Alterations in the Fecal Microbiome and Metabolome of Horses with Antimicrobial-Associated Diarrhea Compared to Antibiotic-Treated and Non-Treated Healthy Case Controls.
Authors: Arnold Carolyn, Pilla Rachel, Chaffin Keith, Lidbury Jonathan, Steiner Joerg, Suchodolski Jan
Journal: Animals : an open access journal from MDPI
Summary
# Editorial Summary Antimicrobial-associated diarrhoea (AAD) in horses represents a significant clinical concern, yet the underlying mechanisms distinguishing horses that develop diarrhoea from those receiving identical antibiotic protocols remain poorly understood. Arnold and colleagues conducted a rigorously matched case-control investigation comparing faecal microbiota composition and metabolic profiles across three groups: horses that developed diarrhoea during antimicrobial therapy (n=17), antibiotic-treated horses without clinical signs (n=15), and untreated controls (n=31), with strict matching for diet and antimicrobial regimen (agent, dose, route and duration). Both diarrheic and non-diarrheic antibiotic-treated horses demonstrated significantly reduced microbial richness and evenness compared to controls, with both groups showing altered representation across 14 phyla; however, elevated Verrucomicrobia populations uniquely characterised the AAD group, suggesting this phylum may serve as a microbiological marker for diarrhoea development. Beyond compositional shifts, untargeted metabolomic analysis revealed seven metabolites—including L-tyrosine, kynurenic acid and xanthurenic acid—were significantly altered in AAD horses relative to controls, indicating that antibiotic-induced dysbiosis triggers distinct biochemical derangements associated with clinical disease. These findings suggest that monitoring Verrucomicrobia proliferation and specific metabolite profiles may help identify at-risk horses during antimicrobial therapy, potentially enabling targeted intervention strategies to prevent AAD and its associated complications.
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Practical Takeaways
- •Antimicrobial-associated diarrhea in horses involves complex alterations in gut microbiota composition and metabolic function; consider probiotic or prebiotic interventions during and after antibiotic therapy
- •Not all horses receiving antibiotics develop diarrhea despite similar microbiome disruption, suggesting individual factors (diet, existing microbiota, specific bacterial shifts) influence clinical outcomes
- •Monitor fecal consistency in antibiotic-treated horses and consider dietary management strategies to support gut health, as microbiome changes occur regardless of diarrhea development
Key Findings
- •Horses with antimicrobial-associated diarrhea (AAD) had significantly different fecal microbiome composition compared to non-treated controls (ANOSIM R=0.568, p=0.001) but not to antibiotic-treated horses without diarrhea
- •Both AAD and antibiotic-treated horses without diarrhea showed significantly decreased microbial richness and evenness compared to untreated controls (p<0.05)
- •Verrucomicrobia was the only phylum that distinguished AAD horses from both antibiotic-treated asymptomatic and control horses (q=0.0005)
- •Seven metabolites were significantly altered in AAD horses including L-tyrosine, kynurenic acid, xanthurenic acid, and 5-hydroxyindole-3-acetic acid (p<0.05)