[Effects of weaning age on behavioural and physiological responses of domestic piglets--a review].

Weaning of farm animals is of biological and economical relevance. Due to economical considerations, the weaning age of piglets (Sus scrofa) has drastically been reduced during the last few years, whereas biological consequences remain ambiguous. This review gives a survey of current international research on weaning and its psychobiological consequences in conventional pig farming. The influence of weaning age on behaviour, neuroendocrine and immune systems of piglets is the main focus of this paper. The abrupt weaning in pig farming comprises multiple stressful events such as change in diet, new physical environment, as well as the often underestimated psychosocial consequences of maternal deprivation and regrouping with unfamiliar conspecifics. Results presented in this review suggest that early weaned piglets (< or = 21 days of age) show enhanced behavioural problems and neuroendocrine stress reactions as well as reduced immune responses. These adaptation problems may have short- and long-term effects on animals' welfare and health, consequently resulting in increased financial requirements and higher management demands. Weaning before the third week of age is not recommended. Additionally, alternative housing systems (e.g. group housing) with adequate weaning methods (e.g. weaning without regrouping, social contacts prior to weaning) to diminish psychosocial stress are discussed.