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 < 0.10) in SID for the 7/11 indispensable AA (Except Arg, His, Met + Cys, and Trp) and the average of all dispensable AA. In phase II, the SID of Ile, Leu, Met, Met + Cys, Val, the average of all indispensable AA, and 4/7 dispensable AA were quadratically increased (P < 0.10). In most cases, supplementation with 30,000 NFP/kg of feed (50 g/ton) resulted in the greatest increase in AA digestibility. However, the linear response in phase I for some AA suggests that diets for younger pigs could be supplemented with a greater level (45,000 NFP/kg or 75 g/ton of feed). Interestingly, younger pigs had consistently increased (P < 0.10) SID of CP and 15/18 AA (Except Arg, Cys, and Ser), being ~5.6% greater for indispensable AA when compared to older pigs. In conclusion, dietary protease supplementation can increase the SID of AA in SBM in both growing and finishing periods. Pig age can potentially influence AA digestibility, possibly related to a greater ileal endogenous AA flow in younger pigs. However, this fact warrants further investigation.