Equine fecal microbiota response to short term antibiotic administration.
Authors: Parker J L, Page A, Jacob O, Stanton V, Davis B, Flythe M, Adam E N
Journal: Journal of equine veterinary science
Summary
# Editorial Summary Short-term antibiotic therapy causes significant and measurable disruption to equine fecal microbiota, though individual horses respond with considerable variability—findings that have important implications for post-treatment management and monitoring. Parker and colleagues administered one of three antibiotic regimens (potassium penicillin/gentamicin, ceftiofur crystalline free acid, or trimethoprim/sulfamethoxazole) or placebo to 24 healthy horses over four days, then tracked faecal bacterial populations and function via qPCR and stool consistency across 28 days. All antibiotic-treated horses produced significantly softer faeces compared to controls, whilst Lactobacillus species—key producers of short-chain fatty acids and competitors against pathogenic bacteria—were dramatically depleted in samples collected immediately post-treatment; simultaneously, treated horses showed markedly higher detection rates of *Clostridium difficile* and *Clostridium perfringens*, known triggers of antibiotic-associated diarrhoea. The degree and duration of microbiotal disruption appeared antibiotic-dependent, highlighting that blanket protocols may not account for differential risk profiles across commonly used agents. Practitioners should consider implementing targeted probiotic or prebiotic interventions and vigilant post-treatment monitoring in horses receiving systemic antibiotics, particularly where gastrointestinal stability is already compromised, recognising that some individuals may require extended observation beyond the treatment period itself.
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Practical Takeaways
- •Expect fecal consistency changes and potential pathogenic bacterial overgrowth in antibiotic-treated horses; monitor closely for clinical diarrhea even on short 4-day courses
- •Different antibiotics produce different microbiota disruption patterns—consider microbiota impact when selecting between KPG, ceftiofur, and trimethoprim/sulfamethoxazole
- •Individual horses respond very differently to the same antibiotic; some may be at higher risk for AAD than others, warranting individualized monitoring and potential preventive strategies
Key Findings
- •All horses receiving any antibiotic experienced significantly softer stool compared to controls within 5 days of treatment
- •Lactobacillus spp. were dramatically reduced in all antibiotic-treated horses by day 5 post-treatment initiation
- •Horses receiving antibiotics were significantly more likely to test positive for C. difficile or C. perfringens on fecal qPCR
- •Inter-individual variability in microbiota response to antibiotics was high, with response patterns depending on the specific antibiotic used