Aimee Wertz-Lutz, IBC director column

Aimee Wertz-Lutz, IBC director, writes this monthly column featured in Iowa Cattleman Magazine.

April 2026

Using Soybean Meal in Feeder Cattle Diets

A focal point of the recent Midwest American Society of Animal Science meetings was the use of soybean meal (SBM) in feeder cattle diets. This topic was also a source of discussion during winter meetings, and so I thought I would share some thought here.

While using SBM as a protein source in feeder cattle diets is not new, the emergence of competitively priced corn co-products as protein sources in the 1990’s has resulted in limited use of SBM in feeder cattle diets in recent years.  However, increasing U.S. soybean crush capacity and impacts of tariffs on soybean exports may result in increased domestic SBM supplies and SBM becoming a more competitively priced option for use in feeder cattle diets. Additionally, research supports that partially replacing distiller’s grains with soybean meal in feeder cattle diets during certain phases may improve feed efficiency of feeder cattle. The response to SBM inclusion appears to be greatest during periods of rapid lean growth such as in young growing cattle, after implanting, and during the use of a β-agonist.

Current thoughts are that soy protein complements corn protein in supplying an ideal amino acid profile and resulting in improved feed efficiency. Protein nutrition in cattle is complicated. While cattle diets are often formulated for crude protein, that crude protein is fractionated into a rumen-degradable protein (RDP) and rumen-undegradable protein (RUP) once in the rumen. Both RDP and RUP fractions are key to meeting amino acid requirements of cattle. The RDP fraction feeds the rumen microbes that ferment feed to energy and become a source of protein as they pass to the lower digestive tract, supplying roughly half of all the protein needed to meet cattle requirements. The RUP fraction remains unaltered by the microbes and passes to the lower digestive tract to supply the remaining protein (amino acids) required by cattle. Because the RUP fraction bypasses rumen degradation, the amino acid composition of this fraction can be controlled in an effort to complement the microbial protein and target amino acids that may be needed for improved growth efficiency.

As Midwestern growing-finishing diets have become composed largely of ingredients such as corn, earlage, corn silage, corn distiller’s grains, and/or corn gluten feed, all amino acids in the RUP are from corn proteins, which have a limited supply of amino acids such as lysine, histidine, arginine, and methionine. If price warrants, inclusion of SBM can be beneficial as supplies of these amino acids are more abundant in its RUP fraction. Traditional heat-treated SBM is an excellent source of RDP to feed microbes, but traditional SBM is only about 30% RUP, whereas bypass SBM is further processed to have 65-70% RUP, which allows producers to manipulate the amount of soy protein that bypasses the rumen by manipulating the inclusions of SBM and bypass SBM.

While the value that corn co-products have brought to the cattle feeding industry as an inexpensive source of protein in feeder cattle diets cannot be refuted, changes in domestic SBM supplies may impact the price of SBM making it a more competitive protein source in Midwest feeder cattle diets. Research supports that SBM is a suitable substitute for at least a portion of the distiller’s grains included in the diet and may result in improved feed efficiency in cattle when used.

The United Soybean Board, which manages the soybean check-off, has funded several projects where SBM has been fed to beef cattle. Results of those projects and additional information on the use of SBM in livestock feed can be found on their website. In addition to the ability to manipulate amino acid supply in feeder cattle diets, SBM has additional functional components that may have anti-inflammatory benefits in livestock as well.

The IBC at Iowa State University serves as the university’s extension program to cattle producers. Our center comprises a team of faculty and staff from the College of Agriculture and Life Sciences, the College of Veterinary Medicine and Iowa State University Extension and Outreach. We work together to develop and deliver the latest in research-based information to improve the profitability and vitality of Iowa’s beef industry. If you’d like to be notified of updates on progress of research projects or programs that might be coming to your area, please subscribe to our “Growing Beef” newsletter by following the link on our website, www.iowabeefcenter.org. If you have a question, use our “Ask our Experts” link. Also, feel free to call us at 515-294-BEEF or email us at beefcenter@iastate.edu. You can follow @iowabeefcenter on Facebook, Twitter, YouTube, and Instagram.