer plus 20% corn gluten feed increased milk yield by 10% over a control diet and was an effective replacement of fiber from corn silage.

Replacement of dietary concentrates with soybean hulls and fat tended to increase milk yield and efficiency of milk production. Although typical diets should contain about 75% of NDF from forage, rations containing 60 to 63% of NDF from forage, and fibrous co-products, decrease negative associative effects and improve efficiency of milk production (12, 24).

Researchers at Wisconsin have developed a system which compares the effectiveness of NDF from co-product feeds to NDF from alfalfa as judged by milk fat yield. Results of this research indicate that the effective fiber value of whole cottonseed and dried distillers grains are equivalent to alfalfa (9). Oat hulls, corn gluten feed, brewers grains, beet pulp, and malt sprouts were half as effective as NDF from alfalfa for correcting fiber deficiency in low-forage diets (21). Wheat midds and cobs were 57 and 45% as effective as alfalfa (23). Other reported values for effective fiber of co-product feeds are given in Table 5.

Researchers at the University of Nebraska observed that cows fed diets in which soybean hulls replaced 42% of dietary silage in combination with coarsely chopped hay in place of 33% of dietary silage yielded 2.8 kg/d more milk and maintained 4% fat-corrected milk yield similar to cows fed 60% forage and no soybean hulls (Table 6). When high quality forage is limited, the percentage of dietary NDF from forage can be reduced successfully to 45% with the inclusion of 25% soybean hulls and 20% coarsely chopped alfalfa hay in the dietary dry matter for lactating dairy cows (26,27). The key is addition of the coarsely chopped hay because it provides adequate effective NDF in the forage fraction of the diet to maintain normal rumination activity.

Table 5. Effective fiber content of selected co-product feeds¹.

Feed	NDF %	Effectiveness factor	eNDF %
Cottonseed	44.6	1.30	57
Oat hulls	66.2	0.72	47
Distillers grains	30.2	0.80	31.5
Corn cobs	72.5	0.45	33
Wheat midds	43.5	0.57	25
Malt sprouts	52.0	0.48	25
Beet pulp	48.3	0.43	21
Brewers grains	58.0	0.33	19
Corn gluten feed	34.3	0.56	19
Soybean hulls	70.0	0.30	21

¹Data from Armentano and Clark (4).

Conclusions

Fibrous co-products can successfully replace starch and forages in diets for lactating dairy cows. When properly fed, these co-products effectively supply both fiber and energy.

Table 6. Replacement of dietary forage with nonforage fiber sources.

Ref#	Fiber source1	Control diet forage level	Forage type	Forage replacement	NDFR2 for control	NDFR for test diet	% Change from control
							NDF intake	DMI	FCM
		(% of DM)		(% of DM)	(%)		(% of BW)		(kg/d)
12	Soyhulls	40.6	alfalfa silage: corn silage (1:3, wt/wt)	7.0	NR3	62.5	2.1	-1.2	-2.3
19	Soyhulls	43.2	alfalfa hay: corn silage (1:1), wt/wt)	4.6 9.1	80.0 80.0	70.0 60.0	-2.6 -2.6	-2.7 0	-0.8 4.4
11	Soyhulls	50.0	alfalfa hay: corn silage (1:4, wt/wt)	12.5 25.0	75.6 75.6	57.8 39.6	0 3.0	-2.2 -4.5	-1.7 -5.2
20	Soyhulls	52.6	alfalfa haylage: corn silage (1:1, wt/wt)	14.1	76.6	51.3	25.6 31.3	9.4 14.7	3.74 3.85
26	Soyhulls	60.0	alfalfa silage corn silage (1:1, wt/wt)	25.0	80.0	45.0	23.7	7.2	5.36

Table 6. (cont.)

References

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