PSIII-21 Optimum SID Threonine to Lysine Ratio in Nursery Pigs

Abstract A total of 270 pigs (PIC 1050 x DNA 600, 6.0 kg) were used in a 42-d nursery trial to determine the optimum SID threonine to SID lysine (SID Thr/Lys) ratio for young pigs. Pigs were sorted by sex and initial BW, and were allotted to each pen (3 barrows, 3 gilts). Pens were then randomly assigned to diets containing incremental levels of SID Thr/Lys ratio (0.55, 0.60, 0.65, 0.70, 0.75), achieved using THRPRO 80 (CJ America, CA) as the source of L-threonine. Each treatment consisted of 45 piglets and 9 replicates per treatment. There were 3 dietary phases (2 weeks each) and the same levels of SID Thr/Lys were tested for each phase. All performance data (ADG, ADFI, and Gain to Feed (G:F)) were analyzed using Proc Mixed in a RCBD model with SID Thr/Lys ratio as fixed effect and weight block as random effect. Orthogonal contrasts were performed to test for linear and quadratic effects of SID Thr/Lys ratio on all performance parameters. Final BW averaged around 20.8 kg (±0.6) and was not influenced by SID Thr/Lys ratio (P>0.20). It was however lower than previously observed from previous nursery batches and might be due to pig infection with Lawsonia intracellularis and Streptococcus suis. A linear trend on ADG was observed during the last phase of nursery (P=0.10) but this response was not significant for the overall study (P>0.15). SID Thr/Lys ratio had no significant effect on ADFI during any phase or overall experimental period (P>0.20). Increasing SID Thr/Lys ratio, however, linearly increase G:F of nursery pigs overall (P< 0.05). The results of this study suggest that there is value in terms of increasing efficiency of gain with higher level of SID Thr/Lys as compared to current NRC recommendation (0.59), especially under disease challenge conditions.