Recurrent airway obstruction (RAO or heaves) is an allergic, inflammatory, and obstructive airway disease that afflicts older horses. It may be initiated by the inhalation of organic dusts such as those associated with hay and bedding materials. Such organic dusts can contain specific allergens, endotoxins, molds, and other small particles and substances that can start the severe inflammation that happens in the lungs associated with heaves. For this reason, RAO is a syndrome that is more common on northern hemisphere countries where horses are stabled and fed hay.

There is also apparently a genetic component of this disease. The genetic association is seen because both affected and unaffected horses are housed under the same environmental circumstances that trigger heaves in susceptible horses while not affecting many of their stable mates.

Concomitant with, and possibly a result of, the severe inflammation, airway obstruction occurs. Airway obstruction is due to bronchospasm (bronchoconstriction, narrowing of airways), mucus accumulation, and airway wall thickening. RAO used to be called COPD, or chronic obstructive pulmonary disease, but in 2000 it was decided that the name be changed from COPD to RAO, or simply heaves, because of differences between the COPD in humans, which is a disease of smokers, and heaves in horses, which is more comparable to asthma in humans.

Clinical Signs

The clinical signs of a severely affected horse are easy to recognize, appearing as marked respiratory distress. In horses undergoing a severe acute episode, the nostrils are flared, there is an increase in respiratory rate, and the horse clearly uses its abdominal muscles to assist expiration. The animal also has an anxious appearance and/or is agitated. Generally the horse is 7 years of age or older and has spent a considerable period of its life stabled and fed hay. The horse may have nasal discharge. The horse becomes increasingly intolerant to exercise, and the chronic use of the abdominal muscles to assist expiration leads to the development and appearance of “heave lines.” In severe stages of the disease, the struggle to breathe is so intense that the horse is unable to eat and, consequently, loses weight. Clinical signs in less severely affected horses include coughing associated with exercise or during feeding or cleaning/sweeping the barn, reduced exercise tolerance and delayed recovery from exercise.

Management and Prevention

• Complete change in the horse’s environment (the best environment for a horse with heaves to be is at pasture year-round)
• When the horse needs to be stalled, it should be in a place where there is less “flying” or airborne particles and allergens. Supportive strategies include changing the ventilation system of the barn, changing general management practices performed inside the barn, such as constant sweeping of the floor, and avoiding storing hay in the barn loft. When horses are confined to the barn, the bedding should also be changed to one that produces the least amount of dust, such as chopped paper or cardboard.
• There should be a change in the horse’s diet. Hay should be avoided at all times, especially round baled hay. In places where this practice is not possible, soaking hay in water for about 10 minutes before feeding is recommended. Note that sprinkling hay with water is not the same as soaking hay in water. Silage, alfalfa pellets, and whole grains contain low amounts of dusts; rolled grains, on the other hand, have very high dust content and should be avoided.
• Corticosteroids to reduce lung inflammation; consult with your veterinarian before attempting to administer any medications to your horse
• Bronchodilators to "open" the airways; consult with your veterinarian before attempting to administer any medications to your horse