The objective of this study was to investigate interactions between phytase and trypsin inhibitors in soybean meal. In Experiment 1, growth performance and amino acid (AA) digestibility in broiler chickens was evaluated. Diet 1 was a control corn-soybean meal- based diet. Diet 2 was similar to 1, except that 15% raw soybeans were added to increase trypsin inhibitor activity. Diets 3 and 4 were similar to 2, except that 4,000 U/kg of phytase and 0.75% phytic acid were added, respectively. All diets were formulated to be nutritionally adequate excluding any reductions in nutrient availability caused by anti-nutritional factors. Diets were provided to birds ad libitum from 7 to 21 days-of-age. In Experiment 2, a precision-fed rooster assay was conducted using cecectomized Leghorn roosters. Diets 1 through 4 were the same as Experiment 1. Two additional diets were fed that consisted of 100% raw soybeans with and without 4,000 U/kg of phytase. Roosters were fasted for 26 h prior to being precision-fed (crop intubated) 25 g of sample and excreta were quantitatively collected for 48 h. Experiments 1 and 2 contained 6 replicates per treatment (pen of 5 broiler chickens or 1 individually caged rooster). Data were analyzed using a 1-way ANOVA and significance was determined at P < 0.05. In Experiment 1 with broiler chickens, feed efficiency and weight gain were reduced (P < 0.05) by raw soybeans. The addition of phytase to diet 2 (15% raw soybeans) caused further reductions in weight gain (P < 0.05). The standardized ileal digestibility (SID) of amino acids at 21 days-of-age was lower (P < 0.05) in diets with 15% raw soybeans compared with diet 1; however, there was no effect (P > 0.05) of phytase or phytic acid on SID of AA. In Experiment 2 with precision-fed roosters, standardized AA digestibility was similar (P > 0.05) among treatments 1 through 4; however, digestibility of AA was reduced (P < 0.05) by 22 to 32 percentage units by feeding 100% raw soybeans. There was no effect (P > 0.05) of feeding phytase or phytic acid on AA digestibility. In conclusion, results from this study indicate that phytase may release active anti-nutritional factors in soybean meal, as shown by the reduction in body weight gain in broiler chickens, which warrants further research.

Drysdale, R. and B. Parsons. 2025. Investigation of interactions between phytase and anti-nutritional factors in soybean meal. 2025 International Poultry Scientific Forum, Abstract P252.