Soybean Based Feeds for Dairy Cows
by H. Gale Bateman, II and Jimmy H. Clark
TAKE HOME MESSAGES
- Soybeans and soybean products are important feeds for the dairy industry.
- The major perceived limitation to using soybean meal as a feed for dairy cattle is the reported low escape of protein in soybean meal from the rumen but this value may be underestimated in cows consuming large amounts of feed.
- Heat, chemical, and mechanical treatments can be used to increase the amount of protein in soybeans and soybean meal that escapes ruminal degradation.
GLOBAL PRODUCTION AND USE OF SOYBEANS AND SOYBEAN PRODUCTS
Soybean meal, heat processed whole soybeans, and soybean hulls are the major soybean products used for feeding dairy cows. They have a nutrient content that is complementary to cereal grains such as corn, which makes this an excellent combination of feeds for dairy cows.
The world harvest of soybeans in 1997 was 173.5 million tons, which is more than one-half of all the oil seeds produced globally. Approximately 79% of the soybeans grown in the world were processed into 107.7 million tons of soybean meal with about 86% of the soybean meal being eaten by animals.
In the United States, 70.9 million acres of soybeans were planted and from that 81.8 million tons of soybeans were harvested, which is almost 50% of the world production of soybeans. About 54% of the soybeans produced in the United States were processed into 35.3 million tons of soybean meal and about 78% of this was eaten by animals. Dairy cattle consumed approximately 1.7 million tons or 6% of the soybean meal produced in the United States.
Estimates of the amounts of other soybean products that are fed to animals are hard to obtain. However, global estimates for the amount of whole soybeans fed to animals in 1996 were 6.8 million tons while an estimated 105,000 million tons of soybean oil were fed to animals.
Current statistics estimate the United States dairy herd at 9.2 million cows. If soybean meal was used as the sole protein supplement for all of these cows, the use of soybean meal as a feed for dairy cows would increase approximately 200%. Accurate estimates of potential increases in the amounts of other soybean products that could be fed to dairy cattle in the United States are not available. This is partially because accurate estimates of the amounts currently being fed are not available and partially because other nutritional factors limit the amount of products that can be included in diets fed to dairy cows.
APPROACHES FOR INCREASING THE USE OF SOYBEANS AND SOYBEAN
PRODUCTS AS FEEDS FOR DAIRY CATTLE
For soybean products to capture more of the market for protein supplements fed to dairy cattle both soybean and dairy producers must be educated about the benefits of feeding soybean proteins to dairy cattle. Optimal returns from protein supplements occur when the supplement maximizes microbial protein synthesis in the rumen and complements the mixture of protein from microbes and other feed proteins that pass to the small intestine. Soybean meal is degraded in the rumen and is an excellent protein supplement for supplying ammonia, amino acids, and peptides for ruminal microbial protein synthesis. However, the reported high ruminal degradability of soybean meal (approximately 65%) implies that it may not be able to supply amino acids from feed at the small intestine to complement that supplied from microbial protein synthesis and other feed proteins. The actual ruminal escape of proteins from soybean meal may be higher than reported values in the literature when fed to dairy cows. Values reported in most tables were measured using animals consuming small amounts of feed or using laboratory methods. High producing dairy cows consume much larger amounts of feed, which reduces the amount of time that the feed is exposed to the ruminal microbes and thus lowers the ruminal degradation of that feed. Furthermore, cows that consume large amounts of feed have ruminal fluid pH values that are about 6.0, which also decreases ruminal degradation of protein from soybean meal.
Illinois researchers summarized eight trials in which soybean meal was compared with other protein sources that had a reported lower ruminal degradability to determine the effects of source of supplemental protein on passage of protein to the small intestine (Figure 1). Only when more than 35% of the total dietary protein was supplied by the protein sources with low ruminal degradability was passage of protein to the small intestine increased and protein supplements typically supply less than 35% of the total dietary protein. Arizona researchers summarized 127 comparisons of soybean meal with other protein supplements and noted that only 22 of the comparisons showed an increase in milk production above that of cows fed soybean meal and eight comparisons showed that the undegradable protein source decreased milk production compared with feeding soybean meal. Because many protein supplements with low ruminal degradability are expensive, their use may not be economically favorable compared with soybean meal.
At least nine reasons may be responsible for the lack of increased production of milk and milk components when protein supplements with a reported high ruminal escape rate replace soybean meal in the diet of dairy cattle. Total protein may be oversupplied due to high concentrations of dietary protein. The proportion of protein supplied by the protein supplement may be too small to influence the amino acids flowing to the small intestine. Replacing degradable protein sources with undegradable sources may decrease microbial protein synthesis. The tabular values reported for ruminal escape of protein from soybean meal may be underestimated. Ruminal escape values for protein may change depending on the amount of feed consumed and other diet and ruminal characteristics. The supplemental protein source may not supply the amino acids that are needed by the cow to increase milk production. The protein supplement may contain the needed amino acids, but its intestinal digestibility may be low and therefore the protein in not digested well resulting in excretion in the feces. Many rations have a greater deficiency of energy than protein. The cow can use body tissues to minimize any protein or amino acid deficiency until body stores are depleted.
In order to increase the use of soybean products as feeds for dairy cattle, commercial heat treatments have been designed that reduce the ruminal degradability of protein from soybean meal. There are three methods used commercially to produce heat-treated soybean meal. These include cooker-expeller processing of soybeans, extruder-expeller processing of soybeans, and non-enzymatic browning of soybean meal. Researchers from the University of Wisconsin and Kansas State University reported that the ruminal escape of protein from cooker-expeller processed soybean meal ranged from 55 to 67% which is a 20 to 32 percentage unit increase from unprocessed soybean meal when determined using laboratory methods. Kansas researchers reported almost a 2-lb/d increase in milk production when cooker-expeller processed soybean meal replaced unprocessed soybean meal in diets fed to lactating dairy cows. To date there are no controlled research studies available to determine the ruminal escape of protein or milk production response to feeding extruder-expeller processed soybean meal. Only limited data from company testing has been reported for the ruminal escape of protein from these feeds. The ruminal escape of non-enzymatically browned soybean meal ranges from 69 to 88% depending on the methods used to measure it. University of Nebraska researchers reported no differences in milk production when diets containing 13% CP with the supplemental protein supplied as non-enzymatically browned soybean meal were compared with diets containing 16% CP with the supplemental protein supplied as unprocessed soybean meal.
The protein in whole soybeans is rapidly degraded in the rumen and the ruminal degradability of the protein in whole soybeans can be decreased by heat treatment. The two most common methods for heating whole soybeans are roasting and extruding. Wisconsin researchers reported from 2.9 to 3.3 lbs/d increased milk production when roasted or extruded soybeans replaced raw soybeans. In addition to supplying protein, the whole soybean provides fat, which may increase milk production above that of a similar amount of soybean meal. The fat in the soybeans contains both mono- and poly-unsaturated fatty acids, which may decrease milk fat test if fed in excessive amounts
Soybean hulls are a highly digestible fiber source that is readily consumed by dairy cows. However, the response in milk production when they have replaced forage, concentrate, or both has been variable. More research is needed to provide a more through understanding of the ability of dairy cows to use the nutrients obtained from fermentation of byproduct feeds such as soybean hulls.
The potential for increased use of soybeans and soybean products as feeds for dairy cattle is excellent. However, both dairy and soybean producers must be educated about the benefits of soybeans and soybean products if these products are to capture a larger portion of the market potential.