Heaves or broken wind are terms used for decades to describe an allergic respiratory disease of mature to older horses manifested by increased breathing efforts at rest and chronic coughing. Over 40 years ago, the German veterinarian H. Sasse used the term chronic obstructive pulmonary disease (COPD) to describe horses with heaves because of similarities with the human disease. However, our knowledge of respiratory diseases in people and horses has grown considerably since then and it is now clear that heaves in horses is more similar to asthma in people rather than COPD.

Veterinarians and scientists prefer using the term recurrent airway obstruction (RAO) that implies the reversible nature of the disease once horses are turned out on grass pasture. Equine asthma is used to describe the state of airway hyper-responsiveness following inhalation of dust particles commonly found in barns. Such exposure is usually the result of feeding moldy hay. However, some horses present identical signs while being on pasture during the summer in response to high levels of grass molds and tree pollen.

Feeding round bales at pasture is more likely to trigger equine asthma and is usually associated with more severe disease. Molds are particularly abundant in moldy hay. However, it is important to note that the same types of molds are also present in good quality hay but in lower numbers. A genetic predisposition has also been shown in some breeds, such as Warmbloods and Lipizzaners.

The goals of therapy are to avoid exposure to dust and to treat lung irritation. The most effective way to avoid dust is by keeping asthmatic horses outdoors all the time and not feeding h