Effect of protease supplementation on amino acid digestibility of soybean meal fed to growing-finishing pigs in two different ages

This study was conducted to investigate the effect of protease inclusion level in two different ages on the apparent (AID) and standardized (SID) ileal digestibility of crude protein (CP) and amino acids (AAs) in soybean meal (SBM) fed to growing-finishing pigs. Ten cannulated pigs (21 ± 2 kg) were assigned to experimental diets in a duplicate 5 × 5 Latin square design. In phase I (23 to 30 kg-pigs, 90 ± 17 d of age), ileal digesta was collected in five periods of 7 d (5 d adaptation and 2 d ileal digesta collection). In phase II, (50 to 65 kg-pigs, 140 ± 17 d of age), ileal digesta was collected in 5 more periods of 7 d. For both phases, a corn starch-based diet was formulated with SBM as the sole source of CP and AA and containing titanium as an indigestible marker. Protease was supplemented at 0, 15,000, 30,000, and 45,000 NFP/kg of feed (0, 25, 50, and 75 g/ton of ProAct 360). A nitrogen-free diet was used to estimate basal ileal endogenous AA losses. Pigs were fed at 4% of their body weight, which was adjusted at the end of each period. Orthogonal polynomial contrasts were used to determine the linear and quadratic effects of dietary protease supplementation in each phase. In phase I, increasing levels of protease resulted in a linear increase (P