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 <i>Bacillus subtilis</i> 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 <i>B. subtilis</i> 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 (<i>p</i> < 0.05). The half-bore weight, half-bore percentage, and breast muscle percentage in group L were significantly higher (<i>p</i> < 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 (<i>p</i> < 0.05). In group L, the jejunal villus height and villus height/crypt depth increased significantly relative to those in group C (<i>p</i> < 0.05). The chymotrypsin and trypsin activities tended to increase in the <i>B. subtilis</i> FRE76 groups (<i>p</i> = 0.072 and <i>p</i> = 0.056, respectively) relative to those in group C. Additionally, the abundance of <i>Bacteroidota</i>, <i>Proteobacteria</i>, <i>Alistipes</i>, <i>Clostridia</i>_vadinBB60_group, and <i>Parabacteroides</i> increased significantly in the <i>B. subtilis</i> FRE76 groups (<i>p</i> < 0.05). In conclusion, dietary <i>B. subtilis</i> FRE76 could improve broilers' body weight, average daily gain, apparent digestibility, protease activity, intestinal morphology, and gut microbiota.