The solid-floor temperature gradually reached equilibrium with the room temperature after the end of the HEAT treatment period within 6 to 10 h. The floor heating system in each pen was turned on at
the onset of the nest-building behavior of the sow, defined as the first occurrence of at least 5 front leg pawings per hour or repeated carrying of straw, without being interrupted by resting periods longer than
2 h [modified from Thodberg et al. (2002) and Pedersen et al. (2003)].