Sarah L. Ralston, VMD, Ph.D., dACVN, Department of Animal Science, School of Environmental and Biological Sciences, Rutgers University

Fact Sheet #934 – Reviewed 2004

Feeding performance horses during conditioning has already been addressed in a previous fact sheet (FS752, 1994). Emphasis should be placed on provision of the best quality forage available free choice and feeding only as much grain or concentrates as needed to maintain desired body condition. Addition of fats (vegetable, corn or canola oils) may be beneficial, especially if the horse is having problems maintaining weight or with chronic tying up. Edible oils however, should be introduced slowly and comprise no more than 10% of the total ration (usually 1–2 cups per day). It takes at least three weeks for a horse to adjust to a high-fat diet. Free-choice salt and water are the only other real requirements. Vitamin/mineral supplements should not be necessary if a balanced ration is fed and, if used, selected carefully to prevent over-supplementation.
Ingestion of concentrates, forages, water, and electrolytes however, have immediate effects on a horse’s metabolism and potentially its performance. There have been relatively few studies that directly correlate feed management on the day of performance and subsequent exercise-related variables. However, there are sufficient data to suggest that the type of performance expected of a horse (aerobic versus anaerobic, short duration versus long) can be influenced by nutritional management on the day of competition. In this fact sheet recommendations are given for feeding horses on the day of competition for various types of performance.
Feeding for Short-Term, Anaerobic Performances
(Racing and Other Speed Events)

Short-term, anaerobic performance is that in which the horse is asked to expend maximal anaerobic effort for less than three minutes. This includes events such as Thoroughbred and Quarterhorse flat-racing and rodeo/gymkhana speed events (barrel racing, pole bending, calf roping, etc.). Glucose and glycogen are the major sources of energy used, though free fatty acids may be utilized during the warm up periods, sparing glucose and glycogen for the main effort.

During this type of exertion glucose and glycogen are the predominant sources of energy used by the working muscles. Depletion of glycogen and glucose, leading to fatigue, are the most common problems. The animal’s metabolism does not have time to mobilize body stores of energy, fluids, and electrolytes during the actual performance. Therefore emphasis should be placed obtaining maximum glucose and glycogen availability immediately before the event.

Body weight is another major consideration. Sweat losses are minimal, and gastrointestinal water content is not mobilized to replace losses during the actual competition. In race-type treadmill training, increased time to fatigue with furosemide (Lasix) was apparently due solely to decreased weight due to urinary losses (Hinchcliff et al, 1993). When urinary water losses were added back prior to exercise, there was no difference in furosemide-treated horses’ performance from saline-treated controls. High forage intake will also increase gut fill and therefore body weight.
Low blood pH also contributes to the onset of fatigue in exercising horses. Anaerobic utilization of glycogen and glucose produces lactic acid, which accumulates in the blood, lowering the pH. A meal of grain will also reduce blood pH by different mechanisms for up to four hours after feeding (Lewis, 1995).
The goal for competition-day feeding therefore should be to minimize weight, maintain optimal but not excessive hydration, and promote increased availability of glucose and glycogen.

If properly conditioned for the event, the horse should not need extra energy intake before the race. Indeed, a 16-hour fast prior to racing may actually optimize energy utilization. Horses fasted for 16 hours then subjected to a prolonged warm up followed by intense exercise had the highest muscle glycogen, plasma glucose, and free fatty acids at the end of exercise relative to when the horses were fed 1 kg corn at 1, 3, or 5 hours prior to exercise (Lawrence et al; 1995, Stull and Rodiek, 1993). If fed at all, a normal ration of concentrates without added electrolytes should be offered at least five hours or more before the competition. If warm time is very short, a small (1 to 2 lbs.) meal of sweet feed 1–2 hours before the race will result in high blood glucose and insulin. This will maximize anaerobic energy substrate (glucose, glycogen) availability during the race but may inhibit fat utilization. Blood pH will also be slightly reduced, so this may not be the best strategy for horses prone to rhabdomyolysis (tying up). Not offering hay on the day of the race may reduce gut fill slightly but it will also increase the duration and magnitude of the reduction in blood pH associated with a meal of grain or concentrates (Meyer 1996a,b; Ralston, Unpublished data, 1993-1995).
Electrolyte supplementation before the race will stimulate greater water intake and therefore gastrointestinal weight. Since sweat losses are minimal during these events, electrolyte supplementation should not be needed until after the race, if at all. However, it is not advisable to withhold access to water for prolonged periods of time since even moderate dehydration may decrease exercise tolerance. It would be better to allow the horse free-choice water, even if fasted, to permit optimal hydration.
While the horse is being cooled out after the race, it is advisable to offer small amounts (0.5-1 gallon) of warm water at frequent intervals until the horse is no longer thirsty. Do not allow free-choice access, especially to cold water. Electrolytes should not be added to the water, as that may reduce intake. After the horse has “cooled out” from the race (heart and respiration rates normal and no longer sweating), it should be offered free choice hay. Feeding small (1– 2 lbs.) amounts of grain hourly for the next 6-8 hours may enhance replenishment of glycogen stores. If the normal grain intake is more than doubled by this technique, however, there may be an increased risk of colic or laminitis.
Bicarbonate administration (up to 1 lb. sodium bicarbonate/1000 lb. horse in 1 gallon of water by nasogastric tube) may reduce the metabolic acidosis induced by intense anaerobic efforts. However, especially at the higher doses tested, bicarbonate administration caused persistently low blood potassium and calcium, which may be more detrimental to performance than moderate metabolic acidosis (Frey et al, 1995; Lewis, 1995). Administration of bicarbonate in any form is illegal in most racing jurisdictions and is not recommended.
Vitamin supplementation on the day of competition has not been reported to be of benefit in horses fed balanced rations.
Feeding During Long-Term, Aerobic Performances
(Endurance, Dressage, Horse Shows)

Long-term, aerobic performance is that in which the work is primarily aerobic and lasts for more than one hour. This includes endurance, competitive trail riding, dressage, three-day events (riding and driving), and horse shows in which horses are entered in multiple classes and often are worked hard before entering the ring. These animals are working primarily on an aerobic basis, generating huge heat loads and sweat losses. These athletes rely heavily on free fatty acids from large intestinal fermentation of forage and mobilization of body fat stores as energy sources. Glycogen and glucose stores are not of as great a concern as in short-duration, anaerobic work, though they are utilized.
Maintenance of hydration, optimal mobilization and utilization of body energy stores (fats) and fatty acids from the gastrointestinal system, and electrolyte balance are the main goals for this type of work, especially in multi-day or endur-ance-type events.
For these horses, feeding large amounts of grain with limited access to hay may increase the risk of metabolic failure, especially for endurance type competitions (Ralston, 1988). A meal of grain will cause insulin release, which inhibits the mobilization and utilization of fats. High circulating insulin will also drive glucose into the working muscle cells more quickly. It has been reported to cause hypoglycemia (low blood glucose) after 1 to 2 hours of moderate aerobic exercise (Lawrence et al, 1995). The night before an event hay should be offered free to maximize intestinal reservoirs of energy, water and electrolytes and the normal amount of grain or concentrates offered. If grain or other forms of concentrates are offered the morning of or during competition, they should be low fat (<5%) and supplemented with an electrolyte mix formulated specifically for equine athletes. The amount of electrolytes given will depend on anticipated heat, humidity, and duration of the exercise, usually 1–4 ounces will suffice.

Electrolytes will stimulate thirst and increase water intake within 3–4 hours of dosing. If top dressed on the concentrates, however, they may reduce intake, so they may need to be force fed. Grain, especially sweet feeds, should not be fed less than four or five hours before the competition starts unless the competitor plans to feed small amounts (0.5–1 lb. per feeding) of these feeds frequently (at one- to two-hour intervals) during actual competition.
Supplementation with electrolytes every 2 hours during competition will help maintain electrolyte status (Ralston and Larsen, 1989; Schott et al, 1997). However the amounts needed are controversial and vary dramatically with climatic conditions, terrain, and fitness of the horse. A general rule of thumb is to give 30 to 90 g per hour of work. However, concentrated electrolyte solutions should not be force fed to horses that are dehydrated as this potentially will compound the dehydration by drawing body water into the gastrointestinal system and cause abdominal malaise. Horses should be encouraged to drink at every opportunity, though rapid ingestion of large amounts of cold water should be avoided if the horse is not going to immediately continue to work. Placing a small amount of sodium chloride on the gums of a horse may also encourage drinking.
In high heat and humidity, high-protein forages such as alfalfa probably should be restricted, since the protein used for energy releases a higher metabolic heat increment than does starch or fatty acids (Lewis, 1995). However, mashes made of soaked hay cubes or bran to which electrolytes are added are excellent ways to get the horse to ingest more fluid and electrolytes. Though alfalfa cubes and bran are both fairly high in protein (about 16%), if fed in restricted amounts (1 lb. cubes, ¼ to ½ lb. bran) the increased water and electrolyte intake plus provision of readily fermentable fiber sources will outweigh the detriments of high protein. Many competitors add apples or carrots to mashes to enhance palatability. Fats and oils should not be supplemented during competition since they will delay gastric emptying and may impede absorption of electrolytes.
While forage/roughage intake should be emphasized, dry hays may compound dehydration problems, especially in horses at multi-day events, if the horses were accustomed to being on lush pasture at home. Soaking hay in water may alleviate this potential problem during competitions. Administering fluids by nasogastric tube may be beneficial in cases of severe losses during multiple-day competitions (if allowed by the competition rules). If at all possible, the horses should be allowed to graze as much as possible.
Most horses performing prolonged, aerobic work have high blood pH and minimal accumulation of acid in blood. Lactate accumulation is not a problem if the horses are properly conditioned. Therefore, administration of sodium bicarbonate is strictly contradicted before, during, or after competition.
After competition is completed, offering free-choice hay soaked in water, small amounts of grain (0.5–1 lb.) at frequent intervals (every 1-2 hours for up to 8 hours) and additional electrolytes will hasten the horse’s recovery. Do not offer grain or concentrates until the horse has been cooled off and its heart rate is back to normal. This is especially important in multi-day events.


Though vitamin supplementation has not been investigated in this type of competition, prolonged stress such as 12 hours of transport resulted in below normal plasma vitamin C relative to non-transported horses (Baucus et al, 1990). Though horses do not normally require dietary ascorbic acid, during periods of prolonged stress (>12 hours), addition of 10 grams of vitamin C twice a day during the competition will not hurt and may help.

Knowledge of the predominant nutritional concerns for a given type of competition will aid in the selection of feeds and supplements for the day of competition. For example, electrolyte supplementation is critical in endurance horses on the day of performance but is probably not necessary and may be contraindicated for the Thoroughbred racehorse. Fasting racehorses up to 16 hours before the competition may improve energy substrate availability whereas horses performing prolonged aerobic work need intestinal sources of nutrients (e.g., hay offered free choice the night before and morning of competition) to maintain adequate energy, fluid, and electrolyte status.
Selected References

Baucus KL, Ralston SL, Nockels CF, McKinnon AO, Squires EL. 1990. Effects of transportation on early embryonic death in mares. J Anim Sci. 68:345-351.

Dalhorn K, Jannson A, Nyman S, Lindholm A. 1994. Effects of dehydration and hyperhydration on fluid balance in the exercising Standardbred. In: Clarke AF, Jeffcott LB, eds: On to Atlanta ‘96, Equine Research Centre, Guelph, Ontario. pp52-57.

Danielson K, Lawrence LM, Siciliano P, Powell D, Thompson, K. 1995. Effect of diet on weight and plasma variables in endurance exercised horses. Equine Veterinary Journal Suppl. 18:372-377.

Frey LP, Kline KH, Foreman JH, Brady AH, Cooper SR. 1995. Effects of warming up, racing and sodium bicarbonate in Standardbred horses. Journal of Equine Veterinary Science Suppl.18:310–313.

Hinchcliff KW, McKeever KH, Muir WW, Sams R. 1993. Effect of furosemide and weight carriage on energetic responses of horses to incremental exertion. American Journal Veterinary Research 54:1500–1503, 1993.

Lawrence LM, Hintz HF, Soderholm LV, Williams J, Roberts AM. 1995. Effect of time of feeding on metabolic response to exercise. Equine Veterinary Journal Suppl. 18:392–395.

Lewis LD. 1995. Equine Clinical Nutrition. Williams and Wilkins, Philadelphia, Pa. ISBN 0-683-04962-3, 587pp.

Meyer H. 1996a. Influence of feed intake and composition, feed and water restriction, and exercise on gastrointestinal fill in horses, Part 1. Equine Practice 18(7):26–29.

Meyer H. 1996b. Influence of feed intake and composition, feed and water restriction, and exercise on gastrointestinal fill in horses, Part 3. Equine Practice 18(10):25–28.

Ralston SL. 1988. Nutritional management of horses competing in 160-KM races. Cornell Vet. 78:53–61, 1988.

Ralston, SL, Larson K. 1989. The effect of oral electrolyte supplementation during a 96-kilometer endurance race for horses. Journal of Equine Veterinary Science 9:13–19, 1989.

Schott HC, McGlade KS, Hines MT, Petersen A. 1997. Body weight, fluid and electrolyte and hormonal changes in horses that successfully completed a 5-day, 424 kilometer endurance competition. Equine Athlete 10:40–44.

Stull C, Rodiek A. 1995. Effects of postprandial interval and feed type on substrate availability during exercise. Equine Veterinary Journal Suppl. 18:362-366.