Equine Asthma or Recurrent Airway Obstruction (RAO) is one of the most common causes of coughing and nasal discharge diagnosed in horses and ponies in the United Kingdom.
The condition itself is non-infectious, non-contagious and the majority of cases are environmentally induced. Most often occurring when the horse develops an allergy/sensitivity to particles that it has inhaled. It is therefore most often seen in stabled horses.
Previously the condition was referred to as COPD (Chronic Obstructive Pulmonary Disorder), however Recurrent Airway Obstruction (RAO) or Equine Asthma is now considered a more accurate description of the symptoms and disease process. In many ways very similar to what occurs in human asthmatics.
The condition is an inflammatory disease of the smaller airways within the lungs (airway branches and air sacs) caused by an allergic reaction, often to tiny dust particles and spores in the air. The reaction in the airways results in an over production of mucus, and thickening of the lining of the small airways, causing them to become partially obstructed and highly congested.
To compensate for this and in order to get enough oxygen into the lungs, the horse has to make an increased effort to breathe. Clinical cases then often develop a cough due to the hypersensitivity and in order to clear excessive trapped mucus.
Equine asthma is often a progressive and recurring disease process, and whilst there isn’t really a cure for the condition, steps can be taken to manage the condition, allowing the horse to cope with it very well.
The disease has a worldwide distribution, affects both sexes and is often seen in all ages of mature horses. Stabled horses are most affected in the winter and spring (when preserved forage is being fed), whereas horses whose clinical signs are exacerbated when at pasture (due to an abundance of pollens etc in the air) are seen mostly during the grazing season.
Affected horses commonly have a chronic, frequent cough and nasal discharge (ranging from clear mucus to thick green/yellow). They have an increased respiratory rate (number of breaths per minute) and effort that will usually worsen when they are put under stress or during exercise.
Over time, due to abdominal muscular development from the effort required for breathing, a ‘heave line’ can develop along the bottom edge of the ribs.
Severe, chronically affected horses may lose weight or their appetite. Pyrexia (raised temperature) is rare unless a secondary infection is involved. Acute severe attacks of respiratory distress can be experienced due to repeated exposure to high levels of dust or pollens
Usually a diagnosis can initially be based on a thorough clinical examination, history of exposure to dust, pollens or fungal spores, and assessment of the horse’s management conditions.
In many cases it is necessary to perform an endoscopic examination and throat washes to allow collection of bronchiolar or tracheal fluid to distinguish between Equine Asthma and other respiratory conditions, such as an infection.
This allows the appropriate treatment to be matched to the diagnosed condition. For example the correct treatment for Equine Asthma could make an established respiratory infection worse, so it is vital to know exactly what is being treated before treatment is initiated.
It is also important to remember that infection can commonly occur alongside and secondary to Equine Asthma, therefore two or more forms of treatment may have to be implemented.
Many cases will respond to changes in management alone if caught in the early stages. This involves removing the possible causes of the allergy (whether this is dust, pollen or fungal spores). In general, affected horses should be kept in a ‘dust free’ management system, designed to keep environmental allergens to a minimum.
Changing bedding from straw to shavings, paper or other non-organic material can help, as well as keeping the bed as clean as possible. Hay should be soaked/dampened before being fed, or haylage may be used if appropriated and dry feed should be fed dampened.
Affected horses should be kept away from stores of hay and straw, and other horses stabled on these types of beddings. Horses suffering from Equine Asthma due to dust should be turned out as much as possible, whereas horses affected by pollen may in fact worsen due to turnout in certain fields, therefore these horses should be moved to low pollen areas or perhaps even stabled until the pollen count has dropped.
Severe or chronic cases often require medication. In an acute severe flare up (sometimes referred to as acute respiratory distress) this is usually in the form of an injection of corticosteroids to reduce the inflammation and the bodies over reaction to the allergen. Sometimes bronchodilators such as Clenbuterol (Ventipulmin) are prescribed. These work by opening the airways allowing the horse to breathe more easily, but they do not treat the underlying inflammation that is causing the airways to be narrowed.
Often it is necessary to prescribe oral or inhaled steroids to manage the condition longer term. Inhaled treatment can be delivered using a spacer and the commonly available human inhalers, or more efficiently by using an equine nebulizer. Because inhaled corticosteroids have a much lower total dose, they may be an option in horses for which side effects of systemic corticosteroid (laminitis being the most concerning in long term high dose systemic corticosteroid use) administration are a concern. In severe cases, inhaled medication may be used concurrently with systemic therapy.
Inhaled bronchodilators such as albuterol provide immediate relief of bronchospasm in some horses and can aid in mucous clearance.
Depending on the clinical signs and severity of equine asthma, affected horses may be managed successfully, not only for pleasure riding, but also for competition. Successful management requires dedication on the part of horse owners. Maintaining a clean, dust-free environment with good ventilation, combined with sensible storage of feed, bedding and any other dusty products will help reduce the severity of this condition. If required drug treatments are available however they must be used alongside excellent management practices.