Dietary supplementation with Bacillus mixture modifies the intestinal ecosystem of weaned piglets in an overall beneficial way

AIMS This study was conducted to investigate the effects of dietary supplementation with a mixture of Bacillus, which serves as an alternative of antibiotics on the intestinal ecosystem of weaned piglets. METHODS AND RESULTS We randomly assigned 120 piglets to three groups: a control group (a basal diet), a probiotics group (a basal diet supplemented with 4 × 109 cfu g-1 Bacillus licheniformis-Bacillus. subtilis mixture; BLS mix), and an antibiotics group (a basal diet supplemented with 0.04 kg t-1 virginiamycin, 0.2 kg t-1 colistin, and 3000 mg kg-1 zinc oxide). All groups had five replicates with eight piglets per replicate. On days 7, 21, and 42 of the trial, intestine tissue and digesta samples were collected to determine intestinal morphology, gut microbiota and bacterial metabolite composition, and the expression of genes related to the gut barrier function and inflammatory status. The results showed that the BLS mix decreased the jejunum crypt depth, while increased the ileum villus height and the jejunum and ileum villus height to crypt depth ratio. The BLS mix increased Simpson's diversity index in the gut microbiota and the relative abundances of o_Bacteroidetes and f_Ruminococcaceae, but decreased the relative abundances of Blautia and Clostridium. Dietary BLS mix supplementation also modified the concentration of several bacterial metabolites compared to the control group. In addition, BLS mix upregulated the expression level of E-cadherin in the colon and pro-inflammatory cytokines and TLR-4 in ileum and colon. Lastly, Spearman's rank-order correlation revealed a potential link between alterations in gut microbiota and health parameters of the weaned piglets. CONCLUSION These findings suggest that dietary BLS mix supplementation modifies the gut ecosystem in weaned piglets. The potential advantages of such modifications in terms of intestinal health are discussed. SIGNIFICANCE AND IMPACT OF THE STUDY Weaning is the most important transition period of piglet growth and development. This study showed that dietary supplementation of a probiotic mixture of Bacillus, an effective alternative of antibiotics, was beneficial in improving the intestinal ecosystem of weaned piglets.