Equine Asthma

What is equine asthma?

Equine asthma is the term now used to describe horses with inflammatory airway disease/IAD (mild-moderate asthma) and recurrent airway obstruction/RAO, also known as heaves (severe
asthma). Equine asthma is the most common chronic inflammatory airway disease of horses, and it shares similarities with human asthma.

What does a horse with mild-moderate asthma look like?

Horses of any age can develop mild asthma but it is most common in young to middle-aged, otherwise healthy horses. Clinical signs can vary depending on the horse’s job. Signs can be subtle in high-level performance horses and can include resisting collection, reluctance to go forward and decreased performance. Coughing is the most common presenting sign. The cough may occur while the horse is in the stall, while eating, or during exercise. A cough so strong that it rips the reins right from the rider’s hands at the beginning of a ride is possible. Varying amounts of white mucoid nasal discharge may be present intermittently as well.

What causes a horse to develop asthma (IAD)?

Poor air quality in the horse’s environment is a key component. Exposure to airborne particulates causes irritation in the airways that then results in airway inflammation and bronchoconstriction. A horse’s environment is naturally full of organic dust, antigens, allergens, ammonia gas from urine, mites and insects, and beta glucans and spores from molds. Even the highest quality hay contains mold spores that can cause airway inflammation. Exposure to noxious gases and pollutants, infectious agents (bacteria, viruses), high levels of pollen in the spring, the heat and humidity of the summer, riding in dusty arenas any season, and barn cleaning techniques that increase the amount of dust in the air are all possible causes of equine asthma.

How do you find out if your horse has asthma (IAD)?

A complete physical exam should be performed at rest to determine respiratory rate and effort. Auscultation of the lungs and trachea is recommended at rest and after exercise to evaluate for abnormal sounds. A rebreathing exam is also performed. This procedure involves placing a bag over the horse’s nose causing it to rebreathe its breath allowing for deeper breaths that accentuate abnormal sounds when present. Diagnostic procedures including airway endoscopy and bronchoalveolar lavage (BAL) allow for more complete examination of the respiratory system. A definitive diagnosis of mild asthma is made when excess mucus is identified in the trachea on endoscopy and increased numbers of inflammatory cells including neutrophils, +/- mast cells, +/- eosinophils are present in BAL fluid.

How do you treat a horse with mild-moderate asthma (IAD)?

A combination of management and nutritional supplements can be used medical therapy, environmental to treat asthma. Medical treatment involves the use of bronchodilators to treat
bronchoconstriction and steroids to decrease airway inflammation.

Systemic therapy with oral or injectable administered medications is an option. Inhalation therapy is administered with metered dose inhalers (MDI) or nebulization of drugs that target the respiratory system. A veterinarian can determine which therapy is the best option for your horse.

How do you treat a horse with mild-moderate asthma (IAD) cont.

Environmental management involves decreasing the horse’s exposure to environmental airway irritants. Reduce exposure to airborne dust and respirable particles by feeding “low dust” feeds such as pelleted rations, chopped hay forage, steamed hay or hay that is soaked for 20-30 minutes then drained before feeding. Steaming hay removes 99% of airborne respirable dust, mold, fungi, and bacteria in hay. Feed hay on the ground or in a feeder rather than elevated in a hay net to allow for adequate airway clearance via gravity and decreased inhalation of hay particulates. Provide good barn ventilation. Keep doors and windows open to allow for adequate ventilation. Do not clean stalls, throw down hay, sweep/clean barn aisles or use a blower while the horse is in its stall. Allow for plenty of paddock turnout. If necessary, provide adequate moisture to the footing in the indoor arena or outdoor ring to minimize airborne dust particles while riding. Nutritional support for asthma involves the use of natural omega-3 fatty acid supplements. Supplements containing high levels of DHA and EPA which are potent marine derived omega-3 FAs, have anti- inflammatory properties and are recommended in the management of equineasthma. Omega-3 FA’s have been shown to provide more rapid and more complete clinical improvement in asthma horses than with medications and environmental management alone.


If you have questions about equine asthma or are concerned about a horse with a cough, nasal discharge, and performance issues, contact 603-842-5037, Jacqueline Bartol, DVM, DACVIM or one of the veterinarians at Atlantic Equine Services for more information or to schedule an evaluation.

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