Chronic obstructive pulmonary disease (COPD), or heaves, is a very common medical problem in mature horses. Laurent Viel DVM, MSc, PhD, professor at University of Guelph, has been studying this condition for more than 25 years, and first points out that there are two respiratory conditions in horses that are sometimes confused. Heaves (also called recurrent airway obstruction or RAO) is a condition in horses 7 to 8 years old or older. Inflammatory airway disease (also called small airway disease or SAD, or non-septic inflammatory airway disease or NSIAD) is an allergic reaction found in young performance horses, usually 2 to 5 years of age.
“In the equine population, heaves can be found in 8 to 10 percent of horses,” says Viel. “As horses get older, however, this percentage increases, so we should always talk in terms of age of the animal.” This disease progresses with time. In horses 15 years of age and older, the percentage affected is much higher.
The bottom line for either one is that management of the horse makes a difference. Horses on pasture all their lives may never experience it, while horses kept in stables or working in dusty arenas are much more likely to develop heaves.
“The main risk factor is stabling,” says Viel. “We’ve created this disease by keeping horses indoors, exposing them to a higher level of dust in their environment.” Even though the barn might have ventilation (see related article on ventilation on page 34), there is always more dust (from hay and bedding materials) trapped in an enclosure than the horse would be breathing outdoors.
“The hay might be good quality, but all hay contains a certain amount of fungi or molds, which predispose horses to a respiratory problem. If you do everything possible to minimize exacerbation of this disease, the less sensitive your horse will be to various molds and fungi. The more exposed he is, the more sensitive he will become,” says Viel.
There is also a form of heaves that appears in pastured horses. This is more prevalent in southern areas. “We used to call it Louisiana disease,” says Viel. This respiratory condition, now called SPAOPD (summer pasture associated obstructive pulmonary disease), may be due to mold on certain pasture plants, or pollen. In these instances, horses do better when you take them off the pasture and put them inside.
Molds are probably the original allergen, but if horses are already sensitized to molds, they are more apt to be sensitive to other irritants. Pollen could trigger an episode of heaves in an already sensitized horse or exacerbate an existing respiratory condition. “We have problems when horses are adjacent to fields of corn or alfalfa. If the horse already has heaves (but is doing well outside), he may get worse when a corn crop reaches bloom stage in July,” says Viel. Wind currents may bring pollen to the pasture, triggering an episode of difficult breathing. When a lung lavage (a lung wash) is done on these horses, pollen is seen.
In this case, the horse must be brought indoors. “This is confusing because people are taught that keeping a horse outside would keep it more healthy. If a horse is next to an alfalfa or corn field, we suggest he be moved away from the area until the peak of flowering is past (about 60 days),” he says. Even if you put the horse in a barn, if you live close to the pollen, there will still be some in the air he breathes—it’s more diluted, but there is no way to completely escape it.
It’s important to have proper diagnosis before you treat heaves. In the past, the only way to diagnose heaves was by listening to lung sounds with a stethoscope, but now there are ways to check for early signs before changes become audible. Lung function tests using a face mask, measuring total respiratory resistance, can be combined with other tests (such as an air flow measuring meter) to detect subtle respiratory disease.
“Today, we also have access to the lower airways to observe the amount of mucus and collect a sample. With a good diagnosis, utilizing bronchoalveolar lavage (BAL), we can then use the proper medication,” says Viel. In this procedure, sample secretions from deep in the lungs (uncontaminated by secretions from nose and throat) are collected. To do this, an endoscope is put into the windpipe with the horse tranquilized, and a half pint of sterile fluid pushed in and then sucked out into a collection flask. The recovered fluid can be examined, to view the type of cells present in the lung.
“It’s an easy technique, and not invasive. Cells present in this fluid can guide you toward proper treatment, showing the type and degree of inflammation present. It’s important to know the stage (seriousness) of the disease, to know how long the animal should be maintained on treatment—as opposed to just putting the horse on steroids,” says Viel. In the long run, steroid therapy costs more than getting a proper diagnosis. If you don’t know how severe it is, you won’t know if treatment should be conservative or aggressive. People tend to take a conservative approach, but by the time they start treating the horse, the disease might need to be treated immediately and aggressively to get the best results.
“There are several treatments that are not steroid oriented, and in early stages these may work well,” he says. These treatments, such as bronchodilators like albuterol and clenbuterol (Ventipulman) and use of Lasix, along with changes in management for the horse, will often halt the progression of heaves and return the horse to normal, without resorting to more drastic treatments.
“With a serious case, there are few alternatives, however. Whether we use inhalers or oral preparations, a corticosteroid is the treatment of choice, to try to halt the inflammation as quickly as possible. I prefer the inhaled steroids, because they work very efficiently topically (locally, in the lung), very quickly, and have less systemic effect on the body than oral preparations.” Many people find it easier to put the steroids into the feed, but the mask inhaler is much more beneficial to the horse.
“Another thing people need to realize is that if you give the medication systemically (orally or by injection), the amount that actually gets to the lung is less; it is much more diluted,” he says.
When a horse starts work again, Viel encourages use of a bronchodilator like Ventipulman before exercise. “One thing the horseman needs to know, however, is that a bronchodilator is not a treatment. It just opens up the airways making it easier for the horse to breathe,” he says. And the bronchodilator is only needed when the horse exercises.
“The worst thing you can do afterward is put the horse back in the barn where it’s dusty,” he adds. “A horse’s reaction to dust is to close off the airways. But with the bronchodilator, he can’t close down the airways and ends up taking in all that dust—and becomes worse. This is a good drug to help him handle exercise, but should not be used if he has to be in the stable,” explains Viel. “If you are going to use a bronchodilator, leave the horse outside. Otherwise the horse may seem to do well for a while (and the owner thinks he’s cured), but the consequences can be very severe; after a month or two he won’t respond anymore, because his condition has been made worse.
“The horse then becomes overly sensitized and now nothing will alleviate the inflammation—and often scar tissue has built up in the airways. The horse will no longer respond to any medication,” he says.
As with most health conditions, heaves can be controlled, but it takes timing and good management.