Investigation of interactions between phytase, protease, and anti-nutritional factors in soybeans

The objective was to investigate interactions between phytase, protease, and anti-nutritional factors in soybeans. In Experiments 1 (in vitro), 2 (broiler chickens), and 3 (precision-fed roosters), trypsin inhibitor activity, growth performance, and amino acid (AA) digestibility were assessed. Diet 1 was a corn-soybean meal-based diet. Diet 2 contained 15% raw soybeans (RSB). Diets 3 and 4 were similar to diet 2, except 4,000 FTU/kg of phytase and 0.75% phytic acid were added, respectively. Experiment 3 (precision-fed roosters) contained 2 additional treatments (100% RSB ± 4,000 FTU/kg). In Experiments 4 and 5 (in vitro), trypsin inhibitor activity was measured in corn-soybean meal or corn-soybean meal-RSB diets ± protease. Experiment 6 was a broiler growth performance assay. Diet 1 was a corn-soybean meal-RSB (15%) diet. Diets 2 and 3 were the same as 1, except phytase (2,000 FTU/kg) or phytase + protease were added, respectively. Diet 4 was the same as diet 2, except phytase did not receive an energy matrix value. In Experiment 1 (in vitro), trypsin inhibitor activity was greater for the RSB + phytase diet compared with the RSB-no phytase diet (P < 0.05). In Experiment 2 (broilers), the addition of phytase to the RSB diet reduced BW gain and feed intake (P < 0.05). In Experiment 3 (precision-fed roosters), there was no effect of phytase on AA digestibility. In Experiments 4 and 5 (in vitro), protease reduced trypsin inhibitor activity in the corn-soybean meal diet (P < 0.05) but not the corn-soybean meal-RSB diet (P > 0.05). In Experiment 6 (broilers), phytase reduced BW gain and feed intake with and without an energy matrix value compared with the no phytase diet (P < 0.05). Protease did not effect growth performance (P > 0.05). In conclusion, phytase addition increased trypsin inhibitor activity and reduced growth performance when added to diets with RSB. Further, protease reduced trypsin inhibitor activity in vitro but did not ameliorate the effect of RSB + phytase in vivo.