Core body temperature does not cool down with skin surface temperature during recovery at room temperature after acute heat stress exposure

Identifying new methods of assessing livestock welfare is a growing area of research. Non-invasive methods such as infrared thermography are valuable for quick and accurate observations and could be utilized to monitor the thermal status of swine without direct contact. The study objective was to determine if infrared thermography could be used as a non-invasive, hands-off approach to accurately monitor the welfare of swine by comparing changes in skin surface temperature (SST), core body temperature (CBT), behavior, and heart rate during acute heat stress (AHS) and subsequent recovery in thermoneutral (TN) conditions. In eight replications, 16 pigs (n=8 barrows and 8 gilts) were subjected to AHS (39.3±0.1 °C) for 30 min followed by TN (20.6±0.1 °C) for 30 min. The SST, CBT, heart rate, and behavioral data were recorded throughout the entire experiment. During pre-treatment, ear base SST was greater (P<0.01; 35.6±0.3 °C) than all other locations. The SST at all locations increased (P<0.01) linearly with duration of AHS exposure. During TN, maximum CBT was greater (P<0.01; 40.6±0.1 °C) compared to during AHS (40.3±0.1 °C). Pigs spent more time standing during AHS (P<0.01) and tended (P=0.10) to lie more during TN; however, heart rate (141±2.3 beats per minute) was not affected by treatment or duration. In summary, rapid TN exposure after an AHS challenge reduces SST; however, CBT was actually increased and this may have implications towards reduced activity and increased organ damage.