Airway allergies: RAO and SPAOPD

Airway allergies: RAO and SPAOPD

In this article the common equine airway allergies Recurrent Airway Obstruction (RAO) and Summer Pasture Associated Obstructive Pulmonary Disease (SPAOPD) will be discussed.


Recurrent airway obstruction (RAO) is more commonly known as a dust allergy and used to be called Chronic Obstructive Pulmonary Disease (COPD). This is the most common respiratory disease affecting horses today. As many as 50 % of all horses over 8 years of age have some degree of ‘dust cough’ which in most cases can be successfully controlled by management changes (avoiding dust). In some cases medication is given for a limited period of time and in extremely sensitive animals a continuous low level of medication is required.


Why do horses get dust coughs?

RAO is caused by an allergy to dust and fungal spores that are present in all conserved grass such as hay or haylage. Straw is also a major source of dust and spores. The degree to which hay or haylage is contaminated depends on the weather at the time the grass was cut and the subsequent storage and age of the product. Wild horses would never be exposed to the fungal spores found in conserved grasses and straw and their lungs are particularly sensitive to these allergens. When breathed in the dust and spores cause a hypersensitivity (allergic) reaction in the lower airways which results in swelling and the production of increased mucus in the small tubules in the lungs restricting air flow. In addition the muscles of the airways may go into a spasm further limiting the free flow of air.


What are the signs of RAO?

The initial sign will often be a slight decrease in performance of the horse – getting tired after work or taking longer than normal to recover. A dry cough is often present, more so first thing in the morning in the case of stabled horses. In some cases, when the nasal passages are particularly inflamed, there is a thick nasal discharge. The disease progresses slowly over time leading to more obvious effort breathing and frequent coughing. In the disease process is not controlled the lung tissue may become damaged beyond recovery (the horse is ‘broken winded’); these horses can lose weight due to the effort going into breathing, they can struggle to eat and get out of breath even when resting. Occasionally horses with dust allergies suffer a severe sudden onset attack, which can be compared to an asthma attack in people, and may appear quite distressed, finding it extremely difficult to breathe – this requires urgent veterinary treatment.


How to avoid RAO and decrease the severity of signs


1. As much turnout as possible.

2. Ventilation in stable:

  • Airflow should be sufficient to give 8-10 complete air changes per hour.
  • A good measure for airflow is the absence of cobwebs: spiders are not able to weave webs if ventilation is sufficient.
  • The patient can be helped by moving to a stable opening directly outside.

3. Soaking of hay

  • When fed while still moist, dust and spores are less likely to be inhaled, when it dries out the dust and spores will come free again however.
  • Most hay made in the UK climate is unsuitable to feed unsoaked to horses with RAO.
  • Soak for a minimum of 30 minutes (totally submerged).
  • Haylage is a good alternative but may still need soaking if dry and of poor quality.
  • Remember hay being fed in the field must also be soaked!

4. Bedding in stable:

  • Many shavings claim to be ‘dust free’ but are often anything but! Grab a handful and throw it up in the air to demonstrate how many small dust particles are present!
  • Straw should be avoided in horses with a dust allergy.

Remember the airspace is shared between stables; if communicating, you must also address management of other stables and hay or straw storage.



Vets use a variety of drugs to help horses with RAO but it is vital to get the management right and not depend on medication if possible. Clenbuterol (active ingredient in Ventipulmin) and Salbutamol (Ventolin inhaler) relieve airway spasm and inflammation and help to clear mucus from the airways, this helps affected horses breathe more easily. Corticosteroids are very potent anti-inflammatory drugs with excellent effect in horses with RAO. Inhalers (Clenil) or tablets (Prednisolone) can be used depending on the problem and horse’s cooperativeness. In many cases a combination will be used depending on severity of the signs. For more information on inhalers, see the topic ‘Using the inhaler system’. If horses don’t tolerate the paediatric mask, other inhaler compatible masks are available which have been designed for horses particularly; these fit over the whole muzzle and can be attached to a head collar or via a poll strap. They can also be used in combination with a nebuliser; a device making tiny droplets of water which can be mixed with medication that when inhaled get into the deepest parts of the lungs.



Some horses which suffer from RAO in the winter will also be affected by summer allergies. This disease is very much like hay fever in people, in horses the most common presenting signs are coughing and nasal discharge. Summer Pasture Associated Obstructive Pulmonary Disease (SPAOPD) can cause sudden onset severe respiratory difficulties requiring the administration of airway dilators and steroids by both inhaler and injection.

Management of SPAOPD can be difficult and sometimes requires almost the opposite to COPD!:

  • Keep the horse in during the day when pollen is most abundant in a dust free stable.
  • Move the horse to a different location away from pollen (e.g. away from wooded areas or rape seed crops).
  • Some horses will require a continuous, low level of medication during the pollen season.


Using the inhaler system

Our vets regularly prescribe corticosteroid or bronchodilator inhalers which are highly effective in treating allergic respiratory conditions such as RAO or summer pasture allergy. By delivering the drug direct to the lungs it is possible to use tiny doses of medication thus minimising the risk of unwanted side effects. These drugs are only licensed for use in humans, there are no similar specific equine medicines.

The inhaler system has two parts. The ‘puffer’ (Metered Dose Inhaler) and a ‘spacer’ (Paediatric mask). The puffer is connected to and discharged into the spacer which in turn is held over the horse’s nostril.

To gain the maximum benefit from the medication the spacer must be looked after carefully:

  • When you first get the spacer, using a soft cloth, bowl of warm water & washing up liquid wash it inside and out.
  • After cleaning remove the spacer from the soapy water. Do not rinse the inside of the spacer. Instead leave it to drip-dry. Washing spacers in this way stops the medicine from sticking to the sides.
  • Repeat the cleaning protocol at least once a month.
  • If used every day, the spacer should be replaced at least every 6 months to prevent the valves getting sticky by normal wear and tear.
  • When using the spacer, make sure that the valve inside is working (you should see it move with every breath the horse takes).


How to use the puffer:

  • Shake vigorously before use for at least 30 seconds.
  • Make sure that the inhaler is upright before use (with the nozzle downwards).
  • Connect inhaler to spacer.
  • Administer one actuation (puff) at a time; if you put in more than one puff, the droplets of spray stick together and coat the sides of the spacer instead of being inhaled.
  • Hold the spacer over the horse’s nostril and cover the opposite one. Administer one actuation as the horse breathes in.
  • Initially it may be necessary to perform the actuation and then hold the spacer over the horse’s nostril until the horse is trained to accept it.
  • Leave 30 seconds between actuations.
  • Each inhaler has 200 doses – it may continue to emit propellant gas after this time. There is no drug present after 200 actuations so keep note of how many have been used.

Dose rate

Generally treatment should be administered TWICE daily.

Your vet will suggest a dose range depending on the severity and history of the problem.


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