Carbohydrates in the Performance Horse: New Trails to Safety and Performance
by Tom Ivers
Through evolution, the equine athlete has been highly tuned to the importance of plant carbohydrates. The horse prefers timothy to steaks, and we are not surprised. In research, and in conditioning our athletes, we've seen that carbohydrate supply is critical for equine athletes. We've known that muscles depleted of carbohydrate-derived glycogen stop functioning and die. We know that carbohydrate-derived blood glucose can drop so low that the central nervous system ceases functioning, with coma and death as a consequence. Indeed, without glucose in the blood and glycogen in the muscle, the horse cannot function, despite large stores of fat and plenty of protein in the lean muscle mass. We've seen hard working horses that are fed too few carbohydrates; they lose lean muscle mass as they attempt to supply working energy by tearing down (catabolizing) their own flesh. And since grade school we've known that carbohydrates in the form of sugars and starches are digested to form simple sugars, readily available energy that powers every organ in the body. How much more can we learn about this basic, simple fuel food?
Plenty. World-wide research with carbohydrates in athletes continues to produce exciting and very useful findings. For example, we now know that sugar is the most anabolic substance available to athletes. Many of you will immediately think of anabolic steroids - testosterone and testosterone-like substances - as the primary anabolic agents. They aren't. Those substances are anti-catabolic; they prevent some tissues from being broken down as the body goes through its normal protein turnover. The result is a gain in lean muscle mass. The actual tissue building occurs due to another hormone, Insulin Growth Factor I (IGF-I)
As you know, athletes proceeding through a conditioning program and competition tend to become fitter, in a process known as acquisition. If the exercise stressors are well matched with energy intake, then the tissues being used hard will strengthen. If the energy intake is too low, then the same tissues will be broken down (catabolized) and the horse will lose weight and fitness. Muscle soreness and stiffness is generally the first outward sign other than body weight loss. The body has a continuing choice, depending on energy supply, to go either anabolic (builds and repairs tissue) or catabolic (tears down tissue for energy).
This situation is best seen immediately after a tough race or workout. In these circumstances, muscle glycogen and blood glucose are depleted. Since the brain needs glucose in the blood, all systems are directed toward raising blood glucose levels as a first priority. But studies in humans and other mammals show that a dose of a fast-acting carbohydrate immediately after a hard workout or hard race solves the blood glucose problem. Then the body doesn't have to catabolize its own tissues for energy. The same dose of concentrated energy - a sports drink containing glucose in humans, or a glycogen loader paste in horses - triggers IGF-1 to go to work, rebuilding injured tissues and overbuilding stressed tissues. The result is faster recovery, increased acquisition, and reduced soreness and stiffness.
We now know that, as local muscle glycogen is depleted, the athlete must experience fatigue and slow down. This does not mean that the muscle cell must be completely depleted of glycogen - as little as 10% glycogen depletion in a muscle cell will begin to cause a decrement in muscle contraction time and power. By the time a muscle cell is 50% depleted of glycogen, fatigue is compromising performance. We discovered this phenomenon in racehorses and endurance horses in experiments with glycogen loading.
We've always thought of lactic acid as being the primary cause of fatigue in the athlete. It's not. Muscle fuel depletion is the principal cause of fatigue, not only in sprinters but in endurance horses as well. For example, the first horse we documented through a glycogen loading protocol was a Thoroughbred named Acey Mack. This horse was trying hard coming out of the gate fast and usually leading the race until the final quarter mile - at which point he would slow down so quickly that the horses coming up behind him had to get out of his way. Race after race, Mack delivered the same kind of failing performance. Post-race bloods demonstrated 22 millimoles of lactic acid and 350 CPK (muscle enzyme indicating muscle damage). These are within the "normal" post race ranges.
We then loaded Mack with a product much like Vita-Flex's CarboCharge (CarboCharge is the improved version), feeding multiple doses each day for the four days before the race. Mack gained 15 lengths and was second by a nose. In his next race, he was second by a nose again. Then he won four in a row - all of these races run under a glycogen loading protocol. What's interesting for our discussion is that immediately after a winning performance, CPK was reduced to 250, but the lactic acid was so high our YSI Sport 1500 lactate analyzer could not give us a reading other than "higher than 35 millimoles." The horse had double his earlier post-race lactic acid and was winning, not slowing down. We were astonished, to say the least.
Since that time, thousands of racehorses, Standardbreds, Quarterhorses, and Thoroughbreds, have been glycogen-loaded and have demonstrated the kind of improvement that brings a horse from the middle of the pack to the winner's circle. We have also run experiments on eventers and endurance horses, and there is a problem. Glycogen loading tends to make a horse feel like Godzilla on race day. This isn't a very good situation for eventers, where control is of primary concern during the dressage section which occurs on the first day. A similar situation exists in endurance horses - you don't want the athlete burning up the trail at the start when he's got 50 to 100 miles of ground to cover.
Still, endurance horses and eventers also need a supply of readily available energy throughout their competitions. Without carbohydrate, fats and proteins cannot be processed. Vita-Flex provided CarboCharge for some experiments with endurance horses. For this protocol we borrowed the human science that demonstrated that periodic intake of sugar-based drinks improved marathon performance. We fed the glycogen loader two hours out from the beginning of the endurance ride and then every two hours during the ride. More than a dozen endurance riders reported back that their horses showed improved energy and enthusiasm throughout the ride and had superior vet checks. None reported anything negative.
Event riders have reported similar results with doses of glycogen loader beginning immediately after dressage, with the pre-competition doses two hours out from the start of competition. And that leads us to another new bit of knowledge about blood sugar; the horse will not perform well if he starts the event with a low blood glucose. Instead he's lethargic; sleepy. This is because the central nervous system is slowing down metabolism in order to preserve the blood glucose that exists. Normally, grain or sugar will produce a peak blood glucose in 1.5 to 2 hours. Vita-Flex has designed a long-chain sugar component for their CarboCharge so that the loader can provide some leeway in feeding times. Still, two hours is the safest pre-event timing we've used and, with continuing work, maintenance doses every two hours seem to be the most productive protocol.
How will carbohydrate ingestion affect other performance categories? Glycogen loading should be effective in polo ponies. It has proven effective in barrel racers. We have not tested the loader on cutting or reining horses, hunter-jumpers, or show horses, but any event that can produce fatigue in the horse should benefit from carbohydrate loading. For example, steeplechasers and timber horses benefit greatly from glycogen loading. The last thing these animals need to face as they go over a jump is fatigue.
And when we talk about preventing fatigue, we're also talking about preventing injury - not just winning an event. In race horses, reducing or eliminating fatigue is very important - a horse that is staggering down the stretch is susceptible to a dozen different injuries as biomechanical stressors multiply with missteps and shortened, delayed strides.
Recently there has been an over-enthusiasm for high fat diets in performance horses. Remember this: fat is fed to "spare" glycogen. If sufficient carbohydrate is fed, glycogen doesn't need to be spared. The problem with chronic fat feeding is that, over time, the muscle cells begin to learn to use fat instead of glycogen, storing away lipolytic enzymes instead of glycolytic enzymes. In racehorses, this causes a slowing in performance. Fat may be useful in endurance horses, but Dr. Gary Potter, the author of many fat-feeding studies, tells me that the first priority in working horses is carbohydrate intake. He says fat can be used as a supplement, but not without a strong carbohydrate presence and not in high percentages of the diet (he suggests 10% max). Sure, it's interesting that the horse can do well on three times as much fat as he would get in a standard diet. But the old saying, "fat burns on the flame of glycogen," still applies.
Now, feeding enough carbohydrate to support hard exercise can be a problem. You cannot feed a racehorse enough plain oats to support a genuine interval conditioning program. Corn and barley can help bring in more concentrated carbohydrates, but even then there are situations that demand a sure-fire energy delivery system. For example, the horse that has been racing hard while being underfed will eventually come up muscle sore, and then anorexic; sore horses go off their feed. You can back off the racing/training schedule, allowing the horse to decondition, or you can fill in the holes of carbohydrate intake with a glycogen loader used as an energy source every day (half doses of the loading protocol) until the horse is back eating and feeling good.
Finally, one interesting side effect of carbo-loaders. Whether it's the chromium or the long chained sugars we don't know, but a dose of the loader tonight will eliminate tying up tomorrow. We don't know why. In fact, we don't really know what tying up is, exactly. But if you have a horse in the middle of the syndrome, tying up every day, you can break him out of it with a dose of glycogen loader the night before the next scheduled exercise.
We are seeing that the horse's inherent preference for dietary carbohydrates runs deeper than we thought, to impact many realms and phases of metabolism. More information will certainly follow. But we know enough now to start applying these findings to improve the energy nutrition of our carbo-centered athletes. In doing so we can reduce the peaks and valleys of blood glucose during and after performance, and help promote efficient, non-damaging metabolism. And that is the biological foundation of safe and rewarding performance.