Fermented soybean meal using Bacillus subtilis and Aspergillus oryzae positively enhances cecal microbial composition and broiler performance

OBJECTIVE: This study investigated the effect of fermented soybean meal (FSBM) prepared through solid-state fermentation using Bacillus subtilis (BS) and Aspergillus oryzae (AO) to replace SBM in broiler chickens' diets on production, digestibility, and cecal microbial profile. METHODS: In total, 160 sex-mixed day-old chicks of Cobb 500 broiler chickens were randomly assigned to four groups, four pens (replicates; 10 birds each pen), and were raised for 35 days under tropical conditions. The treatments were control (basal diet; CON) or SBM replaced by FSBM produced using AO (AO group), BS (BS group), and their combination (AO+BS group). RESULTS: Birds fed the AO+BS diet resulted in higher (p = 0.003) body weight (BW) while the BS diet tended (p = 0.063) to have higher final BW than CON or AO. Similarly, birds fed FSBM prepared under either BS or AO+BS had higher feed intake (p<0.01) than the CON group. No difference was found in feed conversion ratio. Relative organ weights including heart, liver, abdominal fat, and total inner organs were lower (p<0.01) in birds fed the AO+BS diet than the CON group, but relative carcass weight was unaffected. Treatments with BS or AO+BS increased dry matter (DM; p = 0.032), organic matter (p = 0.016), and crude protein (CP; p = 0.044) digestibility, while AO did not affect DM and CP digestibility. Broilers fed the AO+BS diet showed greater abundance of Firmicutes phylum and Bacteroides genus than the CON group. Several microbial taxa biomarkers were identified via linear discriminant analysis effect size analysis, including higher abundance of Enterococcus and Bacillus in the AO+BS group but lower abundance of Erysipelatoclostridium, Odoribacter, Ruminococcaceae bacterium, Staphylococcus, and Clostridium methylpentosum group in the CON group. CONCLUSION: B. subtilis and A. oryzae could synergistically enhance the nutritional quality of SBM, positively alter cecal microbiota, and improve the production performance of broiler chickens.