Influence of dietary lysine on growth performance and carcass characteristics of late-finishing gilts.

We conducted two experiments evaluating the lysine requirement of 91- to 113-kg gilts. Gilts (PIC L326 x C-22) with initial body weights of 42 (Exp. 1) or 39 kg (Exp. 2) were blocked by weight in a randomized complete block design. Experiment 1 included 105 gilts, with seven gilts per pen and five replications (pens) per treatment. Experiment 2 included 125 gilts, with eight gilts per pen and four replications (pens) per treatment. Gilts were fed a corn-soybean meal diet (no crystalline lysine) containing 1.0% total lysine from 39 to 68 kg and .80% total lysine from 68 to 91 kg. In Exp. 1, when the average weight of gilts within a block reached 91 kg, gilts were fed corn-soybean meal diets containing .40, .55, or .70% total lysine. Increasing dietary lysine increased (linear, P < .05) ADG, daily lysine intake (11.3, 15.1, and 19.8 g/d), gain/feed, plasma urea N, and carcass lean percentage but decreased 10th rib fat depth. Because of the linear responses in Exp. 1, Exp. 2 was conducted with corn-soybean meal diets containing .60, .70, .80, or .90% total lysine. Increasing total dietary lysine had no effect on ADG, gain/feed, 10th rib fat depth, or carcass lean percentage (P > .10). Daily lysine intake increased (linear, P < .01) with increasing dietary lysine (18.1, 21.1, 23.9, 26.5 g/d). Based on these results, the total dietary lysine requirement for 91- to 113-kg gilts is approximately .60% total lysine, which corresponds to approximately 18 g/d lysine intake.