Equine Blood Microbiome in a Cohort of Clinically Healthy Trail Riding Horses.
Authors: Simms Noel, Bertone Joseph J, Melgarejo Tonatiuh, O'Shea Caitlin, Linde Annika
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary Emerging evidence indicates that circulating blood contains viable bacterial communities even in clinically healthy individuals, yet characterisation of these microbiomes in horses remains limited. Researchers analysed blood samples from 20 trail-riding horses in a closed Colorado herd using next-generation sequencing alongside routine haematological and biochemical assessment to profile bacterial composition and abundance in clinically normal animals. The study identified 293 bacterial genera across the cohort, with individual horses typically harbouring 55–70 genera; dominant taxa included Gardnerella, Sporomusaceae, Kapabacteriales, and Phascolarctobacterium, whilst potentially pathogenic organisms such as Bacteroides, Clostridium, Peptostreptococcus, Streptococcus and Staphylococcus species were present in all samples. Despite the horses' relative isolation in a uniform environmental setting, principal coordinate analysis revealed marked interpersonal variability with no consistent clustering patterns—suggesting that individual microbial populations are dissimilar even among closely managed animals. These findings establish a baseline characterisation of the equine blood microbiome in health and provide critical context for future investigation of how microbiota dysbiosis may contribute to systemic disease; clinicians should consider that shifts in circulating bacterial communities, rather than their mere presence, may be clinically significant.
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Practical Takeaways
- •Blood cultures in healthy horses may show bacterial growth that represents normal microbiome rather than infection; routine laboratory interpretation may need updating
- •Individual variation in blood microbiota is substantial even in isolated herds, suggesting host factors beyond environment influence bacterial composition
- •Baseline characterization of healthy blood microbiomes provides reference data for identifying pathogenic shifts associated with clinical disease
Key Findings
- •Venous blood in healthy horses is not sterile, containing a mean of 55-70 bacterial genera per individual with 293 total genera identified across the cohort
- •Dominant bacterial taxa included Gardnerella, Sporomusaceae, Kapabacteriales, Beijerinckiaceae, and Phascolarctobacterium
- •All blood samples contained potentially pathogenic genera including Bacteroides, Clostridium, Peptostreptococcus, Streptococcus, and Staphylococcus spp.
- •Principal coordinate analysis revealed large variability and no clustering among horses, indicating marked individual differences in blood bacterial composition despite shared environment