An experiment was conducted to evaluate the interactive effects of soybean meal (SBM) concentration and functional amino acids (FAA) threonine, tryptophan, and methionine supplementation above the requirements on the growth performance of nursery pigs. A total of 2,592 pigs (initial BW = 6.1 kg), placed in pens of 36 mixed-sex pigs, were used in a 33-d trial. Pens of pigs were allotted to 1 of 6 dietary treatments arranged as a 2 × 3 factorial with two levels of SBM (25 or 31%) and three FAA regimens (Low, Medium, and High) with 12 replicates per treatment. Amino acid ratios were: 58.5% SID Thr:Lys, 55% SID Met+Cys:Lys, and 16.5% SID Trp:Lys for the Low treatment; 65% SID Thr:Lys, 58% SID Met+Cys:Lys, and 18.5% SID Trp:Lys for the Medium treatment; and 71% SID Thr:Lys, 66% SID Met+Cys:Lys, and 23.5% SID Trp:Lys for the High treatment. Diets were fed in two phases: phase 1 from d 0 to 19 in pellet form and phase 2 from d 19 to 33 in mash form. Pigs were weighed on d 0, 19, and 33 to calculate ADG, ADFI and G:F. Data was analyzed with the MIXED procedure in SAS. From d 0 to 19, there was no evidence (P > 0.10) for interactive effects. Pigs fed the Low FAA ratios had the poorest G:F (P = 0.004). From d 19 to 33 and overall (d 0 to 33), there was an interaction (P ≤ 0.031) for G:F, where pigs fed 25% SBM had improved G:F with Medium or High FAA whereas those fed 31% SBM had improved G:F only with High FAA. There was no evidence (P > 0.10) for differences on ADG or ADFI throughout the study.
In conclusion, our findings suggest a minor positive effect of FAA supplementation, with no effects of SBM on performance of weaned pigs.