Arey, D. S., Petchey, A. M., Fowler, V. R. 1991. The preparturient behaviour of sows in enriched pens and the effect of pre-formed nests. Applied Animal Behaviour Science 31, 61-68.

Nest building is highly motivated behaviour in sows. Nesting material appears to be a key factor both in the regulation and performance of the behaviour. The study demonstrated that domestic sows housed in enriched pens display nest building behaviour which is very similar to that reported for feral sows, and for domestic sows kept in semi-natural environments. It includes rooting, straw, carrying, pawing and lying. Nest material is essential to the behaviour and therefore to the environmental requirements of the sow at this time.