Estimation of the standardized ileal digestible valine-to-lysine ratio in 13- to 32-kilogram pigs

Three experiments were conducted to determine the optimum standardized ileal digestible Val-to-Lys (SID Val:Lys) ratio for 13- to 32-kg pigs. In Exp. 1, 162 pigs weaned at 17 d of age (8 pens/treatment) were used, and a Val-deficient basal diet containing 0.60% l-Lys·HCl, 1.21% SID Lys, and 0.68% SID Val was developed (0.56 SID Val:Lys). Performance of pigs fed the basal diet was inferior to a corn-soybean meal control containing only 0.06% l-Lys·HCl, but was fully restored with the addition of 0.146% l-Val to the basal diet (68% SID Val:Lys). In Exp. 2, 54 individually housed barrows (21.4 kg) were utilized in a 14-d growth assay. Pigs were offered a similar basal diet (1.10% SID Lys), ensuring Lys was marginally limiting with no supplemental l-Val (55% SID Val:Lys). The basal diet was fortified with 4 graded levels of l-Val (0.055% increments) up to a ratio of 75% SID Val:Lys. In Exp. 3, 147 barrows (13.5 kg) were fed identical diets, only with 1 additional level at a SID Val:Lys of 80% and fed for 21 d. In Exp. 2 and 3, a high protein, control diet was formulated to contain 1.10% SID Lys and 0.20% l-Lys·HCl. In Exp. 2, linear effects on ADG (713, 750, 800, 796, and 785 g/d; P = 0.05) and G:F (P = 0.07) were observed with increasing SID Val:Lys, characterized by improvements to a ratio of 65% and a plateau thereafter. In Exp. 3, quadratic improvements in ADG (600, 629, 652, 641, 630, and 642 g/d; P = 0.08) and G:F (P = 0.07) were observed with increasing SID Val:Lys, as performance increased to a ratio of 65% but no further improvement to a ratio of 80%. Pigs fed the control diet did not differ from those fed a ratio of 65% SID Val:Lys in Exp. 2, but did have improved G:F in Exp. 3 (P = 0.03). To provide a more accurate estimate of the optimum SID Val:Lys, data from Exp. 2 and 3 were combined. With single-slope broken-line methodology, the minimum ratio estimate was 64 and 65% SID Val:Lys for ADG and G:F, respectively. With combined requirement estimates, the data indicate that a SID Val:Lys of 65% seems adequate in maintaining performance for pigs from 13 to 32 kg.