They purport to "Increase power." "Delay fatigue." "Increase stamina." "Build muscle." "Reduce recovery time." "Extensive research has proven..." Doubtless, most of you have seen and read advertisements for nutritional supplements in which the manufacturers make these and other similar claims. In the past decade or so, there has been a tremendous increase in the array of nutritional supplements marketed for use in horses, as evidenced by the huge number of small buckets, tubs, and tubes that line the shelves of tack shops and feed stores. These supplements might contain a specific nutrient or ingredient, or a mixture of ingredients. Of course, the current marketing buzzword for some of these supplements is "nutraceutical," defined as a nutrient that, when taken in large doses, will improve some aspect of body structure or function (see the supplements article in The Horse of February 2000).
In this article, we will consider some of the nutritional supplements that are purported to boost performance in horses. In essence, the major implication of the persuasive advertising referred to above is that administration of these supplements will improve a horse's exercise performance capacity. That is, the horse will be able to run faster, run longer before fatigue, and/or recover more quickly following exercise.
Just how valid are these claims? Can we realistically expect a nutritional supplement to boost a horse's performance? Are there any risks associated with use of such supplements? Unfortunately, for many of the supplements on the market, it is difficult to judge their effectiveness because there is little or no scientific information available. In many instances, there is no understanding of the function a given supplement might have in the body. Even worse, we cannot be sure that the supplement, when ingested, is absorbed into the bloodstream. As well, results from studies in other species, including humans and rats, often are used in support of a claim regarding the efficacy of a supplement intended for use in horses.
Now, I am not suggesting that we discount the claims regarding all supplements just because there is little or no information regarding their use in horses. However, I am suggesting that we apply a healthy level of skepticism to unsubstantiated claims. If the claim seems too good to be true, it likely is! It is important that you, the buyer, educate yourself on the merits of these supplements so that you can make an informed decision regarding their use.
It is only natural that a horse owner involved in competitive events will search for means beyond sound training methods to give a horse an additional advantage. In this vein, the term "ergogenic" has been coined to describe procedures or aids that improve exercise performance. Ergogenic means "work generating," and it is derived from the Greek word ergo meaning "work." Ergogenic aids have been classified into several categories, including:
- Mechanical aids (e.g., lighter shoes or tack).
- Pharmacological aids (e.g., drugs such as anabolic steroids and erythropoietin).
- Physiological aids (e.g., pre-exercise administration of sodium bicarbonate).
- Nutritional aids (e.g., supplements containing vitamins, creatine, or carnitine).
Of course, most equine sporting bodies regulate the use of drugs and employ testing procedures to detect illicit drug use. Therefore, administration of a drug to enhance performance constitutes illegal drug usage. Similarly, racing authorities (Standardbred and Thoroughbred) have banned use of sodium bicarbonate. The use of nutritional supplements and nutraceuticals is legal as long as they are administered by mouth, except in some jurisdictions that ban the administration of certain agents by any route after the horse has been entered.
Then how can an ergogenic aid enhance performance? To answer this question, it is necessary to consider what limits performance during different types of exercise. During high-speed activities, such as racing, it is generally agreed that a horse tires because of the accumulation of metabolic
byproducts--such as lactic acid, ammonia, and heat--in working muscle. So, for example, a substance that reduces the buildup of lactic acid and ammonia or neutralizes their detrimental effects in muscle might delay the fatigue process and allow a horse to run longer or at least maintain maximum speed for a longer period of time.
On the other hand, during more prolonged exercise tasks such as endurance racing, accumulation of these metabolic byproducts does not occur. Rather, depletion of energy reserves and fluid and electrolyte stores are factors that can limit performance and cause fatigue. Therefore, during longer duration exercise, strategies to replace lost fluid and electrolytes or provide energy could allow the horse to run longer before fatiguing.
Keeping these examples in mind, there are several mechanisms by which various foods or nutritional supplements might work to enhance performance:
- Increase the storage or availability of a substance that is limiting for muscular work (e.g., creatine, chromium, carnitine).
- Reduce or neutralize performance-inhibiting metabolic by-products (e.g., phosphates, dimethylglycine, sodium bicarbonate).
- Act as a supplemental fuel source (e.g., glucose, amino acids).
- Facilitate recovery (e.g., vitamins, antioxidants, electrolytes).
Science Or Hype?
As a horse owner or trainer, your job, albeit a very difficult one, is to sort "the wheat from the chaff" concerning the benefits of nutritional supplements marketed for performance enhancement. One way to approach this problem is to consider very carefully the information available on a given supplement. First, is there a scientific rationale that use of a given supplement could produce a performance-enhancing effect? For example, a theoretical basis exists to believe that consumption of creatine will increase the levels of phosphocreatine in muscle, which could possibly improve sprint exercise performance (racing). On the other hand, there is no theoretical basis to suggest that feeding horses bee pollen will enhance performance. In this situation, we all should be very skeptical regarding claims to the contrary.
Even when there is a sound scientific rationale for use of a nutrient or group of nutrients, we are a long way from convincing ourselves that it really works.
The next question is, "Is the substance absorbed from the gastrointestinal tract of the horse such that it is available for use by the body?" If a supplement is supposed to boost performance by increasing the concentrations of a substance in muscle, the supplement must be absorbed and taken up by the muscle.
The final and most important question is: "Do nutritional ergogenic aids work?"
Ideally, the merits of an ergogenic aid have first been tested in a highly controlled laboratory setting, followed by further testing in real performance situations. Unfortunately, very few such studies have been performed in horses. We are not alone in this problem; even in the human field there is a dearth of sound scientific studies regarding the effectiveness of many of the nutritional ergogenic aids.
As a result, the effectiveness of a given supplement usually is based on "anecdotal" evidence and testimonials from those who have administered the supplement to their horses. Again, it is not completely fair to dismiss this information out of hand. However, anecdotal and testimonial evidence tends to be heavily biased--if the marketing claims for a given supplement indicate an ergogenic effect, we expect that this supplement will result in performance enhancement. Yet, it is very possible that any perceived improvements in performance are due to improved fitness, better overall diet, or other factors totally unrelated to use of the supplement in question.
Let's now look at some of the nutritional supplements that have been touted as ergogenic aids in horses. It is not possible to discuss all of these supplements--a staggering number of nutrients and ingredients have been marketed as ergogenics. Rather, I will focus on a few that commonly are used or currently are topics of discussion. Also note that we will not discuss the effects of major changes in diet, such as fat supplementation. That issue will be covered in an upcoming article.
Among human athletes, particularly those involved in strength- or sprint-oriented events, use of creatine (as creatine monohydrate) has become widespread. Similarly, there has been a great deal of interest regarding use of creatine as an ergogenic aid in horses. Creatine is a natural substance--it is synthesized in the liver and kidney, then transported to and stored in skeletal muscle. Also, in meat- and fish-eating species, a significant amount of creatine is provided from the diet. Importantly, however, the creatine content of plant material is low, and therefore, it is not a component of the natural diet of horses.
In muscle, creatine exists in two forms, free creatine and phosphocreatine. Phosphocreatine is important for energy metabolism during muscle contraction, primarily by maintaining levels of ATP. (ATP is the "energy currency" that allows muscle contraction to take place.) Therefore, the main theory behind use of creatine as an ergogenic aid is that increasing the amount of phosphocreatine will help in this maintenance of ATP supply and, as a result, the athlete is able to develop more muscle power during exercise. Higher muscle creatine would also be of benefit when repeated bouts of exercise are performed (e.g., a cutting or barrel racing horse which is required to complete several work efforts over a short period of time) by allowing a more rapid restoration of ATP concentrations. It is also proposed that creatine supplementation results in an increase in muscle mass, although evidence of this is shaky at best.
The rationale for use of creatine as an ergogenic aid is basically sound, but does it work?
Let's first look at the situation in man. Numerous studies have shown that as little as four to five days of creatine supplementation results in a 20% to 50% increase in muscle creatine content, with more modest increases in phosphocreatine. Although this increase in muscle creatine appears to have minimal effect on single bout sprint exercise performance (e.g., sprint track events), there is evidence that weight lifters and other athletes performing repeated exercise tasks benefit from creatine supplementation.
So, in humans, our evaluation of creatine passes scrutiny--there is a sound rationale for its use as an ergogenic, it is absorbed from the gastrointestinal tract, supplementation results in an increase in muscle creatine, and there is evidence of an ergogenic effect. As well, creatine supplementation is safe.
What about creatine for horses?
The rationale for its use holds true, at least for racing horses and those performing other types of all-out effort. However, research studies have shown that creatine is poorly absorbed by the horse. When creatine is fed to horses at doses similar to or even higher than those proven effective in humans and dogs, there is no change in muscle creatine concentration (see figure above). Thus, there is no evidence that creatine supplementation will help the performance horse; without absorption of the ingested creatine and an increase in muscle creatine concentration, there can be no ergogenic effect.
Branched-Chain Amino Acids
Amino acids are the building blocks for protein. The amino acids alanine, valine, leucine, and isoleucine are collectively known as branched-chain amino acids (BCAA) because of their chemical structure. These amino acids can be used as energy sources, and it has been proposed that their administration before and during exercise will decrease lactic acid production by improving the overall efficiency of energy metabolism. Although this rationale is plausible, the data on the ergogenic effect of BCAA are contradictory.
One study (Glade 1989) indicated that horses had slightly lower blood lactate concentration and heart rate during treadmill exercise after nine weeks of supplementation with BCAA. However, this study did not account for improvements in fitness, and it is likely that the changes measured were due to the effects of training rather than the supplement. More recent studies have failed to demonstrate any effect of BCAA supplementation in exercising horses (Casini et al. 2000; Stefanon et al. 2000).
L-Carnitine is another nutrient commonly included in supplements for performance horses. As with creatine,
l-carnitine is synthesized in the body and its highest concentrations are found in muscle. Because l-carnitine is required for metabolism of fat in muscle, it has
been proposed that the availability of
l-carnitine might be a limiting factor for fat use during exercise. This would be a disadvantage during prolonged exercise because use of fat helps preserve the more limited carbohydrate reserves. Indeed, enhanced "fat burning" is often claimed in advertisements for l-carnitine supplements. It is also suggested that increased muscle l-carnitine is beneficial during sprint exercise by reducing lactic acid accumulation in muscle.
At best, the theory behind l-carnitine supplementation is tenuous, and evidence to support use of l-carnitine as an ergogenic aid is lacking. Compared to other species, horse muscle contains very high concentrations of l-carnitine, and research studies have demonstrated that supplementation with very large doses of l-carnitine (up to 60 grams per day) does not alter muscle l-carnitine levels. Although the effects of l-carnitine supplementation on metabolism in horses during exercise have not been reported, the lack of change in muscle l-carnitine does not support an ergogenic effect. On the other hand, it is possible that horses receiving a fat-supplemented diet will benefit from l-carnitine supplementation.
Supplementation with DMG (or its closely related compound, trimethylglycine, also known as betaine) has been theorized to prevent lactic acid buildup in muscle, thus delaying fatigue during high-speed exercise. For this reason, DMG has been widely marketed for use in humans and horses. However, it should now be evident that theory is very different from practice--there is no evidence that supplementation of horses with DMG (or betaine) has any effect on lactate production during exercise, nor exercise performance (see Rose et al. 1989; Warren et al. 1999).
Hematinics, also known as blood builders, are widely used in horses. These supplements usually contain various combinations of iron, copper, zinc, and some of the B vitamins. All of these nutrients are important for the synthesis of hemoglobin (a special protein that carries oxygen in the blood) and red blood cells. Because transport of oxygen from the lungs to working muscle is important for exercise performance, it is common practice to regularly monitor a horse's red blood cell count and hemoglobin concentration. As well, in an attempt to boost hemoglobin levels and exercise performance, hematinics are routinely given to horses.
While it is true that the nutrients contained in hematinic supplements are essential for red cell and hemoglobin production, misconceptions exist regarding use of hematinics in horses. First, in resting horses, measurements of blood hemoglobin levels and red cell numbers can be very misleading and are actually a poor guide to the horse's capacity to transport oxygen during exercise. This is because the horse stores up to one-third of its red cells in the spleen (see AAEP AnswerLine on page 114). During exercise, the spleen releases these red cells into circulation and, as a result, there is a large increase in the horse's capacity to transport oxygen.
Second, administration of these hematinics does not stimulate production of red blood cells and, in this sense, hematinics cannot be regarded as ergogenic aids. Certainly, if the diet is inadequate in these nutrients, the horse will likely benefit from a hematinic. However, horses fed a fortified grain diet (a grain mix to which vitamins and minerals are added) probably is receiving a more than adequate supply of the nutrients required for normal red blood cell production.
Two supplements that recently have come to the fore are gamma oryzanol and hydroxy-methyl butyrate or HMB.
In recent years, these supplements have been used extensively by body builders and weight lifters. Both supplements are touted as "muscle-building" agents. Gamma oryzanol is a natural plant sterol that is found in rice bran. Various supplements containing gamma oryzanol have become available for use in horses. HMB is a metabolite of the amino acid leucine that is thought to prevent protein breakdown in muscle. In doing so, supplementation with HMB might allow for an increase in lean muscle mass.
There is little information regarding
the efficacy of these supplements in horses. Currently, there are no reliable techniques for measurement of muscle mass in live horses. As a result, it will be very difficult to determine whether gamma oryzanol
or HMB truly build muscle mass. Nonetheless, well-controlled studies are needed to evaluate the effects of these supplements.
Do Ergogenic Supplements Work?
If we apply our criteria for evaluation of purported ergogenic nutritional supplements in horses, the answer to this question is mostly "no." With the current explosion in the nutraceutical market, it is inevitable that more so-called ergogenic substances will become available. Before buying these supplements, carefully consider the evidence available and reject claims that seem implausible or those based on data from other species. In many cases, rather than spending money on these supplements, your horse will be better served by evaluation and improvement of its overall feeding program and attention to other aspects of preventive health care.
Casini, L., Gatta, L., Magni, B., et
al. Effect of prolonged branched-chain amino acid supplementation on metabolic responses to anaerobic exercise in Standardbreds. Journal of Equine Veterinary Science 2000; 20: 120-123.
Harris, P.A., and Harris, R.C. Nutritional ergogenic aids in the horse--uses and abuses. In: Proceedings of the Conference on Equine Sports Medicine and Science. Lindner A (ed), 1998: pp 203-218. Wageningen Press. The Netherlands.
Glade, M.J. Effects of specific amino acid supplementation on lactic acid production by horses exercised on a treadmill. 11th Equine Nutrition and Physiology Symposium, Oklahoma State University, 1989: pp 244-251.
Rose, R.J., Schlierf, H.A., Knight, P.K., et al. Effects of N,N-dimethylglycine on cardiorespiratory function and lactate production in Thoroughbred horses performing incremental treadmill exercise. Veterinary Record 1989; 125: 268-271.
Sewell, D.A., and Harris, R.C. Effects of creatine supplementation in the Thoroughbred horse. Equine Veterinary Journal 1995; Supplement 18: 239-242.
Stefanon, B., Bettini, C., Guggia, P. Administration of branched-chain amino acids to Standardbred horses in training. Journal of Equine Veterinary Science 2000; 20: 115-119.
Warren, L.K., Lawrence, L.M., Thompson, K.N. The influence of betaine on untrained and trained horses exercising to fatigue. Journal of Animal Science 1999; 77: 677-684.
About the Author
Ray Geor, BVSc, PhD, Dipl. ACVIM, is professor and chairperson of Large Animal Clinical Sciences at the College of Veterinary Medicine at Michigan State University
POLL: University Equine Hospitals