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Trypsin inhibitors ( TI ) resident in soybeans affects protein utilization. While heat treatment influences residual TI, it simultaneously affects the structure and solubility of the soybean proteins and confounds any response to exogenous proteases. Using purified TI, the effect of exogenous protease to TI can be dissociated from changes in the soybean protein. Thus, the current study was designed to evaluate the growth performance and protein utilization responses of broiler chickens to purified TI and exogenous protease. Soybean meal ( SBM ) was preanalyzed for basal TI (2,996 TIU/g SBM), formulated into nutritionally adequate experimental diets to contain 1,033 TIU/g diet, and purified TI was added at 9,000 TIU/g diet. A total of 320 Cobb-500 broiler chicks were allocated to 4 diets, each with 8 replicate cages and 10 birds per replicate. The experimental diets were arranged as a 2 × 2 factorial with factors being dietary TI (1,033 or 10,033 TIU/g) and exogenous protease (0 or 15,000 PROT/kg). On day 7, 14, and 21 posthatching, protease supplementation improved the BW gain ( P < 0.01) and gain to feed ratio ( P < 0.05) of birds. On day 14 and 21 posthatching, the relative weight of pancreas increased ( P < 0.05) with added TI but was reduced ( P < 0.001) with protease supplementation. Apparent ileal digestibility of all amino acids, except methionine, decreased ( P < 0.001) with added TI but increased ( P < 0.05) with protease supplementation. Jejunal MUC-2 was downregulated ( P < 0.01) and SCL7A-2 was upregulated ( P < 0.05) by protease supplementation. Duodenal trypsin and chymotrypsin activities reduced ( P < 0.05) with added TI but increased (P < 0.01) with protease supplementation. Exogenous protease produced longer villi ( P < 0.05) and deeper crypts ( P < 0.01) in the jejunal tissue. In conclusion, dietary addition of purified TI negatively affects nutrient utilization by broiler chickens. Furthermore, the study showed that the efficacy of the exogenous protease might be independent of dietary TI concentration.

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