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Heaves is a chronic, non-infectious airway condition of horses which goes under the more scientific name recurrent airway obstruction. Heaves is seen more often in older horses (>6-8 years old) and is the result of an allergic reaction to inhaled particles such as mould, which can be found in hay and straw. Affected horses cough (or heave), develop exercise intolerance, often have nasal discharge, wheezing and flaring of the nostrils, and severely affected horses have difficulty breathing at rest.
Once the offending particles are inhaled, an allergic reaction occurs in the small airways of the lungs. In normal airways, the lining is very thin (only 1 cell thick), which makes for very efficient gas exchange. However, once the allergic reaction is underway the airways become narrow and obstructed which decreases the efficiency of the horse's respiratory system. As the horse has irritation in the lower airways, they will often heave to ease the irritation and clear their airways.
This disease tends to be worse in horses that live in dusty environments with poor ventilation. In fact, British veterinarians in 1640 recognised that the best treatment (at the time) for heaves was green grass. Despite its tendency to affect stabled horses, we do see this condition occurring in horses kept outside in paddocks. Generally, it is worst during dry, dusty periods of the spring and summer.
Diagnosis is an important part of working out the best management of these horses. This is often done by taking fluid samples from the lower airways (broncho-alveolar lavage). Once diagnosed, treatment is largely symptomatic using bronchodilators and corticosteroids and reducing exposure to dust and irritants.
If left untreated for a significant period of time, horses will feel short of breath their whole life and even develop a heave line (pictured) from constant contraction of their abdominal muscles while heaving.
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