9 Frequently Asked Questions

Equine asthma, commonly known as recurrent airway obstruction (RAO) or heaves, is a respiratory disease caused by hypersensitivity in the lungs to airborne dusts and molds. 

Horses can develop equine asthma when they’re exposed to airborne organic dust that can be found anywhere — in a dirt paddock, on a gravel road, or in an indoor arena. But the most common culprit is dusty, moldy hay. Round bales can be particularly problematic as horses tend to tunnel their muzzles into the bales and inhale dust and mold.

The disease affects horses of any breed, typically when they are middle-aged and older.

Experts now suggest that veterinarians use the term equine asthma instead of RAO to describe this disease. RAO will be considered severe equine asthma. Less chronic airway inflammation, such as inflammatory airway disease that is commonly found in young race horses, will be termed mild to moderate equine asthma. 

Symptoms of equine asthma commonly include frequent coughing spells and nasal discharge. A diagnosis of equine asthma may seem daunting to horse owners, but most people can successfully adapt their management regimes to ensure their horse’s continued health and well-being, although it can end a high-performance animal’s career. Photo: Pam MacKenzie

#1 – What are the clinical signs of equine asthma?

Affected horses usually have a chronic cough that may occur randomly or while eating or exercising. In addition, they’re often intolerant of exercise, have nasal discharge, and have more laboured breathing. More severely affected horses may have a “heave line,” a ridge of muscle along the abdomen that develops because of the overuse of respiratory muscles.

#2 – How is equine asthma diagnosed?

The veterinarian listens to the horse’s lungs using a stethoscope and a re-breathing bag (a plastic bag placed over the horse’s muzzle). Some abnormal sounds that may be present in the lungs of a horse with equine asthma include harsher, louder lung sounds, wheezes, crackles, and a tracheal rattle. To accentuate these abnormal sounds, your veterinarian may place a re-breathing bag over the horse’s muzzle and allow it to breathe into the bag for a minute or two. Re-breathing the expired air encourages the horse to breathe deeper.

In some cases, the history of the horse’s problem and physical exam can be enough for the veterinarian to start treating the horse for equine asthma. However, to make a definitive diagnosis, it’s necessary to perform a bronchoalveolar lavage (BAL). The BAL procedure, which is very safe for the horse, allows the veterinarian to determine the severity of the inflammation in the lungs. It also provides baseline information that can help clinicians determine if your horse is improving with treatment. It may also be necessary to perform a tracheal wash to rule out pneumonia, an infection in the lungs.

Related: Equine Asthma and Pollution

The classic “heave line,” seen along the bottom edge of the ribs, is due to the hypertrophy of the abdominal muscles, which assist in breathing and become large from excess work.

#3 – How important is an early diagnosis?

If the disease is identified before any permanent damage is done to the lungs, your horse can continue to breathe easy with proper treatment and management. However, once changes occur in the lung, there is irreversible damage.

#4 – How do veterinarians treat equine asthma?

Veterinarians often use drug therapy — a combination of corticosteroids and bronchodilators — to treat horses during acute episodes of respiratory difficulty.

Corticosteroids decrease inflammation by suppressing the horse’s immune system, while bronchodilators act in the lung to open up the airways of horses experiencing respiratory distress.

Clinicians use a plastic bag to encourage horses to breathe deeper. This “rebreathing” technique allows veterinarians to hear more of the horse’s lung sounds. Photo: Hayley Kosolofski

Both steroids and bronchodilators come in oral and inhaled formulations. Oral and inhaled formulations are effective but have different benefits. Oral medications are usually tried as the initial course of treatment and are preferred in severe cases. The inhaled formulations are administered to the horse using a mask. Once the horse inhales the drugs into its lungs, the medication acts directly at the site of inflammation. The result is a faster response to therapy and fewer side effects as the drug isn’t distributed to the whole body.

Related: Heaves - Is Your Horse at Risk?

#6 – Do these drugs cause any side effects?

High doses of corticosteroids over a prolonged period can potentially cause laminitis, particularly in horses that are overweight or otherwise predisposed to laminitis. Other side effects of steroid use include worsening of infections that are already present or the development of new infections while being treated. It’s uncommon for side effects to occur with bronchodilator therapy, but it’s still important to use these drugs judiciously.

#7 – Are there any new therapies for equine asthma?

Researchers at the Western College of Veterinary Medicine (WCVM) have been investigating the role bacteria play in the lungs of horses with equine asthma. According to recent research at the WCVM, some horses may benefit from the addition of antibiotics to the traditional drug therapy.

WCVM researchers Alison Williams (left), Kirsten Henderson (centre) and Dr. Julia Montgomery perform a tracheal wash on one of the horses enrolled in the RAO study. Photo: Christina Weese

#8 – Can horses recover from equine asthma?

Unfortunately, there is no cure for equine asthma. But on the plus side, affected horses can improve with proper management along with early and appropriate treatment when acute episodes of equine asthma occur. Affected horses can be ridden if their breathing permits it. If they appear uncomfortable with laboured breathing, rest is recommended.

#9 – What can owners do to help horses affected with equine asthma?

Environmental management of equine asthma is based on reducing the horse’s exposure to dust and mold. Here are some management changes that can benefit horses with this disease:

• Feed a low-dust feed such as pelleted complete feed, hay cubes, or soaked hay.
• Use square bales as they are less prone to accumulate mold than round bales.
• If feeding from a round bale, unroll the bale, fork off the hay, and inspect it for dust and mold.
• Keep horses outdoors as much as possible, ideally in a low dust environment.
• If horses are stabled, ensure good ventilation to prevent an accumulation of dust, mold, and other airway irritants such as ammonia.
• Use shavings rather than straw for bedding as straw bales tend to accumulate dust and mold.

Related: Breathtaking: A Close Look at Equine Respiratory Diseases

Printed with the kind permission from WCVM Veterinary Medical Centre.

Main photo: iStock/ArisSu