Editor's Note: This excerpt is from Understanding Equine First Aid by Michael Ball, DVM. The book is available from www.ExclusivelyEquine.com.

The ability to exercise and the metabolic responses to exercise differ in each individual horse and can vary greatly depending on many factors. The genetic potential for athleticism, the level of training, the degree of conditioning, the presence of underlying health problems, and environmental variables such as ambient temperature and humidity are only a few of the factors that determine overall exercise tolerance. As many a "weekend warrior-type" human athlete knows all too well, if you have trained to run a couple of miles once a week and then set out to do the 26-mile Boston Marathon, the outcome will be painful. The same is true for your horse.

Many exercise-induced problems could be avoided by applying common sense limits to performance stresses. If you plan to compete at eventing and endurance riding, make sure both you and your horse are appropriately prepared. Know your limits and don’t be afraid to pull up if those limits are going to be exceeded. During the training for such events, monitoring of the health and well being of your horse becomes your responsibility. Seek out advice on training. Learn what the danger signs are and gradually expand your horse’s individual limits.

Exercise exhaustion can occur after relatively brief maximal exercise or after prolonged submaximal exercise. The signs of exercise exhaustion are: 1) a persistently elevated body temperature, heart rate, and respiratory rate; 2) the presence of dehydration with a lack of thirst; 3) an increased capillary refill time observed in the gums; 4) an irregular heart rhythm; 5) decreased gastrointestinal sounds, a flabby dilated anus, and colic; 6) muscle cramps and spasms; 7) depression and lack of desire to eat; and 8) the presence of "thumps" (described later in this chapter).

Many events and endurance trail rides are carefully monitored by veterinarians to make sure that competing horses are not exercised beyond their limits. A prescribed rest period is mandatory during which time the horses 1) rest, and 2) are carefully monitored for signs of exhaustion. The horses’ heart rate, respiratory rate, and rectal temperatures are determined, then monitored to see if they decrease appropriately during the rest period. Typically, the heart rate should become less than 60 beats per minute and the respiratory rate less than 40 breaths per minute within 20 to 30 minutes after the start of the rest period.

If the heart rate and respiratory rate do not decrease during the rest period or if the horse has an excessively high rectal temperature (typically in excess of 105 degrees F) then the horse will be held for a longer time or be excused from the competition because those signs are indications of exhaustion. The rider should not continue to exercise the horse. During this time, the event veterinarian will evaluate the horse’s way of going for signs of lameness or rhabdomyolysis.

Should the horse develop exercise exhaustion or any musculoskeletal abnormalities, prompt veterinary attention can be very important. The horse might be dehydrated and might need, in addition to intravenous fluids, correction of its blood electrolyte levels. If possible, it is best to get help to come to you or to make provisions to trailer the troubled horse to assistance as soon as possible. Further exercise of a metabolically stressed horse can have grave consequences. If medical help or trailering is not available, the rider should allow the horse to rest. While it is not a good idea to offer an overheated horse unlimited water, it is a good idea to offer it a small amount of electrolyte-laced water or to place electrolyte paste on its tongue. Standing the horse in a stream or splashing cool water on its legs will help to reduce its core temperature, slow its respiration and, perhaps, lower its pulse.

This kind of metabolic emergency can be described as exhaustive disease syndrome. It often involves the following complications: severe dehydration, synchronous diaphramatic flutter (the "thumps"), and hyperthermia.

About the Author

Michael Ball, DVM

Michael A. Ball, DVM, completed an internship in medicine and surgery and an internship in anesthesia at the University of Georgia in 1994, a residency in internal medicine, and graduate work in pharmacology at Cornell University in 1997, and was on staff at Cornell before starting Early Winter Equine Medicine & Surgery located in Ithaca, N.Y. He is also an FEI veterinarian and works internationally with the United States Equestrian Team.

Ball authored Understanding The Equine Eye, Understanding Basic Horse Care, and Understanding Equine First Aid, published by Eclipse Press and available at www.exclusivelyequine.com or by calling 800/582-5604.

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