Recurrent Airway Obstruction (RAO)

Recurrent Airway Obstruction (RAO), or heaves, the name which is more commonly known, is a chronic, non-infectious airway condition of horses. Symptoms of this disease are usually seen in horses six to 12 years old and is the result of an allergic reaction to inhaled particles (allergens), such as molds, organic dust, and endotoxins, present in hay and straw. Horses of both genders and all over the world can get heaves.

The allergic reaction that happens after the particles are inhaled causes the small airways in the lung tissue to narrow and become obstructed. A combination of three factors cause this obstruction: bronchiolitis (inflammation and thickening of the tissue lining of the airways), bronchospasm (constriction of the smooth muscles that surround the airways), and accumulation of mucous in the airways. Occasional coughing is one of the first noticeable signs. If the disease is not treated and progresses the coughing will become more frequent, the horse will have an increased respiratory rate even at rest, nasal discharge, wheezing, and can display exercise intolerance. A heave line may become apparent which is caused by the additional workload on the abdominal muscles during the late phase of exhalation. Weight loss and anorexia may be seen in severely affected horses. 

Heaves can be barn or pasture associated. It can also affect horses fed hay in round bales because of the high endotoxin and organic dust content in round bales. If a horse has barn-associated heaves try to maintain them on pasture full-time, while a horse with pasture-associated heaves should avoid access to pastures except during the winter months. Horses with heaves that are maintained in pastures should not have full access to round bales due to the potential cause of treatment failure. Horses with heaves that are kept in stalls should be maintained on low dust bedding. Straw is not recommended as bedding. Stalls should be well-ventilated and kept clean. Avoid storing hay above the stalls and sweeping the floor when affected horses are stalled. Soaking hay in water for approximately 10 minutes and then draining the water before feeding may alleviate the signs of heaves. Soaking grain can also help alleviate signs. Severely affected horses should have all hay removed from their diet and transitioned to a complete pelleted feed. It is very important to remember that although medications can help alleviate clinical signs of heaves, it is pivotal to recognize that without minimizing environmental allergens no long-term benefits will be seen. 

A veterinarian can help diagnose heaves based on the horse's history and clinical signs. They can evaluate the severity of the disease based on the presence and types of inflammatory cells, called neutrophils, in airway secretions. To determine this, fluid samples are taken from the lungs by bronchoalveolar lavage or BAL. The samples taken during a BAL are directly from the small airways, which is the affected part of the respiratory tract in a horse with heaves. Other tests that might be performed are an upper airway and tracheal endoscopy, lung function testing, thoracic radiographs, and ultrasound examination. 

The main medical treatment of heaves is anti-inflammatory medicines, such as corticosteroids and bronchodilators. Generally, these drugs are administered orally or by injection and are usually used together because corticosteroids will decrease inflammation but will not provide immediate relief like bronchodilators. More recently, aerosolized corticosteroids and bronchodilators have become available for the treatment of heaves. Inhaled therapies are beneficial because they target inflammation directly in the lungs and have reduced side effects. Prolonged treatment with oral or injectable corticosteroids can cause laminitis. However, they do require an upfront financial investment to purchase the medications and mask required to administer the medication. 

Many horses affected by heaves are able to be excellent riding partners with a dedicated owner that understands this is a chronic condition that will require life-long management. The course of this disease is largely dependent on the effort put into improving the air quality and decreasing the amount of mold, endotoxins, and organic dust in the environment in which the horse is kept. While there is no permanent cure, complete or near complete recovery from clinical signs may be achieved with diligent management.