Clostridium butyricum Supplementation Reduces Diarrhea in Preweaning Calves by Modulating Fecal Short-Chain Fatty Acids and Gut Microbiota

This study investigated the effects of dietary supplementation with varying doses of <i>Clostridium butyricum</i> (<i>C. butyricum</i>) on growth performance, diarrhea incidence, serum biochemical parameters, fecal short-chain fatty acids (SCFAs), and fecal microbiota in preweaning Holstein calves. Forty healthy newborn Holstein heifer calves with comparable birth weights were randomly assigned to four groups (control, 1 g/d supplementation, 3 g/d supplementation, and 5 g/d supplementation) for a 60-day trial. Growth parameters, diarrhea incidence, serum immunoglobulins (IgA, IgG, IgM), cytokines (IL-1β, TNF-α), antioxidant indicators (T-AOC, MDA), fecal short-chain fatty acids (SCFAs), and microbial composition were measured to evaluate the effects of <i>C. butyricum</i>. The results indicated that calves in the 5 g/d group exhibited a significantly higher average daily gain (ADG) compared with the control group (804.67 vs. 701.67 g/d, <i>p</i> < 0.05), with no significant differences in feed intake observed among groups (<i>p</i> > 0.05). During Days 22-42, the diarrhea incidence in the 5 g/d group was 7.74% lower than that in the control group (<i>p</i> < 0.05). This group exhibited significantly elevated serum IgM levels (Day 42, <i>p</i> < 0.05) and reduced IL-1β concentrations (Day 42, <i>p</i> < 0.05). Additionally, total antioxidant capacity (T-AOC) was significantly enhanced (Days 42 and 60, <i>p</i> < 0.05), while malondialdehyde (MDA) content was significantly decreased (Days 21 and 42, <i>p</i> < 0.05). At Day 42, fecal propionate and butyrate concentrations were significantly elevated in the 5 g/d group (<i>p</i> < 0.05), while the relative abundances of <i>Bacteroides</i>, <i>Acidaminococcus</i>, <i>Bifidobacterium</i>, <i>Olsenella</i>, <i>Faecalitalea</i>, and <i>Ruminococcus</i> were significantly increased (<i>p</i> < 0.05). The increase in these short-chain fatty acids and beneficial bacteria contributes to improved intestinal health and thus helps alleviate diarrhea. These findings indicate that supplementing preweaning calves' milk with 5 g/d of <i>C. butyricum</i> significantly enhances growth performance and intestinal health. This provides evidence for the use of <i>C. butyricum</i> as a natural alternative to antibiotics in calf rearing.