10 ways to help horses with heaves

You can play a vital role in protecting your horse’s respiratory health by making these simple and easy management changes

Although a “wait and see” approach may be appropriate for some conditions that affect horses, heaves isn’t one of them. Of course, a horse in the midst of a flare-up needs immediate help but even one whose heaves are under control requires vigilant care.

Technically known as recurrent airway obstruction (RAO), heaves is respiratory inflammation caused by the inhalation of the types of molds, dusts or pollens often found in barns and around farms. But RAO is much more than just irritation of the lungs—it’s a chronic inflammatory lung disease caused by hypersensitivity to organic particles within the inhaled dust.

“Horses with heaves experience airway inflammation and bronchoconstriction due to an allergy-like reaction to some factor in the environment,” says Virginia Buechner-Maxwell, DVM, MS, DACVIM, of the Virginia–Maryland Regional College of Veterinary Medicine in Blacksburg, Virginia. “In this way, heaves is similar to human asthma, which is a disease caused by an allergy to certain antigens or irritants in a person’s environment.” And like asthma, heaves can have vastly different effects. In its mild form, heaves may result in an occasional cough and/or the intermittent expulsion of mucus. But a horse with severe heaves, in the midst of an “episode” or “flare-up,” has to work hard simply to breathe, even when standing at rest.

By the time a horse is showing outward signs of respiratory distress, the ongoing inflammation and immune reactivity are fairly severe. This does not mean that the disease is irreversible. It is simply an indication that it’s time to make drastic changes in the horse’s environment and to initiate treatment so the horse can return to a normal breathing pattern. Otherwise, he will become uncomfortable and spend a lot of extra effort and energy just trying to breathe. Three major factors contribute to the horse’s difficult breathing:

Bronchoconstriction: The smooth muscle that surrounds the airways of the lung tightens, narrowing the passageways. If the muscle remains tight for a prolonged period it begins to “remodel” so that it becomes enlarged or “hypertrophic.” The increase in muscle makes it easier for the airways to constrict, and this becomes a cycle that is hard to break without intervention and treatment.
Inflammation: The buildup of neutrophils0 and other pro-inflammatory substances can lead to prolonged tissue swelling and fluid accumulation that inhibits the functioning of the small airways.
Mucus buildup: The type of inflammation caused by neutrophils stimulates the overproduction of thicker, stickier mucus than is found in normal horses.

Once a horse has developed RAO, he will always be more susceptible to flare-ups when he encounters even small amounts of the substances that affect him. “I explain it to horse owners by comparing this to human allergies,” says Laurent L. Couetil, DVM, PhD, DACVIM, of Purdue University. “If you are severely allergic to cats, a few cat hairs may cause as much reaction as the whole cat. If you walk into a room where there was a cat, you can tell—because you respond to it. Some horses are very sensitive to dusts containing mold, just as some people are very sensitive to cat allergens, and just a little bit is enough to trigger the reaction.”

Fortunately, says Amy Johnson, DVM, DACVIM, of the University of Pennsylvania, “as far as diseases go, this one is fairly easy to deal with because even though we don’t yet fully understand everything about why RAO happens, treatment and management protocols have been fairly well established. We know what works. It’s not a controversial disease.”

And that’s where your efforts can make all the difference. Although your veterinarian will likely prescribe anti-inflammatories and/or bronchodilators to counter the physiological effects of heaves, management rather than medication is often the key to helping a horse recover. Couetil has seen this firsthand: “Over the years I’ve probably had about 100 horses donated to me because they couldn’t be managed adequately to prevent heaves, but I’ve only had two that needed medication once in a while because respiratory problems would flare up. The rest have done fine just with our management, with no medication. They live at the farm, and when they are not in a study they are outdoors 24-7 with just a shelter in their pasture. They are fed a complete pelleted feed during the winter when there is not enough grass.”

Your best advisor for addressing your horse’s particular situation is, of course, your veterinarian. And you may need to do a little detective work to identify elements in a horse’s environment most likely to trigger RAO. But, to help you get started, we’ve compiled a list of the measures most commonly recommended to reduce the stress on horses with heaves. 


Dry hay is one of the primary sources of dust and mold spores that cause RAO. And the issue isn’t just with “moldy hay.”

“What is difficult for people to understand is that good quality hay can be a problem,” Couetil says. “They realize that moldy hay is bad, but they think their hay is good. But there is still some dust—and some mold spores—in good quality hay. It’s generally a question of how much. Once the horse is sensitive to molds, a breathing problem can be triggered even by good quality hay. We have studies going on right now to demonstrate this. The same molds can be found in good hay, just not as many.”

Wetting down hay prior to feeding has long been a tried-and-true way to reduce the levels of dusts and molds a horse inhales while eating. The amount of water needed depends on the horse’s level of sensitivity. “It’s really a spectrum; some of the mildly affected horses can tolerate even dry hay, as long as they are fed outside,” says Johnson, and for some horses, simply wetting the hay with a hose will be enough. For extremely sensitive horses, however, it may be necessary to submerge the hay in a trough or bucket to soak it thoroughly.


Steaming is a newer option for treating hay. Hay steamers are available from several manufacturers, sized to steam whole bales, half bales, and individual portions. “When considering a steamer, select one that gets the core temperature of the hay up to 212 degrees Fahrenheit; this eliminates or greatly reduce the microbes. You are not just adding moisture to the hay, but also reducing the load of molds and fungi which are considered some of the primary causative agents of equine heaves,” says Buechner-Maxwell, who recently conducted a study to assess the value of steaming hay. She found that RAO horses who were fed steamed hay had reduced respiratory signs than they did when fed untreated hay.

Steamers may require some care and preparation. “The process produces a small volume of runoff water that can be directed into a drain through a hose. In climates where temperatures drop below freezing in winter, the steamer will also need to be kept in a heated environment to avoid freezing or the water will need to be drained from the system between uses,” says Buechner-Maxwell. “Even though steaming takes a little extra effort, owners report that feeding their heavey horses steamed hay reduces or eliminates the need to maintain them long-term on medications like corticosteroids.” 


Many heavey horses kept on pasture have access to round bales, which could exacerbate their respiratory condition. “Round bales have higher levels of endotoxins, dusts and molds compared to other forage sources,” explains Johnson. “People think the horse will be fine just because it is outside, on pasture, and then wonder why he isn’t getting better—and it’s because the horse is sticking his nose into a round bale and breathing the dust.”


Sometimes even soaking hay isn’t enough, says Johnson: “A few horses still inhale enough particles/allergens from wet hay to trigger the disease, and must be taken off hay entirely.” She recommends that those horses receive cubed hay or a complete pelleted ration with no loose forage at all.


Most horses with RAO do best turned out 24-7 on non-dusty pasture. “If that’s not possible,” says Johnson, “then the horse should be in a stall that has the least exposure to these particles in the air the horse is breathing.” Of course, for horses with summer-pasture associated RAO, which is triggered by allergens produced by pasture plants, the best option may be to remain in the barn during the summer months. Either way, the dust levels in the interior environment need to be as low as possible. 


Choice of stall is one of the first considerations when placing a heavey horse in the barn—you want a location with maximum ventilation, well away from any sources of dust, such as an attached indoor arena or a hay storage area. “Make sure the most airflow is away from any storage stall or area where bales of straw or hay might be located,” says Johnson. “The worst barns are the ones with an overhead hayloft, with particles raining down from the ceiling.” A corner stall next to an exterior door that can be left open year-round is a good choice. 


Stall bedding is also an important consideration. Straw is among the worst choices, says Johnson, because it molds readily and can retain dust: “It pays to try to find a low-dust bedding. We use chopped paper or cardboard bedding for these horses at our hospital. Sawdust is also better than straw. Pellets over stall mats also work pretty well.”

Changing the bedding in just one stall won’t fix the problem if the horses in the adjacent stalls are still stirring up their straw. “The whole barn has to be managed to minimize dust,” says Buechner-Maxwell. Nonetheless, if you are boarding a heavey horse, it’s worthwhile to make changes in his stall to try to prevent a flare-up.


Remove your heavey horse, if not every horse, from the barn before sweeping the aisles or doing other chores that churn up dirt. “Cleaning the stalls in the barn generates a lot of dust,” says Couetil. “Even during the winter, if you can take the horse out of the barn while you are cleaning and re-bedding the stalls, this will help. It has been shown in our lab and in other labs that it takes at least an hour for the dust to settle down after cleaning the barn. Wait at least that long before you bring horses back in.” The same goes for sweeping the aisle or using a leaf blower; remove the horses before doing either.

But don’t skimp on cleaning chores. “I’ve found in some cases that there are additional irritating factors,” says Buechner-Maxwell. “If you dig under the stall bedding and find a lot of ammonia, this can be a problem, too. I tell clients to get down on their hands and knees and stick their heads down where the horse does.”


If ammonia smells and dusty air are chronic problems in your barn, you may need to improve the ventilation throughout the structure. The solution may be as simple as setting up fans or opening windows or doors, even in winter, to allow air to be drawn through each stall. A contractor experienced with modern barns may also be able to recommend inexpensive fixes, such as installing soffit or ridge vents or cupolas, to improve airflow. All of your horses will benefit from the cleaner air. 


In human medicine, omega-3 fatty acids are used to help manage a variety of inflammatory conditions, and recently Couetil published a study suggesting that horses with heaves may benefit from them as well. In his double-blind trial, the clinical signs of horses with heaves who received supplemental omega-3 fatty acids showed significant improvement compared to horses who did not receive the supplement. “People started using these for coronary heart disease, and now for arthritis and asthma,” says Couetil. “In horses, this is the first study done with an algae source of omega-3 fatty acid, and it was the first one to show an effect. So now I recommend this to my clients as an alternative, as a drug-free supplement.”

This article first appeared in EQUUS issue #459, December 2015. 

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