Mares with severe equine asthma exhibit a narrower trachea than geldings in a retrospective radiographic study of 189 horses.

Mares with severe equine asthma have significantly narrower tracheas than SEA geldings and healthy mares.

This retrospective case-control study evaluated the relationship between sex, asthma severity, and tracheal diameter in 189 adult horses using thoracic radiography at the Université de Montréal (2018–2024). Horses were classified as controls, mild/moderate asthma, or severe equine asthma (SEA) per current consensus guidelines. To correct for radiographic magnification and body size variation, tracheal diameter was standardized as ratios relative to the fifth thoracic vertebral body length (T5) and aortic diameter. Two-way ANOVA with Tukey post-hoc testing revealed a significant interaction between sex and disease status. SEA mares had a significantly lower trachea-to-T5 ratio (0.7 ± 0.1) compared to SEA geldings (0.8 ± 0.1), control mares (0.8 ± 0.1), and mild/moderate asthma mares (0.8 ± 0.1). The trachea-to-aorta ratio was lower in SEA horses overall compared to controls, regardless of sex. Absolute tracheal diameter was affected by both disease status and sex, with SEA mares demonstrating the narrowest tracheas across all groups. These findings suggest that tracheal narrowing in SEA is not uniform across sexes, with mares disproportionately affected. The authors propose that this sex-related anatomical difference may have implications for airway mechanics and exercise performance, though further investigation is needed to determine the clinical and functional consequences of this finding in equine respiratory disease management.

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