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In order to perform to the best of their ability, elite human athletes pay incredible attention to what they eat, how much they consume, and when they schedule meals before a competition. Feeding a performance horse is similar in that what, when, and how much it is fed is tied to the length and intensity of the work it will be asked to do. A trainer preparing a Thoroughbred for a short, explosive sprint on a racetrack will feed quite differently from an owner who is planning to enter her Arabian gelding in a 50-mile endurance race.

Those who manage equine diets will make better feeding choices if they take into consideration the basic structure of the horse’s digestive organs and the influence of feeding on blood flow distribution. The horse’s digestive tract consists of a rather small stomach, a long small intestine, and a large hindgut that holds gallons of fluid and billions of microorganisms that aid in the fermentation of fiber. Much of the weight of the digestive tract is due to this sizeable fluid content. In the idle horse, somewhat more blood flow is sent to the digestive tract organs. When the horse exercises, blood flow to the muscles increases and the supply to support digestion decreases.

To determine the type of diet and the pre-exercise feeding schedule that will allow horses to perform at optimal levels, it is necessary to balance the horse’s requirement for nutrients with its expected performance. The following guidelines have been based on a classification of exercise performance that uses three categories: high-intensity, short-duration; moderate-intensity, medium-duration, and low-intensity, long-duration.

High-intensity, short-duration exercise

During high-intensity, short-duration exercise, the horse is working at or near its maximum heart rate. The horse can maintain performance at this level of exertion for only a short period of time (less than 10 minutes). One example of this type of exercise is flat-track racing. Due to the short duration of this exercise, it is generally thought that nutrients needed to fuel muscle contraction must be stored in the muscle prior to exercise. Therefore, feeding horses with the intention of loading the blood with nutrients to be metabolized during short-term exercise does not appear beneficial.

In fact, studies at Kentucky Equine Research have shown that feeding grain within four hours of submaximal exercise caused large declines in blood glucose during exercise. These declines in blood sugar may be detrimental to performance since glucose is the only fuel metabolized by the central nervous system. Feeding large fiber meals prior to exercise is not warranted either, because fiber would increase the body weight carried by the horse, slowing its pace.

Racing officials routinely handicap horses by assigning additional weight to superior runners. If racing officials can potentially change the outcome of a race by assigning as little as 4 lb (1.8 kg), what would be the impact of a short-term fast (12 hours) on body weight? This type of fasting would decrease body weight; however, the downside would be potential problems with the digestive tract, namely the development and aggravation of gastric ulcers. When to feed and when to fast becomes a balancing act between keeping weigh down and causing as little harm to the digestive tract as possible.

Feeding recommendations for competing in high-intensity, short-duration exercise:

Offer high-quality grass or grass/legume hay on an ad lib basis with free-choice access to water. The energy sources needed to fuel fast-paced performance are predominately nonstructural carbohydrates (NSCs) provided by processed cereal grains such as steam-flaked corn and barley. Avoid high fat (>10%) feeds and instead select a high-NSC feed with low to moderate fat content (4-7% fat) from ingredients such as vegetable oil or stabilized rice bran.

Moderate-intensity, medium-duration exercise

During moderate-intensity, medium-duration exercise, the horse is working at a heart rate between 50% and 75% of maximum. Exercise of this intensity may be tolerated for several hours. This type of exercise may include a variety of show events in which horses perform in a number of classes throughout the day.

Since speed is not the primary concern, the weight (gut fill) of the animal does not appear to be critical. These horses would benefit from small, frequent forage meals, which also serve to eliminate boredom. Grain meals should be avoided within four hours of performance. This would eliminate the large fluctuations in blood glucose associated with feeding and postprandial exercise.

Feeding directions for competing in moderate-intensity, medium-duration exercise:

Offer high-quality grass or grass/legume hay on an ad lib basis with free-choice access to water. This type of exercise is best fueled by a combination of energy sources from NSCs, fat, and fiber. Concentrate feeds that replace some of the cereal grains with fiber sources like beet pulp and soy hulls are ideal with moderate to high fat content (8-12% fat).

Low-intensity, long-duration exercise

During low-intensity, long-duration exercise the horse is typically working at less than 50% of heart rate maximum. At this intensity, exercise can be tolerated all day. Trail riding and some endurance rides are examples of this type of exercise.

These horses have increased requirements for water and electrolytes due to the duration of exercise. They would benefit from the water-and electrolyte-holding characteristics of high-fiber diets. The fiber should be of high quality (low degree of lignification) such that fermentation can occur, thereby making these nutrients available for absorption. The use of high-fiber concentrate feeds that include soybean hulls and/or beet pulp is warranted due to their high fermentation and water-holding capacity.

Feeding strategy before an endurance-type competition may be different from feeding during a ride. Starting the evening before, horses should have free-choice access to high-quality forage throughout the night with no withdrawal time before the start of the competition along with ad libitum water access. The fiber-filled gut will serve as an energy source and water/electrolyte reservoir. A late-evening grain meal should be adequate until the horse gets to the first stop of the race. No grain should be fed within four hours of the start of the race. High-fiber and high-fat feeds are appropriate at this time with a little starch from oats or sweet feed. Electrolyte supplementation at this time may serve to preload electrolyte stores for the upcoming competition.

Meals provided during the ride should also maximize forage consumption since forage will stimulate water intake and help maintain hydration. A small meal of a grain concentrate can be fed at every pit stop during the ride. Higher starch meals may be appropriate to supply readily usable energy to the horse as it is going down the trail. Horses performing at this level of exercise will benefit from electrolyte supplementation as needed to replace the electrolytes lost with prolonged sweating.

Feeding recommendations for competing in endurance rides or other low-intensity, long-duration exercise:

Feed a quality grass hay on an ad lib basis with free-choice access to water. Endurance exercise is best fueled by a moderate to high fat (8-12% fat) and fiber diet. Feeds containing high-quality soluble fiber sources like beet pulp, soy hulls, and alfalfa meal are ideal. For easy keepers or overweight horses that don’t need a high-fat diet, withholding feed six hours prior to exercise can help release internal body stores of fatty acids to fuel this type of exercise.

The modern endurance horse is traveling at much faster speeds, requiring careful balance of nonstructural carbohydrates and fat in the diet. The traditional low-protein, high-fat feed may not be the best option for these high-performing endurance horses.

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