Equine Asthma Diagnostics: Review of Influencing Factors and Difficulties in Diagnosing Subclinical Disease.
Authors: Lendl Lioba, Barton Ann Kristin
Journal: Animals : an open access journal from MDPI
Summary
Equine asthma diagnostics remain challenging, particularly when identifying subclinical or remissive disease that may be limiting performance without obvious clinical signs. Standard assessment combines respiratory examination (including rebreathing), haematology, blood gas analysis, and airway sampling via bronchoscopy and bronchoalveolar lavage (BALF) cytology, with severity graded primarily on resting respiratory effort and inflammatory subtype determined by BALF cell differentials. However, multiple confounding variables complicate interpretation: short-term exercise, cold or chlorinated air exposure, chronic training effects, and concurrent conditions such as exercise-induced pulmonary haemorrhage all elevate airway inflammatory markers and cell counts in both symptomatic and asymptomatic horses, potentially masking or mimicking genuine disease. The authors highlight that BALF cytology may appear normal during periods of remission or low-grade inflammation, reducing diagnostic sensitivity at precisely the times when early intervention might prevent clinical deterioration. Given these limitations, practitioners should consider provocative exercise testing or other challenges that stress the bronchial epithelium in horses with performance issues and inconclusive routine diagnostics, whilst remaining mindful that environmental and training factors must be controlled or accounted for when interpreting inflammatory findings.
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Practical Takeaways
- •Consider exercise stress testing and environmental factors (cold air, chlorine exposure) when BALF cytology appears normal but subclinical asthma is suspected
- •Understand that tracheal aspirate cytology helps rule out bacterial infection while BALF cytology determines inflammatory subtype and disease severity
- •Be aware that respiratory effort at rest is the key clinical indicator of severe equine asthma, and that multiple concurrent conditions (especially exercise-induced pulmonary hemorrhage) may complicate diagnosis
Key Findings
- •Routine equine asthma diagnostics include clinical examination, white blood cell counts, arterial blood gas analysis, bronchoscopy, bronchoalveolar lavage, and cytology of tracheal aspirates and BALF
- •BALF cytology may be unremarkable during equine asthma remission and low-grade disease, limiting diagnostic sensitivity
- •Short-term exercise increases total cell count and inflammatory mediators in BALF across multiple species including asymptomatic horses
- •Multiple factors including cold/chlorinated air, training effects, and concurrent respiratory disease complicate equine asthma diagnosis and interpretation