Soybeans and soybean byproducts have long been utilized as feed ingredients for livestock. However, with the development of the ethanol industry and increased availability of alternative byproduct feeds, the use of soybean products in beef cattle diets is currently not as prevalent as it was in the past. For example, only 1.9% of the total soybean meal consumed by livestock was consumed by beef cattle in 2023. However, with increased demand for biodiesel, increased development of seed crushing capacity, and unpredictable export markets, increased use of soybeans and soybean byproducts as feedstuffs for beef cattle in the future may become more feasible. The main constituents of soybeans are protein, oil, soluble carbohydrates, insoluble carbohydrates, and minerals. Soybeans also contain bioactive and antinutritional components, such as isoflavones, saponins, trypsin inhibitors, and phytic acid, yet less is known about their effects on digestion, metabolism, and health in ruminants than in nonruminants. The primary feed ingredients from soybeans used in beef cattle diets are soybean meal and soybean hulls, although there are several others, such as whole soybeans, soybean oil, glycerin, okara, lecithin, and fermented soy products. Soybean meal has long been considered the gold standard of plant-based protein sources for use in livestock diets because of its protein concentration, amino acid composition, and nutrient digestibility. Because soybean meal has approximately 65% ruminally degradable protein, the advantages of improved and complimentary amino acid composition as compared with corn or corn byproducts are partially compromised. However, bypass sources of soybean meal can be used to help overcome these limitations. Also, research has suggested that protein supplementation in the form of true protein to supply amino acids and peptides to the ruminal microbes as opposed to nonprotein nitrogen sources can improve ruminal fermentation and growth performance, and other components of the soybean meal other than protein may have beneficial effects on ruminal fermentation and growth performance. It is challenging to design experiments to examine the efficacy of different protein sources because of the difficulties in predicting amino acid flow to the small intestine and in formulating diets to isolate the effects of the protein fraction of the protein source. Soybean hulls also are an excellent feedstuff for ruminants, especially as an energy supplement for cattle fed forage-based diets because of less negative associative effects in the rumen as compared to starch-based supplements. The potential for the use of other soybean products and on bioactive and antinutritional components of soybeans also will be discussed.

Swanson, K. 2026. Soy Use in Cattle Diets: Impacts on Digestive Physiology and Tying It All Together. ASAS Midwest Section Meeting. Abstract 227. https://doi.org/10.1093/jas/skag107.269