Successful performance depends on many things, including training, conditioning and the horse’s inherent talent and heart. But without proper nutrition, the horse will not be able to perform to his full potential. Sporthorse nutrition is primarily focused on providing appropriate fuel to support workload, but it also involves supplying a complete dietary balance to replenish nutrients needed for muscle maintenance, facilitate repair and recovery, maintain normal body functions and balance, and support optimal health.

Energy/Fuel

Energy is the fuel used by the horse for all functions, including maintenance of body tissues and powering exercise. Energy stored in feed is measured in calories, usually reported in megacalories (Mcal) or kilocalories (kcal or Cal). 

All horses have basic energy requirements to support maintenance activity. Energy is the nutrient most influenced by training and work in horses. The harder the horse works, the more energy is needed. In addition, the type of work influences what source of energy (fuel) should be provided. For instance, a hunter or dressage horse primarily works aerobically (longer, slower activities). Consequently, horses in those disciplines need fuel that supports aerobic metabolism. A jumper or eventer (cross country or stadium jumping) needs fuel to support anaerobic work (briefer, high-intensity activities). 

Much of the energy in feedstuffs eaten by the horse can be burned via various biochemical pathways to produce adenosine triphosphate (ATP). This is the molecule that fuels muscle contractions. The horse has a well-developed, complex system to take chemical energy provided by food nutrients and convert it to mechanical energy for muscular movement. 

The body has three “fuel tanks.” These are body stores of biological compounds that can be metabolized to produce chemical energy. The compounds stored in the fuel tanks are glycogen, fat and protein. All three can be metabolized to produce ATP molecules, but there are vast differences in the efficiency of each. 

There are four energy sources that can be fed to horses to fill the fuel tanks—

• Plant fibers (structural carbohydrates)
• Nonstructural carbohydrates (starch and sugar)
• Fats
• Proteins

How a Horse Utilizes Feed 

Before diving further into describing and comparing these energy sources for working horses, it may be helpful to discuss how the horse utilizes feedstuffs in his body. As herbivores, horses naturally wander and graze plants (primarily grasses) and utilize plant fibers as the main source of dietary energy. The equine digestive tract is designed to process large amounts of forage almost continuously. While mammals do not produce enzymes to break down these structural carbs in their digestive tracts, the horse’s voluminous hindgut (including the cecum and large intestine) houses billions of microbes, including bacteria, protozoa and fungi, that are quite efficient at digesting fibers through fermentation. The end products of microbial fermentation of fibers are volatile fatty acids, and those VFAs are absorbed from the horse’s hindgut and can usually provide adequate calories to support a nonworking horse. Some VFAs are easily used to generate ATP in the muscles. Others can be converted to the simple sugar glucose in the liver. This can then be either transported to body tissues and used as fuel or converted to glycogen or fat and stored for later use. 

Historically, when horses were domesticated and put to work, people realized that forages did not provide enough energy to support moderate or hard workloads. This is because the horses were not able to perform their daily work without losing weight and body condition. The earliest solution was to add cereal grains (traditionally oats, barley or corn) to the horses’ diets. These provide high levels of nonstructural carbohydrates (primarily starch) that contribute more calories per pound of feedstuff than forages. Digestion of starch in the horse’s upper gut yields glucose. This is absorbed from the small intestine. Glucose may then be used as fuel immediately, stored as glycogen (usually the major fuel source for activity) in the horse’s muscles and liver, or stored as fat. 

Fuel Tanks Explained

So, back to energy sources and fuel tanks. The first fuel tank is glycogen, the primary fuel used for anaerobic activity. As discussed, dietary fibers and nonstructural carbohydrates both contribute glucose for synthesis of glycogen. The benefit of burning glycogen (glycolysis) is that it’s a readily available fuel when the horse needs to expend energy immediately. The downside of glycogen is that body stores are limited. Consequently, the horse will run out of glycogen after only a few minutes of maximal activity. Additionally, glycogen is not especially efficient at producing ATP molecules. And finally, an end product of the glycolysis is lactic acid, which can be harmful to muscle fibers. The combination of running out of glycogen and lactic acid buildup leads to fatigue in exercising horses.

The second fuel tank is fat, the primary fuel used for aerobic activity. The benefits of burning fat are multiple:

• the storage potential of fat is fairly extensive,
• fats and fatty acids can be used to fuel hours of submaximal exercise,
• burning fat is very efficient at producing ATP molecules,
• end products are water and carbon dioxide, which are not detrimental to the body. 

The main downside of burning fat is that it is a slower process. It cannot be used immediately to support maximal effort.

The third fuel tank is protein, but there are more downsides to burning protein as a fuel than benefits. Metabolizing protein to produce ATP molecules is quite inefficient (costs more energy to metabolize as fuel than glycogen or fat). It also produces more heat than other fuels, which must then be dissipated by the body and can affect performance. Protein is usually only used as an energy source when a horse is either
fed an excessive amount of protein or when the horse is in negative energy balance (more energy is being used than is being supplied by the diet). In that case, the body will break down protein in muscle tissue to supply energy for maintenance activities. 

Feeding Different Disciplines

As mentioned previously, the type of exercise should to some extent dictate the feeding program for the horse to supply appropriate energy sources. For nonworking horses, VFAs from high-quality forages will likely provide adequate energy for maintenance. If a horse is maintaining appropriate body weight and condition on forage alone, a ration balancer or vitamin/mineral supplement will supply nutrients typically missing in forages. 

All working horses need nonstructural carbs in their diets to supply glucose as immediate fuel and as substrate for glycogen synthesis. Forages provide some nonstructural carbs but rarely enough to refill glycogen stores in moderate- to hard-working horses. Anaerobic activities, such as show or stadium jumping, require adequate glycogen to support the high-intensity work. Aerobic performance, including dressage, hunter or the cross-country phase of eventing, will also utilize some glycogen as fuel. However, there also must be adequate fat available to support sustained work lasting more than a few minutes. 

Working English sporthorses participating primarily in aerobic activity often benefit from diets containing supplemental fat. Feeding fat to horses provides benefits beyond simply a substrate for aerobic metabolism. Fats are calorically dense and energetically efficient. This means that they provide more than twice the calories by weight as carbohydrates in general and generate much less heat of digestion than fibers.

Replacing nonstructural carbs with fat in horses’ diets may also affect demeanor. There are some reports of horses being calmer on fat-supplemented diets. Further, research has shown that adding fat to the diets of performance horses may improve performance, such as increased stamina and delayed onset of fatigue. However, dietary fats cannot quickly replenish glycogen stores, so we cannot completely replace nonstructural carbohydrates in horses’ diets. When a horse runs out of glucose, performance will drastically drop.

It would be nice to be able to simply say, “Feed show jumpers higher sugar/starch diets for brief, high-intensity work. And feed dressage, hunters and eventers higher fat/fiber diets for more sustained work lasting more than a few minutes.” However, life is never that simple. The work performed during training and competing in all disciplines is a blend of anaerobic and aerobic work, so all the physiological fuel systems are in play. The art of feeding performance horses comes in finding the best combination of dietary energy sources to meet an individual horse’s fuel needs for a particular activity as well as meeting that horse’s distinct metabolic needs.

Interestingly, a recent study comparing nutrient content of performance feeds fed to elite performance horses in the United States versus Europe noted that European feeds tended to be fairly low in fat and high in nonstructural carbs. The trend in performance horse feeds in the U.S. in recent years has been to utilize feeds high in fat and fiber and low in nonstructural carbs. Research studies have shown that horses who deplete their glycogen stores and are not provided dietary substrate to replenish the glycogen show reduced performance capabilities. 

Additionally, it has been proposed that in some situations, relying on high fat/low nonstructural carb rations may compromise performance, particularly in intensely exercised horses. Further, some warmblood horses diagnosed with myofibrillar myopathy have shown improvement when their diets are adjusted from high fat/low nonstructural carb to low-moderate fat/moderate nonstructural carb (along with specific amino acid and antioxidant supplementation). More research may help to determine the best options and mixtures of fuel sources to support varying exercise levels and metabolic needs of working sporthorses. 

Where Protein Fits Into Nutrition

Although not an efficient source of energy for working horses, protein is necessary to provide essential amino acids. Amino acids are required for muscle mass development and tissue repair. They also supply nitrogen to replace what is lost in sweat. Exercise causes stress and damage to muscle tissue. 

Amino acids (the building blocks of protein) are needed for muscle to adapt to the increased demands of exercise. However, the higher protein requirements are usually met by the increased feed intake necessary to meet the working horse’s energy demands. This is assuming that the protein supplied is high quality and provides adequate essential amino acids. An essential amino acid cannot be synthesized in the horse’s body and must be supplied in the diet. Some essential amino acids in horses include lysine, methionine and threonine. 

Different proteins have different amino acid profiles. Dietary protein sources including soybean or canola meal and alfalfa supply a better mix of essential amino acids than cereal grains or grass forages. Horses actually have an “amino acid” requirement, not a “protein” requirement. When essential amino acids are lacking, muscle development and tone (such as a strong topline) cannot be maintained and performance can be impaired. 

Feeds developed for performance horses contain high quality protein sources to provide required amino acids. Additionally, individual essential amino acids are often added to ensure working horses’ needs are met. A typical performance feed usually contains 12–14% protein to support the working horse’s demands. Again, as the workload increases, feed intake usually goes up with energy demands. Thus the amount of daily dietary protein is higher. 

Keep in mind, however, these feeds are designed with a specific minimum feeding rate to provide sufficient nutrients. Consequently, horses in light work (especially easy keepers) may gain too much weight when fed even the minimum recommended amounts. In such situations, instead of a performance feed, these horses will benefit from a ration balancing feed. This feed contains concentrated high-quality protein, vitamins and minerals to meet nutrient requirements. However, it is fed at a very low rate (usually 1–2 pounds/day for a mature horse) and so does not supply unnecessary calories.

Vitamin and Mineral Nutrition

Similar to protein, requirements for vitamins and minerals increase with bigger workload. But the ratios of these nutrients relative to calorie requirements remain consistent. Therefore, the increased requirements are met with a well-fortified performance horse feed provided in adequate amounts to meet energy demands. 

Vitamins and minerals are needed in very small quantities. It is often difficult to recognize moderate deficiencies or excesses. However, maintaining appropriate levels of these nutrients is essential to ensure long-term health, soundness and performance of the horse. This is particularly true for nutrients involved in energy metabolism including B-vitamins, electrolytes (sodium, potassium and chloride), structural minerals such as calcium and phosphorus, and antioxidants such as vitamin E and selenium. 

Some vitamins, including Vitamin C and some B-vitamins (biotin, riboflavin and niacin) have no established dietary requirement in the horse. They are assumed to be adequately synthesized in the digestive tract and/or provided in natural ingredients in amounts to prevent deficiency symptoms. 

Feeding excessive levels of vitamins and minerals has not proven to be beneficial to performance and in many cases can actually become detrimental. Therefore, choose a properly fortified feed designed for performance horses. It is a more accurate approach to vitamin and mineral nutrition than trying to individually supplement these nutrients.

Katie Young, PhD, is an independent equine nutritionist providing consulting services to horse owners and veterinarians. She also works with Kentucky Equine Research as a consulting nutritionist. Prior to starting her own business, Dr. Young was an equine nutritionist, product manager and technical services manager with Purina Animal Nutrition for several years. There her responsibilities included developing and maintaining horse-feed formulas and standards as well as ingredient and production standards. Dr. Young earned her bachelor’s degree from Missouri State University and her doctorate in equine nutrition and exercise physiology from Texas A&M University. Currently she rides and competes in eventing and works as a trainer and riding instructor in the Kansas
City area.

This article originally appeared in the Fall 2022 issue of Practical Horseman.