Recurrent airway obstruction (RAO)

Recurrent airway obstruction (RAO) is also known as heaves and was previously termed chronic obstructive pulmonary disease (COPD). Horses with RAO may develop an increased effort of breathing, nasal discharge and cough when exposed to allergens (mainly moulds) found in some forms of bedding or forage. Therefore a minimum-dust management regimen is a permanent requirement for horses with RAO to minimise the horse's exposure to potential allergens. Failure to maintain an adequate minimum-dust regimen carries a major risk of recurrence of symptoms in horses with RAO and may be a factor in causing this disease.


The Respiratory Physiology group has identified that the concentration of ascorbic acid in the lung is decreased in horses with RAO and dietary supplementation with derivatives of ascorbic acid may decrease symptoms of the disease.

Studies have also focussed on developing non-invasive and reliable methods for the measurement of airway inflammation and airway constriction in order to diagnose the disease rapidly so that treatment can be administered prior to the development of clinical symptoms.

Other investigations have involved the use of nuclear scintigraphy to image ventilation in RAO horses.


The WALTHAM Centre for Pet Nutrition, Marksway Horsehage and the Home of Rest for Horses have supported RAO research at the Animal Health Trust in recent years.


1. The best method of minimum dust management is to keep your horse permanently out of doors away from all stores of bedding, feed and muckheaps. Your horse should therefore be turned out as much as possible. Even if (s)he cannot be kept permanently outside, turnout encourages horses to lower their heads whilst grazing and to move around, in addition to reducing exposure to stable dust.


2. When your horse is stabled the box should be large, clean and well-ventilated. Loose boxes with external doors and windows are best; American barn systems are generally less satisfactory.

3. Maximum ventilation in stables should be maintained even in cold weather. The top door of the stable should be kept open at all times.

4. Stables should be fully cleaned out and washed down before occupation and on a regular basis to prevent build up of mould and dust (e.g. every 2 - 3 months) using a suitable disinfectant.

5. The horse's stable should not share its air space with stables not on minimum-dust management, feed and bedding stores or muckheaps. Ideally minimum-dust boxes should be located at least 50m upwind of these.

6. The use of rubber matting can in many cases obviate the need for bedding. Paper and cardboard are lower in dust and mould content than other beddings. Some horses can however be adequately managed on wood shavings. Straw bedding generally has the highest mould content and is therefore unsuitable.

7. Bedding should be maintained as clean as possible by efficient regular mucking out to prevent mould build up in soiled bedding. Deep litter systems are totally unsuitable.

8. Your horse should be taken out of the stable for mucking out as airborne mould dust increases dramatically at this time. After mucking out, allow the dust to settle before returning your horse to the box.


9. Mould free products such as Horsehage, complete cubes or silage should be substituted for hay. If hay must be fed, use the best quality hay available, but only feed it after soaking it thoroughly for several hours (even the best hay has a high mould content).

10. Feeding your horse from the floor will encourage lowering of the head and hence aid in clearance of secretions from the lungs.

Travelling your horse

11. If you transport your horse, ascertain beforehand what minimum-dust measures can be provided where (s)he will be staying.

12. If substandard accommodation cannot be avoided it may be possible to prescribe medication to help your horse whilst (s)he is away. If your horse is competing, medication rules may preclude this.

13. The horse's environment in the transporter should conform to a similar standard of minimum-dust management as the stable environment (ventilation, bedding, feed).

14. Your horse should be tied so that (s)he can safely lower his/her head during transport.


15. Avoid working your horse in a dusty environment (e.g. dusty indoor schools)

16. Observe your horse regularly so that you are able to detect the earliest signs of respiratory abnormalities and seek veterinary advice concerning them.

17. If you have any questions concerning the correct environment for your horse, you should contact your veterinarian for advice.

To find out more about the AHT why not visit their website www.aht.org.uk


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