AAEP 2003: Nutritional Considerations for Athletic Horses

"Few will dispute that nutrition is important for optimizing athletic performance in horses," began Ray Geor, BVSc, PhD, Dipl. ACVIM, at the AAEP Horseman's Day. "However, there tends to be less agreement among horsemen, nutritionists, and veterinarians regarding the most important nutritional consideration for athletic horses."

He said the main consideration is whether the diet meets the horse's nutritional needs, meaning adequate water, energy (calories), fiber, minerals (e.g. calcium, phosphorus, selenium), and vitamins. "For athletic horses, energy is the most important nutritional consideration," said Geor. "Energy is not a nutrient per se, but rather a measure of a feed's potential to fuel body functions."

The four main sources of energy in horse rations are:

Fermentable carbohydrates--components of dietary fiber or roughage that cannot be digested by the horse's enzymes, but can be fermented by microorganisms in the hindgut;

Hydrolyzable carbohydrates--simple sugars and starch that are digested by the horse's enzymes in the small intestine, yielding (mostly) glucose;

Oils and fats;

Protein--not primarily fed as an energy source because metabolism of protein to usable energy is inefficient.

The National Research Council (NRC) guidelines for feeding horses use a classification of activity level as light (leisure, trail), moderate (reining, cutting, show horses), or intense (race, endurance). Geor said NRC values might over- or under-estimate dietary needs by 25%, resulting in a horse that is over- or under-fed. The most reliable method to measure body weight is by using a scale, but horse owners also can use body condition scoring, said Geor. That system assesses flesh coverage--mostly fat--over different parts of the body. In the system, the score of 1 indicates extremely thin and 9 obese.

"For most athletic horses, body condition should be between a score of 4.5 and 6.0," said Geor. He added if a horse is under 4 or over 6, then potentially his performance could be affected.

He said research has shown that endurance horses with body condition scores under 4 showed reduced energy stores, decreased muscle mass and strength, and were more likely to be pulled out of an endurance race. Horses over a score of 6 had "dead weight," he said. "In hot climates, extra fat can be compromising because of the insulating effect of fat," he explained.

Meeting Energy Needs
Forage is the ideal feed for the horse's gastrointestinal (GI) system, but the dietary energy needs of horses in moderate and heavy work cannot be met by forage alone, said Geor.

The horse's small stomach, which has a capacity of about two gallons, is only a small percentage of total GI volume, and it is designed for trickle feeding. The cecum and large colon have 70% of the total GI tract capacity. That is where most of the digestive work occurs for the hay or pasture feeding situation.

Fiber/forage are important for several reasons, including maintenance of normal hindgut function. In fact, horses with a low fiber/high grain (concentrate) diet might be at increased risk for some behavioral vices, colic, ulcers, and chronic tying-up, noted Geor.

Horses need a minimum of 1-1.5% of their body weight per day as forage, which is about 17-18 pounds for an 1,100-pound horse. A normal horse can take in 2-2.5%, he added.

Starch Pros and Cons
The traditional diet for horses has consisted of cereal grains such as oats, corn, and barley. Starch (a hydrolyzable carbohydrate) is a primary component of cereal grains. Digestion of starch (mostly in the small intestine) provides glucose, an important energy source for an athletic horse. However, there is evidence that the horse has a limited capacity to digest and absorb starch (and perhaps other simple carbohydrates) from the small intestine. When starch is not broken down or absorbed in the small intestine and escapes to the large intestine (hindgut), rapid fermentation by bacteria there can cause lactate accumulation, excess gas production, and increased risk of colic.

Dietary Fat
The ideal amount of dietary fat for horses has not been determined, noted Geor. Conventional horse feeds are low in fat, but fat is highly digestible and palatable. For example, greater than 90% of vegetable oils are digested in the small intestine. And, Geor added, there is no substantial change in digestibility of other nutrients even when greater than 10% of the total diet by weight is fat.

Also, some sources of fat are rich in omega 3 fatty acids. "Those fatty acids seem to have potential health benefits for horses," said Geor. "In humans, the fish oil might be anti-inflammatory and fight heart disease. In horses, there is some interest in feeding flax/linseed as an anti-inflammatory, and there might be some advantages for reproductive function. In the next few years we'll know more about what these things do and how much we need to feed to get these benefits."

The suggested upper limit of adding fat to the diet is 100 grams (a half-cup) of oil per 200 pounds of body weight per day, up to 2 1/2 cups per day for a 1,000-1,100-pound horse. Geor said if oil is added to a ration, then additional vitamin E should also be added at the rate of 200 IU vitamin E per cup of oil added.

Instead of using oil, rice bran can be fed at up to five pounds per day. Rice bran is high in calcium and low in phosphorus, said Geor, so don't overuse rice bran in growing horses because of a potential nutrient imbalance that could cause disorders of bone metabolism.

Sugar beet pulp might have some of the same metabolic benefits as feeding a high-fat diet to horses, said Geor. Beet pulp can be fed at up to 3.0 grams per kg body weight per day, or more than three pounds per day for a 1,100-pound horse. Geor said there have been no adverse effects noted with overall nutrient utilization.

About the Author

Kimberly S. Brown

Kimberly S. Brown was the Publisher/Editor of The Horse: Your Guide To Equine Health Care from June 2008 to March 2010, and she served in various positions at Blood-Horse Publications since 1980.

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