Effect of standardized ileal digestible arginine:lysine on growth performance of 6 to 13-kg nursery pigs.

Four hundred and eighty newly weaned pigs (PIC 337 × 1050; Genus, Hendersonville, TN) with an initial body weight (BW) of 6.20 ± 0.61 kg were used in a dose-response study to investigate the impact of increasing standardized ileal digestible (SID) Arg:Lys on nursery pig growth performance. At weaning, pigs were placed into 48 pens with five barrows and five gilts per pen. Pens were randomly assigned to one of six dietary treatments. The experimental diets were formulated with increasing SID Arg:Lys, achieved by substituting corn starch, glycine, and L-alanine with L-arginine, resulting in SID Arg:Lys ranging from 45 to 145%. Diets were sub-limiting in SID Lys and exceeded all other essential amino acid requirements. The experimental diets were fed across two feeding phases from d 0 to 10 and 10 to 27, with adjustments made to account for the Lys requirement of the pigs. All pens were placed on a common diet for the remaining 14 days of the study to evaluate carryover effects. Pigs and feeders were weighed at the start and end of each phase to calculate average daily gain (ADG), average daily feed intake (ADFI), and feed efficiency (G:F). Data were analyzed according to a linear regression model, which included the linear and quadratic effects of SID Arg:Lys and initial BW. Pen was the experimental unit, and results were considered significant at P ≤ 0.05 and a tendency at 0.50 < P ≤ 0.10. From d 0 to 27, Arg:Lys tended to have a quadratic effect on ADFI (P = 0.058), where 97.00 ± 7.631% SID Arg:Lys maximized feed intake. Similarly, Arg:Lys had a quadratic impact on ADG (P = 0.046), where ADG was maximized at a SID Arg:Lys of 95.65 ± 7.165. Correspondingly, Arg:Lys had a quadratic effect on pig BW on d 27 (P = 0.014). These effects carried through the end of the study, where Arg:Lys quadratically impacted d 0 to 41 ADFI (P = 0.006), ADG (P = 0.077), and d 41 BW (P = 0.028). There was no evidence of an effect of SID Arg:Lys on G:F throughout the study (P ≥ 0.315). In conclusion, SID Arg:Lys quadratically impacted ADFI and ADG in 6 to 13 kg nursery pigs, where ADFI was maximized at a SID Arg:Lys of 97.00% (95% CI [81.6, 112.4%]), and ADG was maximized at a SID Arg:Lys of 95.65% (95% CI [81.2, 110.1%]). Together, these data suggest that the SID Arg:Lys requirement of nursery pigs is at least 81%, based on the lower bounds of the 95% CI for maximum ADG and ADFI, and excessive Arg supplementation may negatively affect growth performance.