Influence of bacitracin on microbial functions in the gastrointestinal tract of horses.
Authors: Collinder E, Berge G N, Grønvold B, Lindholm A, Midtved T, Norin E
Journal: Equine veterinary journal
Summary
# Editorial Summary Zinc bacitracin, a commonly used antimicrobial in equine production, was investigated for its effects on key microbial functions in the equine hindgut using faecal and intestinal samples from six horses. Researchers employed multiple analytical techniques—gas chromatography, spectrophotometry, gel and paper chromatography—to measure five critical flora-dependent metabolic pathways: cholesterol conversion to coprostanol, bilirubin conversion to urobilinogens, mucin degradation, β-aspartylglycine degradation, and tryptic enzyme inactivation. Treatment with zinc bacitracin significantly suppressed three of these functions (coprostanol and urobilinogen conversion were most notably affected, followed by mucin degradation), indicating substantial disruption to the active microbial ecosystem. Importantly, the horses' intestinal microbiota recovered all measured functions rapidly—a markedly faster normalisation than documented in human or rat studies, likely reflecting the higher microbial diversity and distinct environmental conditions of the equine hindgut. For practitioners, this work suggests that whilst zinc bacitracin does substantially alter microbial metabolism, the relatively quick recovery in horses may mitigate some concerns about long-term dysbiosis, though the clinical significance of temporary functional loss in cholesterol conversion and mucin degradation warrants consideration when treating susceptible animals.
Read the full abstract on PubMed
Practical Takeaways
- •Zinc bacitracin use as a feed additive in horses has reversible effects on intestinal microflora function, with quick recovery suggesting minimal long-term concern for gut health
- •The rapid normalization of gut flora in horses after bacitracin exposure differs markedly from other species, suggesting equine intestinal ecosystems are particularly resilient
- •Monitoring fecal markers like coprostanol conversion may help assess microbial recovery after antimicrobial feed supplementation in horses
Key Findings
- •Zinc bacitracin affected three of five studied microbial functions: conversion to coprostanol, conversion to urobilinogens, and mucin degradation
- •Conversion to coprostanol was the most sensitive indicator of bacitracin's effect on intestinal flora
- •All affected microbial functions normalized rapidly in horses, in contrast to the prolonged effects observed in humans and rats
- •Environmental exposure differences likely explain the faster restoration of intestinal flora function in horses compared to other species