Exercise intolerance in horses has many causes

By Lutz Goehring, DVM, PhD
Colorado State University

Editor's note: Due to the extent of the subject matter, this material will be presented in a series of two articles on exercise intolerance.

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

Exercise intolerance is a syndrome generally caused by one or more underlying diseases which 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, metabolic issue, overtraining and aging should be considered.

To diagnose the problem and provide proper treatment, your veterinarian will need to ask many questions about your horse's recent history and also perform a thorough physical examination of the horse.

What are the signs of exercise intolerance in a horse? They 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 to perform a task you know it is capable of doing. 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 slow down on the feed intake, have poor body condition or even weight loss.

Some other physical manifestations may include increased 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 and or nasal discharge.

Can lameness be a cause of exercise intolerance? One of the most prevalent reasons for this syndrome is lameness. Owners often assume they will recognize a lame horse right away because it does the characteristic head bobbing during a trot. Subtle lameness in the horse can be difficult to pinpoint, however, even for equine veterinarians.

The area of concern could be anywhere from the hoof, up the leg, through the shoulder or along the spine and be related to muscle, bone or joint. A horse may experience low-level chronic pain issues due to a subtle gait problem, which could contribute to exercise intolerance. Some lameness conditions are not revealed with the routine flexion tests or lunging on a hard surface.

Further diagnostics may be required such as nerve blocks, radiographs or nuclear scintigraphy (bone scan). Once the cause or causes of the lameness are understood, veterinarians may treat the lameness with a variety of options and hopefully return the horse to his maximum level of performance.

If your horse is not performing up to par, and does not have a lameness issue, it may have an underlying medical condition causing poor performance. The next article in the November issue of the North Forty News will discuss other reasons for exercise intolerance.

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 Large Animal Reception Desk, 297-4471.