Steamed hay for the prevention of severe equine asthma exacerbations.
Authors: Raïsky Clara, Vives Berta Mozo, Leduc Laurence, Symoens Antoine, Tavanaeimanesh Hamid, Richard Hélène, Juette Tristan, Bédard Christian, Leclère Mathilde
Journal: Equine veterinary journal
Summary
# Steamed Hay and Severe Equine Asthma: What the Evidence Actually Shows Whilst steaming hay is standard practice for managing horses with severe equine asthma (SEA), clinical evidence for its protective effects remains inconsistent. Raisky and colleagues conducted a prospective, cross-over study feeding horses with SEA in remission either steamed or dry hay for four-week periods, separated by a four-week washout, measuring lung function via resistance at 5 Hz (R5), bronchoalveolar lavage (BALF) cytology, and a weighted clinical scoring system. Over the study period, airway resistance increased significantly in both groups (R5 rising from approximately 0.065 to 0.079 kPa/L/s with dry hay, and 0.063 to 0.078 with steamed hay; p<0.001), with no meaningful difference between treatments, whilst BALF neutrophil percentages rose from baseline levels of around 6% to between 10–13% by the end of each four-week phase. Notably, clinical signs as measured by the weighted scoring system showed no significant deterioration in either group. For practitioners, these findings suggest that steaming hay may not provide the expected protective benefit during periods of remission, though the unexpectedly mild inflammatory responses observed throughout the study—and the lack of direct measurement of hay dust and particulate load in the breathing zone—warrant caution before drawing firm clinical conclusions about hay processing as a disease-management strategy.
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Practical Takeaways
- •Steaming hay alone may not prevent airway deterioration in horses with severe asthma in remission—focus on overall hay quality and dust content rather than steaming method alone
- •Both steamed and dry hay resulted in increased airway inflammation and resistance over 4 weeks in SEA horses, indicating environmental management beyond feed preparation is critical
- •Clinical signs (weighted scores) remained mild during the study despite measurable lung function decline, suggesting subclinical deterioration may occur without obvious clinical signs
Key Findings
- •Airway resistance at 5 Hz (R5) increased significantly over 4 weeks in both steamed and dry hay groups (p<0.001), with no difference between treatments
- •Bronchoalveolar lavage fluid neutrophil percentages increased significantly in both groups (dry: 6.7% to 13.1%, steamed: 5.6% to 10.5%, p<0.001)
- •Weighted clinical score showed no significant change between steamed hay (2.9 to 1.9) and dry hay (2.6 to 2.2) groups
- •Steamed hay did not provide protective benefits over dry hay for horses with SEA, suggesting hay quality/dust content rather than steaming method may be the limiting factor