Eye, body or tail? Thermography as a measure of stress in mice

Infrared thermography has been suggested as a non-invasive, objective tool to evaluate animal welfare. In this study, we investigated: 1) how body temperature, measured through thermal imaging, is affected by different mild stressors frequently experienced by laboratory mice; 2) which methodology to use for assessing temperature variations with infrared thermography; 3) whether the chosen stressors cause anxiety in mice. Eighty C57BL/6 male mice were included in the study. The mice were allocated to either a control group or one of three groups being subjected to a mild stressor once daily for 4 days: 1) anaesthesia with isoflurane for 10 min; 2) handling by scruffing; 3) intraperitoneal injection of 0.2 ml 0.9% saline. On all four intervention days, thermal images were obtained in all groups and all animals were assessed for fur status and body weight. On day five, all animals were tested in the elevated-plus-maze for 5 min. From the thermal images, the maximum eye temperature, the maximum tail base temperature and the average body temperature were obtained. Ten minutes of anaesthesia with isoflurane led to a decrease in maximum eye temperature, average body temperature and maximum tail base temperature. The animals recovered from this drop in temperature within 10 min. No drop in temperature was seen after scruffing or intraperitoneal injection of saline. Based on the number of missing values, intra-rater and inter-rater agreement, the average body temperature was found most ideal for measuring body temperature variations in mice. Finally, the elevated plus maze did not reveal any differences in anxiety between the groups and the body weight did not decrease at any time point during the study.