Energy for the Athletic Horse
By By Bruce Arentson, Ph.D.
Let me introduce you to Under Pressure, a fine 7-year-old quarter horse who performs regularly in equine competitions. Under Pressure travels via trailer almost every other weekend to an event. While at these events, his feeding schedule is disrupted, the water and hay are different, and the surroundings are always changing. You wouldn’t believe some of the arrogant stallions and beautiful mares he meets at these events. Though you would think Under Pressure would get use to traveling and the stress of events; the anxiety always seems to affect him. Under Pressure never seems to eat as well as he should, distracted by the activities surrounding him. After the strenuous weekend event, he loads for the tiring trailer ride home. Back at home in the comfort of his own stall, peace reigns, except for the daily two hour workouts he needs to keep his skills sharp.
For Under Pressure to compete in top form, he has to exhibit speed, stamina, and power. Feeding him to maximize his speed and stamina without upsetting his delicate digestive system is a challenge. This article will address how physical demands of performing affect a horse’s energy requirements and feeding management.
The most significant challenge of feeding Under Pressure is maintaining him in ideal body condition. Because of the physical demands his routine places on him and the stress of travel, he doesn’t always eat sufficient feed to meet his energy requirements. Energy intake is the primary nutrient of concern. For Under Pressure to be able to go the distance, he must have sufficient energy intake in his diet. Energy fuels the body functions and muscle contractions during exercise. Because Under Pressure cannot eat while working, he must depend on stored energy. Animals, including horses, store energy as glycogen or sugar in muscle and liver, and as intramuscular fat.
The type of energy stores a horse utilizes during exercise depends on the intensity of the exercise. During mild exercise, when the circulatory system provides sufficient oxygen to cells, the horse’s body can use glycogen and fat stored in cells. Essentially, the stored fat is converted to glucose the cell uses. With sufficient oxygen available, this is known as aerobic metabolism.
During intense exercise, when there is insufficient oxygen at the cellular level, glycogen is the primary energy source, and the utilization of stored fat as an energy source diminishes. After exercising, dietary starch is the energy source of choice for regeneration of muscle and liver glycogen.
To regenerate Under Pressure’s glycogen stores after intense exercise, he requires a grain product along with the roughage (hay or pasture). With all the optional grain products available, the choice for Under Pressure should be based on logic, feeding management capabilities, and past experience with the horse. A grain product with high concentrations of starch and sugars (sweet feed with a significant amount of corn) can be used, but requires careful feeding management to avoid an increased risk of laminitis and colic. Feeding a grain product low in starch and sugars and a moderate fat level (low to moderate energy concentration) may result in a decrease of Under Pressure’s performance capability and a loss of body condition. A grain product with a moderate amount of starch and sugars, and medium to high fat concentrations is most likely the best approach. Feeding Under Pressure should be based on the best science available. However, science may not always define his optimal dietary energy requirements, so experience becomes a trustworthy tool and should be a factor in fine-tuning his diet.
Dietary fat from vegetable oils can be used as a source of energy to partially replace starch. Fat fed in moderate amounts (up to 10% of the total diet) is highly digestible. One benefit of adding fat in the diet is increasing the energy density of the diet without increasing the feed intake. This is especially important for horses like Under Pressure, because it is difficult at times to increase feed intake. Most performance horses require three to four weeks to adapt to and fully utilize dietary fat. An added benefit from feeding additional fat is the improvement in the hair coat shine.
Horses have the capability to utilize forage such as pasture and hay, which can provide a significant amount of energy. The fiber is digested by microbes in the cecum and large intestine. The fermentation products from bacteria are absorbed and utilized as energy by the horse. In most situations with horses like Under Pressure, feeding forage is required. When not on pasture, it is recommended to feed long stem hay free-choice to keep the digestive tract healthy. As a rule of thumb, it is recommended that the amount of forage offered be at least 1% of the horse’s body weight.
Digestible Energy
In the United States, the measure of dietary energy for horses is usually expressed as the term kilocalories of digestible energy. Digestible energy refers to the amount of energy in the diet that is utilized by the horse. Feed ingredients have an estimated digestible energy value. The digestible energy requirement for a horse is calculated based on the horse’s maintenance requirement of digestible energy plus the additional energy needed based on exercise (work). Once the digestible energy requirement is calculated for a horse, then the amount of feed needed to meet the horse’s requirement is determined.
Following is an example to illustrate the difference in the amount of feed required to meet the energy requirements of a 1000 lb horse at maintenance and heavy work. The hay is assumed to have 900 kilocalories digestible energy (DE) per pound and the grain product fed has 1475 kilocalories DE per pound. Hay is being fed at 1% of body weight per day or 10 lb per day. The horse’s energy requirement increases dramatically from 15,000 kilocalories per day to 28,000 kilocalories per day as he goes from maintenance to a heavy work load. To meet the increased dietary energy demand, the feeding rate of the grain product increases from 4.1 lb to 12.9 lb per day. Other factors such as body condition and weather conditions may alter the calculated feeding rate.
Because the performance horse is being fed a significant amount of grain, he must be carefully managed to prevent any digestive upsets and to maximize intake. Use only the highest quality grain products with the most desirable energy content, and feed the daily grain product allotment in three to four feedings per day at regular intervals. To minimize gastrointestinal fill, the weight the horse must carry, it is recommended not to feed within two hours before exercise. Also, wait for one to two hours after exercise to feed the horse to allow him to cool. Typical daily feed intake of forage and grain is 1.5 to 2.5% of the horse’s body weight. Hard-working horses, like Under Pressure, may require 3% of their body weight.
The scenario of the fictional horse, Under Pressure, is similar to many performance horses. Their feeding regime requires careful management to keep them in top condition in order to compete in top form. Getting enough energy into them to retain their top performance and body condition is a challenge, and requires careful feeding management of a scientifically formulated ration.