Heaves is the equine equivalent to human asthma, with owner management as the key to preventing future episodes.

As written by Nancy S. Loving, DVM in “Helping Horses with Heaves”, heaves afflicts many horses, but can be helped:

What is Heaves?

A horse with heaves (generally referred to in scientific literature as RAO) displays distinct signs that alert an owner to a problem. Couëtil notes the most common clinical signs reported by owners of horses with RAO are exercise intolerance, coughing, and increased breathing efforts such as nostril flare and abdominal efforts to breathe. He says that clear to mucopurulent (containing mucus and pus) nasal discharge is also reported in association with these conditions, but less frequently.

Then, he notes, “Inflammatory byproducts thicken the walls of these airways and elicit constriction of the air tubes. These modifications cause widespread airway obstruction in the deep lung areas, forcing the horse to increase his breathing efforts in order to be able to move air in and out of the lungs. I often use the analogy of an inflated rubber balloon that you need to squeeze hard to deflate if its neck is pinched.”

A horse that has endured heaves long-term has had to make extreme efforts to aerate his lungs, and this requires extra work from the breathing muscles. A result of this is a visible “heave line” in the flank area. Couëtil says the heave line is due to the bulge in the hypertrophied (excessively developed) external abdominal oblique muscles

Loving continues to cover prevention and control of horses with heaves, and environmental factors.

Prevention and Control

Couëtil stresses the role environment has on airway reactivity in triggering episodes of heaves in RAO-susceptible horses. He urges owners to concentrate on managing the environment for prevention and control of heaves. “Prevention should be focused on decreasing levels of airborne particles and irritants, referred to as ‘respirable particles,’ that may reach deep in the lungs when horses breathe,” he says. “Most respirable particles are mold spores that originate from feedstuff and bedding materials, such as hay and straw. Other irritants that trigger heaves are endotoxins (potentially toxic compounds found inside pathogens such as bacteria; they are released mainly when bacteria are lysed) and ammonia, which are particularly abundant in soiled bedding.”

He maintains that there are two ways to decrease particle levels in the stable:

1) Use feedstuffs and bedding that generate low levels of respirable dust, and

2) Improve ventilation in the stable to enhance dust removal. Couëtil notes, “Choosing low-dust feed (e.g., complete feed pellets) and bedding (e.g., woodchips or shredded paper) will significantly cut dust levels in the barn, potentially by as much as 97%.”

In addition, air circulation within the stable plays an important role in respiratory health. He says, “Proper building design is needed to ensure adequate ventilation.”

More often than not, it is best to house an RAO-susceptible horse outside. Couëtil suggests, “The ideal environment for most RAO-susceptible horses is grass pasture, because outdoor dust levels are usually markedly lower than in stables. However, some horses develop signs of heaves while on pasture during the summer, due to airborne pollen and outdoor molds. Those horses benefit from being housed in a barn, but dust levels indoors should be kept to a minimum
as discussed above.”

Couëtil says these “summer heaves” horses are different from the classic RAO horses because they improve during the winter while being housed in a barn, yet they get worse during the grazing season. “However,” he says, “a small percentage of RAO horses may be affected by both conditions.” He recommends that it is best to examine all elements of the environment, and he gives cautionary advice: “Feeding hay, and, in particular, from round bales, is the worst in stimulating a heaves episode. I have seen many horses kept on pasture 24/7 that showed severe clinical signs as long as they had continued access to round bales, which tend to grow mold and collect dust. The vast majority of these horses improved within two weeks of removing the round bales from the pasture.”

Environmental factors are to be stressed in the role they play in causing heaves in horses; managing your environment in the way of mitigating irritants that your horses breathe is key.

Take-Home Message

Limiting the presence of environmental irritants is essential in preventing and managing a horse with heaves, so all measures should be taken to keep a horse’s airways functioning as efficiently as possible so he can perform to his utmost potential.

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