PSIV-9 Increasing standardized ileal digestible arginine to lysine ratio in starter diets promotes nursery pig growth performance.

Abstract Limited arginine (Arg) availability may impact growth performance in the immediate post-weaning period. In addition to its main role as a building block for protein, Arg is a substrate for nitric oxide production, a small molecule that mediates vasodilation, which could have implications for gut function, structure, and integrity in nursery pigs. The objective of this study was to determine the impact of increasing the ratio of standardized ileal digestible (SID) Arg to lysine (Lys) in starter diets on nursery pig growth performance. A total of 160 pigs (initial body weight, 8.88 ± 1.24 kg) were weaned at 28 days and assigned to one of four dietary treatments (four mixed-sex pigs per pen): 1) ARG-75 (SID Arg: Lys, 0.75; n = 9); 2) ARG-90 (SID Arg: Lys, 0.90; n = 10); 3) ARG-105 (SID Arg: Lys, 1.05; n = 9); and 4) ARG-120 (SID Arg: Lys, 1.20; n = 8). Arginine, above that provided by the ARG-75 diet, was supplied as crystalline L-Arg. Pigs had free access to treatment diets for 14 d; pig body weights and pen feed disappearance were measured weekly and blood samples were collected by jugular venipuncture on days 0, 7, and 14. Plasma amino acid concentrations were measured by HPLC. Average daily gain (ADG) increased linearly from ARG-75 (187 ± 27 g/d) to ARG-120 (218 ± 27 g/d; P = 0.016; Table 1). Final body weight likewise increased linearly from ARG-75 (11.41 ± 0.42 kg) to ARG-120 (11.84 ± 0.42 kg; P = 0.020). Average daily feed intake was not different among groups, whereas feed conversion ratio (gain-to-feed) tended to increase linearly from ARG-75 (0.503 ± 0.034) to ARG-120 (0.538 ± 0.034; P = 0.09). Plasma Arg and ornithine (Orn) concentrations were not different among groups on day 0 or on day 7 (P > 0.10) but both increased linearly from ARG-75 (Arg, 46 ± 7 µmol/L; Orn, 46 ± 8 µmol/L) to ARG-120 (Arg, 71 ± 6 µmol/L; Orn, 70 ± 8 µmol/L) on day 14 (P < 0.05). However, plasma Lys concentration decreased linearly from ARG-75 (118 ± 22 µmol/L) to ARG-120 (40 ± 21 µmol/L) on day 14 (P < 0.01). The inverse relationship between plasma Arg and Lys concentration could be because both are absorbed by cationic amino acid transporters, such that increased dietary Arg reduced Lys absorption. Alternatively, increased ADG in pigs fed increasing amounts of Arg could drive Lys utilization for weight gain. In summary, increasing SID Arg: Lys ratio in nursery diets increases nursery pig growth performance in the immediate post-weaning period. Future work will evaluate the impact of increasing SID Arg: Lys on nursery pig gut health.