At farrowing time, sows are normally confined in barren environments which prevent the performance of normal behaviour patterns. It has been argued that both the sows welfare and productivity may suffer as a result of these conditions, (Vestergaard and Hansen, 1984). Investigations into the feasibility of an alternative system in which the sows are not restricted have therefore been initiated. The main objective of the present study was to establish design criteria for voluntary accessed farrowing pens which will attract sows by providing them with their preferred environmental requirements.

Previous observations, not reported here, were made of the pre-farrowing behaviour of sows housed individually in large pens which contained a deep sand floor and a straw dispenser. All the sows showed nest building behaviour which culminated in the production of a recognisable nest. Typically they had the following characteristics: a shallow depression; a straw lining and a nest rim which formed a low barrier around the nest. The experiments described here were designed to establish the preferences of the peri-parturient sow for preformed lying areas which incorporated these features.