Question: What are the risks and benefits of carbo-loading an endurance horse?

Answer: Let's begin by identifying the difference between "carbo-loading" and "carbohydrate supplementation" as it pertains to endurance horses.

Carbo-loading is a term primarily associated with human runners who attempt to "super-load" muscle cells with glycogen prior to the start of an event. Although the theory provides a terrific excuse for humans to eat unlimited amounts of pasta, the practice is of little to no benefit unless certain rigid guidelines are met which involve severe depletion of muscle glycogen levels for several days prior to the "loading" regimen.

When extrapolated to horses, the same protocol would equate to intense and exhaustive exercise for several days prior to a ride, a practice which increases risk of soft tissue injury far beyond the minimal benefits obtained by increased muscle glycogen levels. In reality, the average horse is a far better athlete than even an elite human distance runner, naturally able to store and utilize larger amounts of muscle glycogen without extreme manipulations.

In addition, there is increasing research indicating wide variations in horses' ability to store and utilize muscle glycogen stores. For centuries, horses fed high grain rations during the work week and then rested (still on grain rations) resulted in "Monday morning disease," a syndrome currently referred to in endurance circles as "recurrent exertional rhabdomyolysis," "azoturia," or simply "tying up." Although tying up can also be related to exhausted horse syndrome (the condition resulting from heat, dehydration, overexertion, electrolyte depletion and aberrations in acid-base status), an abnormally rapid breakdown of muscle glycogen stores in horses on high carbohydrate rations seems to be a factor in some horses that tie-up soon after commencing exercise.

Beth Valentine, PhD, DVM, a veterinary pathologist at Oregon State University, has postulated that as many as 40% of all horses (including Arabians) may be adversely affected by abnormal glycogen muscle metabolism, a syndrome referred to as PSSM (polysaccacharide storage myopathy). As such, carbohydrate "loading" prior to a ride can present widely varying results, from minimal benefit (true for all horses) and no overtly adverse reactions, to significant muscle pathology, depending on the individual horse's metabolism and ability to store muscle glycogen normally.

Compare this to simply making sure your horse starts a ride with a full gas tank. The horse's superior athletic evolution enables even an average athlete to store adequate muscle glycogen simply by avoiding intense exercise for several days prior to a ride, and by supplying plenty of quality forage with perhaps a few pounds of mixed grain. Although lacking the gee-whiz factor of carbohydrate "loading," a more natural and conservative approach provides virtually the same level of onboard fuel prior to the start of the ride without the risks of more extreme loading protocols.

Lastly, let's briefly discuss carbohydrate supplementation during the ride itself. Field research in human runners has demonstrated an increase in performance when athletes are supplemented with a source of carbohydrates throughout exercise. Likewise, some horses respond well to carbohydrate supplementation during endurance exercise, whether that consists of small and frequent doses of various grain mashes, honey, pancake syrup or a commercial carbo product. However, care should be exercised in assuming every horse will respond the same way to any given protocol. Just as a human diabetic will respond to carbohydrates differently than an elite Olympic athlete, some horses will respond well while others with variably abnormal insulin resistance and muscle metabolism will not. There is no way of predicting results without careful experimentation, observation and well-informed decisions. Take care to realize that a sugar high from any source might inspire your horse to try to write ambitious checks his body can't cash.

As with all things equine, a successful ride is the result of many contributing factors and never just the use of a "magic bullet," regardless of the results obtained by another horse and rider. Do your homework to produce a well-conditioned and experienced athlete and then use carbohydrates judiciously to provide an additional edge to performance--never as a shortcut or substitute for common sense and responsibility for your horse's health and well-being.

Dr. Susan Garlinghouse, DVM, MS is a private practice equine veterinarian and nutritionist with Michael S. Peralez, DVM & Assoc. in Arcadia, California.