Recurrent Airway Obstruction (RAO)
RAO (previously called chronic obstructive pulmonary disease or COPD) is a common cause of coughing and nasal discharge in stabled horses. In long standing cases the horse may have difficulty in breathing and its chest and abdomen can be easily seen to move, hence the even older name 'heaves'. Animals with seasonal pollen allergy may be affected when living out.
What is RAO?
RAO is a disease of the smaller airways (bronchioles) of the lungs and is commonly caused by an allergy to small dust particles and spores that are inhaled by the horse when it breathes. Fungal spores and/or pollen are most important in terms of allergic 'trigger' factors. The allergic reaction in the airways results in the production of fluid and thickening of the walls of the small airways of the lungs, causing their obstruction. This means that the horse has to make an increased effort to breath and usually develops a cough to clear trapped mucus. The pathology that occurs in the horse’s lungs is reversible in the early stages, but if management changes are not made the damage may become permanent and the condition progressive. RAO cannot be 'cured' but the progress of the disease can be halted and the horse can be helped to accommodate to it, particularly when the problem is associated with stable dust. This requires significant adjustment to stable management.
What are the symptoms of RAO?
In early cases, the only clinical sign may be a slight nasal discharge or dry cough, which may go unnoticed. If untreated, the horse may start to find faster work more difficult. The cough will become more noticeable. As the disease progresses, the horse will cough with only slight exercise. In severe cases, the horse will have some difficulty breathing even at rest, causing increased respiratory rate and effort. In very long standing severe cases, the horse has to make a double effort to breath out, using both the chest and abdominal muscles, developing a noticeable 'heave line'. These horses used to be called 'broken winded'.
Symptoms are often mild for years and the condition may only progress slowly with age. In some horses, however, acute attacks of respiratory distress accompany repeated exposure to dust or pollens. This means that the condition may be seasonal (especially when associated with crops such as oil seed rape) or associated with stabling or feeding conditions.
What causes RAO to develop and how is it diagnosed?
For a horse to show signs of RAO, it must have developed an allergy to inhaled dust, spores or pollen or other environmental allergens. A horse may be allergic to pollen but not spores or vice versa. Fungal spores are present in hay and straw, mouldy bedding or feed, and other organic material. Pollens are found just about everywhere but levels in the air fluctuate greatly with season, location and weather conditions. As with human hay fever, the higher the spore or pollen count in the air, the worse the condition becomes. Good air quality in stables is therefore important for maintaining equine respiratory health.
The diagnosis of RAO is based on history, management conditions and clinical signs. Endoscopic examination ('scoping') and the collection of samples from the horse's lower airway, i.e. by tracheal washing or bronchoalveolar lavage (BALs) for microscopic (cytological) examination and bacterial culture, helps to distinguish between RAO and other causes of chronic cough such as infection. Infection may, of course, be a secondary complication of RAO and symptoms may be more difficult to resolve when other diseases are present.
What treatments are available?
Many early stage cases respond to changes in management that remove the cause of the allergy. Horses with RAO related to bedding or feed should be turned out of the stable as much as possible to benefit from fresh air and when indoors, kept under 'dust-free' management, designed to keep environmental dust and spore levels as low as possible. Bedding should be paper, shavings or other non-organic material and should be kept scrupulously clean. Stables should be clean and as free as possible from dust and cobwebs. Hay should be soaked before being fed or haylage should be used. Feeding these materials from the floor also encourages gravitational drainage of mucus from the lower airway. 'Dry' feed should be fed dampened to reduce dust. Horses should be stabled away from other horses that are bedded on straw and away from hay and straw stores, muck heaps and other sites where dust and moulds may be produced. 'Run-in' sheds should also be kept clean and free from remnants of dusty/mouldy hay. The need for good air quality and efficient ventilation cannot be over emphasised.
Horses affected out of doors by pollens should be moved from high pollen areas until the season has passed. However, managing such cases can be quite problematic, especially when several pollens are involved over a prolonged period of the year.
More severe or long-standing cases often require medication. Medicines that dilate the airways (bronchodilators) such as clenbuterol or cromoglycate may help the horse or corticosteroids can be used to reduce the allergic reaction. Such medication is often used for pollen-sensitive horses, when removing the horse from the source of the allergens can be very difficult or impossible.
These medicines may be given by mouth, by injection or by inhalation using a nebuliser. The advantage of a nebuliser (which looks like a face mask) is that the medication is delivered straight to the lungs so the effect is quicker and lower dosages of medicine may be used. Many cases require long-term treatment. Desensitisation treatment is successful in some cases although it can be difficult to know exactly what agent a horse is allergic to. Only a few specialised clinics offer this service and results appear better with some horses than others.
What is best advice?
Good management is the key to owning a horse with RAO. Maintaining a clean, dust-free, well-ventilated environment, correct storage and maintenance of feeds and bedding and the use of hypoallergenic bedding materials all help reduce the incidence and the severity of this chronically incapacitating condition. Remember that fresh air, ideally in a paddock (unless the horse is sensitive to pollens) is the best solution, whenever possible.