Dietary Bacillus subtilis modulates rumen epithelial barrier function and immune responses in weaned Hu sheep

This study evaluated 30- and 60-day dietary Bacillus subtilis supplementation on rumen development and immune indices in weaned male Hu sheep. Forty-five lambs (60 ± 10 d) were randomized to a basal diet (CON) or the basal diet plus B. subtilis at 100 mg/kg (BSN) or 200 mg/kg (BSH) (n = 15). After 30 d, rumen papilla height was significantly higher in the BSN group than in the CON and BSH groups (P = 0.026); Total volatile fatty acids (TVFA) and propionate were significantly higher in the BSN and BSH groups than in the CON group (P < 0.001); Acetate/propionate was significantly lower in the BSN and BSH groups than in the CON group (P = 0.010). BSH increased the relative abundance of beneficial bacteria (including cellulolytic taxa and Lactobacillus), and serum IL-1β decreased; rumen epithelial IL-1β, CCL2, and NF-κB p65 were downregulated in BSN and BSH (P < 0.05). After 60 d, papilla height and total VFA remained higher in BSN/BSH and the acetate to propionate ratio remained lower in BSH, with sustained increases in beneficial taxa (P < 0.05). Serum IgA and IFN-γ increased and IL-1β decreased in BSN/BSH, and epithelial NF-κB p65 decreased in BSN (P < 0.05). Therefore, this study demonstrates that a 30-day supplementation of B. subtilis is effective, while for longer-term (60-day) use, a dosage of 100 mg/kg is optimal for enhancing rumen health and immune function in sheep.