It has been shown that l-carnitine supplementation of sows increases their milk production and the postnatal growth of the suckling piglets. To test the hypothesis that this effect is due to an improved suckling behaviour of the piglets, two experiments with sows were performed. Two groups of thirteen or ten sows each (in experiments 1 and 2, respectively) were fed diets with or without supplemental l-carnitine during pregnancy (125mg/d) and lactation (250mg/d). After birth, the litters of all sows were standardised to equal sizes of eleven and nine piglets per litter in experiments 1 and 2, respectively. In experiment 1, the piglets of l-carnitine-supplemented sows had a higher total suckling time per day on days 3, 6 and 9, and greater weight gains during the suckling period, than the piglets of control sows (P<0·05). In experiment 2, all litters were taken away from their mothers and switched to other sows. Half of the control sows and half of the l-carnitine-supplemented sows were given litters born to control sows, the other half of each group being given litters born to l-carnitine-supplemented sows. Piglets born to l-carnitine-supplemented sows had a higher total suckling time per day on day 3 and greater body weight gains during the first 14d compared with piglets born to control sows (P<0·05). This study shows that piglets born to sows supplemented with l-carnitine are able to suckle for longer, which enables them to obtain more milk and grow faster than piglets born to control sows.