Increased ejaculate volume and more sperm cells have important practical consequences for artificial insemination. An increased sperm count in the ejaculates is probably not due to L-carnitine boosting the spermatogenesis, but it results from the fact that the supplement contributes to increased survival of spermatozoa in the epididymis. L-carnitine takes part in mitochondrial acetylCoA conversion to acetylcarnitine, which prevents accumulation of acetyl groups that inhibit the activity of pyruvate dehydrogenase responsible for mitochondrial energy metabolism (Rebouche and Seim 1998). This function of L-carnitine enhances sperm survivability and, as a consequence, increases the total number of sperm cells in the ejaculate (Jeulin and Lewin 1996). Kozink et al. (2004) have not observed total spermatozoa to increase in the ejaculates of young boars that received 500 mg of L-carnitine per day. However, the authors have observed significant increasing of spermatozoa concentration already after one week of addition of L-carnitine and continued for the majority of the 16-week study. Acetylcarnitine is a source of energy needed by sperm cells for their progressive movement (Jeulin and Lewin 1996). A positive effect of L-carnitine on sperm motility was found in men (Vitali et al. 1995; Matalliotakis and Koumantakis 2000) and rats (Palmero et al. 1990). Our experiment has demonstrated that the administration of 500 mg of L-carnitine per day for 5 weeks only slightly increased the percentage of motile sperm