Influence of l-carnitine on metabolism and performance of sows.

In recent years, l-carnitine has been used increasingly as a supplement in livestock animals. The present review gives an overview of the effects of dietary l-carnitine supplementation on the reproductive performance of sows. Results concerning the effect of l-carnitine supplementation during pregnancy on litter sizes are controversial. There are some studies reporting an increased number of piglets born alive per litter, while others could not find such an effect. In contrast, most studies performed show consistently that l-carnitine supplementation to a sow diet low in native carnitine during gestation increases piglet and litter weights at birth and enhances growth of litters during the suckling period. Biochemical mechanisms underlying the favourable effect of carnitine on intra-uterine growth have not been fully elucidated. There is, however, some evidence that carnitine influences the insulin-like growth factor-axis in sows and leads to greater placentae, which in turn improves intra-uterine nutrition, and stimulates oxidation of glucose in the fetuses. These effects may, at least in part, be responsible for higher birth weights of piglets. The stimulating effect of carnitine on growth of the litters might be due to an improved suckling behaviour of piglets born to l-carnitine-supplemented sows, causing the sows' milk production to rise. In conclusion, recent studies have clearly shown that dietary l-carnitine supplementation increases the reproductive performance of sows. These findings suggest that endogenous de novo synthesis of carnitine is insufficient to meet the metabolic requirement of sows during gestation.