Dietary Bacillus velezensis Improves Piglet Intestinal Health and Antioxidant Capacity via Regulating the Gut Microbiota

Piglet diarrhea caused by weaning stress will increase the mortality rate and seriously affect swine industry production efficiency. Probiotic supplementation has been reported to effectively alleviate weaning diarrhea by inhibiting the colonization of pathogenic microorganisms; however, the underlying mechanisms remain unclear. In this study, we isolated a strain of <i>Bacillus velezensis</i> and conducted a series of <i>in vivo</i> and <i>in vitro</i> experiments to explore its effects on weaned piglets. The piglets were fed for a 28-day period, and the results showed that dietary supplementation of <i>B. velezensis</i> 411 significantly alleviated weaning diarrhea (<i>p</i> = 0.019) and improved the average daily gain (ADG) of piglets throughout the experimental period (<i>p</i> = 0.004). The intestinal antioxidant capacity of piglets was also significantly enhanced. Whole-genome sequencing revealed that <i>B. velezensis</i> 411 contains a protein-encoding circular chromosome, which is involved in biological processes such as sporulation and antibiotic secretion. Supplementation with <i>B. velezensis</i> 411 significantly increased the abundance of <i>Akkermansia</i> in intestine samples and significantly decreased the abundance of pathogenic bacteria, including <i>Escherichia coli</i> and <i>Staphylococcus aureus</i>, in piglets (<i>p</i> < 0.05). The transcriptomic results suggest that <i>B. velezensis</i> 411 supplementation may alter the composition of intestinal microorganisms through regulating the expression of <i>MPEG1</i>. Collectively, dietary <i>B. velezensis</i> can relieve diarrhea in piglets and improve their production performance by influencing the antioxidant capacity of the intestines and the balance of the intestinal flora. This study provides valuable insights into the potential application of <i>Bacillus velezensis</i> in mitigating weaning-associated issues in piglets.