Efficacy of a mono-component protease is affected by trypsin inhibitor concentration in soybean meal

Three experiments were conducted to quantify the efficacy of exogenous protease in poultry diets containing soybeans with varying trypsin inhibitor (TI) concentrations. Test diets contained 4 g/kg of TiO2 as a digestibility marker and protease (CIBENZA® DP100 at 300 U/g diet, Novus International). A randomized complete block design was analyzed using ANOVA with LSD multiple pair-wise comparison used to compare treatment means. For Exp 2 and 3, a common starter diet was fed to broiler chickens until d 16 of life and then switched to test diets. Exp 1 was a 2×6 factorial arrangement of 2 protease levels (0 and 300 U/g) and 6 dietary TI levels (0.72, 1.16, 1.61, 2.06, 2.50, and 2.95 mg/g) with 6 replicates/treatment; 8 chicks/pen. In Exp 2 (12 replicates/treatment; 8 chicks/pen), apparent ileal AA digestibility (AIAAD) was evaluated in diets containing 250 g/kg full fat extruded soybeans (FFES)+SBM (negative control; 5.8 mg/g TI) with or without protease or SBM (positive control; 3.1 mg/g TI). Test diets were fed from d 16–21 of age, AIAAD and relative pancreas weight was measured on d 21. In Exp. 3, broilers were allocated to a 2×2 factorial arrangement of treatments with 9 replicates/treatment and 8 chicks/pen. The dietary factors were SBM inclusion (420 or 960 g/kg; SBM TI = 3.85 mg/g), or protease inclusion (0 or 300 U/g). Test diets were fed from d 22–30, ileal digesta was collected on d 30. With increasing TI, pancreas weight increased (P