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The endurance horse is unique among all other equine athletes. Because of the prolonged demands placed upon the endurance horse with protracted moderate intensity exertion, its performance may be influenced quickly by the quality of its diet. A simple diet of hay and oats may lack essential nutrients that allow the horse to perform as expected. Understanding how competition affects the nutrient needs of the horse will help the owner select the appropriate supplementation program for the individual endurance horse.
Keeping an endurance horse fit and healthy involves more than just putting in a large number of miles on trails.
Improving the diet
Approximately 80 to 90% of the feed eaten by horses is used to satisfy their energy requirements. Horses, like people, utilize energy to run most of the chemical reactions within the body, particularly to fuel muscle contractions vital to the work effort. As such, any horse diet should focus on providing adequate energy (calories). The major source of that energy is dietary carbohydrates (grass, hay, grain, molasses, etc.). Because the amount of energy available from forage alone can be a limiting factor for performance, grain is often added to increase the energy density of a diet.
Dietary fat is another source of energy readily employed by the horse for calories. Fat contains roughly 2.25 as much energy as an equal weight of carbohydrate, so less is needed to fuel body processes. Dietary fat has been scientifically proven to be advantageous to the performance of horses undergoing prolonged bouts of exercise.
During long duration, moderate intensity exercise, the body depends on fat stores to supply energy for work. The addition of fat to the diet has been found to increase the ability of the horse to mobilize fat stores for energy, sparing the muscle glycogen (sugar) stores for more intense bouts of exercise. In a study done at Kentucky Equine Research comparing differences in fat utilization between breeds, it was found that Arabians (the most common breed used for endurance) are much more efficient at mobilizing and burning fat as an energy source than are Thoroughbreds.
There are different dietary fat sources available to the horse, and the most common are vegetable oils. Vegetable oils can be fed safely up to 15% of the total diet. Another source of fat is rice bran, the heat-stabilized outer layer of the rice kernel which contains 20% fat. Compared to oats, rice bran can contain 120% of the digestible energy on a pound for pound basis. Therefore, this source of fat is beneficial in adding calories to the diet without increasing the amount of grain being fed.
The remaining 10 to 20% of the diet is used to satisfy the nutrient requirements that drive the cellular processes inside the body. Protein is the major nutrient the body needs to support normal body functions. Vitamins and minerals play a vital role in metabolism but are needed in relatively small amounts. A simple diet of hay and oats may lack some of these key nutrients. Grain concentrates are designed to complement the nutrient profile of forages but must be fed at the recommended level in order to obtain balanced nutrition. For many endurance horses of Arabian descent, the recommended feeding rate of commercial grain mixes provides too many calories, resulting in excess weight gain.
A horse that eats less than the recommended amount may be short on the supplemental protein, vitamins, and minerals that are added to complement the deficiencies in forages. A specialized grain mixture designed for endurance horses is preferable. Failing that, a specially designed concentrate containing essential proteins, vitamins, and minerals can be used to top off a feed that is provided at a lower rate than recommended. If protein is sufficient in forage and grain, then adding a well-balanced vitamin and mineral supplement will be sufficient to fill in the shortcomings of the diet.
Hooves: Horses often have unique requirements for certain nutrients to help improve performance. This is especially true of endurance horses. For instance, not every horse is blessed with hard, resilient hoof walls. The hooves of endurance horses often take a beating from the long hours on the trail. Research has shown that some horses with weak hooves benefit from supplementation of certain nutrients. Specific additives like biotin, methionine, iodine, and zinc, or a combination of them, can be added to the horse’s diet to improve hoof quality.
Muscles: Endurance competitions can also be hard on the horse’s muscles, which are in constant use during the hours of training necessary to compete successfully. During muscular exertion, free radicals (waste products of oxygen metabolism that can damage cell components) are produced and can cause muscular damage if not eliminated.
Certain nutrients, specifically vitamins C and E and selenium, are key antioxidants responsible for quenching free radicals found to build up in muscle tissue. These nutrients work in concert to reduce muscular soreness and stiffness associated with exercise. Magnesium is necessary for proper nerve and muscle function and may be insufficient in the diet of some hard-working horses.
Immune function:Antioxidants are also important for support of the immune system. Human endurance athletes may have reduced immune function for about 70 hours following a bout of prolonged and intensive exercise. During this period the body may be particularly susceptible to infection, allowing viruses and bacteria to gain a foothold. Lack of sleep, severe mental stress, malnutrition, weight loss, or other stressors commonly associated with shipping and competing can also exacerbate depression of immune function. Although the research has been done in humans, it may very likely be similar for the equine endurance athlete. Whether human or equine, body cells need specific nutrients to be able to properly divide and produce necessary antibodies. Many enzymes in immune cells require the presence of micronutrients, and critical roles have been defined for zinc, iron, copper, selenium, and vitamins A, B6, C, and E.
Electrolyte losses:Electrolytes are ions (charged particles) found inside and outside of cells in the body. Electrolytes play an important role in maintaining osmotic pressure, fluid balance, and nerve and muscle activity. A horse sweats in order to get rid of excessive heat that has built up in the muscles. Horse sweat consists of water and a high concentration of electrolytes. Any level of work produces body heat and subsequent sweating. When an endurance horse sweats, it loses essential electrolytes (particularly sodium, chloride, and potassium) that are necessary for top performance. Other factors may cause a horse to sweat, such as the time the horse spends in or tied to a trailer during the heat of the day or the stress of an unfamiliar environment.
Excessive sweating with subsequent loss of electrolytes can cause fatigue and muscular weakness. Usually, a horse can replenish lost electrolytes from its normal diet. However, under extended work or stressful circumstances, the electrolytes that are lost in sweat cannot be replaced from the daily ration of grain and forage.
The amount of sweat produced by an endurance horse during a competition far exceeds that of any other sport horse. It may be difficult to realize the volume of fluid lost as the sweat may evaporate before it is even seen. Because electrolyte balance is critical for maximal performance, replacement of lost electrolytes is imperative. During long rides, calcium and magnesium may be also be lost in sweat in amounts high enough to cause metabolic disorders. Specific electrolyte supplementation can be provided to the horse during the competition phase, but it may also be necessary to provide a daily dose for horses that are in training for endurance events. Free choice water should always be available to the horse when electrolytes are used.
Stomach problems: The rigors and routines of training often interrupt the natural grazing behavior of performance horses, and consequently their stomach acid buffering mechanism.
Indigestion often results. If a horse has any of the following signs it may be suffering from heartburn: drop in performance, sour attitude, poor hair coat, grinding teeth, inappetance, and weight loss. Many endurance horses enjoy the luxury of having 24-hour turnout on pasture, which is ideal for the prevention of ulcers or heartburn.
However, when this lifestyle is interrupted and the horse is loaded on a trailer, put in a stressful situation, fed differently than normal, and then asked to compete for hours with limited meals, he may end up with a sour stomach that will affect performance or attitude. Medications designed to alleviate these discomforts or those specifically designed to be stomach buffers can help horses with these problems.
Chromium supplementation:Strenuous exercise and high-grain diets increase the excretion of chromium in the urine of equine athletes, thereby depleting the natural reserve of this mineral in the body. Chromium is an integral component of glucose tolerance factor, which is thought to potentiate the action of insulin in chromium-deficient tissue. In a Kentucky Equine Research trial, chromium-supplemented horses showed lower insulin levels in response to a meal, and maintained lower insulin levels throughout a standardized exercise test. This means that with chromium supplementation less insulin is required to assimilate and utilize the same amount of glucose from a meal.
Another significant result was that peak levels of lactic acid were lower when the horses received supplemental chromium. Since lactic acid accumulation contributes to fatigue during exercise, this can be interpreted as being beneficial for the performance horse. For the endurance horse that has a low tolerance to additional grain in the diet, a chromium supplement may be advantageous. Chromium supplementation may also help reduce the incidence of tying-up in certain horses. One of the possible causes of tying-up is related to carbohydrate metabolism, and therefore chromium’s action on glucose and insulin may be beneficial in this situation.
Keeping an endurance horse fit and healthy involves more than just putting in a large number of miles on trails. The work required of these horses is quite different than that of any other equine athlete. The challenge is to provide the correct combination of nutrients that will support the special needs of these athletes during both training and competition.