When to Feed Your Athlete

What is the best feeding practice for horses before competition exercise or a hard training session? There is no real consensus on this issue and, similar to the field of human performance nutrition, there are many opinions on what is best. Some trainers will withhold all feed, some will decrease the amount of hay fed, and others will increase the amount of grain or other high-energy feed provided. These strategies are aimed at extracting the very best performance from the horse on the big day. Others argue that horses function best when there are minimal changes in routine, and favor no change in feeding practices.

Who's right? In part, the answer depends on the type of exercise to be undertaken, i.e., the best strategy for an endurance or three-day event horse is likely different from that best applied to the Thoroughbred racehorse. In all situations, however, there are two main considerations. First, how will a particular feeding strategy affect the availability of energy for physical work? Second, does that strategy have a positive or negative effect on performance and health?

Maximize Energy Stores

The first question to address when discussing pre-competition feeding management is, "Why should the horse's diet be altered?" We are all aware of the potential perils associated with rapid alterations in the horse's diet or pattern of feeding--such changes can precipitate digestive upsets and colic. Thus, drastic changes in diet are never recommended. On the other hand, more subtle alterations in management and feeding practices can be safely used to maximize the horse's fuel stores and optimize use of these fuels during exercise.

There are two time periods to consider-- 1) the one to two days before competition exercise; and 2) the six- to eight-hour period before the horse begins to exercise.

For galloping exercise, muscle glycogen is by far the most important fuel for muscle contraction. During racing, muscle glycogen probably provides more than 80% of the energy. There also is evidence that low muscle glycogen will impair high-intensity exercise performance.

In the days leading up to competition, there should be a tapering of the horse's training program. Hard, prolonged exercise places heavy demands on glycogen reserves in the liver and muscle. During prolonged exercise (e.g., endurance rides), inadequacy of glycogen reserves can limit exercise performance. For shorter-duration exercise (e.g., racing), carbohydrate supply is not normally limiting. However, very low muscle glycogen stores will impair sprint exercise performance. Thus, regardless of the discipline, adequacy of body carbohydrate stores is important for optimal exercise performance. A gradual reduction in training efforts, together with maintenance of the horse's regular diet, will help to ensure that liver and muscle glycogen stores are near optimal levels before the horse is asked to undertake hard exercise.

Grain's Effects on Fuel Metabolism

The feed a horse consumes in the six- to eight-hour period before exercise has only a small impact on energy stores. However, the hormonal fluctuations associated with the digestion of that meal can change the mix of fuels used during exercise. The fuel used by muscle during exercise is largely dictated by the intensity and duration of the work effort. During very fast exercise (e.g., racing), fuels stored within muscle--particularly glycogen--provide most of the energy. On the other hand, when a horse undertakes lower-intensity exercise, other fuels, such as blood glucose and fats, play a bigger role. For endurance exercise, it is to the horse's advantage to utilize fat as this will help to preserve more precious reserves of glucose and glycogen. Remember, the depletion of carbohydrate stores will contribute to the development of fatigue.

When a horse eats a grain meal, first the starch and sugar are broken down into glucose units in the small intestine and absorbed into circulation. Following a 2.2-4.4 pound (1-2 kg) meal of oats, corn, or sweet feed, the peak in blood glucose concentration generally occurs about two hours after feeding. This delay reflects the time required for movement of food from the stomach into the small intestine, breakdown of starch to glucose, and absorption of glucose.

There is also a spike in the hormone insulin (released from the pancreas), which promotes the use or storage of glucose that has just entered the body, so that blood glucose levels begin to decrease. Normally, blood glucose and insulin return to baseline levels by about five hours after a grain meal. So, eating a grain meal (e.g., oats, corn, or a grain mix such as sweet feed) one to four hours before exercise will result in elevated blood concentrations of glucose and insulin at the onset of exercise.1,2 However, if a grain meal is eaten five or more hours before exercise, blood glucose and insulin concentrations will be near baseline when exercise begins.

If blood glucose and insulin are elevated at the start of exercise, there can be a rapid fall in blood glucose, reflecting a marked increase in the rate of glucose uptake by muscle. Some researchers believe that this decrease in blood glucose is detrimental to performance. However, this drop in glucose levels can be short-lived and does not necessarily decrease performance.

In a recent study, horses were fasted for 24 hours or given either a meal of alfalfa cubes or about four pounds of cracked corn two hours before exercise.3 Horses then did one hour of moderate-intensity treadmill exercise. Although blood glucose concentrations did decrease in the corn-fed horses during the first 10-20 minutes of exercise, blood glucose subsequently increased during the remainder of the trial. Overall, utilization of blood glucose in the corn-fed horses was higher compared to fasted horses or when they were fed alfalfa cubes.

Insulin not only drives the use of blood glucose, but also suppresses the use of fat--insulin blocks release of fatty acids from stores in adipose tissue and limits the rate of fatty acid metabolism in muscle. When compared to horses which are fasted or fed forage, horses fed grain or given glucose before exercise have lower blood fatty acid concentrations during exercise. Thus, grain meals that result in a large increase in blood glucose (a high glycemic response) before exercise will shift fuel utilization away from fat toward carbohydrate.

Now, whether this "shift" in metabolism is good or bad is a bit contentious. Critics of pre-exercise grain feeding argue that the decrease in fat use, with a concurrent increase in carbohydrate metabolism, will lead to early fatigue--the horse literally runs out of fuel. However, the true impact of a grain meal will depend on the type of exercise to be undertaken.

For high-intensity, short-duration events, use of fat for fuel is minor in comparison to glucose. Therefore, a decrease in fat utilization might not affect performance. Some argue that giving sugar to the horse two to three hours before a race will enhance performance, although as yet there is no scientific proof that it does. On the other hand, for endurance-type activities where the combined use of fat and carbohydrate is desirable, it is probably wise to avoid grain meals in the period one to four hours before the start of competition exercise.

Much less is known about feeding one hour or less before exercise. Of course, endurance horses are routinely fed at rest stops during rides. In this circumstance, the interval between feeding and the start of exercise is usually less than 45 minutes. Even when grain is fed, there will be minimal increase in blood insulin during this short interval between feeding and exercise. Whether or not the starch in this meal is digested and absorbed (as glucose) during exercise is not known. Continued digestion and absorption of glucose would help to maintain the supply of blood glucose during a time when the horse's supply of liver and muscle glycogen is waning.

Feeding Hay Before Exercise

The potentially negative effects of pre-exercise grain feeding (i.e., suppression of fat utilization and increased reliance on carbohydrates for energy) are manifested through the effects of insulin. Thus, feeds that can provide fuel without causing a large increase in insulin (low glycemic feeds) would be desirable in a pre-exercise meal for horses. The best example of a low-glycemic feed is forage (hay or old grass, not new spring grass). Consumption of a hay meal before exercise has minimal effects on blood glucose, insulin, and fatty acid concentrations, and it does not greatly influence the mix of fuels used during exercise. So, in some circumstances, hay is a better choice as a pre-exercise meal.

Logically, however, it is not a good idea to allow horses to chow down on a bale of hay in the few hours before heavy or prolonged exercise. Horses secrete large amounts of saliva during chewing, and this fluid is swallowed along with the food material. In addition, arrival of food in the stomach and intestinal tract stimulates fluid secretions into the gut. These salivary and intestinal secretions are drawn from elsewhere in the body and actually result in a reduction in plasma (a blood component) volume. This decrease in plasma volume is temporary because virtually all of the secreted fluid is reabsorbed by the large intestine. Nonetheless, consumption of a large hay meal (six pounds, 2.7 kg, or more) within two hours of exercise will result in up to a 15% decrease in plasma volume that persists until the start of exercise.

Such reductions in plasma volume might compromise cardiovascular function during both low- and high-intensity exercise. Presence of a large meal within the digestive tract also alters the pattern of blood flow within the body--more blood is directed to the intestinal tract, potentially limiting blood flow to muscles during exercise. Therefore, large meals--forage, grain, or a combination--are not recommended within five hours of competition exercise. However, small hay (or grass) meals (around 2-4 pounds, or 0.9-1.8 kg) do not result in large fluid shifts and can be fed during this time interval before exercise.

For endurance horses (or horses engaged in other types of prolonged exercise), consumption of forage four to six hours before an event might be beneficial. For every 2.2 pounds (1 kg) of dry hay intake, horses will consume up to one gallon of water. Within the large intestine, the fiber in hay and other forages "holds" this water, and this reserve of water (along with electrolytes) might be available for absorption during exercise, helping to offset fluid and electrolyte losses in sweat. In general, high-fiber diets are recommended for endurance horses because of the associated increase in size of the gut water and electrolyte reservoir.

In contrast to the endurance horse, racehorses will not benefit from consumption of a high-fiber meal in the hours preceding competition. In fact, such practices might adversely affect performance. The amount of energy expended by the horse at any speed depends on how much total weight it carries. At any given intensity or speed of exercise, additional weight requires more energy. If a racehorse consumes 4.4-6.6 pounds (2-3 kg) of hay and has access to water, gut fill and body weight will increase by up to 26 pounds (12 kg).

Increasing weight carriage (adding lead weights to the tack) in Thoroughbred racing is a proven method of handicapping. Therefore, a large increase in body weight will almost certainly be detrimental to high-speed exercise performance. In fact, it's common to limit or eliminate hay feeding on the day of the race--and some will even reduce hay intake for two to three days before a race in an attempt to effect weight loss (reduced gut fill) in their charges. This is a reasonable practice providing the horse receives a minimum of 1% of his body weight in fiber per day to avoid digestive upsets.

What About Gastric Ulcers?

Gastric ulcer disease is very common in athletic horses, particularly racehorses. Among other factors, the "stress" of athletic training and diet (high-concentrate diets) has been implicated in the development of stomach ulcers. There also is new information to suggest that exercise might directly affect stomach health. A recent study at the University of Florida4 demonstrated that the stomach is compressed during intense exercise such that the upper squamous-lined region of the stomach (where ulceration is most common) is exposed to acidic contents (see "Exercise and Ulcers; Is It the Norm?" on page 24). This acid exposure associated with exercise might be the reason why stomach ulcers tend to develop or worsen when horses are in intensive training programs.

An unresolved question that requires further study is whether feeding before exercise helps to minimize this "acid splashing." It is possible that eating a small hay meal before exercise might help buffer stomach acid and reduce exposure of the squamous mucosa to acid during exercise.

Recommended Feeding Strategies

As stated at the outset, there is no easy answer to the question, "What should I feed my horse before exercise?" Nonetheless, based on our current level of understanding, the following recommendations can be made for selected athletic events.

Racehorses--Gut fill is a prime concern when feeding racehorses. Reducing hay intake to 1% body weight for a three-day period before a race will effectively reduce body weight without causing digestive upset. Timing of grain feeding is not as critical for racehorses, but pre-exercise grain meals should be small in size (1.1-2.2 pounds, or 0.5-1 kg) and fed no later than four hours before a race. A small hay meal might be advisable given new evidence regarding the effects of exercise on stomach function.

Three-day event horses--As the speed and endurance test begins early in the day, morning grain feeding isn't recommended--high pre-exercise insulin and glucose might limit fat oxidation and increase reliance on carbohydrates for energy. On the other hand, feeding the horse a high-glycemic meal (grain) or administering glucose after finishing Phase D might help restore muscle glycogen faster. More rapid replenishment of muscle glycogen stores could be beneficial to performance during stadium jumping on the following day.

Endurance horses--Forage intake should be high because of the associated increase in size of the water and electrolyte reservoir in the hindgut. However, as with other disciplines, large hay meals should not be fed within four hours of competition. Also, grain meals should be fed four to six hours before competition. A high-glycemic meal the night before a race is warranted to "top up" liver glycogen stores. High-quality forage (such as alfalfa) should be offered at rest stops/check points. Feeding small grain meals (about 2.2 pounds, or 1 kg) immediately before exercise or at rest stops might be beneficial--this practice will not disrupt fat utilization and might supply carbohydrates during exercise.

Getting your horse's diet and feeding schedule ready before an event, just as you do with your equipment and training schedule, can help him come out on top.


1 Lawrence, L.; Soderholm, L.V.; Roberts, A.; Williams, J.; Hintz, H. Feeding status affects glucose metabolism in exercising horses. Journal of Nutrition, 123, 2152-2157, 1993.

2 Pagan, J.; Harris, P. The effects of timing and amount of forage and grain on exercise response in Thoroughbred horses. Equine Veterinary Journal, Supplement 30, 451-457, 1999.

3 Jose-Cunilleras, E.; Hinchcliff, K.W.; Sams, R.A.; et al. Glycemic index of a meal fed before exercise alters substrate use and glucose flux in exercising horses. Journal of Applied Physiology, 92, 117-128, 2002.

4 Lorenzo-Figueras, M.; Merritt, A.M. Effects of exercise on gastric volume and pH in the proximal portion of the stomach of horses. American Journal of Veterinary Research, 63, 1481-1487, 2002.


See the Feeding High-Performance Horses category under Nutrition/Supplements, and the Ulcers category under Ailments/Syndromes, at www.TheHorse.com.

West, C. Feeding Management for Stressful Situations. The Horse, November 2002, 19. Article #3910 at www.TheHorse.com.

About the Author

Ray Geor, BVSc, PhD, Dipl. ACVIM

Ray Geor, BVSc, PhD, Dipl. ACVIM, is professor and chairperson of Large Animal Clinical Sciences at the College of Veterinary Medicine at Michigan State University

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