By Tori Jordan MA VetMB MRCVS
Recurrent airway obstruction (RAO) is a common, performance-limiting respiratory disease that affects both horses and ponies. Previously known as COPD (chronic obstructive pulmonary disease), this condition is likened to asthma in humans. RAO occurs when the lungs become hypersensitive to inhaled allergens, such as dust particles and fungal spores, which commonly arise from hay and bedding.
RAO mainly affects middle aged and older horses, with an average age of onset of 9-12 years old. The condition may be worse at particular times of year. In the classic form, exacerbations tend to occur in winter, when horses are most likely to be stabled. However, in the less common form, flare-ups occur in the summer due to an association with the pasture.
Signs of RAO include loss of performance, a chronic cough or nasal discharge, weight loss, lethargy and breathlessness. Some horses exhibit a classic “heave line,” which can be seen running along the abdomen. This occurs because the abdominal muscles are working harder than normal to try to assist the expiration phase of the breathing cycle. As a result, these muscles become overdeveloped and stand out more than usual.
Sometimes, RAO can present acutely as a true veterinary emergency. These cases may be struggling for breath, with flared nostrils and a markedly increased respiratory rate; which can be hugely distressing for both owners and the horses alike.
Diagnosing RAO is not always straightforward. Your vet will rely on a thorough history and a full examination of your horse. A blood sample may be indicated to help rule out infectious causes of
respiratory disease. In some cases, your vet may recommend further investigations, such as washes from the windpipe and smaller airways, as the types of inflammatory cells found can significantly aid the diagnosis.
When it comes to treating RAO, the key factor lies in management of your horse’s environment. In many cases, changes to diet and stabling can remove the need to use drugs altogether. The aim is to reduce exposure to the dust and mould particles that aggravate the condition in the first place. It is important to remember that RAO is a chronic condition and so these changes to your horse’s diet and environment will likely be necessary for the rest of his life.
If possible, horses with the classic form of RAO should be kept at pasture all year round, with fresh grass as their source of fibre and supplemented hard feed as necessary. A common cause of treatment failure in horses kept at grass is proximity to round baled hay, which is particularly allergenic and so efforts should be made to avoid this. Where year-round turnout is not an option, horses should be maintained in a clean, well-ventilated environment. The perfect stable would be well away from indoor schools and stored hay or straw. Bedding should be as dust-free as possible – both rubber matting and shredded paper are ideal choices, while straw bedding should be avoided at all costs. The stable should never be mucked out with the horse still inside, as the dust created will undoubtedly reduce air quality and exacerbate his respiratory signs.
In terms of diet, soaking your horse’s hay may be enough to alleviate the clinical signs if he is only mildly affected. However, in the majority of cases, it is necessary to avoid hay altogether due to its high dust and mould content. Complete, pelleted feeds are available as your horse’s sole source of fibre; though haylage may be a more palatable alternative when this is not available.
The most common drugs used to manage this condition fall into two categories. Bronchodilators aim to provide relief against airway obstruction, whilst corticosteroids work by reducing inflammation in the respiratory tract.
In severe flare-ups, when a horse is really struggling to breathe, the vet may need to administer drugs directly into the vein to provide rapid relief. Once stable, medication can be continued in two forms. Tablets and powders for in-feed usage are readily available and convenient to administer. However, sometimes, due to the potential side effects, oral medication may be deemed inappropriate. The alternative is to administer these drugs via an inhaler and mask system. Inhaled medications target the inflammation at the site of the problem, thus reducing the risk of side effects. Using the mask can be tricky at first, and it can take some time to familiarise your horse with the procedure. However, once perfected, this method is both safe and effective.
Above all, it is important to remember that, while medication is useful to alleviate signs of RAO, respiratory disease will return after medication is stopped if the horse remains in an unsuitable, allergen-rich environment. Environmental management must come first and is the single most useful step in keeping RAO under control.