Equine asthma

Equine Asthma (EA)

Affects the horse’s respiratory tract by causing inflammation to the internal structures. Currently, this disease can be broken down into two categories: mild to moderate EA and severe EA. 14% of horses in the UK suffer from severe EA2.


There are airborne particles small enough to enter the horse’s respiratory tract and cause irritation. These are known as aeroallergens and can be increased through poor management practices, such as inappropriate choice of bedding material or insufficient ventilation.

Aeroallergens may include various types of dust, mould, bacteria, mites, plant debris, pollen and toxic gases such as ammonia3. Pollen can sometimes trigger a different type of respiratory disease, known as Summer Pasture Associated Severe Equine Asthma (SPASEA), which occurs in horses kept at pasture and is particularly prominent during the summer months. Susceptible horses will be more sensitive to either a combination of these aeroallergens or all of them, leading to lower airway inflammation and greater mucus production when inhaled (very similar to an allergic reaction in humans).


Every horse is an individual, meaning signs will often present themselves differently. The frequency and intensity of these signs will also vary depending on severity. Most horses will show all or a combination of the following signs:

  • Coughing
  • Difficulty breathing when at rest (characterised by increased nasal flaring and a more obvious heave line)
  • Nasal discharge
  • Fatigue
  • Loss of performance
  • Exercise intolerance

Some signs are only noticeable upon physical examination, such as crackles and wheezes (audible through a stethoscope). Other symptoms can help to distinguish between mild to moderate EA and severe EA – for example, difficulty breathing when at rest is typically only seen in horses with severe EA.


If your horse is displaying signs of EA it’s important to consult your vet for further advice. There are diagnostic tools available which can provide a high level of accuracy in determining the affected area. These tools are also useful for monitoring response to treatment.

Respiratory tract endoscopy is the most used when diagnosing EA4. A long, flexible tube (endoscope) with a tiny camera at the end is inserted up into the horse’s nose and down the trachea (windpipe), allowing the vet a clear view of the respiratory tract. Examination of the trachea may reveal a large build-up of mucus, which can be seen in many cases. Vets will usually sedate the horse for this procedure to not cause unnecessary stress. There are other tests which take fluid from the bronchioles to test what specific allergens the horse is allergic to5. This helps to formulate a more tailored management plan.


Corticosteroids are often used in the treatment of EA. These are anti-inflammatory drugs, and must be administered by your vet either orally, intravenously or via the respiratory tract. Additionally, your vet may advise using medication prior to corticosteroids to open up (dilate) the airway and provide rapid relief. The effects of these medications are short-lived (up to 12 hours) so should be used alongside management practices to reduce aeroallergens and prevent further irritation.