Dietary protease improves growth performance and nutrient digestibility in weaned piglets fed diets with different levels of soybean meal

One hundred and twenty 25-day-old barrows with BW of 7.49 +/- 0.51 kg were used in a 42-d experiment to evaluate the effects of protease in diets with different levels of soybean meal (SBM) on growth performance, diarrhea incidence, nutrient digestibility, blood metabolites, and digestive enzyme activity. The pigs were allotted to 6 treatment groups following a 2 (two SBM levels) x3 (three protease levels) factorial arrangement. Two SBM levels included normal SBM (0 to 14 d, 10%; 15 to 42 d, 22%) and low SBM (0 to 14 d, 4%; 15 to 42 d, 16%), and added protease levels included 0, 150 or 300 mg/kg (0, 1,500 and 3,000 U/kg) of diet. Blood, organ and digesta samples were collected at the end of the experiment, and fecal samples were taken from d 38 to 41. The low SBM level diet significant decreased ADFI (P < 0.01), ADG (P < 0.01), and G:F (P < 0.01) throughout the experiment, except the G:F from 29 to 42 d (P > 0.05). Protease in the normal and low SBM diets increased ADG (P < 0.05) and G:F (P < 0.01) from 1 to 14 d Diarrhea rate was significantly reduced by SBM levels and protease (P < 0.05). An SBM level and protease interaction was observed on digestibilities of dry matter (DM), crude protein (CP), crude ash, organ matter (OM) and gross energy (GE) (P < 0.01). The supplementation of protease in normal and low SBM level diets significantly increased nutrients digestibility (P < 0.01), protease increased the digestibilities of majority of amino acids (P < 0.05). Protease in the normal diets reduced serum urea nitrogen (SUN) (P < 0.01). Low SBM diet reduced the liver relative weight (P < 0.05), supplementation of 150 mg/kg protease to the normal SBM diet increased pancreas relative weight (P < 0.05) and protease in both normal and low SBM diets increased intestine relative weight (P < 0.01). Trypsin activity was reduced by low SBM (P < 0.05), while protease enhanced the activity (P < 0.05). An SBM level and protease level interaction was observed on trypsin and chymotrypsin activities (P < 0.01). In conclusion, protease supplementation in low SBM diet could partly complement the digestible AAs to the piglets fed diet with reduced crude protein.