Residual trypsin inhibitors (TI) in soybean meal (SBM) inhibit endogenous trypsin activity, reduce overall dietary protein digestibility and compromise growth performance and health of poultry. Previous in vivo studies have indicated that dietary TI activity greater than 1 mg/g of feed may cause potential issues in reducing AA digestibility and performance of broilers. The objective of this study was to evaluate TI activity of the United States SBM samples from 2021-2024 to understand their risk in poultry production. A total of 748 SBM samples from 17 companies were analyzed for TI by NIR technology. Wet chemistry TI activity values analyzed by the AOCS Official Method Ba 12a-2020 were used to establish NIR prediction equations. Among the 748 samples, 526 were solvent extract SBM, 165 were expeller SBM, and 57 were full-fat SBM. Due to unequal sample size and unequal variance, data were subject to Welch ANOVA to evaluate TI activity as affected by SBM type, year and company; means were separated by Tukey Cramer test with a significant level of 0.05. Full-fat SBM had significantly higher TI than expeller SBM, and expeller SBM had significantly higher TI than solvent extract SBM (16.7, 9.4, and 5.2 mg/g trypsin inhibited for full-fat, expeller, and solvent extract SBM respectively; P<0.05). Expeller SBM TI activity decreased from 2022 to 2024 (P<0.05), whereas no change was observed for full fat or solvent extract SBM with year (P>0.05). Trypsin inhibitor activity of solvent extract SBM varied among companies (P<0.05) with the highest averaging 7.4 mg/mg and the lowest averaging 3.0 mg/g. samples, 79% had TI activity higher than 4.0 mg/g. In summary, the study revealed a large variation in TI activity of the United States SBM samples, many with TI activity high enough to potentially compromise bird performance and health. Therefore, to achieve precision feeding and improve production efficiency, it is necessary to monitor SBM TI activity with NIR technology to better manage variation in SBM quality through supplier selection, formulation adjustment, and/or supplementation of exogenous proteases effective in hydrolyzing TI in SBM.

Schulz, M., E. Jackson and F. Yan. 2025. Evaluation of trypsin inhibitor activity in 2021-2024 United States soybean meal. 2025 International Poultry Scientific Forum, Abstract P391.