Use of rumen-protected lysine and methionine in beef feedlot diets: Effects on steer performance, nutrient digestibility, and nitrogen balance

Authors: Neville, Bryan; Oliver, William; Wells, James; Crouse, Matthew; SCHOLLJEGERDES, E - New Mexico State University; Lindholm-Perry, Amanda; Kuehn, Larry; FREETLY, HARVEY - Retired ARS Employee

Submitted to: Applied Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/17/2025
Publication Date: 4/1/2026
Citation: Neville, B.W., Oliver, W.T., Wells, J.E., Crouse, M.S., Scholljegerdes, E.J., Lindholm-Perry, A.K., Kuehn, L.A., Freetly, H.C. 2026. Use of rumen-protected lysine and methionine in beef feedlot diets: Effects on steer performance, nutrient digestibility, and nitrogen balance. Applied Animal Science. 42(2):117-124. https://doi.org/10.15232/aas.2025-02742.
DOI: https://doi.org/10.15232/aas.2025-02742

Interpretive Summary: These experiments were conducted to understand how supplying rumen-protected lysine and/or methionine in a low protein diet changes animal performance. One hundred sixty-one beef steers were utilized in the feedlot experiment. Twenty beef calves with duodenal and ruminal cannulas were used in the balance study. Our data demonstrated that feeding adequate protein from conventional feeds resulted in greater average daily gain than feeding a low protein diet with supplemental lysine and/or methionine. Providing methionine improved animal gains; however, at the expense of increased feed intake. Continuing to develop methods like those proposed in the present study which aim to more adequately meet amino acid versus protein demands of livestock may have benefits beyond those of livestock production. However, in doing so, strategies that are developed should keep in mind the logistical and economic considerations of implementing such practices in feedlots.

Technical Abstract: Objective: Evaluate the impacts rumen-protected Lys and/or Met in a 10% CP diet compared to a 13% CP finishing diet on steer performance, nutrient digestibility, and nitrogen balance. Materials and Methods: One-hundred sixty-one beef steers (430 ± 44.5 kg) were utilized in the feedlot experiment. Treatments consisted of: 1) positive control diet (POS), formulated to contain 13.0% CP, 2) negative control (NEG) diet containing approximately 10.0% CP which formed the basal diet for the remaining treatments, 3) rumen-protected Met (RPMET) 7.2 g/d supplemental Met, 4) rumen-protected Lys (RPLYS) 18.5 g/d supplemental Lys, and 5) the combination of rumen-protected Lys and Met (RPMET+LYS) 7.2 and 18.5 g/d supplemental Met and Lys, respectively. Twenty beef steers (423 ± 34.2 kg) were used in the balance study. Results and Discussion: In the Feedlot Study, BW was unaffected by treatment (P = 0.24). Average daily gain for POS steers were greater (1.93 kg/d; P = 0.02) than NEG, RPLYS, and RPMET+LYS, but were not different than RPMET (1.86 kg/d; P = 0.17). Dry matter intake was greater in RPMET (P = 0.01) when compared to POS, RPLYS, and RPMET+LYS. Gain-to-feed ratio was greatest in POS steers (0.17 kg gain:kg DMI; P = 0.04). In the balance study, OM intake did not differ (P = 0.26; 7.55 ± 0.459 kg/d). Feeding a 13% CP diet or adding rumen-protected Lys and/or Met did not alter (P = 0.21) CP digestibility. Intake and excretion of nitrogen were not different across treatments (P = 0.13), which resulted in no differences (P = 0.43) in nitrogen balance which was positive for all treatments (37 ± 14.6 g/d). Implications and Applications: Based on the results of the present and previous research, the impacts of rumen-protected AA on performance of steers fed high-concentrate diets appear to be inconsistent. Present data demonstrated that the supplementation of rumen-protected Lys and/or Met did not affect nitrogen digestibility or retention.