Trypsin inhibitors (TI) in soybeans influence protein utilization but wheth- er this is true for purified TI and if exogenous protease administration will ameliorate such effects are not known. Therefore, this study was designed to evaluate the effect of dietary mono-component protease on growth performance and nutrient utilization of broiler chickens fed diets containing purified TI. Soybean meal (SBM) was pre-analyzed for basal TI concentration (2,996 TIU/g SBM) and formulated to contain 1,033 TIU/g diet. Purified TI was added at 9,000 TIU/g diet. The diets were corn-SBM based, formulated to be nutritionally adequate and supplemented with phytase (1,000 FYT/kg). Using a 2 × 2 factorial arrangement, with two levels of dietary TI (1,033 or 10,033 TIU/g) and exogenous protease (0 or 15,000 PROT/kg), 320 chicks were allotted to 4 experimental diets, each containing 8 replicate cages and 10 birds per replicate. On d 7, 14 and 21 post hatching, protease supplementation improved the BW gain (P < 0.01) and feed efficiency (P < 0.05) of birds fed diets with added purified TI. On d 14 and 21 post-hatching, the relative weight of the pancreas increased (P < 0.05) with increasing dietary TI but reduced (P < 0.001) with protease supplementation. Apparent ileal digestibility of all amino acids decreased (P < 0.001) with added TI, and protease supplementation improved (P < 0.05) the ileal digestibility of all AA except methionine. Protease supplementation upregulated the mRNA expression of MUC-2 (P < 0.01) and SCL7A-2 (P < 0.05) in the jejunal mucosa, as TI concentration increased in the diets. The activities of trypsin and chymotrypsin in duodenal digesta were reduced (P < 0.05) with increased dietary TI but increased (P < 0.01) with protease supplementation. Birds fed diets supplemented with protease had longer villi (P < 0.05) and deeper crypts (P < 0.01) in the jejunal tissue.
These results confirm that dietary TI, supplied in a purified form, negatively affects nutrient utilization by broiler chickens and show the efficacy of exogenous protease in ameliorating these effects by improvements in growth performance, ileal digestibilities of nitrogen and AA and digestive enzyme secretion.