Equine asthma encompasses a spectrum of respiratory disease, ranging from mild to moderate asthma (previously known as inflammatory airway disease (IAD)) through to severe asthma (formally recurrent airway obstruction (RAO)). This new all-encompassing terminology is particularly helpful in aiding owner understanding of the condition, and rationalising subsequent management options.
Severe asthma is reported to affect 10–20% of adult horses in the northern hemisphere, with mild to moderate asthma affecting as much as 60–100% (dependent on population size and geographic region). 1
Mild to moderate asthma is more commonly observed in younger horses, but can occur at any age. These horses are known to be at an increased risk of developing severe asthma, which typically occurs at seven years or older.2
An allergic reaction to inhaled allergens (most commonly those found indoors) is likely to be central to the development of equine asthma; a seasonal pasture associated version of the disease also exists.
Excess tracheal mucus is expected, accompanied by coughing, poor performance and airway hyper-responsiveness. Laboured breathing at rest, pronounced bronchoalveolar lavage fluid (BALF) neutrophilia and marked exercise intolerance in addition, would indicate a more severe case. It is important to note that clinical signs may be subtle or absent in horses in remission from severe asthma.