Recurrent Airway Obstruction
RAO, formally known as COPD, is a hypersensitivity or allergic reaction to inhaled allergens such as mould spores or dust mites. RAO is commonly seen in winter when horses are stabled, however some horses are allergic to pollens and grasses in the environment and so the disease is only seen summer when they are turned out. The latter form is called Summer Pasture Associated RAO or SPARAO.
Signs of the disease
Physical signs and auscultation of the chest are commonly used to diagnose RAO. Those affected will frequently have one or more of the following:
- Nasal Discharge
- Increased breathing effort sometimes with the presence of a ‘heave’ line
- Poor performance
Control of the disease
The most important factor to consider in controlling RAO is good air hygiene. Allergens from hay are the most frequent agent causing RAO but those from pollens and straw bedding are also important. Thus horses suffering from this disease should, in an ideal world, never be stabled and be turned out 24-hours a day with access to a 3-sided shelter. If this is not practical the horse should be housed in a well-ventilated stable with minimal dust bedding (not straw) and should be fed haylage rather than hay as it contains fewer allergens. If hay must be fed it must be soaked for 20 minutes and fed whilst still wet. No further soaking is required otherwise nutrients will be leached, 20 minutes will ensure that all allergens are removed. Haylage or hay should be fed off the ground and not in the usual hay nets.
Horses with SPAROA should be housed in the summer months in order to prevent contact with the irritants, this can sometimes prove very difficult as the allergen may be airborne.
Good management in either case will often reduce the majority of clinical signs.
When the airways are irritated by the allergens they become narrower, thicken and produce more mucoid secretions. Drugs prescribed for your horse will reduce these affects. Bronchodilators such as Ventipulmin act to open the narrowed airways however long term use can reduce their effectiveness.
Steroids have an anti-inflammatory action, dampen down the allergic response and can prevent scarring of the airways. Steroids are not commonly used for long-term treatment due to small but significant side effects; however they may be used at the beginning of treatment. Injectable steroids may be replaced with the tablet form if longer-term therapy is required.
The latest available treatments for RAO are inhaled steroids; they are much safer as the steroid is retained mostly within the lung tissue. They are administered through a metered device inhaler (MDI) with a volumatic spacer (See Fig 1) and depending on the horse’s size, they are usually given several ‘puffs’ twice daily, which is then reduced to the lowest dose possible that can control clinical signs. For instructions and care of your MDI and volumatic spacer then please see The Inhalers in Horses and Ponies advice sheet.
Mucolytics break down the increased respiratory mucous, however their efficacy is often limited and they commonly do not relieve clinical signs.
If you think your horse may be suffering from RAO or SPARAO then please contact the office and speak to one of the vets.