140 Response of 6 to 13 kg nursery pigs to increasing SID Arg:Lys

Abstract Newly weaned pigs (n = 480; 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 evaluate the effects of increasing standardized ileal digestible (SID) Arg:Lys in nursery pigs. At weaning, pigs were placed into 48 pens with five barrows and five gilts per pen and randomly assigned to one of six dietary treatments. The experimental diets were formulated with increasing levels of SID Arg by replacing corn starch, glycine, and L-alanine with L-arginine. Levels of SID Arg:Lys ranged from 45 to 145%. Diets were sub-limiting in SID Lys and exceeded all other essential amino acid requirements. Furthermore, diets were formulated to be isocaloric, isonitrogenous, and met or exceeded NRC (2012) vitamin and mineral recommendations. The experimental diets were fed in two feeding phases from d 0 to 10 and d 10 to 27, with adjustments made to account for the decreasing Lys requirement of the pigs. Pigs were subsequently fed a common diet for the remaining 14 d of the nursery period to determine carryover effects. Pigs and feeders were weighed at the beginning and end of each dietary phase for the calculation of average daily gain (ADG), average daily feed intake (ADFI), and feed efficiency (gain to feed ratio; G:F). The data were fit using linear regression with R version 4.3.1 (R Core Team, 2023). The model included 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 0.05 P ≤ 0.10. There was a significant linear and quadratic effect of SID Arg:Lys on BW on d 27 (P ≤ 0.024), where BW was maximized at a SID Arg:Lys 97.09%. From d 0 to 27 there was a linear and quadratic tendency of SID Arg:Lys on ADFI (P = 0.069), where feed intake was maximized at a SID Arg:Lys of 97.00%. Furthermore, there tended to be a linear and quadratic effect of SID Arg:Lys on ADG from d0 to 27 (P ≤ 0.081), where ADG was maximized at a SID Arg:Lys of 95.65%. There was no evidence for an effect of SID Arg:Lys on G:F at any timepoint throughout the trial (P ≥ 0.298). In conclusion, SID Arg:Lys linearly and quadratically impacted ADFI and ADG in 6 to 13 kg nursery pigs, where ADG was maximized at a SID Arg:Lys of 95.65%, but ADFI was maximized at a SID Arg:Lys of 97.00%. Together, these data suggest that the SID Arg:Lys requirement of nursery pigs is greater than NRC (2012) recommendations, and excessive Arg supplementation may have negative consequences on growth performance.