What You Need to Know About Equine Asthma

Is your horse’s cough a sign of something more? Learn what steps you should take to protect his respiratory health.

Illustration by June Brigman
Illustration by June Brigman

You mount up for your evening ride and, just like clockwork, your horse starts coughing. Three or four coughs as soon as you start trotting—then it’s over and you can get to work. It’s just something
he’s always done. Nothing to worry about, right?

Wrong! While there are plenty of horses that cough at the beginning of a ride, it doesn’t make it normal! In fact, those coughs are telling you there’s something irritating your horse’s respiratory tract. And respiratory disease is nothing to ignore. In fact, respiratory problems are second only to musculoskeletal issues when it comes to limiting athletic performance in horses. Estimates say as many as 20 to 30% of pleasure and performance horses have some level of respiratory disease, and many of those respiratory problems start with a cough. 

If your horse is coughing, has an intermittent nasal discharge, or shows any other respiratory symptoms, he may have equine asthma. In this article, we’ll take a look at the different conditions that fall under this umbrella, including identifying symptoms, learning how your vet might make a diagnosis, and what treatment options are available. Most important, you’ll learn how controlling factors in your horse’s environment can be the most important part of not only reducing signs of equine asthma once it strikes but also for preventing it in the first place. 

Want to learn more? The Nose Knows

Same Problem, Different Name

Do you remember heaves? A horse that earned that diagnosis could sometimes be heard clear across the barn, wheezing as he tried to breathe and straining his abdominal muscles in his efforts to move air in and out. Your vet might have called it Chronic Obstructive Pulmonary Disease (COPD), based on similarities to the human respiratory disease by the same name. If your horse exhibited a cough at the beginning of every ride, your vet might have also warned you that this “allergic cough” could easily lead to full-blown heaves if you weren’t careful.

The terms heaves and COPD fell out of fashion when veterinarians and scientists decided to separate inflammatory airway disease in horses into two separate categories: Reactive Airway Obstruction (RAO) and Inflammatory Airway Disease (IAD).  Both of these conditions are due to chronic inflammation of the airways, and excessive accumulation of mucous is part of the inflammatory process. This mucous causes irritation, coughing, and nasal discharge. If it becomes severe, it causes airways to constrict, making it difficult for your horse to breathe and may eventually lead to thickening of the tissues in the lungs. IAD is typically mild, and the most common sign is coughing at the beginning of work. RAO is much more severe. If your horse has RAO, he’ll look just like that heavey horse who wheezed, coughed, and struggled to take every breath. 

A consensus statement by the American College of Internal Medicine in 2015 suggested that the term equine asthma should be used to refer to all of these airway diseases and would incorporate both IAD and RAO. It’s now accepted that the horse who coughs at the beginning of every ride is best described as being affected by mild to moderate asthma, while the horse that’s struggling to take a breath is a severe asthma sufferer. So, if you’ve been around the barn long enough to remember heaves, don’t despair! Equine asthma is nothing new—other than its name! 

As we investigate the causes and treatments of equine asthma, it’s especially important to know that, while a horse with mild asthma may be at higher risk for developing severe asthma down the road, it’s not a guarantee. In fact, by taking the right steps you may be able to overcome your horse’s mild asthma and avoid progression to more severe disease. That’s why it’s so important to recognize the signs of respiratory disease early, and to do what you can to stop it in its tracks.

The Diagnosis

To get a diagnosis of equine asthma, you first need to recognize the signs. Coughing, nasal discharge, increased respiratory effort (he’ll use the muscles in his belly to move air in and out), and wheezing noises when your horse takes a breath are the most common signs you’ll see.  What does that mean? Any of these signs can mean your horse has asthma­—including that intermittent cough at the beginning of your ride. Even if your horse has “done it forever,” it’s probably worth a call to your veterinarian. 

Your vet will listen carefully to your horse’s lungs as part of their physical exam. They may encourage your horse to take deep breaths by placing a plastic garbage bag over his nostrils, called a “rebreathing bag.” Your vet may hear wheezes when your horse is breathing, and the deep breaths may stimulate a cough. In some situations, the signs you report and this exam might be all it takes for your vet to be comfortable making a diagnosis of equine asthma, and initiating treatment. 

If your vet feels they need additional information about your horse’s condition, either to confirm a diagnosis or help formulate an effective treatment plan, they may recommend a procedure called a bronchoalveolar lavage or BAL. This allows them to collect a sample of cells from deep within your horse’s airway, and is most commonly performed through an endoscope that also allows visualization of your horse’s airways. Some veterinarians will perform a BAL using a blind procedure that can still provide diagnostic samples but doesn’t allow for visualization. The presence of cells indicating inflammation can confirm a diagnosis of equine asthma, and different types of cells, as well as bacteria or other organisms identified on the sample, can help guide treatment. 

Stop Right There!

Your horse has been diagnosed with asthma. What’s next? While it may be tempting to reach for an injection or a bottle of pills, the most important factor for managing equine asthma is to control his environment. 

If your horse lives in a barn (even a clean one!), he lives in an environment where the air is filled with dust and debris. And all of these particles floating in the air are what cause irritation and inflammation of his airways. Inflammatory cells rush to the rescue but only make things worse by stimulating mucous accumulation and eventual thickening of tissues that makes breathing more and more difficult as the disease progresses. The most important tool in your arsenal to reduce the symptoms of equine asthma is to control dust and debris floating in the air your horse breathes. If your horse has mild or moderate asthma (IAD), reducing irritants in the air can even reverse the disease. A cure might be less likely if his asthma is severe, but environmental controls are crucial for controlling symptoms and reducing the chance his symptoms will get even worse. (Refer to the sidebar on page 52 for a guide to environmental changes you can make to help your asthmatic horse.)

Treatment Strategies

While environmental control is most important, there’s no avoiding medications for some equine asthma sufferers. Here are the most common treatments you’ll encounter.

Corticosteroids. Corticosteroids have potent anti-inflammatory effects. In a disease where inflammation leads the way to airway constriction and mucous production, controlling inflammation is a key step to controlling signs. The most common corticosteroid your vet will reach for is dexamethasone that can be given either orally or through injections. Although dexamethasone is arguably the most effective steroid, it can also have side effects—the most significant being laminitis. If your horse requires long-term steroids, your vet is likely to consider prednisolone, a slightly less effective but safer option. 

The Aservo EquiHaler is a recent innovation that delivers a short course of steroids for a period of 10 days. 
Photo courtesy of Boehringer Ingelheim

Steroids can also be administered through nebulization or an inhaler. While inhalers can be an effective option for a horse with chronic, severe asthma, they do require an investment in equipment designed to deliver the medications, as well as some expertise and a cooperative horse. The Aservo EquiHaler is a recent innovation that has hit the market. It delivers a short course of steroids for a period of 10 days through a specialized device that can be an effective “rescue treatment” designed to help reduce symptoms when they are most severe. One advantage of inhaled medications over oral or injectable options is reduced side effects because the inhaled drugs act locally, so aren’t taken up by your horse’s system. 

Bronchodilators. Airway constriction is the feature of equine asthma most likely to cause your horse distress. Bronchodilators that help open airways can provide your horse with significant relief for a period of time. The bronchodilator your vet is most likely to prescribe is clenbuterol, available as an oral syrup for horses. Unfortunately, as your horse’s system becomes accustomed to the bronchodilator the medication will lose its effectiveness. This means bronchodilators typically fit into the category of “rescue treatments,” most useful for getting control of signs when they are severe. 

If your horse is one who does best with an inhaled medication plan, bronchodilators can have a useful role. Administering an inhaled bronchodilator before a steroid will ensure your horse’s airways are as open as possible and allow the steroid to penetrate more deeply so they can be as effective as possible.

Over-the-counter aids. As with all things equine, chances are you’ll see a million products marketed to help your asthmatic horse. Are any of them useful? While most fit under a “can’t hurt might help” umbrella, evidence is clear that omega fatty acids can make a difference. Consider adding a fatty acid supplement (such a flax seed or fish-oil-based product) to your affected horse’s ration. While fatty acids aren’t likely to be enough to eliminate signs, especially for a severely asthmatic horse, they have been experimentally shown to reduce the number of inflammatory cells in BAL samples from asthmatic horses. At minimum, a fatty acid supplement may reduce the amount of medication you’ll have to give to control your horse’s signs. 

Equine asthma is really nothing new.  Experts believe it’s just a more accurate way to describe the continuum of inflammatory respiratory disease that can impact your horse. What’s the most important thing that you should know? Don’t ignore subtle signs just because your horse has “always done that.” And to optimize your horse’s respiratory health, it’s best to do everything you possibly can to reduce his exposure to irritants in the air he breathes.

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