L-Carnitine Supplementation in Horses: The Basics

In simple terms, carnitine is a substance made in the body that helps turn fat into energy, a process known as fat oxidation. It does so by facilitating the transport of fatty acids into the mitochondria (the “powerhouse” of the cell) to metabolize for energy production. L-carnitine is the form that is widely available and economical, with the “L” indicating the chemical structure of the substance. Usually, the body makes enough for its own needs, but carnitine has garnered attention as a supplement to support performance as well as certain health conditions.

In human exercise physiology, L-carnitine has received a lot of attention for its fat-burning properties and has raised the curiosity of equine exercise physiologists and nutritionists. Horses, like most animals, can synthesize L-carnitine in the liver, kidneys, and brain, utilizing the essential amino acids, lysine and methionine, along with vitamin C and several B-vitamins (B6, nicotinic acid, folate).^*

Several studies have examined the possibility of supplementing oral L-carnitine to support athletic performance. For example, researchers in Italy examined the effects of supplementing 10 grams/day to Standardbred horses (mares and geldings) and reported that five weeks of exercise training on a treadmill changed muscle composition, specifically an increase in Type IIA muscle fibers (the type of fibers that support both endurance and speed work) compared to control horses that received no supplementation.^**

Research also suggests that L-carnitine may support antioxidant status in exercising horses. Free radicals were lower and antioxidant status was higher in exercising trotters supplemented with L-carnitine.⁺

Catherine Whitehouse, M.S., a nutritionist with Kentucky Equine Research, commented, “Fat oxidation increases the concentration of free radicals in the body by nature, so the possibility that L-carnitine supports antioxidant status could be useful in athletic horses. More research is needed regarding L-carnitine before choosing it over other proven antioxidants such as vitamin E.”

In a study examining the effect of L-carnitine supplementation on weight loss and insulin sensitivity in obese ponies, researchers reported that while both exercise and controlled diet supported weight loss and insulin sensitivity, L-carnitine did not enhance the results, nor did it improve glucose or fat metabolism.⁺⁺

Overall bioavailability of L-carnitine in horses has been reported to be fairly low at approximately 7%, while giving more did not appreciably increase absorption. That said, researchers measured an increase in plasma total and free carnitine when Thoroughbreds were given an oral dose of 10 grams per day, an amount reported to be safe.^§ Based on these studies, more does not always mean better!

Another point to ponder: generally, horses and humans can synthesize enough carnitine from lysine and methionine, assuming they’re fed adequate amounts, and most research in both species has had mixed results. The most positive results have been attributed to those with a known carnitine deficiency.

In summary, L-carnitine may increase antioxidant status and the development of certain muscle fiber types that support both aerobic (strength, endurance) and anaerobic (speed) work. More research is necessary to fully understand how L-carnitine can support overall performance, but research suggests it is safe to feed at appropriate doses.

^*Zeyner, A., and J. Harmeyer. 1997. Metabolic functions of L-carnitine and its effects as feed additive in horses: A review. Archives of Animal Nutrition 52(2).

 ^**Rivero, J.L.L., H.P. Sporleder, E. Quiroz-Rothe, I. Vervuert, M. Coenen, and J. Harmeyer. 2002. Oral L-carnitine combined with training promotes changes in skeletal muscle. Equine Veterinary Journal 34(S34):269-274.

⁺Trombetta, M.F., and A. Falaschini. 2003. Influence of L-carnitine on fitness and oxidative stress parameters in Trotter horses subjected to Laval’s test. Italian Journal of Animal Science 2(3): 231-236.

⁺⁺Schmengler, U., J. Ungru, R. Boston, M. Coenen, and I. Vervuert. 2013. Effects of L-carnitine supplementation on body weight losses and metabolic profile in obese and insulin resistant ponies during a 14-week body weight reduction programme. Livestock Science 155(2-3):301-307.

^§Harris, R.C., C.V. Foster, and D.H. Snow. 1995. Plasma carnitine concentration and uptake into muscle following oral and intravenous administration. Equine Veterinary Journal Suppl. 18:382-387.