Take note of signs of exercise intolerance in horses

By Lutz Goehring, DVM, PhD
Colorado State University

Editor's note: An introductory article on exercise intolerance was published in the September 2009 issue.

If your horse is not performing at a level that meets your expectations, it may be suffering from a condition known as exercise intolerance.

In review, exercise intolerance is a syndrome generally caused by one or more underlying conditions that can affect your horse's performance and well-being. It can come on gradually or suddenly and become chronic over time. Lameness, a heart problem, respiratory disease (recurrent airway obstruction commonly known as heaves), muscle or nervous system disease, a metabolic issue, overtraining and aging should be considered.

What are the signs of exercise intolerance in a horse?

The signs exhibited when a horse has exercise intolerance are as varied as the causes. It may be as subtle as your horse feeling "off" when being ridden with no specific lameness detected or unwillingness. Stamina can be affected with the horse appearing to be lazy. Attitude and demeanor can change due to difficulty in performing some tasks.

Horses may eat more slowly, have poor body condition or even weight loss. Some other physical manifestations may include an elevated respiratory rate at rest, slow recovery to normal respiratory rate after work, excessive sweating, sheath edema (not related to fat storage in older geldings), unresolved leg edema, cough or nasal discharge.

Can respiratory disease be a cause of exercise intolerance?

Yes, an upper respiratory infection can affect your horse's performance. When respiratory disease is acute and your horse has a fever it is most likely caused by an infectious agent such as a bacteria or virus. Early diagnosis and successful treatment of these infections should not cause long-term problems and your athlete should return to full performance. Other conditions in the lung such as pleuropneumonia (inflammation of the lungs and pleural space) are extremely rare in horses but are very serious.

A common respiratory disease that often results in exercise intolerance is recurrent airway obstruction (RAO). The condition is caused by airway inflammation and is similar to asthma in humans. Mold that can be present in hay or straw can trigger an allergic reaction in a horse's small airways (bronchi) and air sacs (alveoli). This reaction results in swelling, increased mucous production and a spasm of the small airways. All these impair oxygen exchange, particularly while your horse is at work.

How is respiratory disease diagnosed in the horse?

A veterinarian can provide information regarding your horse's respiratory health by several methods. First, a good medical history will be taken, then questions regarding your horse's living environment, feed regime and travel. A complete examination will be done including an assessment of temperature, pulse, respiratory rate and listening to lung sounds (auscultation). This information should help determine whether the problem is in the upper or lower airway. Other diagnostics that could be recommended by your veterinarian include a TTW (trans-tracheal wash), upper airway endoscopy or BAL (broncho-alveolar lavage).

What is the treatment for respiratory disease causing exercise intolerance?

Treatment is dependent on what type of respiratory disease is diagnosed in your horse. If it is an uncomplicated airway bacterial infection, it should respond with appropriate antibiotic therapy, rest and time. If it is a viral infection, supportive therapy and time should take care of it. If it is allergy related, then removing the allergen (dust, molds in hay or straw) is important. Most horses also require treatment with bronchodilators or steroids to reduce inflammation. Some horses stabilize with temporary treatment and environmental changes; others need low-dose medical management all year.

If you think your horse is exercise intolerant due to a respiratory problem, have a veterinarian examine the horse as soon as possible. This will determine the severity of disease and a treatment plan to help prevent long-term complications from a potentially serious lung disorder.

This series has dealt with two areas of concern when a horse is exercise intolerant – lameness and respiratory problems. Other reasons that may cause exercise intolerance are mentioned in the second paragraph. If your horse is "off" and not rebounding as you think it should, it is time to give your veterinarian a call.

Dr. Lutz Goehring is a specialist in equine medicine at the Colorado State University Veterinary Teaching Hospital. He regularly treats patients for a variety of medical problems and specializes in neurology and infectious disease. He can be reached through the CSU-VTH at 297-5000.