Bronchial Asthma

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Also Known As

Allergic bronchitis


In horses that have bronchial asthma, the breathing tubes or bronchi and the smaller bronchioles become hyper-reactive to many pollutants in the air.

During an asthma attack, the muscle tissue in the walls of the bronchi go into a spasm, the cells lining the airways swell and secrete mucous into the air spaces. This causes the bronchi to become narrowed and the horse has to make a greater effort to breathe in sufficient air and expel it.

The cells in the bronchial walls release substances that cause the bronchial muscle to contract and stimulate mucous formation. These substances include histamines and a group of chemicals called leukotrienes that bring white blood cells into the area. This is a key part of the inflammatory response.

Bronchial asthma in horses is very similar to chronic obstructive pulmonary disease which is also known in its more advanced form as "heaves," because of enlargement of the abdominal muscle running obliquely down the middle of the flank toward the back of the elbow.


  • Fatigue
  • Shortness of breath
  • Exercise intolerance and weakness
  • Decreased appetite


Bronchial asthma is caused by pollutants in the air, allergies related to dust from hay, grain, bedding, mold spores, pollen and, in some cases, by inhalation of cold air. Attacks of bronchial asthma may also be caused by stress and anxiety.


The best way to prevent bronchial asthma is to keep the stable and barn areas clean and free from dust and other pollutants. Extra turnout time so the horse can breathe fresh air is also recommended. When the weather is cold, make sure that drafts of cold air are blocked from reaching the area where the susceptible horse is stabled.

Changing bedding to shredded paper or wood shavings helps reduce dust and pollutants. Soak hay flakes or switch to pelleted feeds or hay cubes to cut down on mold, fungal spores and dust from regular hay.


Early diagnosis of the problem is essential to the well being of the horse. The most important part of treatment is to keep the horse in a clean, dust-free environment with plenty of fresh air along with as much reduction of stress and anxiety as possible.

Medical treatment is similar to the treatment for chronic obstructive pulmonary disease which is triggered by the same kind of irritants in the atmosphere. Bronchodilators and a mask inhaler system may be recommended by a veterinarian. Corticosteroids are effective in reducing the inflammatory response brought on by the allergens. .

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EquiMed Staff

EquiMed staff writers team up to provide articles that require periodic updates based on evolving methods of equine healthcare. Compendia articles, core healthcare topics and more are written and updated as a group effort. Our review process includes an important veterinarian review, helping to assure the content is consistent with the latest understanding from a medical professional.