A preference testing apparatus was used to provide sows with continuous access to three identical farrowing crates, each with a different floor temperature. The concrete floor under each crate contained copper pipe through which temperature-controlled water was circulated to achieve unoccupied floor temperatures of 22°C (± 3.5), 29°C (± 1) and 35°C (± 1). Eighteen sows were tested in the apparatus. Video recording was used to determine sow position from 7 days before farrowing (Days ‒7 to ‒1) to 14 days after (Days 1 to 14). On Days ‒7 to ‒1, sows showed no significant preference among the three temperatures when selecting a resting area. Once farrowing had begun, there was a significant increase (P \u3c 0.01) in the use of the 35°C floor and it became the most preferred resting area for Days 1 to 3. After this interval, use of the 35°C floor declined significantly (P \u3c 0.01), and use of the cooler floors increased, resulting in no significant thermal preference during Days 4 to 6. There was a further decline in the use of the 35°C floor after Days 4 to 6 (P \u3c 0.01) to the extent that the coolest floor (22°C) became the most preferred from Days 7 to 14. In summary, sows showed a pronounced increase in preference for a warm floor during the 3 days after the start of farrowing. This change in preference may explain how free-living sows select a suitable thermal environment for their young, and why sows try to avoid metal flooring at the time of farrowing
