Respiratory problems can be addressed by carefully managed careSome horses, like some people, are more sensitive to respiratory irritants, developing allergic reactions and difficulty in breathing if exposed to certain types of dusty conditions.
The horses lungs are strong and highly resistant to disease, as a general rule. But the domesticated horse has to put up with conditions unknown to his wild ancestors. He is often confined indoors or in a small pen or paddock with all the grass beaten out, creating dust when conditions are dry. He is usually fed haywhich may occasionally be dusty or moldy. He may be worked in a dusty arena.
Some horses respiratory systems cannot withstand these extra stresses, and they develop chronic respiratory problemsa condition called heaves by old-time horsemen.
Chronic respiratory disease is characterized by loss of performance (the horse does not have enough wind to work at the best of his abilities), chronic cough, weight loss, lack of response to antibiotics, and labored or wheezy breathing, similar to a case of asthma or emphysema in humans.
The most characteristic symptom (from which the term heaves is derived) is a forced effort at exhaling, sometimes described as double expiration. The air is drawn into the lungs easily enough, but the horse has trouble forcing it out. Simple relaxation of lungs and rib cage, as in a normal horse, will not do the job, so the horse must follow that up immediately with a concentrated effort in which he contracts his abdominal muscles to force out the air, with an extra lift of the flank (thus two movements of the abdominal wall with each expiration).

Forcing air
In the normal horse, inhaling is the active process and exhaling is just a relaxation of the chest wall and diaphragm, requiring no effort. But with heaves, the horse has to force the air out, and many of these horses develop an enlargement or heave line along the lower side of the abdomen, from the overworking of these muscles in forcing the air out of the lungs.
Your veterinarian can diagnose chronic respiratory disease by listening to the horses chest sounds with a stethoscope, especially after he exercises. Normal lung sounds in a healthy horse are barely audible, but a horse with heaves makes abnormal lung sounds, due to extra air turbulence from the restricted airways.
Over time, the lungs lose their elasticity and the horses breathing becomes more and more forced. Eventually he develops a big chest and pot belly because the diaphragm muscles enlarge. He is short of breath and has no endurance. In mild or early cases, coughing spasms may be brought on by only exercise, or by eating dusty feed, or by being confined indoors in a dusty barn. But as the problem progresses, the horse may have frequent coughing spells and have difficulty breathing even when resting.
A number of things can cause chronic respiratory disease, but allergy to dust, mold, pollen, bacteria, or other alien substances are the leading causes. Chronic heaves, which develops gradually and becomes progressively worse, is often associated with prolonged feeding of dusty hay. This respiratory problem is almost unheard of in horses that run at pasture all their lives, eating grass instead of hay and never having to eat dry, dusty, or moldy feeds.
A horse with an advanced case of heaves or a severe, acute attack of breathing difficulty will need veterinary attention. He will need antihistamines and bronchodilators to help him breathe. But the horse owner can usually keep a horse from getting this bad with careful management. Any horse that is sensitive to dust should have special consideration in feeding to prevent chronic respiratory disease. And this means meticulous care to make sure that each feeding is dust-free. Even one slip-up and the horse may be in serious trouble.

Turn him out
The horse with sensitive lungs should be kept outside, not in a barn or stall. Dust from hay and bedding in the enclosed area, and the ammonia created by manure and urine in the stall, are all very irritating to the horse with respiratory problems. It may take several days of being turned out for the worst of symptoms to subside in a horse with heaves, and all symptoms may quickly return if the horse is put back in the barn.
If the horse must be in a barn for some reason, major steps must be taken to have the barn dust-free. Peat moss or wood shavings can be used for bedding instead of straw (which tends to be dusty), but be careful when selecting wood shavings: Some kinds of hardwoodsuch as black walnutare toxic and can cause founder and other problems. Hay fed to the horse with respiratory problems should be soaked in a tub of water and allowed to drain before feeding. If grain is fed, it can be given as a mash, or with molasses added to dampen it and reduce dustiness. But none of these efforts will help if other horses in the barn have dusty straw bedding or if dust drifts in from another source such as a dusty pen or paddock nearby.
Legume hay (alfalfa, clover) is always dustier than well-cured grass hay, and should be avoided when feeding a horse with respiratory problems. The leaves tend to shatter and create fine particles and dust. Alfalfa and other legumes are also richer in protein and other nutrients than grass hay, and provide a more ideal environment for molds when wet or damp. A tiny bit of mold in alfalfa hay may trigger the horses allergy and start him coughing and wheezing. The horse with respiratory problems will do much better if fed only well-cured grass hay that is not dusty or moldy.

Dust-free hay
If the horse is being fed hay outside, you may not need to soak it in water to prevent coughing and irritation. You can often get by with just shaking the hay thoroughly to get rid of any dust, then sprinkle it with water to dampen it and settle any remaining dust particles.
Keeping hay as dust-free as possible will prevent a horse with heaves from getting worse, and can help prevent a normal horse from developing lung irritation, cough, and sensitivity. Any horse that coughs when eating his hay should be given hay that is less dusty or have his hay dampened to keep it from irritating his airways.
Pelleted feeds are often less dusty than hay, and there are some made especially for horses with heaves. You might try those if you have a horse that keeps coughing on hay. If the horse lives in a dusty pen or paddock, the area can be sprinkled several times a day to settle the dust. An early case of respiratory sensitivity will usually respond very well to good care and a change in the horses environment or feeding to prevent exposure to dust. Conscientious management will stop that cough.