Heaves is a term that has been used to describe equine allergic respiratory disease. Other terms to describe it are chronic obstructive pulmonary disease (COPD), recurrent airway obstruction (RAO), inflammatory airway disease, equine asthma or simply “broken wind”.
A horse develops this condition by being sensitive to mold, dust, pollen, or some other stimuli in its environment that acts as a “trigger”. If the horse is sensitive to mold found in hay or bedding then he will have more problems when kept indoors such as during the winter months or may cough while eating hay. Other horses are sensitive to the pollens and grasses they are in contact with while on pasture. These horses may exhibit worse symptoms during the spring and summer. It is important to try and figure out what is acting as the trigger for your horse. Keeping a log of when your horse is affected and what the conditions were or what was changed in his environment may help determine his triggers.
Exposure to this “trigger” leads to an allergic reaction that causes irritation, constriction and mucus production in the small airways of the lungs. Over a period of time this inflammatory reaction in the lungs leads to the development of scar tissue which makes the lung stiff and unable to collapse when trying to breathe out.
Horses with this condition initially may have mild symptoms such as coughing, nasal discharge and exercise intolerance on hot “muggy” days. Some horses will show more extreme signs including wheezing, difficulty breathing and increased effort to expire air. Some horses will have symptoms that get gradually worse from year to year and others will be acutely affected from even a brief exposure to their trigger. Horses with this condition are predisposed to developing bacterial infections in their airways and may show symptoms of pneumonia or sinus infection. Chronically affected horse may have weight loss and develop a “heave” line along the side of their chest from trying to push air out of their lungs.
Diagnosing airway disease in the horse is based a lot on history and physical exam. Often, treatment can be initiated on those alone. Horses that do not respond or who are more severe may need further diagnostics which may include x-rays, endoscopy, ultrasound, or culture and cytology of the airway. These tests can give valuable information for directing treatment for individual cases.
There are no magic bullets to cure this disease and in fact it can be very frustrating to manage. Regardless of the cause, the most effective treatment is to avoid exposure to the triggers that irritate the horse. Horses that are triggered by indoor mold and dust should live outside and vice versa for horses allergic to pollens and grasses. Often this is not practical or effective so compromises have to be made. If affected horses must be kept inside then there are ways to limit their exposure. Reduce triggers in hay by submerging in water for several minutes or invest in a hay steamer. Merely spraying it with the hose is not adequate. Some horses will do better with no hay at all and need to live on a complete pelleted feed or hay cubes. Choose low dust bedding and avoid straw. Remove the horse from the barn during cleaning and feeding and return only after the dust has settled. Store hay and bedding in a different barn. Provide good ventilation to the stall. Horses that do not improve completely with management changes will require medication at least temporarily.
Medication is directed at reducing irritation and inflammation, dilating the airways and eliminating secondary infections. Corticosteroids and antihistamines reduce the inflammatory reaction to a trigger and allow the airway to be cleared normally but steroids can have toxic side effects and can only be used for limited times and antihistamines can help initially but typically become ineffective. Bronchodilators make the small airways larger so air can flow through them more easily. These medications are usually given orally or by injection. As the disease progresses their effectiveness wears off and higher doses are required resulting in greater risk of toxicity. To avoid this some of these medications can be given through inhalers directly into the lungs. These medications require more frequent administration and are typically more expensive and may require special equipment.
Things to remember.
- Affected horses have a “trigger” like mold or dust or pollen.
- The most important management tool is identifying and removing the trigger.
- Keeping a log may help identify the trigger.
- Diagnostics and medications can help get it under control.
- Treatment is likely to fail if exposure to the trigger is not eliminated.