Equine Recurrent Airway Obstruction (RAO)
Overview: Recurrent Airway Obstruction, also referred to as heaves, is characterized by bronchoconstriction, mucous production and bronchospasm. Recurrent Airway Obstruction (RAO) is similar to asthma in people and is often triggered by inhaled allergens. The most common triggers include mold, dust and endotoxin present in hay and straw. RAO most commonly onsets at ages 9-12, but can occur at any age. There are two types of RAO that are recognized: the barn-associated form and the pasture-associated form. The most common form seen in Ohio is the barn-associated form. The barn-associated form is often worse in the winter and spring and the pasture-associated form is often worse in the summer and fall. RAO is a lifelong disease and requires long term management.
Clinical Signs: Signs of RAO include chronic coughing, increased respiratory effort, nasal discharge and/or exercise intolerance. A “heave” line may also be present, which is a line along the edge the ribs that occurs due to the abdominal muscles enlarging due to increased respiratory effort. Severe cases may show anorexia and weight loss.
Diagnosis: In most horses, a diagnosis of RAO is based on clinical exam findings. Occasionally, a horse may need further diagnostics and possible referral to an internal medicine specialist.
Management: Many horses do well with environmental management alone. Round bales should be avoided in all RAO horses due to high endotoxin and dust content. Horses with barn-associated RAO should be kept on pasture as much as possible and those with pasture-associated RAO should avoid pasture except for the winter. Horses that must be kept in a stall should be in a clean and well ventilated area. It is also recommended that hay not be stored above the stalls, the floors not be swept when the horse is in the stall and do not bed the horses on straw. Chopped paper and cardboard are good, low-dust bedding for these horses. Another option includes wetting down dusty bedding. Options to reduce dust in the feed include wetting down hay or switching from hay to pellets.
Medications: Horses that cannot be managed by environmental management or where management changes are not possible are often controlled on medications. There are several medications available for RAO. The most common medication used is corticosteroids, such as prednisolone or dexamethasone. These are often tapered down until the horse can be maintained without it. However, many horses have to stay on a low dose. Another medication commonly prescribed is Ventipulmin, which is a bronchodilator that is very effective in horses. Another option is an equine inhaler, which often includes inhaled corticosteroids and bronchodilators.
Prognosis: With good management, many horses can be maintained long term with minimal clinical signs. In severe cases, athletic performance may be limit to more mild activities.
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