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Equine Asthma Syndrome (IAD/RAO)

Is your horse breathing heavier or faster than normal? Coughing frequently? Or maybe they just have some extra goobers coming out of their nose? These can all be signs of Equine Asthma Syndrome, a newly coined term that describes a spectrum of chronic inflammatory respiratory disorders. This includes recurrent airway obstruction ‘RAO’ (more commonly known as ‘heaves’) and inflammatory airway disease ‘IAD’ (a milder version that occurs mostly in young athletic horses).

Equine asthma syndrome is a non-infectious airway condition in horses that is the result of an allergic reaction to inhaled particles. The most common allergens are found in hay, straw and poorly ventilated barns. Once inhaled, an allergic reaction occurs causing the small airways in the lungs to narrow and become obstructed. The airway obstruction is caused by a combination of 3 things:

  1. Mucus accumulation in the airways

  2. Airway constriction

  3. Inflamed and thickened airways walls

Younger horses are most prone to the milder version of equine asthma syndrome, IAD. These cases can resolve spontaneously or may be permanent but manageable. Older horses with equine asthma syndrome are more commonly coined with the term RAO, as they have suffered repeated bouts of airway inflammation leading to permanent changes in the lung.


The early stage of the disease is characterized by a cough but over time clinical signs can become more severe. Below is a list of clinical signs to watch for.

  1. Cough

  2. Exercise intolerance

  3. Elevated respiratory rate and/or an obvious abdominal lift as they breath out

  4. Nasal discharge

  5. Nostril flare (a sign of increased effort to breath)

  6. Wheezing


More severe cases are typically identified based upon clinical signs. However, for diagnosis of more mild cases, a bronchoalveolar lavage (BAL or ‘lung wash’) is performed. The numbers and types of cells found in the airways aid in diagnosis as well as characterizing disease severity. Additional diagnostic tests may also be necessary to rule out other potential causes of airway inflammation.


The best way to begin treatment of your horse with equine asthma syndrome is management changes. The two cornerstones of management are improved barn ventilation and low-dust feedstuffs and bedding. Below is a list of things to consider when housing a horse with equine asthma syndrome.

  • Maximize grass pasture turnout

  • When stabled, pick a stall with maximal ventilation (stalls in the middle of the aisle or adjacent to the arena have very high dust levels)

  • If feeding hay, use only the best quality, which is neither dusty nor moldy.

  • Hay steamers are a good management tool for reducing dust, mold, and mites in hay. Alternatively, soaking hay and draining off excess water (do not feed hay IN water) can be helpful for these cases.

  • Pelleted feeds can also be beneficial.

  • Feed hay on a matted surface as opposed to a hay rack or manger.

  • Straw bedding should be avoided. Preferred bedding materials include peat moss, wood pellets, paper, clay, wetted wood shavings, or sand.

  • Clean stalls frequently to minimize ammonia buildup from wet/soiled bedding and poor stall drainage. It is also important to remove your horse from the stall during cleaning.

  • When possible, store hay and bedding separately from where horses are housed.

Medical treatment is also necessary in certain cases of equine asthma syndrome. This typically involves a combination of anti-inflammatory medicine and bronchodilators. However, medication without environmental changes will not provide prolonged benefits. There are also reports showing that omega-3 fatty acid supplementation can help improve clinical signs, when implemented in conjunction with environmental changes.

Equine Asthma Syndrome is a non-infectious inflammatory disease of the lungs which has no permanent cure but, complete recovery from clinical signs can be achieved through appropriate management.

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