Influence of Bacillus subtilis supplementation on growth performance and gut microbial composition in broiler chickens based on low-protein diets

The supplementation of direct-fed microbials (DFMs), specifically Bacillus subtilis, can enhance nutrient digestibility and intestinal health, particularly under low-protein dietary conditions. This study assessed the effects of B. subtilis on broiler chickens through a controlled experiment involving 96 broilers randomly allocated to two groups: one fed a low-protein diet (13.5 % crude protein) alone, and the other supplemented with B. subtilis (1.0 × 10⁹ CFU/mL daily) in same diet. Growth performance, intestinal histology, digestive enzyme activity, and gut microbial high-throughput sequencing (HTS) techniques were evaluated. By day 42, supplemented birds weighed 2176 ± 45 g versus 2,023 ± 51 g in controls (+7.6 %, P = 0.003) while consuming 5.2 % less feed, reducing FCR from 1.71 to 1.55. Enhanced intestinal morphology was evidenced by increased villus height and villus-to-crypt ratio. B. subtilis supplementation also increased α-amylase activity while modulating gut microbiota composition, notably by elevating Firmicutes and Butyricicoccus abundance and reducing Bacteroidetes, Bacteroides, and Faecalibacterium. Hence, these findings underscore the potential of B. subtilis as a dietary supplement to improve poultry performance and gut health under protein-restricted conditions.