Farriers know that there are as many different types of sport horses out there as there are ways to shoe them. The demands that humans place on their animals vary dramatically, from the intense bursts of speed required of a barrel racer or polo pony, to the animated strut of a park-seat Morgan, to the sustained output of an endurance horse or a trail horse working in the Rockies.

All of these activities have one thing in common: they represent more work than the horse would ordinarily choose to do on its own.

That’s not to say they don’t perform for us willingly; horses have been our partners and workers for hundreds of years, and their generosity is one of the most admirable things about the species.

But given their druthers, horses wouldn’t be sprinting anywhere unless a cougar was in pursuit, and they certainly wouldn’t be jumping fences or chasing cattle of there own volition. The work we ask of them represents a level of exertion over and above what their natural diets of gritty, low-quality pasture forages are designed to fuel. That’s why almost all performance horses need a little dietary help in the form of high-energy feeds.

The questions we might ask include: what’s the best way to provide a horse’s muscles, heart and lungs with the “juice” they need without risking colic, founder or a horse that’s bouncing off the walls? Which feeds are the best at delivering energy? Should all performance horses be fed alike? Are there different strategies for different types of work?

Energy In Kernel Form

Carbohydrates, as provided in concentrated form with grains, are the traditional way of supplementing the diet of a performance horse, and in many ways they’re still the best. Carbohydrates are highly ergogenic — meaning that they support or stimulate athletic performance by supplying a serious energy boost.

The downside is that equine digestive systems are actually pretty poorly adapted to digesting large quantities of carbs. If you feed a horse too much grain at one sitting, his gastrointestinal tract may go into a dangerous fermentative overload with colic and/or laminitis the possible result.

How about protein? The fact that protein is a fuel for performance is a long-standing feed myth that I’d like to dispel. While, in a pinch, the horse’s body can convert protein to energy, it’s a very poor way to fuel the muscles. The breakdown of protein molecules releases very little energy, compared to other dietary sources, and the process is metabolically expensive (meaning that almost as much effort goes into getting that energy release as the eventual benefit).

Higher protein diets don’t fuel an adult horse for performance any better than lower-protein ones and they’re often more expensive. Even under maximum conditions, such as Olympic-style or Kentucky Derby exertion, a horse’s protein requirements don’t increase by more than about a single percentage point. So stick to a level of 8% to 11% crude protein in the overall diet (unless your horse is a breeding stallion or a pregnant mare) and save yourself some money.

Fantastic Fats

Are fats the answer? Much has been written in recent years about the benefits of adding vegetable oil, or a high-fat supplement such as rice bran, to the diet of a performance horse. And it’s true that fats are an even more concentrated energy source than grain. Pound for pound, fat supplies almost two and a half times as much energy as an equivalent quantity of carbohydrates, so you can deliver lots of fuel without lots of bulk in the feed tub.

Although the horse’s natural diet contains almost no fat, it easily metabolizes in the small intestine — even animal fats, as it turns out. Studies have shown that as much as 20% of the overall fat in the diet is well-tolerated by horses, with no noted ill effects. Indeed, fat may well be easier, and safer, for horses to digest than carbohydrates.

Fat-supplemented diets have also 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 makes more energy available for physical activity — sometimes as much as 60% more (regardless of the ambient temperature or how skinny or plump the horse is at the time).

So why not eliminate carbohydrates completely from the diet of a performance horse? Well, for one thing, horses will only consume so much fat before palatability becomes an issue. Even with 6% to 8% fat in the total diet, you might have to become quite creative to get a horse to eat his dinner (a problem seldom encountered with grain).

Though fat is a concentrated energy source, it’s not a very versatile one. The horse’s system can only burn it to fuel one type of energy pathway — aerobic metabolism, the type that performance horses draw on to power long-term, light-to medium-intensity efforts such as show-ring performance, most types of ranch work or trail riding. Carbohydrates, on the other hand, can fuel both aerobic metabolism and anaerobic — the latter being the energy pathway which fuels intense, short-term bursts of maximum effort, such as Western games, polo, upper-level show jumping and some forms of racing.

Because most athletic horses draw on both energy systems as they work, the optimum diet provides some of each type of energy substrate.

Power For Pathways

Discussions of the energy systems that horses (and humans) use during athletic effort can get very complicated, so here’s the Reader’s Digest version. 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, is a “start-up” system, which 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. These are used for all low-intensity and endurance activities, especially those requiring a continuous effort of longer than 2 minutes (and possibly lasting many hours).

Glycogen, which is derived from carbohydrates and starches when they are broken down in the gut, is the main energy substrate for aerobic metabolism, though volatile fatty acids (VFAs), derived from fats and fiber, are also used.

The muscle cells will draw on these substrates as needed. Oxygen, from the lungs, is the “fuel” used to burn the glycogen in order to produce ATP (adenosine triphosphate, the “energy molecule”) along with the non-toxic by-products, water and carbon dioxide.

As long as a horse stays below a certain performance threshold, which may vary somewhat depending on the horse’s activity, conformation, muscle bulk and degree of fitness, it 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 if levels of glycogen in the muscles are depleted, fatigue can set in and force the horse’s body to switch to another energy pathway.

During high-intensity exercise bursts of short duration, or whenever glycogen depletion no longer allows a horse to work aerobically, his muscles switch to anaerobic lactic metabolism. 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. For example, an event horse will rely on anaerobic metabolism for the extra burst he needs to take off to jump a fence.

The anaerobic lactic system is completely dependent on stored glycogen in the muscles as an energy source. Since it is a far less efficient system than aerobic metabolism in terms of the ATP produced per molecule of glycogen, it depletes glycogen rapidly.

Conventional wisdom for many years told us that the anaerobic lactic system also had a toxic by-product called lactic acid, or lactate, which was thought to be the trade-off for that second wind that the pathway provides. Nutritionists believed that lactic acid was usually swept away from the muscles by the bloodstream. Yet if a horse is exercising at high intensity, the rate of production might exceed the rate of removal, resulting in lactic acid buildup in the muscles. The point at which lactic acid began to build up was called the anaerobic threshold (usually occurring at a heart rate of about 150 beats per minute), and until recently it was considered a major contributor to fatigue and subsequent performance reduction.

Lactic Acid Vs. Muscle Fatigue

Lactic acid was an equine athlete’s archenemy. Or that’s what everyone believed.

We’re just beginning, rather belatedly, to understand what human exercise physiologists have known for decades: lactic acid is actually an ally. It’s an energy substrarte, rather than a monkey wrench in the works, and a favored fuel of the mitochondria in muscle fibers. Furthermore, progressive conditioning programs can as much as double the mass of those mitochondria so they can use lactic acid more efficiently. It turns out that a muscle awash in lactic acid is one with a plentiful fuel supply.

The belief that lactic acid was responsible for muscle fatigue is now being called “one of science’s classic mistakes.” Its origins lie in a study by a Nobel laureate, Otto Meyerhof, who in the early years of the 20th century cut a frog in half and put its hind legs, no longer privy to blood circulation or oxygen, in a jar.

Then he applied electric shocks to the legs and after a few twitches, the muscles stopped contracting. When Meyerhof examined the muscles, he discovered they were bathed in lactic acid — and concluded, erroneously as it turns out, that a lack of oxygen supply to muscles leads to lactic acid buildup, which leads to fatigue of the muscles.

It took George A. Brooks, a professor in the department of integrative biology at the University of California at Berkeley, to shoot holes in Meyerhof’s logic. But when Brooks first conducted studies, which showed rats burned lactic acid as an energy source, in the late 1970s, he was ridiculed. It took decades of persistence, and repeatable lab results, before the gospel of lactate began to be seriously questioned.

Brook’s evidence was eventually acknowledged as overwhelmingly convincing. Not only is lactic acid an energy substrate, but also it’s the preferred energy source for nerve endings, cardiac muscle, skeletal muscle and even the brain.

As for the idea that lactic acid causes muscle soreness, that doesn’t make much sense either. Studies have demonstrated that lactic acid is swept from the muscles within an hour of exercise and muscle soreness generally appears a day or more later. The time frame doesn’t compute.

Small Proteins Affect Muscles

So what does cause fatigue in equine (or human) muscles? Mike Lindinger, an associate professor in the department of Human Health and Nutritional Sciences and an instructor in the Equine Science Certificate program at the University of Guelph, says it’s mostly due to cytokines. These are small proteins that act as chemical messengers between cells. They react to nerve endings in the muscle, causing pain. Imbalances in the levels of sodium and potassium ions across cell membranes also have something to do with it. And damage from free radicals can contribute in horses exercising over the long term. But there’s no single super villain to slay.

This information isn’t likely to drastically change the way we feed equine athletes, but it does free us from blaming certain feeds for limiting performance by boosting lactic acid levels. It also eliminates trying to moderate the “acidity” of the horse’s system by dosing with vast quantities of alkaline substances such as sodium bicarbonate (a banned practice known as “milk shaking” in the racing industry).

Back To Fat

It’s still preferable for the performance horse to try to work under the anaerobic threshold — the point at which the body has depleted the aerobic system and switches to burning stored glycogen. Pushing back that anaerobic threshold is a major goal of performance enhancement.

That’s where fat comes in. Adding fat to the diet provides a second source with which the body can continue to work aerobically. This delays the switchover to anaerobic metabolism and thus postpones fatigue and performance deficits.

Recent 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. This “glycogen sparing” helps delay fatigue, an important factor in performance enhancement.

So what level of fat is really optimum for an increased performance benefit? That number is still actually under debate. Some researchers recommend 10% to 15% (by weight) of the total daily diet for horses working at the extreme end of the athletic spectrum. Slightly lower levels (6% to 8%) may be fine for the majority of performance horses working at more typical intensities.

Since fat is often touted as an ingredient that provides energy without the “hotness” that carbohydrates provide, it is sometimes recommended in an effort to calm down a hot horse. Unfortunately, this is another myth.

As experts in both human and equine research have noted, carbohydrates are falsely accused of causing a “sugar high.” As a result, substituting fat for a portion of the fed grain will make no difference to a horse’s temperament or attitude. The idea of horses getting “hot” from high-grain diets has more to do with them 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. As most trainers know, when you’re exercising vigorously, you feel good and you have more energy. The fact that you’re getting more groceries is coincidental.

While using fats to partially replace carbohydrates in the diet is a good way to encourage a healthy digestive system, your clients need to be careful with how they feed grain. Instead of delivering it in one big meal, they should feed small amounts more often. And always make sure a performance horse’s diet consists of at least 50% fiber (hay, haylage, beet pulp, pasture, roughage chunks or a combination) by weight.

Fiber is what the horse is really designed to digest, after all.