It is well known that broiler meat has high-quality protein and low fat content. Thus, the demand for broiler meat has increased, and the broiler industry needs to augment production to respond to higher demand. This aim can be achieved by improving the body weight gain (BWG) and feed efficiency (FE) of broilers. Given the importance of efficiently raising broilers with less feed, we have focused on diet supplements, especially, L-carnitine. L-carnitine is involved in fatty acid metabolism in that it promotes ß-oxidation by acting as a carrier for the transport of long-chain fatty acids from the cytosol into the mitochondria (Metzler, 2003). Research on pig metabolism has shown that body fat decreased with the addition of L-carnitine to the feed (Heo et al., 2000). This contributes to fat oxidation and energy production. L-carnitine can be synthesized endogenously from methionine and lysine (Cox & Hoppel, 1973a, 1973b); however, it is well known that these amino acids are first-and second-limiting amino acids in poultry diets. Furthermore, in general, the amounts of L-carnitine in plant-based feedstuff are low (Borum, 1983; Borum & Broquist, 1977; Mitchell, 1978). Thus, it is unlikely that a diet contains sufficient amounts of L-carnitine as well as methionine and lysine. With respect to de novo synthesis of L-carnitine, it is necessary for a diet to meet or exceed the required levels of methionine and lysine. For these reasons, the addition of L-carnitine to the diet is as necessary as the addition of methionine and lysine. In addition, L-carnitine may affect not only lipid metabolism but also protein