Effect of dietary concentration of metabolizable lysine on finishing cattle performance.

A finishing trial and a metabolism trial were conducted to determine the effect of supplemental metabolizable Lys level on finishing calf performance and to estimate the metabolizable Lys requirement of finishing calves. The finishing trial included 60 individually fed crossbred beef steer calves (237 kg; SD = 20 kg) supplemented with either incremental amounts of rumen-protected Lys and Met, or Met alone. Addition of Lys and Met improved gains and efficiencies (quadratic; P < .02) during the first 56 d. There was no response to supplemental Met alone, suggesting that supplemental Lys rather than Met was responsible for the improvement in performance. Using nonlinear analyses to compare gain relative to supplemental Lys intake, maximum gain was determined to be 2.10 kg/d, or .27 kg/d above the zero Lys control, at a supplemental Lys intake of 2.56 g/d. Steers supplemented with 3 and 4 g of Lys had a weight advantage over the control steers of 16 kg at 56 d and 32 kg at the end of the 161-d trial. However, there were no statistical responses to Lys or Met during any periods after 56 d. During a separate metabolism trial, four steers fed the control finishing diet were slaughtered, and abomasal contents were collected for amino acid analyses. The predicted (Level 1 NRC, 1996) metabolizable protein flow to the abomasum for the control diet was 715 g/d, and the predicted Lys flow was 37.9 g/d. A supplemental Lys intake of 2.56 g/d would increase the Lys flow to 40.5 g/d. Feedlot diets low in ruminal escape protein may be deficient in metabolizable Lys, especially early in the feeding period. The metabolizable Lys requirement of steer calves gaining 2.10 kg/d is estimated to be 40.5 g/d.