Bacillus subtilis M2-Fermented Soybean Meal Improves Growth Performance and Modulates Cecal Microbiota in Dongxiang Green-Shell Laying-Type Chicken.

Feeding animals with soybean meal (SBM) fermented by probiotics normally confers benefits. This study evaluated the growth-promoting effects of SBM fermented with Bacillus subtilis M2 (M2-FSBM), a probiotic strain with antimicrobial activity, as a replacement for conventional SBM in chicken diets. A total of 264 one-day-old Dongxiang green-shell laying-type chickens were randomly assigned to four groups (six replicates/group, 11 birds/replicate) and fed a basal diet with 0% (control, with 35% SBM), 25%, 50%, or 75% of SBM replaced by M2-FSBM for 45 days. Growth performance, feed consumption, serum insulin-like growth factor and epidermal growth factor, small intestinal morphology, and cecal microbiota diversity were evaluated. Compared with the control, M2-FSBM replacement significantly increased body weight at day 15 (all replacement levels) and day 30 (50% and 75% groups), and at day 45 (75% group) (p < 0.05). The improved growth was attributed to increased average daily feed intake rather than improved feed conversion ratio. The 75% M2-FSBM group showed significantly increased villus height in the duodenum, jejunum, and ileum, and elevated jejunal villus height-to-crypt depth ratio (p < 0.05). Cecal microbiota analysis revealed increased abundances of Faecalibacterium and Negativibacillus and decreased abundances of Mediterraneibacter, Blautia, and unclassified_f_Lachnospiraceae, while Lactobacillus and Limosilactobacillus remained stable. Replacing SBM with M2-FSBM improves growth performance in young chickens, likely through increased feed intake and improved intestinal morphology, accompanied by beneficial modulation of cecal microbiota. M2-FSBM shows promise as a growth-promoting alternative feed material for poultry.