Thermography as a measure of the effects of enrichment and repeated mixing on resilience in pigs
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In current husbandry systems, pigs are frequently exposed to a variety of physiological and psychological challenges that may impact their ability to recover from stress i.e., resilience. Estimating an animals’ welfare is a multi-dimensional concept, which requires multiple measurements to obtain a picture of an animals’ physical and mental state. In practice, a great deal of animal welfare estimation procedures are highly invasive and in themselves, may induce undue stress. There is a strong demand for alternative and reliable non-invasive methods to gather data, to ensure that the animals do not endure unnecessary suffering. In this study we investigated temperature responses to the combined effects of differing enrichment conditions and allostatic load, achieved through repeated mixing, on the resilience of pigs. Pigs were either exposed to barren housing (B) post weaning, or provided with enrichment (rooting material, extra toys, access to extra space, and positive human contact (E)). Half of the pigs were exposed to repeated mixing (RM) while the other half were only exposed to one mixing event at weaning (MM) in an attempt to create varying states of allostatic load. To assess their resilience, their temperature response to a physiological challenge in a lipopolysaccharide (LPS) sickness test, and a psychological challenge in a Frustration (isolation) test were measured using infrared thermography (IRT). Pigs demonstrated a temperature response as a result of the challenges. E pigs had faster recovery rates during the LPS challenge, returning to baseline temperature earlier than B pigs. However, enrichment did not seem to impact the temperature response to the Frustration challenge. Repeated mixing did not have an effect on resilience in both challenges, contrary to the expectations. The accuracy and repeatability of using thermography to measure temperature was convincing for this study, insofar as its intra-observer repeatability which showed strong positive correlations and non-invasive nature. To conclude, enrichment enhanced the recovery rate in pigs to a LPS challenge, which seems to indicate a better resilience in a sickness challenge. Repeated mixing did not seem to create a state of high allostatic load, and the combination of barren housing and repeated mixing did not seem to exacerbate the effects of lack of enrichment, as measured by temperature. The utilization IRT as a measure of resilience and the use of thermography as a non-invasive measurement tool was promising.