Building Endurance Through Nutrition
Building Endurance Through Nutrition
Ralston-Purina Nutrition Specialist
As the growing number of recent studies attest, the equine endurance athlete is receiving increasing consideration. Particular attention is being paid to the effects of certain nutrients on performance.
In general, feed is digested to from chemical energy which is used for metabolic processes, aerobic work and anaerobic work. This is accomplished by converting the chemical energy to mechanical energy. The amount of energy required by the athlete is determined by the duration (distance) and intensity (speed) of the exercise.
What follows is an attempt to clarify some of the pertinent issues facing equine nutritionists. The specific topics to be addressed include feeding carbohydrate, fat, protein, and fiber. The consumption of water, vitamins and minerals will be addressed, but only briefly.
Carbohydrates (starches and sugars) are a primary source of energy. They are present in considerable levels in grains such as corn (70% starch), barley (66%), and oats (50%). Carbohydrates are broken down to simple units of glucose and absorbed through the small intestine. The glucose units travel through the blood to the muscle tissue or liver, where they are stored as glycogen. When the muscle is used for work the glycogen is broken down for energy. If the activity is high intensity (i.e... anaerobic), the end product of this process is lactic acid. Lactic acid is one of the contributing factors that may result in muscle soreness or "tying up." Under certain conditions, a diet higher in carbohydrates can lead to increased glycogen levels in the muscle. Therefore there is more potential with a carbohydrate-rich diet for lactic acid build up in the muscle after exercise.
Human athletes use a technique referred to as "carbohydrate loading" to increase performance in endurance-type events. The technique involves depleting the glycogen stores in the muscle through strenuous exercise while feeding a high fat, high protein diet. The next step involves feeding a diet that is high in carbohydrate and the athlete is rested in order for the glycogen levels to be "super saturated." The extra glycogen is available for the muscle to use as fuel. Muscle glycogen can be increased but whether this technique enhances performance in horses is questionable. In some cases, performance may even be impaired due to increased water retention. The horse has a sensitive digestive system and rapid changes in diet may result in colic, and increase the chances of "tying up'" other exertional myopathies, or founder. The rate of glycogen synthesis during heavy work is only 2% of the rate at which it is used by the muscle. Therefore it is desirable to enhance the fat utilization during long periods of exercise to spare the finite stores of glycogen. When the glycogen is depleted, the blood glucose level decreases, indicating the onset of fatigue.
Some carbohydrates reach the hind gut unchanged. Here, bacteria are responsible for breaking the carbohydrates down to usable fatty acids, which are absorbed through the large intestine and subsequently used for energy.
Fiber, found in grains and roughages, contains carbohydrates. The horse is well adapted to the digestion and utilization of Faber. Upon reaching the hind gut, the bacteria act on the Faber. by releasing enzymes, resulting in the fermentation process. The result of this process is the release of usable fatty acids which are an aerobic energy sources. It is interesting to note that by feeding yeast culture to the bacteria in the hind gut of the horse, the aerobic capacity may be enhanced. The yeast culture may induce an increase in muscle mass and metabolic efficiency, increase vascularization of the muscle and increase cardiovascular capacity and efficiency. To the endurance horse, the resulting increase in blood flow through the muscles would help to decrease the lactic acid build up and increase the oxygen supply to the muscle. However, this area of research needs further evaluation.
Fat contains more energy than the same weight of carbohydrate, making fat a more concentrated source of energy. As a result, the volume of feed required to maintain condition is decreased when a fat supplement is used. Since energy is the dietary factor most influenced by exercise it is the factor of primary importance when feeding performance horses.
Fat in horse feeds is most palatable and digestible if in the form of vegetable oils. For this reason, the most common sources of fat in equine feed are corn, soybean and canola oils. Animal fat is used in horse feeds but rancidity and palatability are concerns when this form if fat is used.
Fat is catabolized (broken down) in the small intestine to form glycerol and free fatty acids. In this from it can be transported through the blood to be stored in the adipose (fat) tissues.
When fat is mobilized to supply energy, the end products are carbon dioxide and water, whereas with muscle glycogen breakdown lactic acid may also be one of the end products.
Definitive research has yet to be done, however, if exercising horses are conditioned to use fat as a fuel source during aerobic work, increased glycogen in the muscle could be a significant energy source when the animal is fatigued.
The source of protein in the horse diet is primarily from seeds such as soybean (48%), linseed (21%), and canola (37%). Although grains and roughage both contain suitable levels of protein, the significant difference is in the digestibility of that protein. Grains are 80% digestible and roughages are 50% digestible.
Proteins are acted upon by digestive enzymes to break them down to their building blocks or amino acids. These are absorbed through the small intestine and carried through the blood via the liver to the site of muscle synthesis. In situations where the consumption of protein far exceeds the requirement of the animal, it can be metabolized as an energy source. However, this is a very inefficient source of energy. Since protein tends to be an expensive nutrient, this practice is not recommended. What may prove useful, is supplementing specific amino acids, since deficiencies of some of these have been associated with performance problems.
Vitamins and Minerals
Vitamins are organic compounds required in very small amounts for different functions. All vitamins are necessary for normal body functions, however several can be toxic in high doses and there are some which are washed out of the body when given in excess. Consult your veterinarian for advice on appropriate vitamin dosages.
Vitamin A is important to several body systems. Insufficient levels are associated with poor coat condition, respiratory infection, decreased disease resistance, poor performance, and nerve degeneration.
Vitamin E is responsible in part for regulating metabolism and affects muscle. Therapeutic levels of Vitamin E can help to reduce the incidence of exertional myopathy, however selenium levels are essential in this respect since these two substances work together.
Biotin plays an important role in both protein metabolism and energy release. To a performance horse, with a high metabolic rate, adequate levels of biotin are crucial. Biotin is a part of the coenzymes required for energy metabolism. An endurance horse, which requires high levels of energy, also requires adequate biotin levels to ensure energy availability.
Although the exact levels of folic acid required have not been determined, its importance has been associated with cell formation and function. Anemia is one of the first indications of folic acid deficiency.
Iodine is an integral part of the hormone thyroxin, which controls the rate of energy metabolism. Thus, its importance to the performance horse is evident. If the iodine level is inadequate, this is reflected in its energy metabolism with the result that the horse may not reach its performance potential.
Hemoglobin formation depends on iron, which is essential for oxygen transport through the body. Low iron levels reduce oxygen transport, which in turn reduces aerobic capacity.
When horses are fed a balanced diet, the mineral requirements tend to be met. Specific levels for minerals have yet to be determined, although general guidelines are available. Certain trace minerals may be of particular importance due to their relationships with other nutrients.
The relationship between vitamins and minerals in their roles within the body are quite complex. Specific vitamins are required in combination with minerals to carry out daily metabolic functions within the body. It is then only logical to assume that when the metabolic processes are elevated by exercise, that the need for higher levels of those vitamins and minerals are necessary.
For example, the more that an exercising horse sweats, the more sodium, chloride and potassium it will lose. Sweat loss during an endurance ride can be 5% to 10% of the horse's body weight. Please refer to the papers by Dr. Kerry Ridgway and Gayle Ecker for further information in this area.
The provision of good quality, clean water is crucial to the equine species, as 60% of a horse's body weight is composed of water. For each kilogram of feed consumed, three kilograms of water are required. Among other purposes, water is responsible for transporting nutrients through the body, removing waste, and controlling body temperature. An average total body water loss of 40 liters was measured in endurance horses on an 80 km ride. An estimated six liters of water were lost from the plasma. Because of these water losses, it is recommended that horses be encouraged to drink at every opportunity, particularly since total water loss is rarely replenished.
The nutrient requirements of the endurance horse are currently under investigation. As the research continues, advances are made in understanding the reasons why the horse is able to perform as it does, and responds positively or negatively to certain nutrients. Like any group of athletes, each individual will respond differently, in part, to the levels of nutrients offered. Understanding the changes in the metabolic processes that occur in the exercising equine athlete remain ahead. Feeding practices before, during and after competition are also under investigation.
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The Equine Research Canter
University of Guelph
Guelph, ON N1G 2W1