Bronchoalveolar Lavage Cytology Characteristics and Seasonal Changes in a Herd of Pastured Teaching Horses.
Authors: Davis Kaori Uchiumi, Sheats Mary Katherine
Journal: Frontiers in veterinary science
Summary
# Editorial Summary: Bronchoalveolar Lavage Cytology in Pastured Teaching Horses Equine asthma syndrome affects a substantial proportion of the adult horse population globally, with clinical management typically advocating full-time pasture turnout to reduce exposure to stable-based respiratory irritants such as hay dust and mould; however, the baseline prevalence of lower airway inflammation in horses maintained solely at pasture remains poorly characterised. Researchers at a southeastern United States teaching facility used bronchoalveolar lavage cytology to assess lower airway inflammatory profiles in a herd of adult pasture-kept horses with no clinical respiratory disease history, sampling both summer (May–August 2017) and winter (November 2017–February 2018) periods. Severe equine asthma was identified in 10% of horses during summer and 4.3% in winter, whilst mild-to-moderate disease was remarkably prevalent at 60% in summer and 87% in winter—substantially higher than anticipated for animals with continuous pasture access and no prior respiratory concerns. Notably, 61.1% of horses demonstrated different bronchoalveolar lavage fluid cytology profiles between seasons, indicating that EAS phenotype in pastured horses is dynamic and not uniformly stable year-round. These findings suggest that subclinical lower airway inflammation is considerably more common in pasture-kept populations than currently recognised, challenging assumptions that unrestricted grazing alone eliminates respiratory disease risk and highlighting the importance of routine cytological assessment to detect and monitor evolving inflammatory status across seasons.
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Practical Takeaways
- •Full-time pasture turnout does not eliminate mild/moderate airway inflammation in horses; expect that ~60-87% of pastured adults will have some degree of lower airway disease detectable on BAL
- •Respiratory status changes seasonally in pastured horses, so clinical assessment and treatment decisions may need seasonal adjustment rather than assuming one-time year-round management solves respiratory issues
- •Round-bale hay storage and feeding methods may contribute to airway inflammation in pastured horses; evaluate forage quality and hay management as part of EAS management even for full-time pastured horses
Key Findings
- •Severe EAS prevalence was 10% in summer and 4.3% in winter in pastured horses with no respiratory disease history
- •Mild/moderate EAS prevalence was unexpectedly high at 60% in summer and 87% in winter despite 24-hour pasture turnout
- •61.1% of horses with both seasonal samples showed different bronchoalveolar lavage fluid cytology profiles between summer and winter
- •Seasonal variation in airway inflammation occurs in pastured horses fed round-bale Bermuda-grass hay