Protein requirements of growing steers limit-fed corn-based diets

Abstract

Seven steers (513 lb) were used in an experiment to investigate optimal levels and sources of protein in diets limit-fed to allow gain of 2.2 lb/day. Treatments were: a negative-control diet (urea; supplemented, 11.7% crude protein) and six diets containing either 13.5, 15.4, or 17.2% crude protein with either solvent-extracted (SSBM) or expeller-processed (ESBM) soybean meal, in which the soybean meal replaced corn in the control diet. Diets provided 75, 87.5, 100, or 112.5% of estimated crude protein requirement for a gain of 2.2 lb/day. The basal diet contained 83% rolled corn, 15% alfalfa , and .2% urea. Nitrogen (N) retention was increased linearly (P<.01) by SBM addition with no differences between sources. Because N retention increased to the highest level offered, the steers apparently required more protein than estimated by the 1984 National Research Council' s Nutrient Requirements of Beef Cattle.