Effects of Dietary Supplementation with 2-Hydroxy-4-(methylthio)-butanoic Acid Isopropyl Ester as a Methionine Supplement on Nitrogen Utilization in Steers

SIMPLE SUMMARY: Ruminants excrete large amounts of nitrogen (N), which negatively affects the environment. Supplying limiting amino acid (AA) methionine (Met) usually considerably improves the N utilization rate of ruminants. 2-Hydroxy-4-(methylthio)-butanoic acid isopropyl ester (HMBi) has been widely used as a Met supplement to ruminants. However, the effects of HMBi on the N utilization rate in ruminants usually vary widely. The experiment assessed the effects of dietary addition with HMBi on the N metabolism in beef steers and elucidated the mechanism using the plasma metabolome. Adding HMBi upregulated the plasma concentration of Met but did not improve the N utilization rate in steers. The main reason for the results could be that steers used in the experiment were in the fattening period. It is suggested to evaluate the effects of dietary addition with HMBi using growing cattle. ABSTRACT: The objective of the experiment was to investigate the effects of dietary supplementation with 2-hydroxy-4-(methylthio)-butanoic acid isopropyl ester (HMBi) on the nitrogen (N) metabolism in beef steers. The plasma metabolites analyzed by metabolome profiling were used to clarify the impact mechanism. Three Simmental steers (body weight, 593 ± 23 kg) were used as experimental animals. Three levels of HMBi (i.e., 0, 12, and 24 g d(−1)) were added in a basal ration as experimental treatments. The steers and the dietary treatments were randomly allocated in a 3 × 3 Latin square design. The results showed that supplementing HMBi up to 24 g d(−1) did not affect the N retention and N retention rate (NRR), and the fecal N/urinary N ratio even though it tended to linearly increase the uric acid N/urinary N ratio in steers. The results of plasma metabolome profiling showed that supplementing HMBi at 24 g d(−1) upregulated the plasma concentrations of L-methionine (Met); Met-related metabolites including betaine, Met sulfoxide, and taurine; and L-isoleucine and tyrosine, whereas it downregulated L-serine, glycine, diaminopimelic acid, and other metabolites. The reason for the nonsignificant effect of HMBi on improving the N utilization in steers could be that the steers used in the experiment were in the fattening period. It is suggested to evaluate the effects of the dietary addition of HMBi using growing cattle in further research.