Equine heaves (also called recurrent airway obstruction (RAO)) is a common chronic inflammatory disease that affects adult horses in temperate climates. It is characterized by recurrent episodes of severe breathing difficulties that leads to poor quality of life, early retirement, and euthanasia. There is no cure for the disease, and the goals for treatment are aimed at improving lung function and inducing clinical remission. Current treatment strategies include the use of corticosteroids, bronchodilators, and decreased antigen exposure (reduced exposure to dust from barn conditions, feed, bedding, and stored hay).
RAO shares many similarities to asthma in humans. RAO-affected horses develop marked airway obstruction as a result of bronchospasm, inflammation, accumulation of mucus and remodelling. Clinical signs demonstrated in horses with RAO include coughing and difficulty breathing, triggered by hypersensitivity reactions to irritants and allergens in their environment.
Environmental risk factors are similar to those seen in humans with asthma, which include indoor and outdoor allergens (mites, pollens, dust, endotoxins, mold spores, mycotoxins) and irritants like lipopolysaccharides (LPS). Horses with RAO tend to be extra sensitive to exposure of dust and molds commonly found in stored hay. Noxious fumes and high humidity can also act as triggers.
The severity of airway obstruction, inflammation, and associated symptoms can vary widely among horses. Recent studies confirmed that the plasma cortisol concentration in the horse increases concurrently with the development of acute exacerbation of RAO. In RAO, haptoglobin is a marker of both acute and chronic systemic inflammation, whereas high concentrations of SAA indicate acute inflammation.