Clinical and microbiota alterations in performance horses undergoing long-distance transport

Transport-associated pneumonia contributes substantially to morbidity, impaired welfare, and economic loss in high-performance horses and may be associated with alterations in the respiratory microbiota.

Examine the effect of long-distance transport on the respiratory microbiota and correlate changes in microbiota diversity and composition with systemic and airway inflammation.

Seventeen client-owned performance horses transported from New England to Florida under optimized trailering conditions, and 12 non-traveling horses.

Physical examination, blood testing, nasopharyngeal wash, endoscopy, tracheal aspirates, and thoracic ultrasonography were performed 48 h before, and 24 and 72 h after transport (T1-T3). Upper and lower respiratory microbiota were characterized using high-throughput 16S rRNA sequencing and correlated with clinical variables using constrained ordination. Transport effects were evaluated using repeated measures analysis of variance (ANOVA).

Cortisol concentrations decreased post-transport (P = .02), whereas ultrasound scores (P = .01) and serum amyloid A concentrations (P = .03) increased from T1 to T3. Timepoint explained a small but significant portion of microbiota variability (P < .001). Upper and lower airway microbiota differed, with the lower airway showing more β diversity (lower stability; P < .001). Together, timepoint and ultrasound scores explained 19% and 10%, respectively, of nasal and tracheal bacterial microbiota variability. Operational taxonomic units with the highest fit to timepoint and ultrasound were enriched for plant-associated bacterial taxa, mainly Hyphomicrobiales.

Even under standardized, optimized transport conditions, respiratory microbiota alterations occurred in healthy, athletic horses, correlating with ultrasonographic evidence of pulmonary inflammation. Inclusion of the fungal mycobiome may further improve our understanding of transport-associated respiratory disease.