Equine asthma
Vet notes on the condition
The condition
Equine asthma is a condition that causes some horses to be hypersensitive to molecules in the air (known as allergens). This results in symptoms that range from mild to severe. This hypersensitivity (allergy) causes lower airway inflammation and results in increased mucus production and constriction of the airways in the lungs. A particular type of equine asthma involves horses that suffer during summer while spending most of their time outside. The condition is better known as summer pasture associated obstructive pulmonary disease (SPAOPD). It’s thought that SPAOPD is associated with an increase in airborne particles and environmental allergens such as pollen, mould spores and mycotoxins. Some horses can be affected throughout the year and also suffer with the more classical form of equine asthma called RAO (also known as ‘heaves’) when stabled and on dry roughage during the winter. SPAOPD is most commonly seen in horses that are aged seven and over.
Symptoms
In summer, horses with SPAOPD have symptoms that can be mild to severe. These include the occasional cough, coughing during exercise, nasal discharge and/or laboured breathing. Moderate to severely affected horses will have noticeable nostril flaring and abdominal excursions during the respiratory cycle (similar to those seen with ‘heaves’). In excessive cases, you’ll be able to hear wheezing noises while standing beside your horse’s nostrils. Horses usually remain bright, alert and have an appetite, but severely affected horses will get more depressed and can go off their food. Symptoms can vary and be intermittent and dependent on the weather. For example, on cooler, windier days, a horse’s symptoms may almost be non-existent, while severe symptoms will appear on hot, humid days.
Diagnosis
Diagnosing SPAOPD in moderate to severely affected horses is often based on clinical signs, such as laboured breathing with flaring nostrils, wheezes when listening to the heart and lungs and the absence of a fever. These symptoms are considered in relation to your horse’s management, as well as any previous history and the time of year. Additional tests that can be done may include endoscopy of the lower airway and then analysis of the fluid collected from the lungs (also called a ‘lung wash’). Radiographs and blood tests can also be helpful to rule out other potential causes.
Bronchodilators (a drug that dilates the bronchi to increase airflow) can open up the lower airways, while mucolytic drugs may loosen mucus. Some horses may need a course with glucocorticoids – these drugs stop the hypersensitivity reaction. Many of these can be given by injection, orally or inhaled. Inhalation therapy may be a better long-term option as the drug dose is targeted to the respiratory system, minimising side effects. Some horses benefit from antibiotics if the airway mucus has allowed for bacterial growth. It’s important to minimise allergen exposure, so horses with SPAOPD will benefit from staying inside in a dust-free space when it’s hot and when the pollen count is high.