Asthma isn’t just a condition in people—it affects horses too. In fact, equine asthma is one of the most common chronic respiratory problems veterinarians see. It can impact any horse, from backyard companions to elite athletes, and ranges from subtle performance issues to severe breathing difficulties.
Veterinarian using endoscope to assess asthma in a horse.
Equine asthma is an umbrella term used to describe chronic, non-infectious airway inflammation in horses.
© 2012 by Eauine Guelph New window.
The good news is that, with awareness and proper management, most horses with asthma can live comfortable, useful lives.
What Is Equine Asthma?
Equine asthma is an umbrella term used to describe chronic, non-infectious airway inflammation in horses. You may have heard older terms such as heaves, recurrent airway obstruction or inflammatory airway disease. Today, veterinarians group these conditions under “equine asthma,” which better reflects their similarity to human asthma.
There are two main forms.
• Mild to moderate asthma: Seen commonly in younger horses, especially those in training or competing (80% of Thoroughbred racehorses have mild asthma). Signs can be subtle— occasional coughing, nasal discharge or decreased performance—while the horse otherwise appears healthy. Frequently, horses show no overt signs of mild asthma.
• Severe asthma: Typically affects mature to older horses. Signs include frequent coughing, labored breathing at rest, flared nostrils and reduced tolerance for exercise. Horses usually show signs seasonally, typically during winter when fed hay, but others show signs during summer pasture turnout.
What Causes It?
The key trigger is exposure to dust and airborne irritants (allergens). Horses are exposed to millions of microscopic particles every day, especially when kept in stables. Common culprits include:
• Hay dust and molds. Even good-quality hay contains microscopic mold spores capable of triggering asthma. Round bales and hay nets/racks result in the highest exposure to dust.
• Straw bedding – produces more respirable dust than low-dust options like shavings or paper.
• Poor ventilation – traps dust and ammonia inside barns.
• Seasonal allergens – molds and pollens outdoors can trigger pasture-associated asthma during summer. Other factors, such as genetics, immune sensitivity and possibly bacteria or viruses, may contribute, but dust and mold exposure remain the biggest drivers.
Recognizing the Signs
Asthma may develop gradually, and many early signs are subtle. Watch for:
• Coughing, especially during exercise (not all horses with asthma cough).
• Slower recovery after work or reduced performance.
• Increased respiratory effort—flared nostrils, abdominal “heave line” or breathing difficulty at rest in severe cases.
How Is It Diagnosed?
Veterinarians diagnose equine asthma using a combination of history, physical examination and sometimes additional tests. Endoscopy can reveal excess mucus in the airways, while a bronchoalveolar lavage — a wash sample from the airways in the lungs — helps identify airway inflammation. Lung function testing is available at specialized centers.
Managing Equine Asthma
Most horses with mild to moderate asthma will recover with prope management. While there is no cure for severe asthma, management can greatly improve the quality of life. The most effective approach combines environmental changes with, when necessary, medical treatment.
Environmental Strategies
Since dust and molds are the main triggers, reducing exposure is key: • Turnout: Pasture living is often the best environment, as it dramatically lowers dust exposure. However, horses with summer-pasture asthma do better in the barn when outdoor allergens are high.
• Feed adjustments: Replace dry hay with haylage, hay cubes/ pellets, steamed hay or soaked hay.
• Bedding: Avoid straw; use low-dust options such as wood shavings, paper or specialized dust-free products.
• Barn ventilation: Keep windows and doors open when possible; avoid sweeping or feeding hay from hay nets/racks.
These changes can make a big difference, but it may take five to six weeks to see the results.
Medical Treatment
When environmental management alone is not enough, or to hasten recovery, veterinarians may prescribe medication:
• Corticosteroids: Reduce airway inflammation. These may be given orally, by injection or as an inhaled therapy. Inhaled steroids are increasingly preferred because they deliver the drug directly to the lungs with fewer side effects.
• Bronchodilators: Relax airway muscles to ease breathing. These provide relief but are best used alongside steroids, since they don’t control inflammation.
• Other therapies: Supplements such as omega-3 fatty acids greatly benefit some forms of asthma (neutrophilic), especiallywhen combined with a reduction in dust exposure. The mo
effective omega-3 supplements are from marine sources (e.g., algae and fish oil).
Living With a Horse with Asthma
Asthma is a common condition, but horses can do very well with proper management. Many continue to train and compete successfully. The key is recognizing early signs, minimizing dust exposure and working closely with your veterinarian to tailor a management plan. Owners often find that once they understand asthma’s triggers, they canprevent many flare-ups and reduce the need for long-term medication.
Recent research showed that wearable dust monitors help identify sources of dust exposure. Hopefully, commercially available devices will soon help owners and veterinarians better manage asthma.
Press release by Equine Disease Quarterly - Article by Laurent Couetil, DVM, PhD, DACVIM-LAI, Professor, Large Animal Internal Medicine, Purdue University College of Veterinary Medicine