“Doc – What Can I Do For A Mare With Heaves?”
© A.J. Neumann, D.V.M.
published in The Draft Horse Journal, Spring 1999

“Heaves” is a chronic disease of the equine family, characterized by a dry, wheezy cough, expiratory breathing, over-production of intestinal gas, and eventually terminating in emphysema of the lungs. Down through the years this condition has been recorded under a host of different names, such as chronic alveolar emphysema, broken wind, asthma, pulmonary emphysema, dusty hay cough, and lately the condition is now known as Chronic Obstructive Pulmonary Disease or COPD. It seems to me that during the last two decades we have labeled many organizations, diseases, programs, and such by using letters to show an abbreviated form of their real name. So maybe I am old-fashioned, but I just like to use the term “heaves” in labeling this condition of the equine. Most horsemen understand the term and would get lost when exposed to the abbreviation COPD or its long, fancy proper name.

The disease is interesting in that it is unknown among the horses of the Arab countries. It is also practically unheard of in Spain and Portugal. The condition is rare in certain areas of England and France.

In the United States, heaves did not become a problem with horses until the introduction of timothy, alfalfa, red clover, and other cultivated grasses which were pastured and used for hay. Western states such as Colorado, Montana, Utah, Idaho, Wyoming, and California seemed to be free of the disease. This all changed with the introduction of large scale irrigation for the production of hay.

Cases of heaves are much more frequent in those areas where the climate is unfavorable to the proper curing of hay. Cases seem to be more prevalent in those areas of the country where farm horses spend much of their time stabled in barns, with the hay before them.

New cases of heaves are reported following a season when the harvesting of hay is difficult because of extended periods of wet weather.

In more recent times the feeding of the “big round bale” to horses has caused a dramatic increase in the number of these horses suffering from the heaves. This was reflected in my own practice. On those premises where loose hay or the small rectangular bales were fed to horses, an occasional horse would be treated for heaves. However, on the premises where the round bale was being fed, it would not be unusual to treat all of the horses for the heaves. I have treated as many as 60 horses on one farm at one time, all suffering from this disease.

Another curiosity about the disease is that it rarely occurs in horses under the age of 5 years, and it is not a problem for mules or members of the ass family. It was also known for many years that horses fed on clean oat straw and barley never developed the condition.

For many years the exact cause was unknown. The horsemen did know that excessive feeding of dusty hay and clover to stabled animals would cause the disease. Red clover hay was especially bad. It was also known that some pastured horses would develop the clinical signs, usually in the late summer.

We now know the cause of heaves in horses is a hypersensitivity, most commonly to fungal spores found in some hay and bedding, and also to a hypersensitivity to pasture grass pollen. This latter sensitivity to grass pollen explains the fact that some horses will develop heaves on pasture during the late summer months. As a general rule, the more dusty the hay or bedding, the greater the number of fungal spores present.

An inherited predisposition to heaves in the horse has long been suspected. We know definitely that humans with low antitrypin levels are predisposed to emphysema. It is well documented that low antitrypin levels are inherited, so possibly an inherited factor could be at work in the horse as well as man.

Recent studies have shown that some cases of COPD will follow certain respiratory viral infections. In the human population of the U.S., COPD is most often due to cigarette smoking. It is the fifth leading cause of death in this country for humans.

Most generally heaves develops slowly in the horse. As I stated before, it is rarely diagnosed in horses younger than 5 years. As the animal is exposed to the allergen (fungal spores or pollen) one might notice a decrease in the animal’s ability to perform. Exercise will tire the animal much sooner than usual. The affected animal will then develop a dry, “hacky” cough, which will appear first upon exercise, and later even when the animal is at rest. A clear nasal discharge may be seen.

As the disease progresses, one will notice labored breathing as the patient is exercised. In chronic cases the breathing can be seen when the horse is at rest. These patients often display the so-called “heave line.” In these cases the lungs have lost much of their elasticity, and the animal compensates by using its abdominal muscles to force the air out of the lungs. This lifting procedure will increase the size of the abdominal muscles which are located from the middle of the flank forward along the edges of the ribs to the point of the elbow. The thickening of these muscles along this area can readily be seen and is called “the heave line.”

The diagnosis of COPD or heaves is made by a careful observation of the horse, along with an interpretation of the animal’s history.

Most old-time horse buyers always carried a cane, whether they personally needed it or not. When examining a horse for “broken wind,” the animal was led off at a fast trot for about 50 yards, turned and brought back to the examiner at the same pace. Upon stopping the animal, the prospective buyer would punch the horse directly in the abdomen right at the “heave line” area with the sharp end of the cane. A “heavey” horse, which often had been doped, would emit a loud grunt which, to many prospective buyers, was diagnostic for heaves. I have seen this done many times and have used the trick myself on a horse or two. Remember, not all sellers of horses are honest! A horse with an early stage of the heaves can be doped to look perfectly normal for at least 24 to 48 hours. The old-time cane trick will often reveal these cases.

Once the horse develops an allergy to fungal spores, the allergy will remain for the horse’s life. Therefore, the affected animal must be removed from the source of the allergen. The animal must be removed from any source of feed dust or mold, be it present in the grain ration or, most commonly, in the roughage or hay. If the animal is to be stabled, it must be in a clean, well-ventilated stall bedded with wood chips, peat moss, shredded paper, or other synthetic bedding material. Straw or moldy hay should never be used as bedding for these animals. The stall must be thoroughly cleaned each day to prevent the build-up of ammonia and fungal spores.

Many of these horses will do well if kept outside and fed a ration of hay cubes or pellets. Often haylage or silage is fed to these animals with good results. If need be, dusty hay can be fed by placing it in a hay bag and soaking it in a tank of clean water for 5 to 10 minutes. Any dusty grain should not be fed. If it becomes absolutely necessary to feed this grain, it must be soaked in clean water prior to feeding. However, it is my experience not ever to feed dusty or moldy grain to a horse, soaked or not.

The horse who is allergic to grass pollen can only be pastured in the early spring. This animal must be dry-lotted during the summer and fall, so that its exposure to grass pollen is kept to a minimum.

Most horses, when diagnosed early with heaves and placed in a good and safe environment with proper feed and feeding practices, will recover in about 3 to 4 weeks. Some medication may be necessary for those animals having severe respiratory problems. Anti-histimines, bronchodilators, and corticosteroids are often used to alleviate the respiratory problems.

If you have an animal which exhibits severe respiratory distress your veterinarian may treat this horse with the bronchodilator clenbuterol. The drug can be used intravenously or by inhalation. Either way, clenbuterol is quite effective in treating these animals and in relieving the respiratory distress in 30 to 45 minutes. An oral syrup of this drug is also available. About 75% of “heavey” horses treated twice daily with the syrup will respond favorably to this treatment.

When treating these horses it is imperative to remember good management practices to keep the animal away from the offending allergens; this is absolutely essential in the treatment and prevention of heaves.

It has been my experience that improperly cured hay is the biggest factor in causing heaves in horses, along with the advent of the large round bale. Hay that is to be baled for horse consumption must be processed when it is dry. If it is baled when it is damp, the roughage will mold and turn “dusty.” When the bale is opened, one can often see areas of mold, or when the hay is “shook” a cloud of white fungus spores can be observed. This hay is not fit to feed to any horse.

In my practice area the big round bale is the major offender in causing heaves in horses. This method of baling has become very popular, due to its labor-saving features. If the forage is baled with these machines when it is properly cured and dry, and the bales are stored so they will not be exposed to weather, the hay baled in this fashion should be free of fungus and mold and should be fine to feed to horses. However, most of these bales are stored outside, and spoilage occurs around the bale. Often these bales are then placed into a feeder or just placed in a corral or yard for horses to eat. When a horse eats on a round bale, it will often make a hole into the hay and eat into the bale. Sometimes this hole will be 12 to 16 inches in depth. If there is any spoilage at all, the horse not only eats the spores, but will inhale vast quantities of them.

Sometimes the hay will look perfectly good on the outside of the bale, but when you put your hand and arm into the holes the horses are making in the bale and withdraw some of the forage and shake it in the sunlight, you will notice a white cloud of the spores coming from the shaken hay. This forage is not fit to feed to horses and will invariably cause many cases of heaves. Sixty head of brood mares on one farm alone were diagnosed with heaves from just such a cause.

This brings us to another point about heaves. I have often heard that a mare with the heaves will not become pregnant or carry a foal to full term. This is not true. Many mares suffering from heaves become pregnant year after year and deliver fine, healthy foals.

Stallions with the heaves can and will remain sound breeders for many years, far up into what is considered old age for a horse. I am thinking of at least two famous, well-known draft stallions who had heaves, yet produced offspring for many years.

Now that you understand something about the causes of heaves in horses, we can surely see that prevention of the condition is relatively easy. This is a disease of horses that is much easier to prevent than to cure. The old adage “An once of prevention is worth a pound of cure” is certainly a fact when discussing heaves in horses.