Feeding the Endurance Horse
The nutritional needs of the endurance horse are somewhat unique compared to horses used for other athletic disciplines. The metabolic demands of endurance racing (including competitive trail riding and ride and tie events) are high, requiring the horse to draw heavily upon his energy reserves to fuel muscle contraction and other body functions during exercise. As well, very large sweat fluid losses mandate aggressive replacement strategies to keep the horse hydrated during this extended exercise. Most importantly, we know that depletion of energy reserves, dehydration, and electrolyte imbalances can all contribute to poor performance and fatigue during endurance exercise. Therefore, optimal endurance exercise performance is critically dependent on sound nutritional management.
In this article, we will discuss feeding the endurance athlete, emphasizing the nutrients of greatest importance, as well as feeding management before, during, and after events.
Endurance racing, competitive trail rides, and ride and tie competitions are extremely popular equine sports. Currently, the American Endurance Riding Conference (AERC) sanctions more than 700 rides each year throughout North America. This popularity has spread worldwide--in 1978 the Federation Equestre Internationale (FEI) recognized endurance racing as an international sport, and in 1993 endurance racing became the fifth discipline under the United States Equestrian Team (USET). In the early years of international competition, teams from the United States and Canada were dominant. Today, however, teams from several countries--notably France, the United Arab Emirates, Australia, and New Zealand--are extremely competitive. This intense competition has "raised the bar" in terms of the athletic demands placed on the successful endurance horse.
These demands are highly dependent on race distance, course footing and terrain, and running speed. Most endurance rides range from 25 miles to 100-plus miles (40 to 160 km) per day, and there are a few multi-day events with a total distance of 250 or so miles (400 km). When major elevation changes (uphill and downhill running), soft footing, and a brisk running speed are factored into the equation, it is easy to appreciate that an endurance horse must "burn" a large quantity of its fuel stores to provide energy for muscle contraction. Indeed, average running speeds of the top-placing horses at some recent international competitions have been astounding--upwards of 13.5 to 14 miles per hour (21.6 to 22.4 km/hour or 360 to 373 meters/minute), with much of the distance covered at a medium canter.
There are two main fuel stores: 1) carbohydrate in the form of muscle and liver glycogen (the storage form of glucose); and 2) fat, which is stored in adipose (fat) tissue throughout the body and in muscle. While protein can be broken down for energy, it is not a primary fuel source. Therefore, the availability of fat and glucose (from glycogen) and the efficiency of utilization of these fuels are of primary importance for the endurance horse.
The typical endurance horse is fairly small (900 to 1,100 pounds or 405-495 kg), and he has lean, physical attributes that favor efficiency of movement and thermoregulation. Heavy, over-conditioned horses tend to do poorly in endurance competitions, perhaps due to a greater risk for lameness problems and metabolic failure associated with inefficient thermoregulation and heat exhaustion. On the other hand, very thin horses also might be at a major disadvantage during long endurance rides (e.g. more than 75-80 miles or 120-128 km) because they have less energy reserves stored as fat.
Two recent studies investigated the relationship between body condition score and completion rate during the Tevis Cup (100-mile) endurance ride. The standard body condition scale of 1 to 9 was used, where a score of 1 is applied to very thin horses and 9 to extremely fat horses (see Garlinghouse and Burrill 1999). The mean body condition score of horses which successfully completed the ride was 4.5, whereas horses which were eliminated for metabolic failure (colic, heat exhaustion, synchronous diaphragmatic flutter/thumps, or tying-up) had a mean condition score of 2.9. Horses which were eliminated for non-metabolic reasons such as lameness and going over time had a mean condition score of 4.3. (For more information on body condition scores, see "Weighing In" in the October 2000 issue of The Horse, online at http://www.thehorse.com/ViewArticle.aspx?ID=111.)
The researchers were careful to point out their results might not apply to endurance competition as a whole given the difficult nature of the Tevis Cup. Nonetheless, the take-home message from these studies is that there is an optimal level of "fatness" for horses competing in endurance events, and that training and feeding programs need to be adjusted accordingly. Thin horses (with a condition score of less than 3) might be at a disadvantage because of low energy reserves, while over-conditioned horses could experience detrimental effects due to the insulating effect and weight of a thicker fat cover. You should aim for a body condition score between 4 and 5.
The nutritional factors of critical importance to the endurance horse are energy, water, and electrolytes. Dietary energy is expressed in terms of megacalories (Mcal) of digestible energy (DE), which is the amount of energy contained within feed that is actually absorbed by the horse. The National Research Council (1989) set energy requirements based on body weight and activity level. For example, a 450-kg (990-pound) endurance horse has a maintenance DE requirement of 14.9 Mcal per day based on the formula:
DE(maintenance) = 1.4 + (0.03 x body weight in kg)
Researchers have also estimated the energy requirements associated with different intensities of exercise, taking into consideration the energy cost of carrying a rider (see "Digestible Energy Requirements for Carrying Weight" on page 64). For this 450-kg horse to complete three hours of exercise at an average speed of 300 meters/minute (18 km/hour) while carrying 75 kg (165 pounds) of rider and tack, the additional DE requirement is more than 21 Mcal (525 kg x 0.0137 x 3 hours = 21.6 Mcal). Add the 21.6 to the 14.9 and you get a total DE requirement of approximately 36.5 Mcal per day.
This arithmetic gives us a rough estimate of the DE requirements for an endurance horse at work. However, he will not "burn" this many calories every day. Rather, his DE needs will depend on the amount of training and racing during a given period. As a general rule, an endurance horse in training will need about 30 Mcal of DE per day to maintain body condition. It is important to assess body condition on a regular basis and adjust energy intake (and perhaps training volume) accordingly, shooting for a body condition score between 4 and 5.
If you are regularly read The Horse, you will recall that energy is provided by four components--starch, fat, fiber, and protein (see "High-Energy Feeds" in the June 2001 issue of The Horse, online at http://www.thehorse.com/ViewArticle.aspx?ID=37). A balance of these nutrients is required for an endurance horse, but with emphasis on high-quality fiber and fat. Forage and other sources of high-quality fiber should be the dietary mainstay (and provided free-choice), since adequate dietary fiber is essential for maintaining gut health. Studies have shown that a high-fiber diet can help the horse stave off the detrimental effects of sweat fluid losses during prolonged exercise.
Researchers at the University of Kentucky recently compared fluid balance in one group of horses which tried two diets, one high in fiber-containing feedstuffs (80% fiber provided by orchard grass hay and beet pulp), the other lower in fiber (50% fiber provided by alfalfa and wheat bran). Water intake was about 1.5 gallons/day (six liters/day) more when the horses consumed the high-fiber diet, resulting in a larger fluid volume in the gastrointestinal tract--this reflects the water-holding capacity of fiber. It is thought that this fluid can be absorbed from the gut during long exercise, helping the horse maintain hydration and electrolyte balance.
Not all fiber sources are created equal. Very mature hay contains large amounts of lignin (a non-digestible fiber) and has a low DE value. The protein and calcium content of the hay is another consideration. For the most part, endurance horses require a diet that is about 10-12% protein. Therefore, an 8-14% protein hay will be appropriate. For example, if the horse is eating about 13 pounds (5.85 kg) of a 12% protein concentrate and 17 pound (7.65 kg) of timothy hay that is 8.5% protein, the overall diet (65% forage, 35% concentrate) is about 10% protein. Therefore, an early- to mid-cut grass hay will fit the bill.
In general, alfalfa is not an ideal choice for endurance horses. Feeding some alfalfa is okay (e.g. up to half of the forage allowance), but many endurance riders avoid an all-alfalfa diet because of concerns about high protein and calcium intake. A higher-protein diet can increase urine production because of the need to excrete the extra nitrogen. In turn, the higher urinary water loss increases water requirements and perhaps exacerbates dehydration during exercise. In my opinion, the protein issue has been over-emphasized, but it is probably safest to go with alfalfa with no more than 50% of the forage component.
It has been proposed that horses are more prone to thumps (synchronous diaphragmatic flutter) when fed an all-alfalfa diet--thumps is triggered by drastic changes in blood electrolyte balance, including calcium. (Alfalfa is high in calcium.) The theory goes that the horse is less able to mobilize body calcium reserves during exercise when fed a diet high in calcium. Again, this is less of a concern when alfalfa is mixed with a grass hay. (For more information on thumps, see "Dehydration Alert!" in the July 2001 issue of The Horse, online at http://www.thehorse.com/ViewArticle.aspx?ID=908) However, a 75% grass/25% alfalfa diet is an acceptable compromise.
Of course, wherever possible, the horse should have daily access to pasture. The balance of the horse's energy requirements will come from some type of grain concentrate. A combination of cereal grains, vegetable fat, and a vitamin-mineral supplement, such as that provided by many performance horse feeds, is suitable. Some beet pulp, a highly digestible fiber source, can be added to the mix. The starch in cereal grains will provide glucose for replenishment of glycogen stores (remember that the energy from fat and fiber are not used as much for this purpose). Keep in mind that for all horses, individual grain meals should be no larger than five to six pounds (2.25-2.7 kg) to avoid digestive upsets.
The grain concentrate should contain fat at a 6-10% concentration (found in many commercial feeds). At typical intake rates (e.g., 10 pounds or 4.5 kg of grain concentrate per day), this will provide a significant amount of energy. Introduce fat when the horse begins conditioning. Training results in an increased capacity to utilize fat during endurance-type exercise, and there is some evidence that this effect is enhanced by a higher-fat diet (see "Fat Burning" in the November 2000 issue of The Horse, online at http://www.thehorse.com/ViewArticle.aspx?ID=96).
Liquid and Electrolyte Losses
Water and electrolyte replacement is equally important for the endurance horse. I refer you to an earlier article for a detailed discussion of this subject (see "Fluids and Electrolytes" in the April 2000 issue of The Horse, online at http://www.thehorse.com/ViewArticle.aspx?ID=214). Suffice it to say that plenty of fresh water must be available at all times and, during rides, the horse must be offered water at frequent intervals, especially in hot weather (e.g. every 30-40 minutes). Electrolytes must be supplied as they are easily lost in sweat and are necessary for maintaining proper fluid balance, acid-base balance, and nerve activity.
Endurance riders and trainers employ various methods for administration of electrolyte concoctions. Many will give electrolyte pastes via dosing syringe before and during the ride. Others will add some electrolyte to slurry-type meals fed at vet checks during the ride. Remember that the electrolytes are given for two reasons. First, to replace the electrolytes lost in sweat and, second, to stimulate water intake so that the horse replaces fluid losses, which can approach 2.6-3.1 gallons (10-12 liters) per hour in some circumstances. Therefore, it is very important to monitor water intake during rides.
Regarding other nutritional supplements, I do think there is merit in the use of the so-called "joint supplements," particularly those containing glucosamines. The glucosamines might help maintain cartilage health, an important consideration given the wear and tear on joints in these horses. (For more on joint problems, see "Joint Disease."
Before, During, and After a Ride
In the four- to five-day period before a race, training should be light. This reduction in activity combined with regular feeding will ensure that glycogen stores are "topped up" before competition. Most nutritionists discourage the feeding of large meals, particularly grain, before vigorous exercise. For early morning starts (many rides), the last grain meal should be given the night before. However, the horse should be allowed to nibble on hay or other forage in the hours before the race starts.
Aside from water and electrolytes, the horse should be offered high-quality feedstuffs at rest stops during the ride. Horses tend to vary in their preferences, so you might need to experiment (at home!) to find the best combination for your horse.
Offer water as soon as the horse enters the checkpoint. My preference is to delay the administration of electrolyte pastes until the horse has eaten since electrolyte pastes can sometimes cause a little irritation of the gums, discouraging food intake. Alternatively, add some electrolyte to the feed. Mash or slurry combinations of, for example, alfalfa meal, grain, wheat bran and/or rice bran (perhaps with a little molasses and some chopped apples or carrots for added palatability) are popular. Also offer plain forage, which can be soaked in water to encourage fluid replacement. This combination of feedstuffs should provide some energy for use during subsequent phases of the ride.
After the ride, the horse should be offered water (immediately) and free-choice hay, followed by a grain meal (or a mash combo similar to that offered during the race). At this stage, particularly after long rides, the horse will be in a significant energy deficit with low liver and muscle glycogen stores. The starch in a grain meal will help to kick-start glycogen replenishment. However, it is not realistic to restore these energy reserves in the immediate post-ride period. Muscle glycogen reserves will buildup over the next three to four days providing the horse is rested and fed its normal diet. Some well-deserved rest and relaxation is the most important aspect of post-ride management.
Maintaining your horse at a body condition score of 4-5, conditioning him for long rides, and supplying enough energy, water, and electrolytes will give you a fit, fierce endurance competitor.
Duren, S.E. Feeding the endurance horse. Advances in Equine Nutrition, edited by J.D. Pagan. Nottingham Press, 351-363, 1998.
Garlinghouse, S.E.; Burrill, M.J. Relationship of body condition score to completion rate during 160-km endurance races. Equine Veterinary Journal, Supplement 30, 591-595, 1999.
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.
Warren, L.K.; Lawrence, L.M.; Roberts, A.; et al. The effect of dietary fiber on gastrointestinal fluid volume and the response to dehydration and exercise. Proceedings of the 17th Symposium of the Equine Nutrition and Physiology Society, Lexington, Ky., 148-149, 2001.
About the Author
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
POLL: University Equine Hospitals