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The effects of dietary Bacillus subtilis(BS) on the meat quality of broilers were evaluated, with an emphasis on the regulation of muscle fiber types and antioxidant capabilities. One hundred and forty-four Arbor Acres male broilers were divided into 3 treatment groups (0, 300 mg/kg and 500 mg/kg dietary BS) and raised for 35 d. The results suggested that BS improved meat quality by improving the muscular pH, meat color, water holding capacity and shear force. Immunofluorescence staining revealed a positive impact of BS on the muscle fiber transformation in thigh muscles, and the gene/protein expression data from specific muscle fiber types confirmed this finding. BS activated AMP-activated protein kinase (AMPK), silent information regulator 1 and peroxisome proliferator-activated receptor gamma coactivator 1alpha. The postmortem analysis revealed that BS increased the activity of glutathione peroxidase and total antioxidant capacity while decreasing the malondialdehyde content. Additionally, BS increased the gene and protein expression of nuclear factor-like 2 (Nrf2) and activated the Nrf2 signaling pathway, including its downstream factors, such as heme oxygenase-1, catalase, superoxide dismutase and glutathione peroxidase. In conclusion, dietary BS improved meat quality by modifying muscle fiber types and enhancing the antioxidant capacity in broilers.

The study investigated the effects of dietary probiotic of dual-strain Bacillus subtilison production performance, intestinal barrier parameters, and microbiota in broiler chickens. In a randomized trial, male broiler chickens were allocated into 3 groups, a control group (basal diet), BS300 group (basal diet with 300 mg/kg of B. subtilis), and BS500 group (basal diet with 500 mg/kg of B. subtilis). The inclusion of 500 mg/kg of B. subtilissignificantly reduced the feed conversion ratio by 4.55% during the starting phase. Both 300 and 500 mg/kg of B. subtilissupplementation increased jejunal villus height (by 17.89% and 24.8%, respectively) significantly and decreased jejunal crypt depth (by 27.2% and 31.9%, respectively) on day 21. The addition of 500 mg/kg of B. subtilissignificantly elevated the gene expression of occludin on day 35. Moreover, of B. subtilissupplementation enhanced cytokine levels and immunoglobulins in both serum and jejunal mucosa. Microbial analysis indicated that B. subtilisincreased the abundance of potential probiotics (Sutterella) and butyrate-producing bacteria (Lachnoclostridium, Tyzzerella, Anaerostipes, Clostridium_sensu_stricto_13, Prevotellaceae_NK3B31_group, and Lachnospiraceae_UCG-010). The abundances of Anaerostipesand Sutterella, are significantly correlated with growth performance and immune function. In conclusion, dietary supplementation with B. subtilisimproved the growth performance, potentially through the regulation of immunity, intestinal barrier function, and microbiota in broilers. Notably, 500 mg/kg of B. subtilisexhibited more benefits for broilers compared to the 300 mg/kg.This research highlights the efficacy of dual-strain Bacillus subtilisin improving feed conversion, intestinal morphology, immune function, and the gut microbiota in broiler chickens under the conditions of this experiment.Bacillusemerges as a promising probiotic candidate, offering a suitable alternative to antibiotics in animal feed. However, previous research predominantly focused on single-strain Bacillus, with limited exploration into dual-strain Bacillus subtilis-based probiotics. This study demonstrates that dietary supplementation with dual-strain B. subtilisenhances feed conversion ratio, intestinal morphology, gene expression related to tight junction proteins, Th1-like cytokines, immunoglobulins, as well as the abundance of potential probiotics (Sutterella) and butyrate-producing bacteria (Anaerostipes, Tyzzerella, UCG-010, etc.) in the cecum. The abundances of Anaerostipesand Sutterella, are significantly correlated with growth performance and immune function. These findings lay a foundation for incorporating dual-strain B. subtilis-based probiotics in broiler feed.