Effects of Dietary High-Yield Protease Bacillus subtilis Strain FRE76 on Broiler Growth, Slaughter Performance, Intestinal Morphology, and Gut Microbiota

This study aimed to investigate the effects of supplementing broiler feed with high-yield protease Bacillus subtilis strain FRE76 on growth performance, slaughter performance, apparent digestibility, intestinal morphology, and intestinal microbiota. One-day-old Arbor Acres broilers (n = 240) were randomly assigned to four groups (n = 6 replicates; 10 animals per replicate), in which their basal diet was supplemented with B. subtilis strain FRE76 at 0 CFU/kg (group C), 3.60 × 108 CFU/kg (group L), 1.08 × 109 CFU/kg (group M), and 1.80 × 109 CFU/kg (group H). The experiment lasted for 42 d and comprised two phases: Days 1–21 and days 22–42. The broilers’ body weight at 21 d and the average daily gain at 1–21 d in the L and H groups increased significantly relative to those in group C (p < 0.05). The half-bore weight, half-bore percentage, and breast muscle percentage in group L were significantly higher (p < 0.05) than those in group C. The apparent digestibility of crude protein in group L and the ether extract in groups L, M, and H were significantly increased at 22–42 d compared with those in group C (p < 0.05). In group L, the jejunal villus height and villus height/crypt depth increased significantly relative to those in group C (p < 0.05). The chymotrypsin and trypsin activities tended to increase in the B. subtilis FRE76 groups (p = 0.072 and p = 0.056, respectively) relative to those in group C. Additionally, the abundance of Bacteroidota, Proteobacteria, Alistipes, Clostridia_vadinBB60_group, and Parabacteroides increased significantly in the B. subtilis FRE76 groups (p < 0.05). In conclusion, dietary B. subtilis FRE76 could improve broilers’ body weight, average daily gain, apparent digestibility, protease activity, intestinal morphology, and gut microbiota.