Amino acid requirements of growing steers

Methionine and lysine requirements of growing steers were investigated. In preliminary work, steers were abomasally infused with graded levels (0, 100, 200 and 300 g/d) of casein or mixes of crystalline amino acids simulating the nonsulfur amino acid pattern of casein, both with and without 12 g/d abomasally infused L-methionine (4 replications/treatment). Nitrogen retention increased linearly in response to casein infusion and in response to infusion of the amino acid mixture when methionine was supplemented. Methionine supplementation increased N retention when steers were infused with 200 or 300 g/d of the amino acid mix; postruminal supplementation with nonsulfur amino acids increased response of steers to methionine supplementation. Sulfur amino acid requirements of growing steers were studied in an 8 x 8 Latin Square experiment in which treatments were abomasal infusion of L-methionine (0, 3, 6, 9, 12, 15 or 18 g/d) or DL-methionine (6 g/d). All steers were abomasally infused with 300 g/d of an amino acid mixture simulating the nonsulfur amino acid pattern of casein. Nitrogen retention responses of steers infused with L-methionine and measures of intestinal amino acid flows indicated that steers (294 kg) gaining 1.3 kg/d required 14.7 g/d absorbable sulfur-containing amino acids. Nitrogen retention of steers infused with 6 g/d DL-methionine and those infused with 6 g/d L-methionine were not different, but the efficacy of DL-methionine in supplying sulfur-containing amino acids to steers could not be evaluated because infusion levels were above requirements. Plasma methionine concentrations were higher for steers receiving DL-methionine than for those infused with L-methionine, implying that metabolism of D-methionine by steers is different than that of L-methionine. Lysine requirements of growing steers were studied with a replicated 4 x 4 Latin Square in which treatments were abomasal infusions of L-lysine (0, 8, 16 and 24 g/d). All steers were abomasally infused with 300 g/d of an amino acid mixture simulating casein, except lysine was deleted. Nitrogen retention was not affected by treatment; lysine requirements of 355 kg steers gaining.77 kg/d were less than 40.2 g/d intestinally available lysine.U of I OnlyETDs are only available to UIUC Users without author permissio