The objective of this study was to determine the effect of increasing dietary synthetic amino acids L-Lysine HCl, L-Threonine, Alimet®, and L-Tryptophan inclusion level at the expense of soybean meal on growth performance during the grow-finish period (46.2 ± 0.55 to 127.4 ± 0.83 kg BW) and carcass characteristics of pigs reared under commercial conditions. The study used a RCBD with 2 dietary treatments: 1). Control: 0.309, 0.029, 0.028, and 0.000 g/kg of synthetic lysine, methionine, threonine, and tryptophan, respectively; 2). High Inclusion: 0.422, 0.069, 0.047, and 0.014 g/kg, respectively. Diets were corn-soybean meal based with DDGS (20.6% for both diets) formulated to be isocaloric and to the same SID amino acid levels but varied in soybean meal inclusion (14.1 and 10.2%, for the Control and High Inclusion, respectively) and crude protein content (17.7 and 16.4%, respectively). A total of 3,520 barrows and gilts were used, housed in single-sex pens of 32 (22 replicates) at a floor space of 0.67 m2/pppig. Pigs had ad libitum access to feed and water throughout the study. Pen was the experimental unit and data were analyzed using PROC MIXED of SAS; the model accounted for fixed effect of dietary treatment and the random effect of block. There was no effect of dietary treatment on final live weight, overall ADFI, hot carcass weight, backfat depth, or longissimus muscle depth. However, the High Inclusion treatment had lower overall ADG (P ≤ 0.01) and overall G:F (P ≤ 0.05), but greater (P ≤ 0.01) carcass yield than the Control treatment.
These results suggest that increasing the inclusion of synthetic amino acids in corn-soybean and DDGS based diets for growing-finishing pigs to the levels evaluated negatively impacted growth rate and feed efficiency but increased carcass yield.