Your most recent hay delivery contained some particularly dusty bales. While the leaves are still green and appear that they’d be appetizing to a horse, should you go ahead and feed it? You might want to think twice.

Heaves, also known as chronic obstructive pulmonary disease, is an equine lung disease that’s caused by an allergic reaction to inhaled particles. Those bales just might cause more harm than good if the horse inhales the “dust” as he eats.

Even the highest quality hay contains bacteria, fungi, and other tiny particles that become aerosolized in hay dust. So, when a horse inhales these particles, it may cause an allergic reaction that results in inflammation and constriction of the airways (the trachea, bronchi, and bronchioles).

The term heaves was developed to describe the clinical sign of the disease in which the horse must “heave” at exhalation to push air out of the lungs through the constricted airways. Coughing, wheezing and nasal discharge are also symptoms. A horse with severe heaves often develops a “heave line,” a ripple of muscle he builds behind his ribcage in his effort to exhale.

Heaves is most often seen in older horses, especially those that have been stabled throughout their lives. Although COPD
doesn’t appear to be breed or gender related, there’s evidence that it may be hereditary.

A horse with heaves may also have exercise intolerance and may lose weight due to the difficulty of eating when normal breathing is impaired.


Diagnosing Heaves
If you suspect your horse has respiratory allergies, you can take him to a veterinary clinic for a lung function test. There they use a facemask on the horse and measure his total respiratory resistance, airflow, and they might collect a sample of mucus from the lower airways.

“We can sample secretions from deep in the lungs [uncontaminated by secretions from nose and throat], utilizing an endoscope and bronchoalveolar lavage,” said Laurent Viel, DVM, PhD, from the University of Guelph (Ont.).

The recovered fluid is then examined to view the types of cells present in the lung. This test can guide you toward proper treatment, showing you the type and degree of inflammation present.

“It’s important to know the stage of heaves, to enable the clinician and horse owner to know how long the animal should be maintained on treatment–as opposed to just putting the horse on steroids,” said Viel.

People tend to take a conservative approach with heaves, but sometimes by the time they start the horse on serious treatment he must be treated aggressively to get the best results.

Sarah Gardner, DVM, PhD, of the department of clinical sciences at North Carolina State University, uses a non-invasive pulmonary function test to evaluate hyper reactive lungs in horses.

“This equipment allows us to determine if horses have airway hyper reactivity, which can be a sign of recurrent airway obstruction [heaves] or inflammatory airway disease. The test can aid in diagnosis and also enables us look at a horse’s response to therapy and environmental management, to see if they’re improving.”

For testing, Gardner mildly sedates the horse and attaches a facemask over the nostrils. The horse’s airway reactivity is tested at rest, and if it’s normal, the horse is given a histamine challenge test to determine if he has airway hyper reactivity.”

This test gives the veterinarian an idea as to how the horse’s lungs would react if he came in contact with an allergen in the air. If the initial test is abnormal, instead of the histamine challenge the veterinarian will do a bronchodilator challenge.

“This helps us evaluate the reversibility of the airway obstruction and gives us an indication about how the horse might respond to that bronchodilator therapeutically–to see how well the treatment might work for that horse,” she said

The testing system Gardner uses for evaluating pulmonary function is one of only two in the United States (the other is at Tufts College of Veterinary Medicine in Massa-chusetts). The University of Guelph also employs a system.

This type of test may also have future potential in evaluating horses during pre-purchase exams, noted Gardner.


Keep Him Outside
Treatment for heaves can involve environmental changes to avoid the allergen. Horses should be kept outdoors instead of in stalls. Pasture, rather than a dusty dry lot, is the best environment for the horse.

Many horses with heaves cannot be fed alfalfa hay because it has a higher level of mold dust than grass hay. Regardless of type, any hay fed should be carefully selected, be clean and dust-free, and dampened, or even completely soaked in water to eliminate any possible dust particles. You can also use pre-packaged forage such as Dengie to minimize mold and dust.

David Cross, DVM, PhD, of the University of Missouri, recommends feeding all hay at ground level and removing any dampened hay that’s not eaten right away to avoid mold. He advised against round bales.

“People feeding round bales often have horses with problems, even if the horses are outside. They’re burying their heads in the hay bale to eat,” said Cross.

There’s no air circulation within the large bale, and the first 6″ of the bale is loaded with dust. The quality of the hay in most round bales is also diminished because it’s exposed to rain and weather and tends to mold.

Horses with heaves shouldn’t be fed using hay feeders or hay nets. If a horse must reach up for his hay, he’s more likely to breathe in dust as he pulls the hay down. In addition, he can’t expel mucus buildup when his head is up. If a horse can’t be on pasture, he may do best on pellets; there are pellets formulated especially for horses with heaves.

In severe cases, you may need corticosteroids or other products (systemic or inhaled) to reduce inflammation in the airways. One advantage of using inhaled medication is the rapid response seen in the horse. There are several devices available commercially for administrating inhaled medication through the nostrils.

Philip J. Johnson, DVM, PhD, professor of equine internal medicine at the University of Missouri, said the most important factor in heaves is keeping the horse from inhaling particle matter. If this situation is impossible for the horse owner to control, he suggested medications.

Johnson said there are two major drug categories that are always–where practical–best administered via inhalation. They’re glucocorticoids (also known as corticosteroids) and bronchodilators. Usually the bronchodilator is administered first to open the airways, then the glucocorticoid to reduce inflammation. These drugs can also be used systemically via injection or as tablets/ syrup by mouth.

Johnson noted the best approach to treating heaves is proper management–without over reliance on drugs, whenever possible.
Cross said that dexamethasone and bronchodilator drugs like albuterol and clenbuterol are usually helpful.

“A mild case [of heaves] will generally respond to dexamethasone to ease the swelling that’s constricting the airways. Horses that have a hard time breathing, however, may need bronchodilators such as clenbuterol,” noted Cross.

Viel said that in early stages, conservative treatments and bronchodilators that aren’t steroid oriented can work well in conjunction with changes in management. This treatment will often halt the progression of heaves and return the horse to normal, without resorting to more drastic treatments.

“With a serious case, however, there are few alternatives. Whether we use inhalers or oral preparations, a corticosteroid is the treatment of choice to halt the inflammation as quickly as possible. I prefer the inhaled steroids because they work very efficiently [in the lung] very quickly,” said Viel.

Also, inhaled steroids can be used at a lower total dose so they don’t have as many side effects as systemic steroids.

Pasture-associated respiratory problems are generally more difficult to manage, though some horses respond well to a simple change in environment such as removing them from the pasture that caused the problem or reducing the time turned out.

If a horse with respiratory problems is pastured near fields of corn or alfalfa, move him to another area until the peak of flowering is past and the pollen is reduced. Long-term inflammation can cause permanent damage to the airways.

Before starting a treatment plan make sure to contact your veterinarian. Owners should be aware that medication rules and withdrawal times for competition horses should be carefully followed when using systemic and inhaled medications.