Stress-free measurement of body temperature of pigs by using thermal imaging – Useful fact or wishful thinking

Abstract

Growing concern regarding animal welfare has increased the need for reliable methods of assessing the animal health status without stress during commercial farm practice. Measuring the body temperature with a thermal imaging camera is one possible stress-free technique since it is non-contact and non-invasive. The first objective of this study was to determine the best anatomical site in healthy pigs for measuring the temperature with a high spatial resolution thermal imaging camera that gives results equivalent or related to the temperatures measured in the rectum. The second objective was the assessment of the possibility to accurately and reliably measure or predict the pigs’ temperature with a low spatial resolution thermal imaging camera. Reference temperatures, measured with a calibrated thermometer in the rectum, were compared to the measurements of two calibrated thermal imaging cameras (a low resolution camera and a high resolution camera) on four anatomical sites of pigs (ear canal, eye canthus, outer ear and perianal area). We found that it is not possible to accurately measure or predict the pigs’ body temperature with a high noise equivalent temperature difference (NETD), low accuracy, low spatial resolution thermal imaging camera. However, a low NETD, high accuracy, high spatial resolution thermal imaging camera gives at least results that enable prediction (using a linear regression model) of the pigs’ body temperature. We showed that there are three anatomical sites in healthy pigs (ear canal, outer ear, perianal area) that are statistically similarly suitable for predicting the body temperature with a calibrated high spatial resolution thermal imaging camera under non diseased thermal neutral conditions.