[The development of the relationship between sow and piglet in the domestic pig--a sociobiological observation].

The nursing and suckling behaviour of the domestic pig is a complex social behavioural interaction aimed to ensure the milk flow from the sow to the piglets. Ultimately caused theoretical frameworks from basic ethology and/or sociobiology are increasingly used to explain such social behavioural patterns. The present paper gives a short survey of ethophysiological aspects of the nursing and suckling behaviour in domestic pigs and, thereafter, discusses the development and consequences of some parts of the suckling behaviour and the maternal lactation performance in terms of a possible parent-offspring and weaning conflict. It is concluded that--additional to proximately caused mechanisms--the ontogeny of domestic pigs can be interpreted with such principles. In housing systems allowing the animals more control over their behaviour (e.g. their investment) ultimate causes should be more considered. Especially the pathways on which the ultimate strategies become effective via proximate mechanisms do not seem to be understood in total and require specific research. However, it is suggested that effective improvements of welfare, health and productivity can only be reached with the knowledge and integration of both ultimate and proximate causes of behaviour.