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The nutritional demands of endurance horses are unique because their events often require them to perform for many hours a day. Meeting their requirements for energy will help these equine athletes compete to the best of their ability.

Of the feeds offered to endurance horses, forage is by far the most important. Horses have evolved as grazing animals and have a unique ability to take in large amounts of forage. Through the action of bacteria in the hindgut, the horse utilizes this forage primarily for energy production. The ability of the horse to effectively utilize forages is evident if one considers that many horses are maintained on all-forage (hay/pasture) diets. Occasionally, a competitive endurance horse can be maintained solely on good-quality pasture, but this is certainly the exception and not the rule.

In addition to being a steady source of energy for the endurance horse, forage is essential to maintain intestinal health. A diet containing large amounts of good-quality fiber can increase water consumption and provide a reservoir for both water and electrolytes. This water and electrolyte reservoir can be utilized throughout the ride to minimize dehydration and electrolyte imbalances. Finally, the presence of fiber in the digestive system can help ensure that blood is being distributed to the digestive system during the ride. This maintenance of blood flow to the digestive system aids in the ability of gut tissue to remain active and could help prevent colic.

A logical question often asked is “What type of forage do I feed my endurance horse?” To determine which type of hay to buy, one should consider the fiber, digestible energy (DE), protein and calcium content of the hay. First, to prevent digestive upset, it is absolutely essential to provide the horse’s hindgut with an adequate source of digestible fiber. This would mean maximizing the use of good-quality hay/pasture with a high NDF value and a low ADF value. Second, the digestibility and thus the DE content of any given plant decreases with maturity. Therefore, horse owners should avoid feeding extremely mature forages. Since endurance horses do not have high protein requirements and have to expend energy and use extra water to get rid of excess protein, select hay with a lower protein content (8% to 14% as fed). Finally, since chronic oversupplementation with calcium can cause problems with endurance horses, avoid high-calcium hays. With these selection criteria, the endurance horse would be well suited with free-choice access to good-quality grass hay. Mixed alfalfa/grass hay is also acceptable provided it is predominantly grass.

Most competitive endurance horses are unable to maintain body weight on all-forage diets. These horses need additional sources of energy that are usually provided by a commercial grain concentrate that provides starch, fat, fiber, and protein. There is a limit to the amount of starch that an endurance horse’s diet should contain. If more than about 5 lb of grain is fed in a single meal, the small intestine’s ability to digest and absorb the starch may be overwhelmed, and a substantial amount of the starch may pass into the large intestine. This triggers a cascade of reactions that can result in laminitis (founder) or colic.

There also is a limit to the amount of fat that can be added to the diet. First, from a palatability standpoint, horses will indicate when they have reached their peak level of fat intake by refusing to eat the feed. The threshold level of fat necessary to reach this stage varies with the horse and the type of fat; however, grain concentrates with over 20% added fat (top-dressed) are prone to feed refusal. The other limitation on the amount of fat that can be added to the diet occurs in situations where calories from fat are replacing calories from starch. These high-fat, low-starch diets can limit the amount of starch available for glycogen synthesis and actually decrease liver and muscle glycogen stores. Grain concentrates that have between 7 and 10% added fat appear optimal for endurance horses.

To obtain the best results with the addition of fat to the diet, begin adding the fat during the conditioning phase of training and continue throughout the season. This will expose the muscles to high levels of fat and condition the body to use fat as an energy source. The combination of dietary fat and fitness will allow endurance horses a greater mobilization and utilization of fat during long distance exercise. The addition of fat only on race days will be of limited value.

Just as there were limitations in the amount of starch and fat appropriate for endurance horses, so are there limits on the amount of protein. The actual protein requirement for the endurance horse is only about 8 to 10% of the total diet. This is much lower than what is usually fed to endurance horses because there are few ingredients that are this low in protein. For example, corn is around 9% protein, oats 11.5%, timothy hay 10% and alfalfa hay 15 to 20% protein. Therefore, it is not practical to restrict protein intake to the horse’s actual requirement. Instead, protein content of the ration should be monitored and not allowed to become extremely high.

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