Postruminal lysine and methionine infusion in steers fed a urea-supplemental diet adequate in sulfur.

Postruminal utilization of methionine by growing steer calves fed ground shelled corn, urea, and cottonseed hulls adequate in sulfur was studied by abomasal infusion of graded quantities of methionine with lysine adequate. A 6 X 6 Latin square of treatments was replicated in which infusions provided lysine and methionine in grams per day: A) 0,0; B) 24,0; C) 24,4; D) 24,8; E) 24,12; and F) 24,12 plus 140 g sodium caseinate. Treatments were brought to volume in 2 liters of water and infused continuously over 24 h. Responses measured were nitrogen retention, urea nitrogen in plasma, and concentrations of free amino acids. Retention of nitrogen was increased in steers abomasally infused with lysine or lysine in combination with graded quantities of methionine. Infusion of 4, 8, or 12 g/day of methionine with constant lysine (24 g/day) did not alter nitrogen retained from lysine infused alone. Infusion of a lysine-methionine-sodium caseinate positive control raised nitrogen retention compared with no caseinate. Lysine of plasma was higher in treatments in which lysine was infused compared with the negative control. Methionine increased linearly with infusion of incremental quantities. Methionine was not limiting when infused prostruminally with adequate lysine to growing steers fed the urea-supplemented diet with sulfur adequate.