Dietary Fat's Role in Equine Athletic Performance

Dietary Fat's Role in Equine Athletic Performance

Fat is an energy substrate that helps the horse’s body use itself with more efficiency with less fatigue.


Grains, the “traditional” feed for high-level physical activity, supply carbohydrates and starches—versatile energy substrates that fuel the horse’s muscles for athletic endeavors of all kinds. Fat is also an energy substrate which, while not as flexible as carbohydrates in terms of the types of activities it can fuel, might in many ways help the horse’s body use itself with more efficiency and less fatigue.

Two main energy pathways fuel a horse’s muscle cells to do work. (A third pathway, called “anaerobic alactic” metabolism, is a “startup” system that only comes into play for extremely short bursts.) The predominant energy pathway is aerobic metabolism, which the muscles use whenever they can, for all low-intensity and endurance activities, especially those requiring a continuous effort of longer than two minutes (and possibly lasting many hours).

Blood glucose, derived from carbohydrates and starches when they are broken down in the gut, is the main energy substrate for aerobic metabolism, and muscle cells will draw on blood glucose as needed. Oxygen, from the lungs, is the “fuel” used to burn the glucose to produce ATP (adenosine triphosphate, the “energy molecule”) along with the non-toxic by-products, water, and carbon dioxide.

Blood glucose levels are regulated by insulin, which responds to high blood-glucose levels (as happens two to three hours after a high-carbohydrate meal) by increasing and converting excess glucose to glycogen, the form in which it is stored in muscle, fat, and liver cells. Another hormone, glucagon, can reverse the process, converting glycogen back into glucose and releasing it into the blood. This mechanism, while efficient, is not fool-proof—sometimes insulin might “spike” in response to a large load of carbohydrates being introduced, causing large amounts of blood glucose to be converted to glycogen and stored away. This can leave a horse hypoglycemic (low in blood sugar) and feeling weak and fatigued.

As long as a horse stays below a certain performance threshold (which can vary somewhat depending on the horse’s activity, his conformation and muscle bulk, and his degree of fitness), he can work aerobically. It’s essentially a “clean-burning” system that horses can maintain indefinitely, as long as fuel continues to come in on a regular basis. Thus, it’s the least taxing to the system—but as blood glucose drops and as glycogen is drawn upon and then depleted, fatigue can set in and force the horse’s body to switch to another energy pathway.

During high-intensity exercise of short duration, or when glycogen depletion no longer allows a horse to work aerobically, his muscles will use anaerobic lactic metabolism. “Sprint” type activities of about ten seconds to two minutes in length are typical “anaerobic” activities; barrel racing is a good example. When the aerobic system is working close to its full capacity, the anaerobic system also will “kick in” like a supercharger, augmenting rather than replacing the aerobic metabolism. The anaerobic lactic system is entirely dependent on stored glycogen in the muscles as an energy source. It is a far less efficient system than aerobic metabolism in terms of the ATP produced per molecule of glycogen, and so it depletes glycogen rapidly.

Here’s where fat (finally!) comes in. Fat broken down in the digestive tract becomes fatty acids—which can fuel aerobic metabolism but not anaerobic. Adding fat to the diet provides a second source with which the body can continue to work aerobically, delaying the switchover to anaerobic metabolism and thus postponing fatigue and performance deficits.

Studies have indicated that if the horse’s system has supplemental levels of fat available as an energy source, it can “learn” to use it in preference to glycogen, thus increasing the amount of muscle glycogen the horse maintains.

That’s good, because while glycogen stores in the body are limited, fat (in the form of stored short-chain volatile fatty acids, or VFAs) is the most abundant energy source in the body. Horses fed a high-fat diet appear to have better muscle glycogen utilization during anaerobic (sprint-type) activities and no change in their blood glucose concentration (and thus their insulin concentration) while working anaerobically. During aerobic (endurance-type) activity, the same horses showed less decrease in their blood glucose concentration than did horses fed a traditional grain diet, and there was muscle glycogen sparing (less utilization of stored glycogen). This glycogen sparing helps delay fatigue, an important factor in performance enhancement. As a racing sage once observed, it isn’t so much which horse is going the fastest at the end of the race — it’s more about which horse is slowing down the least!

In a future article, we'll weigh the pros and cons of adding fat to a horse's diet.

About the Author

Karen Briggs

Karen Briggs is the author of six books, including the recently updated Understanding Equine Nutrition as well as Understanding The Pony, both published by Eclipse Press. She's written a few thousand articles on subjects ranging from guttural pouch infections to how to compost your manure. She is also a Canadian certified riding coach, an equine nutritionist, and works in media relations for the harness racing industry. She lives with her band of off-the-track Thoroughbreds on a farm near Guelph, Ontario, and dabbles in eventing.

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