The suckling behaviour of domestic pigs living in a socially and ecologically rich outdoor environment was examined in order to obtain a baseline for comparison with behaviour in more restricted and barren environments. It was found that the piglets' growth rates were not consistently influenced by their suckling location along the udder, and that the concept of dominance at the udder was not justified. Crowding at the udder was probably an important factor prompting piglets to seek milk and solid food elsewhere, and two piglets switched from suckling from their own mother to suckling from another sow. True communal suckling was not exhibited. Piglets were responsible for locating their preferred teat and defending it from others. Sows did not attempt to prevent familiar piglets from other litters from suckling from them, although they sometimes terminated a suckling bout when disturbed by fights at the udder. Synchronization of suckling between litters was common. Suckling bouts did not always result in milk let-down, indicating that this is not a phenomenon exclusive to intensive housing systems. Weaning occurred naturally between 60 and 100 days after birth, and its timing varied both within and between litters but was not closely linked to the amount of aggression received from the sow.