Heaves, also known as Recurrent Airway Obstruction (RAO), is a chronic respiratory condition found most commonly in older horses. It is similar to asthma in humans and is caused by a hypersensitivity to inhaled triggers, usually hay and barn dust, or in the case of travel, fumes and particulates from car and truck exhausts. Horses with heaves will have difficulty breathing at rest, and in advanced cases, its efforts to breathe using abdominal muscles will produce a pronounced line along the lower half of the animal’s barrel, below its rib cage, known as a "heave line".

The symptoms of heaves include a persistent, chronic cough, difficulty breathing, wheezing, and nasal discharge. Horses with classic heaves have flared nostrils and difficulty breathing, and mild to moderately affected horses may present with minimal clinical signs at rest, but coughing and exercise intolerance are noted during performance. Severely affected horses may also exhibit weight loss, anorexia, and even respiratory distress.

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 may be indicated to provide additional information in some cases. 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 an environment where allergens are present[[6]](https://www.petmd.com/horse/conditions/respir...