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

Overview

• This study investigates the relationship between sex, severity of equine asthma, and tracheal diameter in adult horses using thoracic radiographs.
• It found that mares with severe equine asthma have a narrower trachea compared to geldings and other groups, suggesting sex and disease status affect tracheal size.

Study Objective and Design

• The goal was to evaluate how sex and severity of equine asthma relate to tracheal diameter in horses.
• The study was retrospective, analyzing thoracic radiographs from horses examined at the Université de Montréal between 2018 and 2024.
• Horses were classified into three groups: control (healthy), mild/moderate asthma, and severe equine asthma (SEA) based on the latest consensus guidelines.
• Data on tracheal diameter was gathered and standardized to account for differences in horse body size and radiographic magnifications.

Measurement Techniques and Analysis

• Tracheal diameter measurements were normalized by creating ratios relative to:
  • The length of the fifth thoracic vertebral body
  • The diameter of the aorta
• This normalization helped compare tracheal sizes across horses of varying sizes accurately.
• Statistical analyses involved:
  • A 2-way ANOVA to examine effects of sex, asthma severity, and their interaction on tracheal diameter.
  • A Tukey multiple-comparisons test for pairwise group differences when significant effects were found.

Key Findings

• A total of 189 horses were included in the study across the different categories.
• The ratio of tracheal diameter to the fifth thoracic vertebral body length varied significantly based on disease status and sex interaction:
  • Mares with severe equine asthma had a significantly smaller ratio (mean 0.7) compared to SEA geldings (mean 0.8), control mares, and mares with mild/moderate asthma.
  • Confidence intervals supported these significant differences.
• The trachea-to-aorta diameter ratio was lower in horses with severe asthma compared to healthy controls, indicating narrower airways in SEA generally.
• Absolute tracheal diameter was influenced both by sex and asthma severity with notable sex-disease interaction effects.
• Overall, SEA mares had the narrowest tracheas among all groups evaluated.

Implications and Future Directions

• This research indicates that both the sex of the horse and the presence and severity of asthma affect tracheal dimensions.
• The narrower trachea observed in SEA mares may have implications for lung function and exercise capacity, although this aspect remains unstudied.
• Further research is needed to determine how these anatomical differences impact breathing mechanics, respiratory health, and performance in affected horses.
• Understanding these differences might influence management and treatment strategies for severe equine asthma, potentially taking sex-based anatomical variations into account.