Microbial populations vary between the upper and lower respiratory tract, but not within biogeographic regions of the lung of healthy horses.
Authors: Bishop Rebecca C, Migliorisi Alessandro, Holmes Jessica R, Kemper Ann M, Band Mark, Austin Scott, Aldridge Brian, Wilkins Pamela A
Journal: Journal of equine veterinary science
Summary
# Microbial populations vary between the upper and lower respiratory tract, but not within biogeographic regions of the lung of healthy horses Understanding what constitutes a normal respiratory microbiome is fundamental to distinguishing health from disease in horses, particularly since different anatomical regions offer distinct environmental conditions that shape microbial communities. Bishop and colleagues characterised microbial populations across the equine respiratory tract using samples collected via nasopharyngeal lavage, transtracheal aspirate, and bronchoalveolar lavage (BAL) from six distinct lung regions in four healthy horses, analysing full-length 16S ribosomal DNA sequencing to identify and classify the microbial taxa present. Significant differences emerged between upper respiratory tract sampling (nasopharyngeal and transtracheal) and lower respiratory tract sampling (BAL) in terms of richness and phylogenetic diversity; however, when comparing six different BAL sites within the lung itself, no statistically significant variations in microbial composition were detected—a notable finding suggesting the lung microbiota remains relatively consistent across biogeographic regions in health. The predominant phyla identified were Firmicutes, Proteobacteria, and Actinobacteria, with over 1797 distinct microbial sequence variants detected across all samples, though considerable individual variation existed between horses. For practitioners conducting respiratory investigations or monitoring, these findings suggest that blindly obtained BAL fluid using standard clinical techniques provides microbiologically representative sampling of the lower respiratory tract, potentially simplifying future diagnostic protocols and reducing the need for site-specific sampling strategies in healthy animals.
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Practical Takeaways
- •Blind BAL sampling using standard clinical techniques appears adequate for respiratory microbial assessment in healthy horses, as specific lung location does not significantly alter microbial populations
- •Upper and lower respiratory tract samples yield distinctly different microbial profiles, so sampling location choice should be determined by clinical question rather than regional variation within the lung
- •Understanding baseline microbial populations in healthy horses provides reference data for identifying pathogenic shifts in diseased animals, potentially aiding diagnosis of respiratory disease
Key Findings
- •Over 1797 ASVs were identified in respiratory samples, reduced to 94 taxa after filtering, with Firmicutes, Proteobacteria, and Actinobacteria as predominant phyla
- •Significant differences in microbial richness and phylogenetic diversity existed between upper respiratory tract (NPL, TTA) and lower respiratory tract (BAL) samples (p=0.02 and p=0.01 respectively)
- •No significant differences in microbial populations were detected among six biogeographic regions within the lung, suggesting uniform microbial distribution throughout lung lobes
- •Sample type and individual horse significantly affected microbial composition (p=0.03 and p=0.005), but BAL location within lung did not affect alpha or beta diversity