If there was a nutritional buzzword that was started in the '90s, it was fat. We fitness-conscious (and frequently overweight) North Americans still might not fully understand the differences between "good" cholesterol and "bad" cholesterol, but we all know how to count our fat grams! While we struggle to keep our diets as low-fat as possible, fat has a different focus when it comes to our horses because it's only in recent years that we've recognized the value of raising the fat level in an equine athlete's diet.

Of course, the average human diet (at least in North America) contains well over that recommended 30 grams of fat per day that nutritionists enthusiastically endorse. The horse's natural diet, in contrast, contains almost no natural fat at all. Forages and fibers contribute none, and most grains fed to horses only contain between 2% and 3.5% fat overall. While this leaves the horse at low risk for cardiovascular clogging, it does mean that, traditionally, carbohydrates have been considered the obvious and "natural" energy source for performance horses, and fat rarely has been considered, beyond that little splash of corn oil that's considered good for a shiny coat. Only in the last couple of decades have we begun to realize that fat is also a valuable energy source--and one with many advantages.

Why Feed Fat?

High-fat diets (anything over and above the 2% to 3.5% supplied by a standard grain-plus-forage diet) provide several perks, most notably in terms of energy production for high-level equine performance. Pound for pound, fat supplies almost 2 1/2 times as much energy as the equivalent weight of carbohydrates or starches (traditionally supplied by grains such as oats, corn, or barley). So, if you want to supply more energy to your horse without increasing his overall feed intake, supplementing the fat in his diet can be an excellent way to accomplish that.

Fat also is easily metabolized by horses, despite the fact that their digestive systems (best adapted for the processing of fiber) didn't evolve to deal with it. Studies have shown that as much as 20% overall fat in the diet is well tolerated by horses, with no ill effects noted. Indeed, fat might well be easier for horses to digest than carbohydrates, as it has been demonstrated that a fat-supplemented diet, unlike a high-carbohydrate diet, has no effect on the pH of the cecum (and thus no detrimental effect on the beneficial microflora inhabiting the large intestine). Fat appears to be absorbed almost exclusively in the small intestine.

Another interesting fat digestion fact is that horses can utilize fats well despite the fact that they have no gall bladder. In most mammals, the gall bladder excretes bile and salts to help break down fats, but in horses, the liver seems to take over that function, with no fat digestion problems that research has been able to identify.

Fat-supplemented diets also have been shown to decrease the amount of energy used for heat production in the horse's body. This decreases the horse's heat load, and increases the amount of energy available for physical activity. In one study where horses were fed a fat-supplemented diet, the horse's total body heat production decreased by 14%, and the diet had no effect on the amount of energy needed for maintenance metabolism, therefore leaving more energy available for performance requirements (or for energy storage in the form of glycogen or fat). As a result, 60% more energy was available for physical activity (regardless of the ambient temperature or the horse's body condition score at the time).

Gary Potter, PhD, of Texas A & M University, is a leading equine nutrition researcher who has focused much of his work on the effects of feeding supplemental fat levels to horses.

"Virtually every piece of research published," he affirms, "indicates that there are no detrimental effects to feeding fat. It's beneficial physiologically in a number of ways. The only reason a person would not want to put some extra fat in the diet is if the horse doesn't find it palatable."

Some of the most compelling research behind fat is that which demonstrates a fat-supplemented diet's benefits for high-performance horses (in sports such as three-day eventing, racing, endurance racing, polo, and cutting). To understand how fat acts as a performance enhancer, we first have to understand some exercise physiology basics.

Dietary Fat For Athletic Performance

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

There are two main energy pathways by which a horse's muscle cells are fueled to do work. (A third pathway, called "anaerobic alactic" metabolism, or sometimes "phosphogen" metabolism, is a start-up system that only comes into play for bursts of hundredths of a second.) 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, which is 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 is the fuel used to burn the glucose in order to produce ATP (adenosine triphosphate, the "energy molecule") along with the non-toxic byproducts 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. The process, while efficient, is not foolproof--in particular, insulin can 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 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, conformation, muscle bulk, and degree of fitness), he can work aerobically. It's essentially a "clean-burning" system, which 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 glycogen is drawn upon, then depleted, fatigue can set in and force the horse's body to switch to another energy pathway.

During high-intensity activity exercise of short duration, or when glycogen depletion no longer allows a horse to work aerobically, his muscles will utilize anaerobic lactic metabolism. Sprint-type activities of about 10 seconds to two minutes in length are typical anaerobic activities--barrel racing is a good example. When the aerobic system is working near its full capacity, the anaerobic system will also "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 far less efficient a system than aerobic metabolism in terms of the ATP produced per molecule of glycogen, and so it depletes glycogen rapidly. It also has a toxic byproduct, lactic acid, which is the payoff for that sudden burst of energy. Lactic acid is usually swept away from the muscles by the bloodstream, but if a horse is exercising at high intensity, the rate of production can exceed the rate of removal, allowing lactic acid buildup in the muscles.

The point at which lactic acid begins to build up is called the anaerobic threshold (occurring at a heart rate of 140 to 150 beats per minute), and it is a major contributor to fatigue and subsequent performance reduction. In the short term, lactic acid accumulation lowers the pH within the muscles, inhibiting enzyme action. In the longer term, it can damage muscle fibers and create muscle stiffness that develops after exercise.

Pushing back that anaerobic threshold is a major focus of performance enhancement, and that's where fat comes in. When fat is broken down in the digestive tract, it 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 switch-over to anaerobic metabolism, and thus postponing lactic acid buildup, fatigue, and performance decreases.

Studies have indicated that if the 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. Horses fed a high-fat diet also 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 fastest!

Horses fed high-fat diets (15% added soy oil) appear to perform better than those fed either a high-starch diet (40%) or a high-protein diet (25%). This increased performance was noted for both high-speed activities (racing) and moderate-speed activities (fast trot/slow canter speeds of about five meters per second). The increase in performance was judged in terms of the blood glucose concentration (which decreased less, and for a shorter duration) and in terms of plasma lactate (lactic acid) levels, which were substantially lower than those found in horses on high-carbohydrate diets.

These benefits might produce only subtle results--but even a gain of a few feet on a racetrack might result in a Derby win. Even at lower levels of performance, the change can be valuable. For example, a low-goal polo player might find that his horse can recover more quickly, and perhaps be able to play one more chukker.


All of this information is not saying that fat is a miracle ingredient. The body must "learn" to use fat as an energy source, a process that requires considerable metabolic adaptation, according to Potter.

"The muscle cells have to adapt to fat as a fuel source, and that can take three to four weeks," he observes. "In fact, the blood chemistry may continue to adapt for up to six weeks. What this means is that you can't just start feeding fat the day of the big race and see results. You not only have to put him on the fat-supplemented diet a good month in advance, but you also have to challenge the system so that it begins to adapt. For a racehorse, that means you have to race him on the new diet, not just train him conservatively, in order to help him begin to assimilate the new energy source."

As nice as it might be to contemplate improving further on the benefits of feeding fat by feeding greater amounts--perhaps eliminating grain altogether--unfortunately, it just doesn't work that way. Remember that only carbohydrates can fuel the anaerobic system of metabolism, which all horses use to some degree in their work. Also, forages alone provide a minimum of carbohydrates. (Fed by itself, forages provide plenty of fuel for maintenance metabolism, but not enough, for the vast majority of horses, to do the work we ask of them.) Grain in the diet is an important fuel source for any performance horse, and Potter notes that in his nine years of study of supplemental fat diets, it was confirmed that high-fat diets work best in conjunction with fairly high grain diets, for maximum benefit in hard-working horses (such as 100-mile endurance racers, Thoroughbred and Standardbred racehorses, and upper-level three-day event horses).

"You do have to make sure there's enough carbohydrate in the diet, too," he says. "The combination of grains and fats should make up half the total diet, by weight, or even a little more, if you're feeding a horse who's really working hard."

So what level of fat is optimum for a performance benefit? Potter recommends a level of 10% (by weight) of the total daily diet, though John Burton, PhD, an equine nutritionist at the University of Guelph in Ontario, suggests that slightly lower levels might be more appropriate for horses working at a lower level of intensity. The level of fat you choose will depend somewhat on the activity you're asking your horse to perform. Some studies have indicated that levels up to 15% are beneficial for horses which are involved in intense, long-term endurance activities (chiefly competitive trail and endurance racing, and upper-level three-day eventing). However, even a level of 6-8% will result in some performance benefit for horses involved in more moderate activity.

Other Perks

For the vast majority of us who are dealing with horses not at the cutting-edge of high performance, feeding fat can be well worth considering for reasons other than performance enhancement.

First, it's true that supplemental levels of fat can enhance the quality and shine of the hair coat, giving your horse a healthy glow that reflects particularly well in the show ring. Supplemental fat also can help put or keep weight on a "hard keeper," provided he is not in heavy work. Just as we do (far too efficiently, sometimes), horses will store excess fat in the adipose tissues--so for plumping up a skinny horse, added fat is an excellent solution that carries far less risk of stomach upset and other complications than does a switch to a high-carbohydrate diet.

Older horses also can benefit from a high-fat diet. As the condition of their teeth starts to deteriorate and their digestive efficiency begins to wane, easily digested fat can help prevent them from losing condition and becoming ribby. Broodmares, too, can reap the rewards of added fat. Studies have indicated that a mare which recently has gained some condition (easily achieved by feeding added fat for a month or two before breeding) might get in foal more easily and maintain her pregnancy with less difficulty (if she was not obese to begin with). In addition, a high-fat diet can help her deal with the stress of lactation, which can be considerable. A third perk is that her milk will be higher in fat (mare's milk being fairly low to begin with), and as a result, her foal will tend to gain weight and condition more easily.

Fat is often touted as an ingredient that provides energy without the "hotness" that carbohydrates provide--so it is sometimes recommended in an effort to calm a hot horse. Unfortunately, this perk is a myth. As experts in both human and equine research have noted, carbohydrates are falsely accused of causing a sugar high, and so substituting fat for a portion of the grain being fed will make no difference to a horse's temperament or attitude. Potter surmises that the idea of horses getting "hot" from high-grain diets has more to do with their being in hard training at the same time their grain ration is increased than it does with any physiological effects on a horse's manners.

"When you're exercising vigorously, you feel good, and you have more energy," he says. "The fact that you're getting more groceries is coincidental."

How To Feed Fat

Adding fat to your horse's diet can be done in a number of ways, and Potter says that practically any digestible source of fat, either vegetable or animal, can be used. The only source he does not recommend is the rumen-protectant variety of fat that is designed for cattle, which horses will find at best indigestible, and at worst, toxic.

It's interesting to note that horses actually can digest fat from animal sources (such as tallow) very well, and animal-fat products generally are much less expensive than comparable vegetable fats or oils. However, animal fats seldom are used in horse rations for two reasons: First, at room temperature, they usually are solids, so they must be heated to liquid in order to mix with a grain ration; second, their palatability is generally low (try to get a horse to eat something that smells like bacon grease!).

Of the vegetable sources of fats (which usually come in the form of oils), corn and soy oil are traditional favorites, and are available at most feed mills as well as many supermarkets. Other vegetable oils are just as suitable, however, although many horse owners avoid canola oil as its palatability isn't as good as some of the others. Top-dressing your horse's grain ration with oil is a simple process of measuring and pouring--but like any feed additive, it should be introduced gradually, over a period of two to three weeks.

There also are other feed additives that are relatively high-fat, most notably rice bran, which has gained considerable popularity in parts of the United States. Rice bran products, which come either as a powder or as an extruded pellet, are approximately 22% fat, which means you have to feed considerably more of them to get the same benefits as you would from a 100% fat product such as vegetable oil. Rice bran has the advantage of being much more stable, however, and is often preferred in warm, humid climates where oils and animal fats tend to go rancid very quickly. Extruded soybeans, another high-fat product, are good for young growing horses because they also are a good protein source; they're not as appropriate, for that same reason, for mature animals.

One of the simplest ways to add fat to your horse's diet is to choose a commercial grain ration that is fat-supplemented. Many feed companies now offer these products, usually as part of their premium line, and the feeds often are equipped with extra anti-oxidants to prevent spoilage, a management perk. Look for a crude fat level of 8-10% on the label (and if your horse is a mature animal not being used for breeding, a protein content of 10-12% at most), and introduce it gradually to your horse's diet. If your horse objects to top-dressed oil or rice bran, a commercial product (in which the fat is disguised) might be the best way to go.

Whatever way you decide to add fat to your horse's diet, you must consider how it will affect the overall nutrient balance of his daily ration.

"You have to adjust the feed intake for the increased energy intake," says Potter. "Otherwise, the horse gets fat, which is counterproductive to his training."

But in the process of cutting back on your horse's grain, you also reduce the concentration of vitamins and minerals he receives. Potter stresses that it is very important, when making this change, to work with an equine nutritionist (whom you can contact through your feed dealer, local veterinary college, or state extension service) to make the necessary adjustments so that your horse doesn't get cheated out of essential minerals, like calcium and phosphorus. You might have to consider adding a supplement to compensate for these losses.

If you're feeding a commercial ration that is a premium product, you might not have to worry about deficiencies of vitamins and minerals, since many of these are deliberately designed with an excess of most nutrients. If you decide to go with an all-inclusive, high-fat feed, the feed company has likely already done the ration balancing for you. Consult with your equine nutritionist to be sure.

One thing fat is not going to do is make feeding any cheaper--pound for pound, it usually works out about as expensive, if not a little more so, than a comparable quantity of carbohydrates.

"Is it cost-effective?" says Potter. "I don't think anyone knows. But if you can move a racehorse up six feet in a mile and a half, it doesn't really matter what it costs--does it?"

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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