Chronic obstructive pulmonary disease (COPD) also known as recurrent airway obstruction (RAO) or “broken wind” is a chronic condition of horses involving an allergic bronchitis characterised by wheezing, laboured breathing, coughing (usually associated with exercise or eating) and nasal discharge (especially when the head is lowered or after exercise).
The condition was known as ‘heaves’ because horses with COPD have very inflamed narrow airways and as such breathing both in and out is difficult and requires recruitment of other chest and abdominal muscles to aid with respiration, these muscles become enlarged and hence the horse develops “heave” lines.
COPD is an allergic reaction to certain otherwise innocuous substances - allergens. These allergens are typically dust, mould and fungal spores (e.g. Aspergillus). It is therefore most common in horses fed hay and bedded on straw. It is similar to asthma and farmer’s lung in humans.
Allergens enter the horse’s lungs and the horse’s hypersensitive immune system over-reacts to the “normal” pollens. The lungs become inflamed and swollen, causing the airways to become narrowed and mucus production to increase, which then leads to the signs we see in our horses.
Diagnosis is usually based on the results of a clinical exam and auscultation of the horse’s lungs. However sometimes further diagnostics are required, in which instance an endoscopic exam of your horses trachea and bronchioles can be performed and samples can be taken.
Acute flare ups can present dramatically, your horse maybe distressed with markedly elevated respiratory rate and effort, flared nostrils and sweating. If a horse is severely dyspnoeic (really struggling to breathe), the most important measure to take is to REMOVE IT FROM THE STABLE OR BARN into FRESH AIR. Keep the horse (and yourself) CALM and CALL YOUR VET IMMEDIATELY.
Treatment is all about management and minimising exposure to the allergens. When removed from the allergens the symptoms will usually subside, although they will recur if the horse is exposed to the allergens again, even short periods of re-exposure can induce acute episodes.
If it is not practical to stop stabling all together then the following changes will be of benefit:
• Minimise dust and maximise air quality in the stable.
• Soak hay or feed a low dust alternative such as haylage or bagged grass. If you are going to feed hay it should be soaked hay, you only need to soak the hay for an hour to remove the majority of pollens and allergens 60 minutes. Soaking hay for longer will reduce the carbohydrate load of the forage, good for horses and ponies that suffer from laminitis or are looking to lose weight but not necessary in managing COPD.
• Feeding from the ground allows any mucous to drain out of the lungs. Horses are designed to graze for approximately 20 hours a day, during which time the horse has its head down to the ground where mucus within the horses trachea and bronchioles can be expelled, because of this design the horse is very poor at clearing mucus from its lungs without the aid of gravity, by feeding on the floor you encourage the horse natural mucus clearing function.
• Bed on a dust free bedding. Those horses that must be stabled should be bedded on rubber matting and paper, or low-dust wood shavings. Straw contains dust, moulds and fungal spores and so is least advisable. In severe cases horse may be intolerant of any bedding in which case the mats can be washed daily. The matting has a fairly high initial cost but there is a considerable saving in bedding (and veterinary costs if your horse has RAO).
• Make sure the stable is well ventilated.
• Don't muck out or brush up while your horse is in the stable to minimise the dust in the air.
All the stables in the vicinity need to be similarly maintained or the environment will remain high risk for the horse and aim to stable your horse away from the muck heap.
Despite management changes, medication is often required, these break down into 3 broad categories:
• Bronchodilators, theses dilate (open) the bronchioles and smaller airways allowing the horse to breath more freely.
• Corticosteroids: these reduce the inflammation in the airways and damped down the immune hypersensitivity reaction.
• Anti Histamines: these damped down the immune hypersensitivity reaction that leads to the inflammation in the lungs.
• Mucolytics: these make the horse’s mucus less viscose and so easier to clear form the airways.
Care should be taken with all these drugs in competition horses, as many of them are forbidden substances under racing and FEI rules.
If the condition occurs in the summer when the horse is at pasture then it is known as summer pasture associated obstructive pulmonary disease (SPAOPD) In this case, the allergens are derived from the pasture. This is more common is summer, and management is reversed: horses should be stabled in well ventilated areas. Some horses can suffer from RAO and SPARAO which can be very difficult to manage.
RAO often limits the horses' ability to work, and it may find strenuous activity difficult. However, with prompt diagnosis and treatment the condition can be managed successfully.