Recurrent Airway Obstruction (Heaves) in Horses: Causes, Signs, and Management

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By Kyla Szemplinski, MS, UT TSU Shelby County Extension

Spring is on the horizon, bringing warmer weather, longer days, and vibrant colors from blooming flowers, hay pastures, and trees. While scenic, this seasonal change can be a trigger for respiratory allergies in horses; most commonly a condition known as Recurrent Airway Obstruction (RAO), also called "heaves" or equine asthma. RAO is a prevalent and chronic horse lung disease linked to allergens like pollen, mold, and dust.

What is RAO?
RAO or heaves, is also referred to as equine asthma, equine chronic obstructive pulmonary disease, and inflammatory airway disease (IAD). The condition affects about 20% of adult horses, with symptoms often appearing at 9 to 12 years old. It is characterized by inflamed airways in the trachea, bronchi and lungs. RAO is not contagious; instead, it results from an allergic reaction to inhaled particles such as pollen or mold from stall bedding or feed. When these particles are inhaled, lung tissue can become inflamed and thickened, causing excess mucus production.

Symptoms of RAO include:

• Coughing or abnormal lung sounds

• Exercise intolerance

• Increased respiratory rate at rest

• Nasal discharge

• Wheezing and flaring nostrils

• "Heave line" along the horse's abdomen from the work of exhaling

As the disease progresses, exhalation becomes more difficult. If left untreated, horses can develop emphysema, permanent lung damage, pneumonia, or loss of lung function.

Causes of RAO
Much like human allergies, RAO is triggered by a horse's sensitivity to environmental allergens. No particular breed or gender is more prone to RAO. Triggers include:

• Hay and straw: mold and dust from dry hay and straw bedding are usually the primary culprits

• Bedding: straw bedding produces more dust

• Pasture grass: some horses develop summer pasture-associated obstructive pulmonary disease due to increased fungal spores in spring and summer grasses

4 Tips for Managing RAO Symptoms
Although there is no permanent cure for RAO, targeted treatments and careful management can greatly reduce equine asthma symptoms.

1. Turnout
   Horses sensitive to bedding and hay dust should be moved to pasture with fresh grass. If the horse is reacting to outdoor allergens, stall confinement on low-dust bedding, such as shredded paper or cardboard, is beneficial.

2. Good Ventilation
   If stabling is necessary, ensure the barn has proper ventilation. Open bay doors and windows, and use fans to help circulate air. Stalling your horse near the end of the aisle can also improve airflow.

3. Nutrition
   Feed is a primary source of dust, so carefully inspect hay for mold and avoid bales with excess moisture. Rather than letting a horse burrow its nose into a round bale, fork off portions for feeding to reduce allergen exposure. Feed hay and grain at chest height and use hay bags to limit dust inhalation. Consider soaking hay or using pelleted or complete feeds. Consult your veterinarian about supplements—such as zinc, copper, manganese, selenium and vitamin E—to support immune health. Aim for organic mineral sources for better absorption.

4. Medications
   Some horses require medication to control symptoms. Systemic steroids, administered orally or by injection, are most common and reduce airway inflammation and mucus production. Antibiotics may be prescribed if there is an infection. Some veterinarians recommend inhalers containing steroids, or in severe cases, aerosolized corticosteroids or bronchodilators administered with special masks.

Concluding Treatment for RAO in horses
The prognosis for horses with RAO can be positive if the condition is identified early and managed promptly. Advanced RAO may not be reversible. Successfully caring for a horse with RAO takes a coordinated team effort focused on diet, environment, and medical care. With attentive management, many horses with recurrent airway obstruction can continue to enjoy regular riding and a good quality of life.

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