To wallow or nurse: Sows housed outdoors have distinctive approaches to thermoregulation in gestation and lactation

Abstract

The objective of this study was to determine which behaviours may be important for thermoregulation when gestating and lactating sows are housed outdoors in Québec, Canada during the summer. We kept six groups of four Yorkshire-Landrace sows, from July to September 2018, in outdoor paddocks outfitted with a wallow, shade structure, individual farrowing huts and a pasture plot. From week 15 of gestation to week 3 of lactation, we recorded the location of each sow during five daily observation periods (5 days/week), each consisting of 15 consecutive scan samples at 1-min intervals. Simultaneously, we monitored environmental conditions with temperature and humidity loggers. We analyzed the impact of day relative to farrowing and the temperature humidity index (THI) on the percent of daily observations in the wallow, shade, and farrowing hut with polynomial regression models, with day and THI as covariates and the sow as the subject of repeated measures. In gestation, sows were mainly observed in the wallow (40 ± 2% of observations), while in lactation, sows were primarily observed in the huts (54 ± 17%) and were only in the wallow for 6 ± 4% of observations. THI was associated with the percent of observations in the wallow (P < 0.001) during both gestation and lactation. Day also had a significant association with wallowing; gestating sows were observed in the wallow more often as farrowing drew nearer (P = 0.029), while lactating sows were observed in the wallow more often as the number of days since farrowing increased (P < 0.0001). In gestation, THI was negatively associated with the percent of observations in the farrowing hut (P < 0.0001); however, in lactation, only day predicted the use of the farrowing hut in a non-linear fashion (P < 0.01). In gestation, the sows’ wallow use was associated with THI. However, lactating sows exhibited low wallow usage even when THI was high, instead prioritizing the farrowing hut, especially in the first few days after farrowing. The differences between gestation and lactation in the timing and frequency of the sows’ use of the wallow and farrowing hut may indicate a conflict of motivation between thermoregulatory and maternal behaviours when sows are nursing their piglets.