Effects of increasing amounts of true ileal digestible lysine on the growth performance of growing-finishing pigs reared in a commercial facility

Two 28-d experiments using 2,259 gilts were conducted to determine the growth and economic effects of increasing dietary true ileal digestible (TID) lysine in commercially reared growing-finishing pigs. Both experiments included 6 dietary treatments of incrementally increasing TID lysine in diets containing 6% added fat. The dietary TID lysine ranged from below to above our current requirement estimates to determine if there were any changes in lysine requirements during the past five years. In Exp. 1, pigs were initially 132 lb and averaged 192 lb at the end of the 28-day study. The TID lysine rates were 0.65, 0.75, 0.85, 0.95, 1.05, and 1.15%, which corresponded to lysine:calorie ratios of 1.80, 2.08, 2.35, 2.63, 2.91, and 3.19 g/Mcal, respectively. Increasing TID lysine increased ADG (linear, P<0.01) and improved F/G (quadratic, P<0.06), with optimal performance at 1.05% TID lysine (TID lysine:ME ratio of 2.91 g/Mcal). Pigs fed this diet consumed approximately 22 g of TID lysine per day, and used 21.6 g of TID lysine/kg of gain. Although not significant, margin over feed cost (MOF) was numerically greatest for pigs fed 1.05% TID. In Exp. 2, pigs were initially 177 lb and averaged 241 lb at the end of the 28-d study. The TID lysine rates were 0.52, 0.62, 0.72, 0.82, 0.92, and 1.02%, which corresponded to lysine:calorie ratios of 1.44, 1.71, 1.99, 2.27, 2.55, and 2.83 g/Mcal, respectively. In Exp. 2, the optimal TID lysine rate changed over the course of the experiment. During the first 14 d, pigs fed 0.92% TID lysine had the greatest ADG and lowest F/G, whereas pigs fed 0.72% TID lysine had the numerically highest ADG and lowest F/G from d 14 to 28. Pigs fed these diets required approximately 19.5 g of TID lysine/kg gain. Margin over feed costs increased (quadratic, P