This thesis is a study of the behaviour and physiology of gestating and lactating sows living outdoors in Québec, Canada during the summer in 2018. Six groups of four sows (N=24) were kept in outdoor pens with a wallow, shade structure, pasture, and farrowing huts. During late gestation and early lactation, we observed the sows’ behaviour, respiratory rate and body temperature, and recorded environmental conditions. In gestation, the sows’ wallow usage depended on the temperature humidity index (THI). However, in lactation, sows exhibited low wallow usage even when THI was high, instead prioritizing the farrowing hut, especially in the first few days following farrowing. Lactating sows appeared to be at a greater risk of heat stress based on their behaviour and physiological responses to warmer conditions. In general however, the sows seemed to thermoregulate effectively in this outdoor environment, with wallowing likely playing an important role.