G. D. Potter and P. G. Gibbs
Equine Science Section,
Dept of Animal Science
Texas A&M University

Horses that perform at moderate and intense levels of activity have very high requirements for energy. While the work they do often requires a combination of aerobic and Anaerobic metabolism, those horses frequently have trouble obtaining sufficient energy from conventional concentrates. Research has shown that fat can be utilized as part of the total dietary energy source to provide a more concentrated supply of energy in an amount of feed that can be safely consumed. Fat or oil can be incorporated into a grain mix and increased to 10% of the concentrate without negatively affecting dry matter or fiber digestibility. Adding fat to the diets of horses in race and cutting training improves muscle glycogen storage and work performance. This is due to a "glycogen sparing" effect of feeding fat. Therefore, the daily quantitative supply of energy is important, but it is equally important to supply significant amounts of that energy in a form to promote synthesis and storage of muscle glycogen in horses that are expected to do short term, high-velocity, anaerobic work.

Several factors need to be considered when fat supplemented diets are to be fed. First of all, horses need time to adjust to fat utilization and this adaptation time can be as much as three weeks. Secondly, a fat-supplemented diet will provide more energy, so total daily feed intake must be decreased if the work level and body condition are to remain the same. Horseowners who intend to top dress fat or oil on the feed should begin with a small amount of added fat and increase amounts gradually, keeping an eye on eating behavior and general well being. And thirdly, on-the-farm supplementation of fats/oil requires a reassessment of the total dietary nutrient balance, especially for young, growing horses that receive exercise.

Energy requirements for work take precedence over the storage of energy as fat in the body. Therefore, animals that are not fed sufficient energy to maintain body weight will mobilize stored energy to meet energy requirements for work. If a horse isn't fed sufficient energy to meet energy requirements, the horse will metabolize energy stored in body tissues, including muscle glycogen stores, in an attempt to maintain body weight. Therefore, the very thin horse may not be physiologically capable of strenuous exercise because of an inadequate supply of available energy. So, to maintain reasonable levels of body fat in horses that are being worked hard it is important to increase the energy density in the diet and adjust the amounts of feed proportionally. Adding fat to the diet of exercising horses results in muscle glycogen concentrations that are higher in thin horses than when they are fed conventional diets. Therefore, feeding some fat to equine athletes helps protect them from fatigue even when their body condition is reduced.

While it is important to maintain equine athletes in adequate body condition to do their job, excess body fat causes thermal stress on the horse. Research has shown that, regardless of body condition, feeding a fat-supplemented diet reduces thermal stress on horses. Thus, if performance horses can be maintained in lean condition (but not thin), fed a fat supplemented diet with adequate carbohydrate and other nutrients, and trained properly, perhaps performances can be improved, fatigue can be delayed and injuries can be reduced in equine athletes.