Acetyl-L-carnitine is a metabolite of L-carnitine, derived from the amino acid L-lysine in a series of reactions which require cofactors of methionine, zinc, iron, vitamin C, niacin and vitamin B6. It is synthesized in the horse’s liver, kidney and brain. Carnivores and omnivores have a rich dietary source of carnitine from animal products but herbivores like horses must make their own supply.
Active horses have higher carnitine requirements
Since there’s none in their diet, horses can obviously make enough L-carnitine to survive as a species but supplies may not be optimal for muscular demands, especially since lysine and methionine are the two most commonly deficient amino acids. L-carnitine is essential for the aerobic burning of fats because it acts as a carrier to bring the fatty acids across the mitochondria membrane. Only the volatile fatty acid acetate and the medium chain triglycerides don’t require the carnitine carrier.
In normal muscle metabolism, the acetyl-l-carnitine metabolite of L-carnitine naturally has even more important effects via activation of an enzyme called AMPK:
- helps direct glucose into energy pathways and away from storage as glycogen
- signals the cell to produce more mitochondria
- assists burning of fatty acids
- aids in inhibiting storage of fat
- encourages increased blood supply to muscle
This basically mimics the normal effect of exercise on muscle, which makes the muscle level of L-carnitine drop and the level of acetyl-L-carnitine significantly increase.
The well documented effects of L-carnitine and acetyl-L-carnitine make it a logical possibility as a supplement for athletically active horses but it goes beyond just theory. Rivero et al  showed support of the metabolic response to training with supplementation. Sato et al  showed moderation of the serum muscle enzyme release that normally occurs in early training and less exercise-related muscle pain when supplementation was paired with the antioxidant astaxanthin.
Acetyl-L-carnitine is also well documented to protect the myelin sheath surrounding nerve axons and to help preserve normal sensory nerve function. In addition, acetyl-L-carnitine is important for normal semen quality.
L-carnitine and acetyl-L-carnitine can be interconverted by the body. When you supplement one form, the other form also increases but higher levels will be achieved of the one supplemented.
Horses have been supplemented with dosages ranging from 10 to 100 mg/kg. An easy to remember dosage which was used successfully in the Rivero study is 1 gram/100 lbs of body weight.
Acetyl-L-carnitine is a white crystalline solid that resembles snow. It has a mild odor similar to vinegar. Humans react differently to the taste. To me, it is “tart”. Horses very rarely object to having it added to their feed. Side effects are extremely rare. Mild bloating has been reported on occasion and disappears by splitting the daily dose between two meals.
Consider supplementation for stallions, horses just starting a training program and horses that may benefit from muscle or nerve support.
Eleanor Kellon, VMD