Although sow confinement at farrowing is inherently stressful, farrowing crates remain in widespread commercial use. Sows adapt to their environment, however adaptation may be counter-productive if the farrowing system changes. The current study observed the behaviour of second parity sows throughout farrowing in a straw pen system to determine if their previous farrowing experience, in either the same pen system (n = 11) or a temporary confinement crate system (n = 11), affected current nest-building, farrowing and nursing behaviour. Data were analysed using PROC MIXED, with sow ID as the repeated subject. Sows which previously farrowed in pens tended to have a higher pre-partum peak nesting intensity (P = 0.081), and throughout parturition exhibited increased lateral lying (P < 0.01), decreased ventral lying (P < 0.001), decreased sitting (P < 0.01) and a decreased frequency of dangerous posture changes (P < 0.05). Post-partum, sows that previously farrowed in pens had a lower percentage of sow-terminated nursing (P < 0.01), a longer average duration of successful nursing bouts (P < 0.05) and a lower frequency of sow-terminated nursing bouts (P < 0.001). Seasonal effects were also seen in this naturally-ventilated system, both pre- and post-partum, with autumn/winter farrowings associated with more pre-partum nesting (P < 0.01), a higher pre-partum peak nesting intensity (P < 0.05), a longer average duration of successful nursing (P < 0.05) and a higher percentage of nursing bouts ending with piglets asleep at the udder (P < 0.05) than in the spring/summer. Individual variation in pre-partum nesting behaviour was associated with differences in parturient and post-partum behaviours. The results show that the prior experience of confinement, or a change of farrowing system, significantly affects sow farrowing behaviour in free farrowing pens, which may compromise the welfare of both sows and piglets.