A case of the heaves: Veterinarians deal with recurrent airway obstruction in horses
Attempts at control—a confluence of factors
Heaves is a chronic condition. The propensity to develop airway obstruction doesn't go away, so such horses have to be continually managed. Add to this the fact that the stable is a complex environment, and you see that there are many factors to consider.
"We know endotoxin present in hay dust plays a role in the inflammation response," says Robinson. "When trying to figure out what to do to help the affected animal, there's no point where a horse owner can decide to try to take 'this' or 'that' out of the horse's bedding or hay, because they'll never know exactly what to take out."The horse owner, instead, needs to focus on reducing the particulate exposure. The best solution is pasturing these horses. For many horses with heaves, keeping them on pasture grass in spring and summer and in run-in sheds with pelleted food during winter can help keep them free of signs of disease—though this may not be practical for many clients.
"One concern about horses eating hay is that they sink their noses directly into the hay net or manger. As they tug at the hay, they create dust," says Robinson. "Also, if it's a show horse, people need to think about this when they travel with the animal."
Owners and equine specialists should also think about reducing particles in the stable. "Keep the doors and windows open. For a particularly 'heavey' horse, take it off hay and give it something that has less dust, such as a complete pelleted feed," Robinson says.
Soaking hay may be an easy solution because it significantly reduces the particles. But note it also may wash out the nutrients. "Unless the horse eats it all at once, it dries out again. As it dries, it may grow more mold," Robinson cautions.
Stall cleaning is another factor. Consider a horse that has been away from its stall for 24 hours, and the stall hasn't been cleaned out during that time, Robinson says. Mold grows in the bedding, the horse walks on it and the spores are kicked up into the stall environment as a cloud of dust. Clients with RAO-afflicted horses should be educated about keeping the stall cleaned and the horse out of the stall while it's being mucked out.
"I'm not as concerned about the bedding, per se, but about getting the chaff hay out of the bedding," says Robinson. "The particles from hay are a lot more of a concern that the particles from straw, which are larger and don't get very far into the lungs."
A final factor, says Robinson, is noxious gases, such as ammonia, which are respiratory irritants and enhance the production of mucous, so they may contribute to airway obstruction.
"With heaves, often a little bit of this by itself may not cause a problem," says Robinson, "but when it's mixed with a little bit of that, the two together may have a synergistic effect. There are all kinds of interactions between particles, endotoxins, molds, ozone, ammonia—all are in some way interacting with each other. But predicting what exactly may be affecting a particular horse—that's not easy. One almost needs a diary to keep track of what may be the problem."
And stabling is not a problem for all horses, just for certain RAO-afflicted horses, he continues. "I have a former graduate student who has a 'heavey' horse that she can manage quite well housed in a stable. She has a low-dust stall for it, but its big trigger is a dusty arena. If it goes outside and runs around a dusty arena, it will be affected. Similarly, some horses are affected by certain pollens outdoors. Some horses have seasonal problems, and you can manage those with the proper medications at those times of the year."