Effects of reduced-protein diets with protease supplementation on growth, carcass yield, intestinal morphology, organ development, nutrient digestibility, and blood biochemical of broiler chickens

This study was conducted to evaluate growth performance, carcass yield, intestinal morphology, organ development, nutrient digestibility, and blood biochemical parameters of broiler fed 1 reduced-protein diets with/without protease supplementation. A total of 1,120 one-day-old male broiler chickens with average initial body weight (BW), 46.45 ± 0.49 g, were divided into five groups with seven replications and 32 birds per replication. The treatment varied according to the protein and protease enzyme levels: positive control (PC), negative control (NC, PC with reduction of 1 protein), PC supplemented with 50 g/t protease (PC + 50), NC supplemented with 50 g/t protease (NC + 50), and NC supplemented with 100 g/t protease (NC + 100). The results showed that there was no significant effect of 1 reduced-protein diets, with or without protease on feed intake, final BW, average daily gain, feed conversion ratio, and nutrient digestibility. The changes in dietary protein level and supplementation of protease did not affect carcass yield, but significantly affected abdominal fat content, PC + 50 group had significantly lower abdominal fat content than NC-based diet including NC, NC + 50, NC + 100. Reduced-protein with protease supplementation strongly affected organ weight, especially on day 21: the pancreas was heavier in PC and NC + 50 group than other groups, spleen was heaver in NC group than in NC + 100 group, thymus was heavier in NC + 50 group than in PC, NC and NC + 100 group, small intestine was heavier in NC + 50 and NC + 100 group than in PC group, and large intestine was also heavier in NC + 50 group than in NC group. Villus height sampled at 35-d was significantly increased with protease supplement, and which was significantly higher in NC + 100 group than NC group. Regarding on blood metabolites, only urea and uric acid were affected by the reduction of dietary protein, broiler fed PC diet had higher urea and uric acid content than fed NC diet. In conclusion, supplementation of 50 g/t protease in 1 reduced-protein diets does not negatively affect on growth, nutrient digestibility, carcass yield, organ development, and blood metabolites. Moreover, supplementation of protease in low-protein diet could effectively promote organ development and benefit intestine morphology. © The Author(s) 2023. Published by Oxford University Press on behalf of the American Society of Animal Science.