Endocrine regulation of periparturient behaviour in pigs.

Pigs begin behavioural preparations for birth about 1-2 days before parturition. Prepartum sows wander to select a suitable site and then construct a maternal nest. The signal that initiates this behavioural cascade probably results from fetal maturation but is unknown. However, endogenous PGF2 alpha appears to be involved early on in an endocrine pathway that projects to the brain and can generate most of the prepartum behavioural components. This period of intense activity is followed by a quiescent phase of lying in the nest for some hours before fetal ejection occurs. Feedback from a completed nest or abdominal discomfort may both contribute to the end of nest building. In the postpartum phase, sows have to deal with the apparently conflicting drives of remaining passive to reduce accidental or deliberate damage to piglets, while at the same time responding actively to their needs. In commercial environments, animals frequently fail in this task. Although environmental influences on piglet survival have received much experimental attention, the genetic, social and endocrine drives that control sow behaviour after parturition remain poorly understood and their clarification is a major challenge for the future.