Summertime Joys: Heaves

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Recurrent Airway Obstruction in Horses

Ah, summer. For most folks, it's time for pool parties and sipping lemonade on the veranda. For some horse owners, it is time for dust - dust and "heavey" horses. No, I did not misspell heavy. Heavey horses are affected by a disease commonly called Heaves or Recurrent Airway Obstruction (RAO). Think of this disease as similar but not identical to human asthma or chronic obstructive pulmonary disease (COPD). It is a relatively common disease of horses that requires addressing a multitude of factors to manage and treat (translation: it can be a pain in the behind for many owners to treat).

Heaves is classically triggered by dusty environments and poor ventilation. Affected horses usually start coughing and demonstrate exercise intolerance starting around eight years of age. This typically progresses over time to difficulty breathing, even at rest. The airways of a horse with heaves become obstructed by inflammation, mucous and bronchospasm (bronchial muscle contraction). Horses with heaves spend a lot of time simply breathing, so much so that their abdominal muscles become enlarged with the effort. This creates a so-called "heave line" that runs diagonally from the point of the hip forward to the lower edge of the ribs. Horses also tend to lose weight during this disease because they are unable to sufficiently eat to replace the calories burned by breathing hard. If you know anyone with asthma, you know they feel rotten when they cannot breathe properly. Horses feel the same way, but it can be a little trickier to treat them than simply taking a few puffs of an inhaler. Heaves also can render a horse virtually useless for any work. Some cannot breathe well enough to be ridden, which is another reason why this disease frustrates owners.

Diagnosis is generally based on the clinical history and physical examination. Wheezes in airways are often heard with a stethoscope. Some horses wheeze so loudly that you can hear it just by standing beside them! Absence of fever or any increase in white blood cell numbers further rule out infection such as acute pneumonia. Radiographs (x-rays) or ultrasound can be used to rule out other chronic diseases and endoscopy typically shows mucus and inflammation within airways.

The mainstay of treatment is management and avoidance of triggers (dust, pollen, mold, etc). It is recommended that heavey horses spend as much time as possible out of the barn and on pasture, not dirt paddocks. If a horse must be kept inside, he should be moved during high dust times - while his stall is cleaned, if aisles are being swept or blowers used. Barns should be free of cobwebs and hay should not be stored above horses. Ventilation is key, especially in the winter. Soaking hay or using high quality low-dust hay is also an important component of treatment. With some horses, hay must be removed from the diet altogether and replaced with other fiber sources such as beet pulp, hay cubes or complete feed. Round bales should also not be fed as they expose horses to high levels of dust. Maintaining heavey horses in a minimally dusty environment is hard, as you can well imagine. Not everyone has access to pasture or can control the dust levels at a boarding facility. Since this is a chronic, recurring disease, it can be very frustrating to manage these horses successfully.

Medications are also essential in treating heaves, especially during flare-ups. Bronchodilators and corticosteroids are the most common medications used. Bronchodilators (such as clenbuterol or albuterol) are used to relax airways and make breathing easier. Clenbuterol is typically administered intravenously or orally in a liquid preparation. Albuterol is typically inhaled with a mask, similar to a human inhaler. Corticosteroids (such as dexamethasone or prednisolone) reduce the severity of inflammation in airways. They can be administered by injection or orally (in tablet or powder form). Corticosteriods should be used with caution as they do have a potential association with laminitis. Many times, horses must be placed on both of these medications at once to control heaves. Some horses require chronic medication, but many only require it during flare-ups or until other management techniques create a better environment. Anti-histamines are also sometimes used with varied success under the assumption that some horses may have underlying allergies that trigger heaves.

As I mentioned earlier, management is the most important part of preventing this disease. You can give all the medication in the world, but until something changes in your horse's environment, heaves will not go away or be adequately controlled. Sometimes, this is as simple as keeping them on pasture all day. But in some cases, extra pasture can trigger heaves! There is a condition called summer pasture-associated heaves or RAO that occurs out on pasture. This condition usually occurs late spring to mid-fall with exposure to pasture in the southeastern region of the US, especially Florida, Georgia, Louisiana and Mississippi. Clinical signs are similar and this condition is thought to be triggered by inhalation of mold spores or grass pollens. Treatment is the same in terms of maintaining a low dust environment, removing hay from the diet, etc. The only difference is that these horses should NOT be kept on pasture, but instead in a low-dust barn. These horses should only be on pasture during times of disease remission, usually the winter.

For those of you suffering from allergies, asthma or COPD, it can be easy to understand a heavey horse's plight. It is rotten not being able to breathe properly and it is rotten for a horse owner to watch their horse working so hard to simply breathe! Hopefully, you are not unlucky enough to have a horse with heaves, but if you are, I hope this article gave you a little more understanding in this disease and its management. Every heavey horse is a little different, but for the most part, the basic treatment is the same. With any luck, both you and your horse can enjoy a heave-free summer and get in a few trail rides before winter comes again.