Equine Internal Medicine
Heaves (recurrent airway obstruction, COPD, broken wind, emphysema) is a common, performance-limiting, allergic respiratory disease of horses characterized by chronic cough, nasal discharge, and respiratory difficulty. Heaves in horses is most similar to asthma in humans. Episodes of heaves are usually observed when horses are stabled, bedded on straw, and fed hay, whereas, elimination of these inciting factors results in remission of clinical signs.
The average age of onset of RAO is 9 years of age. Approximately 12% of mature horses have some degree of allergen-induced lower airway disease, and over 50% of horses that present for evaluation of respiratory disease are diagnosed with heaves. There is no breed or gender predilection, however, there does appear to be a heritable component to this condition. Just as with human asthmatics, there is a broad spectrum of sensitivity to molds and severity of clinical signs.
Horses with classic heaves have flared nostrils and difficulty breathing. The abdominal muscles are recruited to assist with expiration, and hypertrophy of these muscles produces the classic heave line.
Heave Line Flared Nostrils
Mild to moderately affected horses may present with minimal clinical signs at rest, however, coughing and exercise intolerance are noted during performance. Horses with heaves do not have a fever, unless secondary pneumonia has developed.
The diagnosis of heaves is determined on the basis of history and characteristic physical examination findings. Radiographs of the chest and sampling of respiratory secretions is indicated to provide additional information in some cases. Blood work should be normal in horses with uncomplicated heaves.
The single most important treatment for heaves is to improve the environment to reduce exposure to dust and molds. Medication will alleviate clinical signs of disease, however, respiratory disease will return after medication is discontinued if the horse remains in a dusty, moldy environment. The most common offending allergens are molds present in hay and straw. Hay does not have to appear overtly moldy to precipitate an episode in a sensitive horse. If possible, horses should be maintained at pasture with fresh grass as the source of roughage and supplemented with pelleted feed. Round bale hay is particularly offensive to heavey horses, and a common cause of treatment failure for horses on pasture. Horses that must be stalled should be maintained in a clean, controlled environment and fed a complete commercial feed, which eliminates the need for roughage in the diet. Hay cubes and hay silage may be an acceptable, low-allergen alternative roughage source. Soaked hay is unacceptable for highly sensitive horses. Horses maintained in a stall should not be housed in the same building as an indoor arena, and hay should not be stored overhead. Straw bedding should be avoided.
Medical therapy should consist of an anti-inflammatory drug and a bronchodilator. Medication may be given by aerosol, oral, or injectable routes of administration. In general, aerosol therapy is more expensive and requires more frequent administration. Most aerosol preparations are more effective and safer for long-term administration. The ideal combination of medications should be determined with your veterinarian based on the use of your horse and the severity of disease.