Two experiments were conducted to determine the optimum standardized ileal digestible (SID) Lys and CP concentrations in finishing pig diets.

In Exp. 1, 253 pigs (DNA 600 × 241, initially 102.0 kg BW) were used in a 23-d trial. Pens of 7 or 8 pigs were allotted by BW and randomly assigned to 1 of 4 dietary treatments with 8 replications per treatment. Diets contained 4 SID Lys concentrations (0.45, 0.55, 0.65, and 0.75%). Increasing SID Lys influenced (quadratic, P<0.05) ADG (0.86, 0.97, 0.94, and 0.92 kg) and ADFI (2.79, 3.01, 2.85, and 2.87 kg) with pigs fed 0.55% SID Lys having the greatest final BW. Marginal improvements (quadratic, P=0.058) in G:F (0.307, 0.323, 0.329, and 0.319) and (linear, P=0.051) carcass yield (73.7, 74.2, 74.1, and 74.5%) and reduction (quadratic, P=0.074) in backfat (15.7, 16.3, 15.7, and 15.0 mm) were also observed with increasing SID Lys. Carcass ADG (0.63, 0.72, 0.70, and 0.68 kg) increased (linear, P=0.014) and carcass G:F (0.226, 0.240, 0.244, 0.238) was marginally influenced (quadratic, P=0.063), resulting in pigs fed 0.55% SID Lys having the greatest HCW. The quadratic polynomial model for ADG and G:F predicted maximum response at 0.62 and 0.63% SID Lys, respectively. The broken line linear model predicted no further improvement in G:F over 0.55% SID Lys.

In Exp. 2, 238 pigs (DNA 600 × 241, initially 111.8 kg) were used in a 26-d trial to determine the optimum dietary CP concentration. Pens of 7 or 8 pigs were allotted by BW and randomly assigned to 1 of 5 dietary treatments with 6 replications per treatment. Diets included 5 levels of CP (9, 10, 11, 12, and 13%). Increasing CP influenced (quadratic, P<0.05) ADG, G:F, carcass ADG and carcass G:F with the greatest response for pigs fed the diet with 13% CP. Increasing CP marginally influenced (quadratic, P<0.074) HCW, with the greatest response for pigs fed the diet with 12% CP.