Effects of Increasing Standardized Ileal Digestible valine:lysine Ratio on the Growth Performance of 21 to 40 kg Pigs

A total of 351 pigs (DNA 600 × 241; initially 21.4 ± 0.35 kg) were used in a 21-d experiment to determine the effects of increasing standardized ileal digestible (SID) Val:Lys ratio in 22 to 36 kg pigs. Pigs were randomly allotted to one of six dietary treatments with five pigs per pen and 12 replications per treatment. Diets were corn-soybean meal-based and fed in meal form. A basal diet with 1.10% SID Lys was formulated to a 60% SID Val:Lys ratio, and L-Val was added to create a second basal diet that provided a 75% SID Val:Lys ratio. These two diets were then blended to create intermediate Val:Lys ratios of 63, 66, 69, and 72%. On d 0, 10, and 21, pigs were weighed to determine ADG, ADFI, and G:F. On d 10, pigs were fasted for 5 h then blood was drawn for plasma urea nitrogen (PUN) analysis. From d 0 to 10, BW, ADG, and G:F increased (linear, P < 0.05) as SID Val:Lys ratio increased, but with little improvement past the 72% Val:Lys ratio. No differences were observed from d 10 to 21. Similar to d 0 to 10, overall G:F increased (linear, P = 0.012) as the Val:Lys ratio increased, but with little improvement past the 72% SID Val:Lys ratio. As the SID Val:Lys ratio increased, there was an increase in PUN concentration (linear, P = 0.029). Valine intake in grams per day and g per kg of gain increased (linear, P < 0.001) as SID Val:Lys ratio increased. Lysine intake per kg of gain decreased (linear P = 0.029) as the SID Val:Lys ratio increased. Modelling the G:F response suggested a broken line linear model was the best fit, with increasing SID Val:Lys improving G:F to a breakpoint of 69% SID Val:Lys, with no improvement when the ratio was further increased. The results of this study suggest that a 69 to 72% SID Val:Lys ratio may be ideal for 21 to 40 kg pigs.