A cross-sectional observational study of birefringent particulates in bronchoalveolar lavage cytology in horses with equine asthma from the West v East coasts of the USA.
Authors: Mazan Melissa R, Deveney Edward F
Journal: PloS one
Summary
Equine asthma represents a significant economic loss across the US horse industry, with organic dust exposure traditionally blamed as the primary culprit; however, this cross-sectional analysis of bronchoalveolar lavage fluid (BALF) from 381 horses across the West and East coasts reveals that geogenic (earth-derived) inorganic particulates may play a previously underappreciated role, particularly in arid regions. Using polarising microscopy to identify birefringent material alongside standard cytological assessment, researchers found that Western horses showed birefringent particulates in their BALF at substantially higher rates (40.5%) compared to Eastern horses (8.6%), whilst simultaneously displaying lower airway neutrophil proportions (27.1% versus 10.9%), suggesting a different inflammatory pathway. When geographical location was modelled as a predictor alongside other variables, living in the West retained highly significant association with birefringent particulate exposure (odds ratio 8.0), independent of other factors. Whilst the precise composition of these inorganic particles cannot be determined through polarising microscopy alone, the findings suggest that dust arising from mineral-rich soils warrants consideration as a distinct contributing factor to respiratory disease in horses from arid climates. For practitioners managing asthmatic horses in Western states, this distinction may influence environmental modification strategies and diagnostic interpretation, particularly when standard organic dust mitigation measures fail to resolve clinical signs.
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Practical Takeaways
- •Horses stabled in arid Western regions face substantially higher inorganic dust exposure—farriers and veterinarians should prioritize aggressive dust control measures (wet bedding, ventilation, air filtration) in these areas
- •The different inflammatory response (lower neutrophils but higher particulate load in Western horses) suggests geogenic dust may trigger different airway pathology than traditional organic dust, affecting treatment strategies
- •Consider geographic location as a risk factor when evaluating recurrent airway obstruction; horses in arid climates may need enhanced management protocols regardless of stable conditions
Key Findings
- •West coast horses had significantly higher prevalence of birefringent particulates in BALF (40.5% vs 8.6%, p<0.001) compared to East coast horses
- •East coast horses had higher BALF neutrophil proportions (10.9% vs 27.1%, p<0.001), suggesting different inflammatory patterns
- •Geographic location in the arid West was a significant independent predictor of birefringent particulate exposure (OR 8.0, 95% CI 4.3–14.8, p<0.001)
- •Inorganic geogenic dust from arid environments may contribute to equine asthma signs independent of organic particulate exposure