top of page

How Exercise Affects Nutrient Requirements of the Performance Horse

When feeding a performance horse, the goal is to provide adequate fuel for energy expenditure, replenish nutrients required for muscle function and repair, and support optimal health through a balanced diet. In this article, I will discuss specific nutrient requirements affected by exercise and how these nutrients influence a horse’s ability to perform.


The primary means by which energy is supplied to the horse’s diet are through carbohydrates and fat. Dietary carbohydrates can be classified into two general categories: non-structural and structural.

Non-structural carbohydrates (NSC) include sugars and starches that are digested in the small intestine, while structural carbohydrates include fibers digested in the hindgut (cecum and large colon). The end product of NSC digestion (blood glucose) serves as a readily available source of muscle fuel, or it can be stored as fat or glycogen. The end products of fiber digestion (volatile fatty acids) are used primarily for maintenance energy requirements, but they also can be used less efficiently as fuel for exercise.

Fat, the other primary dietary energy source, contains 2.25 times more energy than an equal quantity of carbohydrate and is the most abundant source of stored energy in the horse’s body. It also provides essential fatty acids, which are important components of all cell membranes and are vital for skin, coat and hoof health, and certain aspects of immune function. Good-quality sources of fat include vegetable and marine oils, flaxseed and rice bran.


One of the most overlooked nutrients affected by exercise is water. A horse can ingest water either by drinking or by eating moist feed, which can contain anywhere from 10 percent (hays/grains) to 80 percent (fresh grass) water. A horse loses water through urine, feces, the respiratory tract and sweat. Lactating mares will also lose water through milk.

Loss of water through sweat is greatly affected by the environment, because a horse will lose 1 to 2 gallons of sweat per hour of moderate exercise at temperatures below 68°F and up to 3 to 4 gallons per hour at temperatures above 86°F. To maintain proper hydration, an exercising horse should consume 10 to 20 gallons (or more) of water per day. Ensuring that water buckets and troughs stay clean and providing adequate electrolytes through the diet will promote water intake and help prevent dehydration.


Electrolytes are not stored by the body and must be provided through the diet daily to replenish what is lost in sweat. Horse sweat contains a high concentration of the electrolytes sodium and chloride, followed by potassium and relatively smaller amounts of calcium and magnesium. Maintaining the correct electrolyte balance is essential to support the horse’s thirst reflex, proper neuromuscular communication and muscle contractility.

Generally, proper electrolyte levels can be met by the horse’s diet if the daily ration consists of moderate-quality forage (provided at a minimum of 1 percent of the horse’s bodyweight) and a fortified commercial grain mix (fed according to the manufacturer’s directions) supplemented with 1 to 2 ounces of plain white salt. Because forages generally contain 1 to 2 percent potassium, typical horse diets contain excess potassium, and supplemental potassium in electrolyte preparations may not be required.

Supplemental salt should be provided via plain white non-iodized salt in block or loose form for free choice consumption, or it may be top-dressed. But because horses are not natural lickers and may not be able to consume adequate amounts of salt from a salt block, providing loose salt for free-choice consumption or as a top-dress may be preferable.

Over-supplementation of electrolytes should be avoided. Administering supplemental electrolytes to an already-dehydrated horse can cause major problems, and repeated oral administration of electrolyte solutions has been shown to exacerbate gastric ulcers.

Protein and amino acids

Not all protein is created equal, and horses actually have an amino acid requirement rather than a protein requirement. Feeding a commercially prepared concentrate containing high-quality protein sources such as soybean and alfalfa meal, along with additional individual amino acids, will promote muscle tone and a strong topline.

Often, horses in low to moderate work that are also easy keepers are fed a diet that is deficient in proteins or amino acids. These horses do not require many additional calories and often are fed primarily grass hay and little to no concentrate. They have plenty of rib cover, and may even be overweight at a 6.5 to 7 body score, but have a poorly developed topline, especially over the loin, due to protein and amino acid deficiency. These horses would benefit from a ration balancer supplement or feed, such as Purina® Enrich Plus®, horse feed as ration balancers are formulated to be fed at 1 to 2 pounds per day and supply the necessary protein, vitamins and minerals needed for work without unnecessary calories.

Feeding excess protein to performance horses can also be a common scenario, especially for horses with high energy demands. This may occur when high-quality alfalfa or alfalfa-mix hays are fed in large quantities, or when protein supplements are added to a diet that already contains adequate protein. Horses are fairly tolerant of a moderate excess of protein in the diet, as excess nitrogen will be converted to ammonia and eliminated through the urine. Athletic performance seems only to be affected when the total protein level of the diet approaches 25 percent, which will result in increased sweat loss, heart rate and respiratory rate. To prevent the negative effects of protein excess, the total protein concentration of the performance horse diet should be kept between 10 and 16 percent.

Certain amino acids, such as lysine, threonine and methionine, have been identified as major components of muscle protein and are essential for growth, proper muscle development and muscle repair. They are considered essential amino acids, meaning that a horse cannot make them; they must be supplied through the diet.

Purina® SuperSport™ amino acid supplement is a newly developed product that offers a blend of amino acids, vitamins and minerals proven to support muscle performance in exercising horses. In a controlled study, horses fed Purina® SuperSport™ showed statistically significant improvements in muscle development, exercise recovery, and overall athletic fitness and performance when compared to horses not receiving the supplement.

Vitamins and minerals

The increased vitamin and mineral needs of the exercising horse can generally be met with a well-fortified diet. Feeding a concentrate from a reputable feed manufacturer formulated specifically for the performance horse will ensure these needs are being met. Because of the complex nature of balancing a diet for proper nutrient levels and ratios, it becomes more challenging when an owner attempts to meet a horse’s vitamin and mineral needs through straight grains and/or individual supplements.

One vitamin that becomes especially important during exercise is vitamin E, an antioxidant that can neutralize free radicals produced during exercise. Free radicals can be particularly damaging to healthy muscle tissue, and a minimum level of 1,000 IU of vitamin E per day should be fed to the moderately exercising horse. There is some evidence that vitamin E supplied at levels up to 3,000 IU per day may provide additional benefit, especially for horses suffering from neurological or muscle abnormalities.

Bottom line

By taking the time to understand the exercising horse’s nutrient requirements, you can more effectively choose a nutrition program that will complement your training program. Seeking advice from professionals is also a good option when you have a specific question. Purina offers personalized assistance with your feeding program at

bottom of page