RECURRENT airway obstruction – otherwise known as heaves and previously as chronic obstructive pulmonary disease (COPD) – is an allergic respiratory condition that affects horses of all types.

It is similar to asthma and is caused by hypersensitivity to dusts and moulds, which are breathed in from hay and straw. Most affected horses are seven years of age or older.

It has been estimated that 14% of horses in the UK are affected by recurrent airway obstruction. Signs include poor performance, a nasal discharge, cough, laboured breathing and the appearance of a characteristic 'heave' line on the flanks. Treatment involves avoidance of dust forage and bedding along with therapies to open the airways and reduce inflammation.

The high prevalence of recurrent airway obstruction together with problems inherent in its management – after all it is difficult to avoid hay and straw on most years – mean that the disease continues to attract considerable scientific research. Recent efforts have focused on the genetic basis for the condition, testing of medicines for both prevention and treatment, and reducing the amount of dust in hay.

It has long been believed that recurrent airway obstruction is more common in certain breeding lines or families of horses. How it is inherited appears complex and latest research suggests that several genes may play important roles. These appear to be inherited in different ways, with some being dominant and others recessive traits.

Scientists have begun to hone in on specific chromosomes where these genes may reside. Notably they have identified two chromosome areas that are strongly associated with recurrent airway obstruction. Located in these regions are a number of genes involved in inflammation. While helping identify new areas for therapy, these findings also bring the prospect of genetic tests for the diagnosis of recurrent airway obstruction and to help in breeding programmes to reduce the disease's prevalence.

Management of the stable environment to reduce exposure of horses to dust and moulds usually involves soaking hay or feeding haylage or dust-extracted forages. It may not be practical to feed haylage to some horses and ponies, especially those prone to digestive upsets or laminitis. Wood shavings, shredded paper or cardboard should be used in preference to a straw bed.

The question of how long to soak hay has long been a topic of discussion. Inadequate soaking will lead to persistence of clinical signs, but excessive soaking results in loss of essential nutrients from the hay.

Contrary to popular belief the action of soaking does not remove dust and spores but instead causes them to 'stick' to the hay stems. This means that the offending particles are ingested rather than being released into the air and subsequently inhaled to cause inflammation in the airways.

It is now thought that short soaking periods are preferable, with five minutes reducing the number of particles released by 97%. While soaking for 24 hours improves this figure to 99%, there is considerable loss of nutrients. It is important, regardless of how long hay is soaked, to ensure that it is wet through and not allowed to dry out before being fed.

Steaming is an alternative to soaking and the availability of commercial steamers makes this a viable proposition for many horse owners. Steaming hay for 50 minutes in the Haygain steamer has been shown to eliminate all fungi and yeast, cut bacteria by 99%, and reduce all breathable particles by 94%.

Less than 2% of nutrients are lost in this system and feeding studies have shown horses prefer steamed hay to soaked hay. The UK distributor of Haygain has recently launched a rental scheme, which is administered through your vet, which is ideal for helping bring new cases of recurrent airway obstruction under control.

Dust extracted forages are also suitable for horses with recurrent airway obstruction. These products are dried quickly, usually within one-hour of being harvested, and at a high temperature so there is not the build-up of moulds and dust that occurs when hay is left to dry naturally. Furthermore any dust that might be present is extracted during the subsequent cooling process.

The key medical therapies for recurrent airway obstruction are corticosteroid anti-inflammatories, which are administered either orally or from metered dose inhalers via special masks. Recent research has shown that the steroids prednisolone and dexamethasone are highly effective in reversing the signs of recurrent airway obstruction even in the face of continued exposure to dust and moulds.

There are concerns over the potential for these drugs to induce laminitis and so care has to be taken with the dosing schedule, especially in ponies and horses that are overweight or have other risk factors for laminitis. Oral steroids are probably best used to get animals affected by recurrent airway obstruction 'over the worse' as it can take 7-14 days for changes in stable management to take effect.

Risk of laminitis is much lower with inhaled steroids found in human asthma inhalers. These are expensive to buy and so best used as an aid to preventing recurrence of airway obstruction in cases where environmental management alone is ineffective. Drugs used for this purpose include fluticasone, which is found in Flixotide and Serotide inhalers, and beclomethasone.

Recent research has confirmed that fluticasone is highly effective at preventing episodes of recurrent airway obstruction but is not as good as the steroid dexamethasone when it comes to treating the condition.

Some inhalers also include drugs that dilate or open the airways and so provide additional relief. These include albuterol or salbutamol, which is in Ventolin, and salmeterol, which is found along with fluticasone in Seretide. These drugs work in the same way as clenbuterol, which is in the oral medication Ventipulmin, but, because they are inhaled, tend to be more effective.

The administration of drugs via metered dose inhalers does require the use of a specific mask or device, such as the AeroMask or EquineHaler. A more economical way of administering drugs is through a nebuliser, which transforms liquids into an aerosol that is inhaled. The recent launch of a light weight, battery-powered nebuliser – the Flexineb – that works with cheaper liquid forms of albuterol, clenbuterol, dexamethasone and fluticasone provides an effective alternative to sometimes expensive inhalers.

One final piece of research tested a handheld acoustic device. This propels sound waves from the nose down to the lower airways, with the intention of dislodging mucus and relaxing spasm of the airways. Treatment did not alter clinical signs of recurrent airway obstruction or improve lung function in affected horses. Yes, I did check that the paper was not published on April 1!

With the winter period of more intense stabling approaching it is likely that we will encounter new cases of recurrent airway obstruction as well as seeing episodes of disease in previously affected horses. Recent scientific advances have gone some way to helping us treat these cases and prevent relapses, giving more confidence in the management of this common and sometimes difficult condition.