Saturday 17th of October 2020
Vet Advice

Recurrent Airway Obstruction

Scott Dunn’s Equine Clinic have put together this useful article looking a respiratory condition in horses known as Recurrent Airway Obstruction (RAO).


inhaler rao

What is RAO?

Recurrent Airway Obstruction (RAO) is a respiratory condition in horses characterised by difficulty breathing, wheezing, coughing and mucopurulent nasal discharge. Sometimes known as Chronic Obstructive Pulmonary Disease (COPD) or ‘Heaves’. 


RAO is caused by an allergic reaction to allergens found in the hay, straw and/or bedding. The most common allergens are dust and moulds (Aspergillus spp.). Airway obstruction happens due to a combination of acute bronchoconstriction; airway narrowing due to inflammation and plugging of small airways (Bronchiole) with mucopus.

Episodes are usually more frequent during the winter period, where horses are stabled for longer hours with restricted turn out. Some horses are affected by a similar condition in the summer known as Summer Pasture Associated RAO (SPARAO). In this case, the allergens are from the fodder and the pasture.


Coughs, nasal discharge, increased respiratory effort at rest and exercise intolerance are the most common symptoms. Increased rectal temperature is an unusual finding in this kind of disease. Secondary infection in RAO patients is uncommon. Antimicrobial therapy should be avoided unless there is evidence of bacterial growth in the culture. Neutrophilic inflammation and mucus accumulation are not indicators of bacterial infection.

In severe cases wheezes can be heard when the affected horse is breathing. Cough normally happens more frequently when the horse is on exercise or eating. In those severe cases where the horse has increased respiratory effort and the respiratory rate is greater than 30 breaths per minute, immediate veterinary assistance is required.


History of recurrent and/or seasonal disease. It is based on the thorax auscultation and symptomatology. Thorax auscultation: variable sounds in different locations can be heard on both sides of the thorax, especially wheezes in the expiratory phase. Crackles are common on the trachea due to the mucus accumulation.

The definitive diagnosis is achieved by performing an endoscopic examination of the lower respiratory tract and collecting a sample of broncho-alveolar fluid. Broncho-alveolar lavage (BAL) is a simple procedure of collecting fluid from the lower respiratory tract. A sample with high percentage of non-toxic neutrophils, normally greater than 20%, suggests a diagnosis of RAO.


The treatment is based on corticosteroids, bronchodilators and management.

–   Bronchodilators (Atropine, N-butylcopolammonium Bromide or Clenbuterol). Bronchodilators are a type of medication that make breathing easier by relaxing the muscles in the lungs and widening the bronchi (airways). Usually in the form of an inhaler.

–   Corticosteroids can be administered orally, intravenously or inhaled. The route of administration will depend on the severity of the diseases and the specifics requirements of every case.

–   Management. Minimise the dust in the stable, barn, bedding and forage. Increase ventilation in the stable. Kept affected horse as long as possible in the field when suffering from RAO or stabled if suffering from SPARAO.

–   Feed and forage. Soak hay or haylage for 30 minutes to reduce the dust. Feeding from the ground helps to clear the mucus from the lungs.

–   Bedding. Dust free shaving, paper or cardboard big flakes are recommended. Straw can irritate the upper and lower airways, causing the condition to deteriorate.

–   Do not muck out the stable when the horse is in it. Turn out the horse or leave out of the barn whilst it is happening, leaving the horse out until the atmosphere has settled and there is no evidence of dust floating in the stable.


A prompt diagnosis will help to keep the disease under control and avoid the factors that will trigger the disease.

RAO may limit the working activity of the horse, but an accurate diagnosis, adequate treatment and management will help to achieve a successful working life.

Written by Yolanda Serrano LDOvet MRCVS

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