The use of infrared thermography to assess stress in pigs

Stress can negatively impact animal health and production, therefore to improve current management practices it is important to be able to measure stress in animals. Most methods for measuring stress in pigs are invasive (e.g. blood sampling) or require fitting animals with devices (e.g. heart rate monitors). These techniques can cause a stress response themselves and perturb the measurement of interest. Infrared thermography (IRT) has been validated as a non-invasive measure to detect pain and stress (e.g. fright, disbudding, and castration) in cattle. The objectives of this pilot study were to 1) investigate the potential for IRT as a non-invasive measure of stress in pigs and 2) compare the eye and snout as regions to provide the most sensitive measure of stress. Ten, 5-week-old, pigs received all three of the following treatments in a randomised cross-over design: 1) saline infusion (SAL), 2) epinephrine infusion (EPI) and 3) restraint (RES) for 2 minutes. Continuous IRT images of the eye and snout, heart rate (HR) and heart rate variability (HRV) were recorded 5 minutes prior and 10 minutes post-treatment. Eye temperature was lower in response to an infusion of EPI and RES than SAL, but only RES caused a change in snout temperature. Conversely, HR was higher in RES and EPI than SAL pigs. Temperature changes suggest that the eye may be a more sensitive area to assess stress than the snout. However, there were some methodological issues associated with taking IRT images of the eye including the small size of the eye and mobility of the pigs. IRT has potential for measuring stress in pigs non-invasively, however, further research needs to be undertaken to improve the methodology for collecting the images and correcting the data for environmental conditions.