Effects of Intravenous Antimicrobial Drugs on the Equine Fecal Microbiome.
Authors: Liepman Rachel S, Swink Jacob M, Habing Greg G, Boyaka Prosper N, Caddey Benjamin, Costa Marcio, Gomez Diego E, Toribio Ramiro E
Journal: Animals : an open access journal from MDPI
Summary
# Editorial Summary: Intravenous Antimicrobials and the Equine Microbiome Systemic antimicrobial therapy is essential for treating serious equine infections, yet concerns persist about disruption to the beneficial gut bacteria that protect against pathogenic overgrowth and dysbiosis-related diarrhoea. This 2022 study investigated how three commonly used intravenous antimicrobials—ceftiofur, enrofloxacin and oxytetracycline—altered the faecal microbiota composition over 30 days in 16 horses, using 16S rRNA gene sequencing to track bacterial populations before, during and after a five-day treatment course. Ceftiofur proved most disruptive, significantly reducing microbial richness by day 3, whilst both ceftiofur and enrofloxacin caused marked suppression of Fibrobacteres and increases in Clostridia and Lachnospiraceae—shifts that persisted through day 5 despite apparent clinical stability. Notably, horses receiving these drugs showed no overt clinical signs of diarrhoea or gastrointestinal upset during the study period, yet the documented changes in bacterial taxa suggest a mechanistic pathway toward future dysbiosis-related complications, implying that vigilant post-treatment monitoring and consideration of microbiome-protective interventions (probiotics, prebiotics or dietary management) may be warranted when systemic antimicrobials are unavoidable.
Read the full abstract on PubMed
Practical Takeaways
- •IV antimicrobials (particularly ceftiofur and enrofloxacin) disrupt beneficial gut bacteria within 3 days of treatment; consider probiotic or prebiotic supplementation during and after therapy to support microbiome recovery
- •Monitor horses receiving prolonged IV antimicrobial therapy closely for subclinical microbiome changes even when clinical signs are absent, as altered bacterial composition may predispose to delayed-onset digestive problems
- •Oxytetracycline showed fewer significant microbiome effects than ceftiofur or enrofloxacin in this study, suggesting it may be a preferable choice when prolonged IV antimicrobial therapy is necessary and gut health is a concern
Key Findings
- •Intravenous ceftiofur significantly reduced alpha diversity (richness) by day 3 compared to day 0 (p < 0.05)
- •Ceftiofur and enrofloxacin markedly decreased Fibrobacteres relative abundance on day 3, a taxon associated with gut health
- •Both ceftiofur and enrofloxacin increased Clostridia and Lachnospiraceae from day 0 to days 3-5, potentially predisposing horses to gastrointestinal inflammation
- •Microbial composition changes were detected by day 3 and persisted through day 30, despite no observable clinical signs in any treated horses