Host-derived bacillus spp. as probiotic additives for improved growth performance in broilers

In recent years, the utilization of antibiotics in animal feed has been restricted, probiotics have been increasingly used to replace antibiotics in maintaining animal health. The aim of this study was to screen and evaluate probiotics with excellent probiotic potential from the gut of healthy goslings for clinical application. Thirteen strains of Bacillus (named AH-G201 to AH-G2013), including 2 strains of Bacillus subtilis (B. subtilis), 6 strains of Bacillus licheniformis (B. licheniformis) and 5 strains of Bacillus amyloliquefaciens (B. amyloliquefaciens), were isolated and identified. Then, acid and bile salts tolerance tests were performed to screen probiotics strains that could survive under different environments. The effects of screened probiotics on the growth of pathogenic Escherichia coli (E. coli) and Salmonella were assessed. Furthermore, we performed the drug resistance tests and safety tests in animals. The results showed that B. Subtilis AH-G201, B. licheniformis AH-G202 and AH-G204 exhibited higher gastrointestinal resistance under in vitro conditions, and showed a moderate level of resistance to the tested antibiotics. Importantly, AH-G201 and AH-G202 showed 24 to 60% inhibition rate against pathogenic E. coli and Salmonella. Moreover, the safety analysis of AH-G201 and AH-G202 suggested that the 2 probiotics strains have no adverse effects on body weight gain and feed intake in the broilers, and in addition, they have significantly improved growth performance. Finally, we analyzed effects of B. Subtilis AH-G201and B. licheniformis AH-G202 on growth performance, immune organ index and the feces microbes of broilers. The results showed that broilers fed with high doses (5 × 10⁹ CFU/mL, for single strain) of a mixture of AH-G201 and AH-G202 exhibited good growth performance, and exhibited the greatest gain in spleen weight and the highest lactic acid bacteria counts. These findings indicate that the combined addition of B. Subtilis AH-G201 and B. licheniformis AH-G202 has the potential to replace antibiotics and to improve the growth performance of broilers.