Research in the past several years has provided a great deal of information on meeting energy requirements of performance horses. However, there is still an element of art to balancing the various fuel sources to meet an individual horse’s needs. Depending on the workload, type of work and individual metabolic differences, the type of feeding program can look quite different even among horses with similar lifestyles.
As a horse’s level of performance effort increases, higher energy requirement is the most obvious change in his nutrient needs. Energy is the fuel used by the horse for all functions, including performance and maintenance of body tissues. Energy itself cannot be measured, but it can be converted to heat, which can be measured. We measure the energy stored in feed in megacalories (Mcal) or kilocalories (kcal). Kilocalories may also be reported in literature as Calories (with a capital “C”).
Visual appraisal of body condition is a good indicator of whether dietary calories are being provided in adequate amounts. Due to the subjectivity of assessing how fat or thin a horse may be, a numerical body condition scoring system was established. The scores range from 1–9 with 1 representing a very emaciated horse and 9 an extremely obese horse. While there may be some slight individual variation, performance horses are at their best when maintained at a moderate body condition score of 5–6. The description of a 5 body condition score is back flat (no crease or ridge), ribs not visually distinguishable but easily felt, fat around tailhead beginning to feel spongy, withers appear rounded over spinous processes, shoulders and neck blend smoothly into the body.
For practical purposes, energy requirements for work are being properly met if the horse’s ribs are not visible but are easy to feel. If ribs can be seen, the horse is not receiving adequate dietary calories to support his level of work and maintain condition. If ribs are hidden under a thick cover of fat and are difficult to feel, calorie intake exceeds requirements for that level of work. Excess fat is not only additional weight for the athlete to carry but also provides unneeded insulation which may make cooling the body more challenging. While it is easy to determine when total energy needs are being met, understanding the sources of energy needed and utilized during exercise is a bit more complicated.
Understand Energy Sources
The discussion of energy sources for performance must cover dietary energy (calories) and physiological energy (the type of exercise and fitness level of the horse), both of which drive how calories are stored and utilized.
Different calorie sources are utilized and stored in the body in very specific ways. There are two primary energy stores, or fuel tanks, in the horse’s body:
• fat deposits. Body fat is the major energy source during low-intensity aerobic activities that can last for several minutes or even hours, including dressage, hunter or endurance phases of eventing rides.
• glycogen (a polysaccharide) is stored in the liver and muscles. It is the primary fuel source for higher-intensity anaerobic work that lasts for seconds or just a few minutes, such as show or stadium jumping.
The amount of energy stored in these fuel tanks depends on the calories available from the diet. Dietary calories can be supplied by carbohydrates, fats or proteins in the horse’s ration.
Horses eat plants, and plants store energy primarily as carbohydrates and a small amount of fat. Plant carbohydrates include simple sugars, starch and fibers. Hay and pasture primarily provide calories from fibers although some grass and hay can have relatively high sugar content.
Digestible fibers are fermented by microbes in the horse’s hindgut and converted to volatile fatty acids, which are then absorbed. These acids provide the majority of energy required for the horse at maintenance but have limited capacity to fuel hard work. Dietary fibers cannot quickly replenish glycogen stores.
The immature leafy portions of plants and grains such as oats, corn and barley provide more calories from starch. During digestion, starches are broken down into simple sugar building blocks, which are absorbed primarily in the small intestine. The sugars may then be immediately used as fuel for work or stored as glycogen in the muscle fibers and liver. Once the glycogen fuel tanks are full, they will contribute to body fat stores.
Fats are calorically dense and energetically efficient, providing more than twice the amount of calories by weight as carbohydrates in general and generating much less heat of digestion than fibers. In general, 1 pound of fat (two cups of vegetable oil) provides the same number of calories as 3 pounds of oats. So adding fat to the diet allows the horse to ingest more calories in a smaller quantity of feed. 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. Dietary fats cannot quickly replenish glycogen stores.
Proteins are not major contributors of fuel during exercise and are a very inefficient source of energy.
When glycogen stores are inadequate, proteins can be used for energy, but their metabolism into energy produces three to six times more heat than that of carbohydrates or fat. This is wasted energy and may burden a horse trying to cool his body during work.
Proteins are essential in the body for maintaining muscle mass and as a component of antibodies, enzymes and some hormones, so it makes much more sense not to utilize protein stores for energy.
Remember, fats are the primary fuel for aerobic work while glycogen is the primary fuel for anaerobic work. Dietary fats and fibers cannot quickly replenish glycogen stores needed for high-intensity work. This is important when designing feeding programs for competition horses.
Fuel for a Working Horse
The best feeding program for a working horse should include dietary sources that supply fuel to meet his maintenance and workload needs.
Anaerobic activities, such as show or stadium jumping, require adequate glycogen supplies to support the high-intensity work. Aerobic performance, including dressage, hunter or endurance phases of eventing rides, will also pull on glycogen stores but must have adequate fat available to provide fuel for sustained work lasting more than a few minutes.
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.
Horses performing mostly aerobic work, especially at lower workloads that rarely leave them fatigued, will often perform well on a ration that provides the majority of dietary calories from fiber with a smaller amount of calories from starch, sugars and fat. Easy keepers in this category may require only good quality hay and 1 to 2 pounds per day of a ration-balancing feed to provide essential protein, vitamins and minerals lacking in hays.
If the horse is a harder keeper and does not maintain body weight and condition or if he is working hard enough to require more calories, a moderate- to high-calorie feed with added fat will supply more energy for maintenance as well as fuel for sustained activity. The balance of fuel sources between fats, fibers and soluble carbohydrates for horses in less strenuous activities and lower workloads is usually based more on caloric requirements than specific fueling demands.
Higher-level performance horses often have more particular dietary requirements, necessitating additional attention to the various fuel sources provided in the diet. For instance, a horse competing at Novice level horse trials may do quite well on a diet that provides a moderate level of calories primarily from fiber with a minor amount from fats, starch and sugars. But a three- or four-star eventing athlete requires much higher calories with higher fat sources to supply fuel for prolonged activity and sufficient starch and sugar levels to refill glycogen storage after maximal exertion. Further, the high-level eventing horse must be worked on a regular schedule for conditioning between events, which requires the feeding program to provide appropriate fuel sources throughout to support the activity as well as refill glycogen stores.
Similarly, a Training-level dressage horse who competes a few times per year may meet calorie requirements from a diet of mostly hay, but a Grand Prix competitor will likely require a substantial amount of feed to supply fuel for training and competing at that level. For high-level competitors, a bit of trial and error may be required to determine the best blend of calorie sources to support the fuel needs of the particular individual. Some horses perform at their best utilizing higher levels of dietary starch and sugars while others reach peak performance on diets containing higher amounts of fats and fibers.
Many horses can eat feeds containing fairly high levels of starch and sugars (grain-based or sweet feeds) and perform beautifully while remaining calm and steady while other horses seem to become more reactive or nervous when fed enough calories from typical grain rations to maintain good condition. This has led some horse owners to prefer feeding very low starch and sugar rations or to not feed concentrate feeds at all, only hay, to their performance horses in an effort to maintain a quiet, relaxed attitude. While these diets will often lack important amino acids, vitamins and minerals, they may provide adequate calories to support a horse performing in low-level competitions or participating in only a few classes over a weekend show where they don’t have repetitive training sessions, warm-ups and multiple classes several days in a row. A horse in good body condition who competes at infrequent intervals will have time for the body to replenish used-up glycogen stores to re-fuel the tank.
However, during long competitions or strenuous work over several days, the horse’s glycogen tank may be depleted and without adequate starch and sugar in the diet will often not refuel quickly enough for the next round of competition. There may be horses who perform beautifully during the early rides and then appear to “run out of gas” later in the competition. It is important that a feeding program designed for hard-working performance horses or horses competing over multiple days provides adequate amounts and the proper blend of calorie sources to help top off those fuel tanks within hours following feeding.
Taking all this physiology into consideration, the recommendations for dietary calorie sources to fuel performance horses would be a blend of fats and digestible fibers to fuel aerobic work with sufficient starch and sugar to maintain glycogen stores for use during the anaerobic portions of activity.
In general, good-quality hay combined with feed providing more calories from fats and fibers and a moderate amount from starch and sugar may help maintain a level, obedient attitude while supplying appropriate fuel to support the work. However, individual horses at higher levels may require careful attention to the balance of each of the dietary fuel sources in providing the best nutrition to support the workload of training as well as optimal competition performance.
Katie Young, PhD, is an equine nutritionist and technical services manager with Purina Animal Nutrition. Her responsibilities include 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.
Karen Davison, PhD,is an equine nutritionist and sales support manager with Purina Animal Nutrition. She received her master of science degree and PhD in equine nutrition from Texas A&M University. Her research included early work investigating the use of added fat in horse diets. She spent eight years with the Texas Agricultural Extension Service in the State Horse Specialist Office before joining Purina 22 years ago. She and her family are involved with breeding, training and competing cutting and rodeo-performance horses.
This article originally appeared in the January 2016 issue of Practical Horseman.