Recurrent airway obstruction (RAO, heaves) is one of the most common respiratory conditions in horses, caused by hypersensitivity to organic dust including hay spores and stable bedding. The condition causes progressive breathing difficulty that severely impairs athletic performance and quality of life if poorly managed.
Horses with active RAO episodes show visible breathing difficulty at rest — flared nostrils, heave lines from repeated abdominal muscle use, and respiratory rate elevation. The welfare cost is immediate and severe: breathing difficulty at rest represents significant suffering. Environmental management — turning horses out rather than stabling, soaking hay, using paper or rubber bedding rather than straw — eliminates the allergen challenge that drives disease. Without environmental change, medication provides only temporary relief. Horses managed well with environmental modification maintain good athletic performance for years; horses kept in dusty hay and straw environments suffer progressive lung damage. The welfare imperative is environmental change, not medication alone.