Few dispute that nutrition is important for athletic performance in racehorses. However, I'd wager that there is much less agreement among horse owners, nutritionists, and veterinarians when asked to expound upon the "nitty gritty" of what works (and what doesn't) when feeding a horse in race training. Some focus on the virtues of the latest fad supplement, while others emphasize the importance of getting the basics right--i.e., plenty of high-quality forage supplemented by grains or other energy-laden concentrates. Who's right?
Certainly, in a sport where a fraction of a second is the difference between success and failure, it is very easy to be swayed by the marketing hype associated with the latest supplement or testimonials from high-profile trainers. However, to put this hype in perspective, it is useful to remind ourselves that the nutrients provided in one of these "magical" supplements likely represents considerably less than 0.1% of the total diet--it stands to reason that the other 99.9% of the diet is more important in terms of meeting a horse's nutritional needs, keeping him healthy, and ensuring that he is primed for the job at hand.
Here, we consider some aspects of the feeding management of racehorses, first focusing on the important fundamentals, then examining the interplay between feeding management and the development of gastric ulcers and chronic tying-up, disorders that commonly afflict racehorses.
Back to Basics
As with any feeding program, the main consideration is whether the diet meets the horse's nutritional needs--adequate water, energy (calories), fiber, minerals (e.g., calcium, phosphorus, selenium), and vitamins. For the racehorse (or any athletic horse), energy is the most important nutritional consideration. Daily training and racing burn a lot of body fuel, particularly muscle glycogen, and these fuel reserves must be replenished. Overall, the calorie needs of a racehorse are about double those of a horse at maintenance (i.e., a horse not in training). For an 1,100-1,200-pound (500-544-kg) horse, this is upward of 34-35 Mcal of digestible energy (DE) per day. Studies of horses in race training have estimated DE intakes of 28-32 Mcal/day for Standardbreds and 31-36 Mcal/day for Thoroughbreds (or roughly 3 Mcal per 100 pounds, or 45 kg, of body weight per day).
Another consideration is how much feed we expect a racehorse to eat each day. On average, we might expect him to consume 2-2.5% of his body weight as feed per day (22-30 pounds, or 10-14 kg, for an 1,100-pound, or 500-kg, horse). For argument's sake, assume a racehorse needing 35 Mcal DE/day will eat 28 pounds (12.7 kg) of feed per day. This means that the overall energy density of the diet must be around 1.25 Mcal DE/pound. Even good-quality hay is no more than 0.9-1.0 Mcal/lb; it is obvious that hay alone will not get the job done.
While these numbers help determine how much feed is required, they are just a starting point. There can be substantial variation between horses in terms of calorie needs and how much they will eat in a day. Some horses become overweight when fed according to these guidelines, while others lose weight. Maintenance of body weight and condition is the best indicator of energy sufficiency. So, on a regular basis (every month), it's important to assess body condition and adjust feed intake accordingly.
What is the ideal body condition score (BCS) for racehorses? Research surveys have indicated that most Thoroughbred and Standardbred racehorses have a BCS between 4 and 5 (remember that BCS assesses flesh coverage--mostly fat--over different areas of the body, where a score of 1 is extremely thin and 9 is obese).
Large deviations from this range of BCS might impair performance because of changes in lean body mass. Studies in humans, and more recently in horses, have shown that athletic performance is associated with lean body mass, i.e., muscle. This makes sense--the more muscle mass, the greater the power that can be generated during running. Although loss of fat tissue predominates during weight loss, there is also a decrease in lean tissue. Therefore, marked weight loss could impair athletic performance because of a decline in muscle mass.
Speak of muscle and thoughts usually turn to the amount of protein in the diet. Although a high-octane athlete does require more protein than a horse at maintenance, the increase in calorie intake usually more than covers the racehorse's needs for protein and the other essential nutrients. In fact, when a legume hay (alfalfa or clover) is fed, protein intake is generally far in excess of requirements. For young horses, providing some very high-quality protein (such as that provided by soybean meal) is important to ensure intake of adequate lysine. Inadequate dietary lysine can limit proper growth and development.
Hay and cereal-based concentrates (especially oats) have long been the mainstay of racehorse feeding. Certainly, it can be difficult to meet the racehorse's high energy needs unless grain or concentrate feeds comprise more than 50% of the total diet (with the remainder coming from forage, i.e., hay). Indeed, it is not uncommon for a racehorse to receive more than 18 pounds per day (8 kg/day) of grain or grain concentrate.
Two concerns arise with this type of diet. The first is low fiber intake, one factor thought to increase the risk of colic and perhaps gastric ulcers. Second, high-grain diets are also high in starch, the main component of cereal grains. The horse's digestive tract appears to have a limited capacity for complete starch digestion. This is not a problem at low levels of starch intake (e.g., less than five pounds, or 2.3 kg, of grain per day), but can be problematic with heavy grain feeding. For an 1,100-pound (500-kg) horse, and individual grain meal should not exceed seven pounds (3.2 kg). Therefore, for horses receiving more than 14-15 pounds (6.4-6.8 kg) of grain or grain concentrate per day, the ration should be fed in three rather than two meals per day.
When starch is not digested in the small intestine, it passes into the hindgut, where it is fermented. This process is not only inefficient with respect to the assimilation of energy from the grain, but also can be detrimental to overall digestion. Starch overflow to the large intestine can result in a decrease in gut pH (acidosis), disruption of the normal gut microbial population, and increased risk for colic and diarrhea. Some horses on very high-grain/low-fiber diets develop loose stools and lose weight even in the face of higher grain feeding. These abnormalities, likely a reflection of the disturbance to hindgut function as a result of starch overflow, usually resolve with the feeding of more fiber and less grain.
The flip side of the starch equation is that racehorses need some starch and sugar in their diets for replenishment of muscle glycogen stores. For galloping exercise, muscle glycogen is by far the most important fuel for muscle contraction. In fact, 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. From this viewpoint, it is clear that at least some starch and sugar are essential components of a racehorse diet.
The risk of digestive upsets can be minimized by restricting the size of individual grain concentrate meals and by using other high-energy feedstuffs in the grain concentrate mix.
Fat and highly digestible fiber sources such as beet pulp, dehydrated alfalfa meal, and soy hulls are now commonly included in commercial racehorse feeds. These feeds are not only lower in starch (and therefore safer to feed compared to "straight" grains), but they also contain additional vitamins and minerals so that supplementation with these nutrients is not necessary. These feeds are also formulated to deliver the right balance of minerals and vitamins.
The calcium:phosphorus (Ca:P) ratio is a good example--commercial feeds have a Ca:P ratio of 1.5:1 to 2:1 (the Ca:P ratio should never be lower than 1:1). On the other hand, diets that make heavy use of oats and wheat bran (both feeds have a low Ca:P ratio and are low in calcium) can result in a calcium deficiency and/or an inverted Ca:P ratio. Both situations could contribute to bone problems.
Fat contains twice as many calories as starch and is well tolerated by the horse's digestive tract, and vegetable fats are very palatable. For picky eaters or those with trouble maintaining body condition, the higher energy density of fat-supplemented concentrates can make a difference over the course of a racing campaign.
Less certain is the ideal level of dietary fat for a racehorse. Many commercial rations are 5-10% fat (by weight), so a typical daily concentrate intake of 15 pounds (6.8 kg) represents up to 1.0-1.5 pounds (0.45-0.68 kg) of fat per day. Although higher levels of fat intake might be possible, one concern is impairment to glycogen replenishment. As fat can't be used for glycogen synthesis, an overemphasis on fat feeding--with a drastic reduction in starch and sugar--could result in sub-optimal muscle glycogen levels.
Beet pulp is another feedstuff prevalent in modern racehorse feeds. This by-product of the sugar beet industry is a good source of energy, is easy on the gut, and might even improve the efficiency of digestion of other sources of fiber (hay) in the diet. A feed containing beet pulp and fat (5-8%) will have considerably less starch than grains (approximately 35% vs. 50% for oats and 65-70% for corn). Although these feeds are usually more expensive than a grain such as oats because they typically have a higher caloric density, less feed per day is needed. This somewhat offsets the price differential.
Feed Enough Fiber
Although grain concentrate typically represents more than 50% of a racehorse's ration, forage (and the fiber within) is still a critical part of the diet. Adequate fiber intake is essential for proper gut function. A general recommendation is that the horse should receive at least 1% of his body weight per day as hay (or an alternative forage)--one pound per 100 pounds (0.45 kg per 45 kg) of body weight, or 10-12 pounds (4.5-5.4 kg) for the average-size Thoroughbred or Standardbred racehorse. More ideal is closer to 1.5% of body weight, or 16-18 pounds (7.2-8.2 kg) per day. Feeding below the minimum forage amount might increase the risk of gastrointestinal problems such as colic and gastric ulcers. The inclusion of beet pulp in the ration also helps to ensure adequate fiber intake.
Gastric ulcers are of particular concern for racehorses, and there is some support for the idea that the feeding management common in race training situations is a contributing factor. When a horse grazes at pasture or nibbles on hay for extended periods, a great deal of saliva is produced. Saliva contains sodium bicarbonate (what makes up baking soda), which helps buffer acid produced in the stomach and therefore minimizes damage to the stomach lining. In contrast, when a horse eats a grain meal, saliva production is less than half of that produced when eating an equal amount of hay, basically because less chewing is required.
The horse produces gastric acid on a continual basis. Therefore, if a horse is fed morning and afternoon/evening (i.e., two meals per day), the chances are that there will be lengthy periods when the stomach is practically devoid of food, but fully exposed to the "burning" effects of gastric acid. This might be one factor that contributes to ulcer development in racehorses on low- fiber/high-grain diets. It has also been proposed that large grain concentrate meals favor feed fermentation in the stomach, and the volatile fatty acids yielded by this process have also been implicated in the development of gastric ulcers.
All of this suggests that racehorses should have free access to forage. In an ideal world, each would have a few hours at pasture daily. Splitting the grain into three or four meals per day, rather than two, also is helpful. Finally, there might be some merit in letting the horse eat some hay (one to two pounds, 0.45-0.9 kg) before exercise. Recent research has shown that the stomach contracts (shrinks) during exercise--this circumstance also might favor a "splashing" of gastric acid over the areas of the stomach prone to ulcer formation. On the other hand, if a little food and saliva are present in the stomach during exercise, the burning effect of gastric acid could be lessened.
Forage quality is also important for the racehorse. Early-cut hay (without seed heads) has the highest nutritional value and is preferred. As an example, young timothy hay might contain as much as 1 Mcal DE/pound, whereas more mature timothy can contain as little as 0.7 Mcal DE/pound. For a horse eating 12 pounds (5.4 kg) of hay, this difference in energy content (approximately 3 Mcal) is the equivalent of more than two pounds of oats. Therefore, feeding early-cut hay is another way to boost the energy density of the diet and reduce overall starch intake.
Strict control of the diet is especially important for racehorses which are afflicted with recurrent exertional rhabdomyolysis (RER), a form of chronic tying-up. Survey research has demonstrated that up to 5% of racing Thoroughbreds have RER, and a similar condition is commonly seen in Standardbreds. It is now clear that dietary starch and sugar impact the severity and frequency of muscle damage in these horses, perhaps by making these horses more nervous and excitable. A nervous, excitable temperament is an important trigger for tying-up episodes in susceptible horses.
All of this means that dietary starch must be minimized in a horse with RER. Aim for 1.5% of body weight per day as high-quality hay (16-17 pounds, or 7.3-7.7 kg, for an 1,100-pound, 500-kg, horse), and supplement the forage with a feed high in fat and fiber and low in starch.
Specialized feeds are available for horses with RER--these feeds have a restricted amount of starch and sugar with much of the energy supplied by fat and fiber sources such as beet pulp and soy hulls.
Alternatively, an 1,100-pound (500-kg) horse with RER could be fed a minimal amount of straight grain or traditional sweet feed (no more than five to six pounds or 2.3-2.7 kg per day) along with three to four pounds (1.4-1.8 kg) of beet pulp per day and 400-500 mL of vegetable oil (2-2 1/2standard measuring cups). Rice bran (two to three pounds, or 0.9-1.4 kg, per day) could be used in place of the vegetable oil. Diet is not a cure-all for horses with RER, but research and clinical experience has indicated that this approach does lessen the severity of exercise-associated muscle damage.
Gallagher, K.; Leech, J.; Stowe, H. Protein, energy, and dry matter consumption by racing Thoroughbreds: A field survey. Journal of Equine Veterinary Science, 12, 43, 1992.
Southwood, L.; Evans, D.; Hodgson, D.; Bryden, W.; Rose, R. Nutrient intake of horses in Thoroughbred and Standardbred stables. Australian Veterinary Journal, 70, 164, 1993.
Briggs, K. Feeding Racehorses. The Horse, August 1999, 61-74. Article Quick Find #355 at www.TheHorse.com.
Geor, R. Pre-Exercise Feeding. The Horse, May 2000, 81-88. Article Quick Find #177 at www.TheHorse.com.
5 TIPS: Feeding Racehorses
- Long periods of time between feedings can keep stomach acidity higher and might contribute to ulcer development.
- Minimize digestive upsets by restricting the size of grain concentrate meals and by using other high-energy feedstuffs in the grain concentrate mix.
- Give young racehorses very high-quality protein (such as that in soybean meal) to ensure intake of adequate lysine for proper growth and development.
- Starch overflow from oversized grain meals to the large intestine can result in increased risk for colic and diarrhea.
- The nutrients provided in supplements likely represent considerably less than 0.1% of the diet; the other 99.9% is likely more important to performance.
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: Colic Surgery