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And Breathe…

And Breathe: A look at common breathing problems

Recurrent airway obstruction (RAO) is a common condition in many different types of horses. It is a performance limiting problem commonly caused by an allergic respiratory response. Signs include:
– chronic cough
– nasal discharge
– increased respiratory rate (tachypnoea) and effort (dyspnoea)

Episodes of RAO are usually caused by exposure of susceptible animals to common allergens. The most common culprits are organic dusts when horses are stabled, bedded on straw, and fed hay (in particular round bales). Removal of these causal agents will usually result in recovery and stopping of any signs. It most commonly starts at around 9 years of age, although 12% of mature horses have some degree of allergen induced lower airway inflammation. There is no breed or gender predilection, but there does seem to be a heritable component to susceptibility.

Summer Pasture Associated RAO (SPA-RAO) is an inflammatory condition of the lower airways affecting pasture-kept horses, in contrast to RAO which, as stated before, affects horses kept in a stabled environment. SPA-RAO is characterised by airway inflammation, increased airway mucus production, reduced mucociliary clearance and bronchoconstriction in response to allergen exposure. The cause of the disease is largely unknown but some suggestions include inhaled pollens or outdoor moulds, or ingestion of a pasture-derived pneumotoxin. It occurs most commonly in the southern states of America but has also been reported in the United Kingdom.

Clinical Signs

Signs of RAO and SPA-RAO include flared nostrils, increased respiratory rate (tachypnoea), and cough, if the problem has been going on for long enough then the horse can have a heave line. Breathing usually includes a prolonged, laboured expiratory phase. Usually a cough is heard when the horse is exercised or being fed. Mildly affected horses may present with minimal signs at rest but coughing and exercise intolerance are noted during increased performance.

When the vet listens to your horse’s chest it may reveal fine crackles and wheezes. In severe cases, wheezes may be heard even without a stethoscope. An increased temperature may be a feature if a secondary bacterial infection has occurred. Affected horses often stand with their neck arched.

Diagnosis

Most commonly diagnosis is made on clinical exam and history alone, routine blood samples are commonly unhelpful in this scenario, x-rays of the chest are also not commonly not beneficial. Bronchoalveolar lavage (BAL) is usually not required in horses with obvious clinical signs and can be contra-indicated in horses with breathing difficulties at rest.

Treatment

The most important aspect of treating RAO is to limit exposure to the causal agents. Horses should ideally be kept in a dust-free environment such as a clean stable with rubber matting and no bedding. If hay appears to act as a trigger to the horse, a complete pelleted diet can be fed or alternatively hay should be thoroughly soaked. Alfalfa hay has been previously associated with less respiratory problems than grass hay and may be a preferable source of roughage for affected horses. Horses with severe problems should be rested until their condition has improved.

Medical treatment will stop the signs and symptoms but these will return as soon as it is stopped if management changes haven’t been put in place. Medical treatment consists of a combination of drugs to open up the airways (bronchodilators) and steroids to reduce inflammation.

Corticosteroids (e.g. dexamethasone) are used in order to reduce airway inflammation and can be administered via nebulisation using an inhaler in order to produce the maximum concentration of the drug in the respiratory tract. There have been fewer side effects induced with this mode of administration when compared to the use of steroids in the feed, but oral steroids may be required initially if the horse has severe respiratory problems. This treatment can be combined with a bronchodilator such as clenbuterol to reduce smooth muscle contraction in the lower airways. Antibiotics may be required if secondary bacterial infection is present.

Management of SPA-RAO is similar to RAO except with the addition of pasture avoidance. Affected horses should only be allowed access to pasture during late autumn, winter and early spring.

Complimentary medication can include the use of herbal products which will commonly contain Malabar nut tree, liquorice, and/or cedar. These can help to maintain normal breathing, normal mucous production and clearance, soothe inflamed mucous membranes, and have anti-bacterial actions.