Amino acid requirements for beef cattle

Trials were conducted to determine the methionine and lysine requirements of growing and finishing beef steers based upon gain response to incremental amounts of rumen-protected methionine and lysine. A finishing trial was conducted to determine the lysine requirement for feedlot cattle. Addition of rumen-protected methionine and lysine improved gains and efficiencies (P \u3c .05) during the first 56 days. There was no response to methionine alone (P \u3e .30), suggesting that lysine was the first-limiting amino acid. Although steers supplemented with 3 to 4 g/day had the greatest gains, nonlinear analysis predicted a supplemental lysine requirement of 2.5 g/day. The calculated metabolizable lysine requirement was 57.9 g/day or 5.5% of the metabolizable protein. Two growth trials were conducted to determine the methionine and lysine requirements for growing cattle consuming forage diets. For steers supplemented with meat and bone meal, the addition of 2.9 g/day of rumen-protected methionine maximized gains. The calculated metabolizable methionine requirement was 11.6 g/day or 3.1% of the metabolizable protein. In steers supplemented with corn gluten meal, the addition of .9 g/day of rumen-protected lysine maximized gains. The calculated metabolizable lysine requirement was 22.5 g/day or 5.7% of the metabolizable protein. Two growth trials were conducted to evaluate feather meal as a source of sulfur amino acids. In steers supplemented with meat and bone meal, addition of feather meal resulted in a linear increase in gain (P \u3c .01). However, addition of rumen-protected methionine further improved gains (P \u3c .10). In steers supplemented with blood meal, addition of sulfur amino acids, from either feather meal or rumen-protected methionine, improved gains (P \u3c .05). However, the maximum gain response obtained with feather meal was 50% of the maximum gain response obtained with rumen-protected methionine. Feather meal is an effective source of sulfur amino acids, but methionine may still limit gain. Formulation of diets to provide adequate amounts of metabolizable amino acids can improve gain in beef cattle