Optimum Dietary Standardized Ileal Digestible Lysine and Crude Protein for Growth and Carcass Performance in Finishing Pigs after 100 Kg BW

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. In conclusion, the SID Lys requirement was 0.62 to 0.63% with performance maximized with diets containing 13% CP and HCW maximized with 12% dietary CP in pigs over 100 kg BW.

			CP, %
	9	10	11	12	13	SEM	Quadratic, P<
ADG, g	810	851	894	912	930	22.5	0.001
ADFI1, g	2,994	3,143	3,137	3,118	3,109	55.3	0.322
G:F	0.270	0.272	0.285	0.293	0.299	0.0044	0.001
HCW, kg	99.7	100.7	101.4	101.6	101.3	0.87	0.074

¹Linear, P = 0.073.