INFLAMMATORY conditions of the lower airway which are not due to infection occur commonly in the domestic horse. The terminology used to describe these conditions has ebbed in and out of favour over time. Currently the term equine asthma (EA) is recommended to describe horses with chronic respiratory signs, ranging in severity from mild to severe, that were previously referred to as inflammatory airway disease and recurrent airway obstruction respectively. Mild EA can affect horses of any age including young performance horses. Moderate to severe EA is typically associated with mature horses. Within the severe EA category, this may be housing associated or pasture associated.

How common is Equine Asthma?

Studies have found that severe EA affects approximately 14–17% of horses in countries with cool climates comparable to Ireland. Mild-moderate EA affects approximately 70% of pleasure horses and up to 80-90% of racehorses.

What causes Equine Asthma?

For both severe and mild/moderate EA, the presence of lower airway inflammation is attributed to inhaled airborne triggers such as dust, mould, and bacterial components which horses encounter at high levels in stable environments. Horses with pasture associated EA experience allergic lower airway inflammation when exposed to seasonal airborne triggers in the outdoor environment. Regardless of the trigger(s), the consequences for the airway follow a similar pathway: an increase in inflammatory cells, an increase in mucus production and narrowing of the lower airways.

What are the signs associated with Equine Asthma?

Horses with mild to moderate equine asthma may show signs including variable cough, nasal discharge, or reduced performance. Equally horses with mild EA can be sub-clinical, i.e., the horse shows no obvious signs despite presence of inflammation in the airways. Horses with moderate to severe EA are likely to have outward signs including cough, increased respiratory rate and nasal discharge. Severely affected animals may put extra effort into expiration, even at rest.

How do we diagnose Equine Asthma?

A useful tool for veterinarians diagnosing EA is bronchoalveolar lavage (BAL) sampling, known in layman’s terms as taking a lung-wash. Fluid is instilled into the lower airways via a cuffed tube and is carefully retrieved; the retrieved fluid contains representative cells from the lower airway.

The BAL sample is then submitted to a diagnostic laboratory for processing and analysis. The results for an individual animal are compared to established reference values which have been agreed by experts in this field.

How is Equine Asthma treated?

Improvements in air hygiene are central to the effective control of EA regardless of severity.

For horses which require medical treatment, corticosteroids are the drug group of choice. Inhaled therapy is generally preferable and there have been recent advances in the delivery systems available for equine use.

Bronchodilators are valuable to relieve clinical signs in severely affected horses but should be regarded as an adjunct to corticosteroids and are not indicated as a stand-alone therapy. EA is not an infectious disease and use of antimicrobials is rarely justified.