Pain in mammals; physiology, management and assessment

Pain is a sensory and emotional experience that has significant consequences on an animal's welfare. To improve animal welfare, there is a need to prevent as well as manage pain, but we cannot manage what we cannot measure. In this chapter we highlight pains complexity, with the experience affected by multiple factors, including age, sex, personality and previous experience and remains a critical issue in veterinary care. We provide details on the physiological mechanism of pain and show how with this knowledge we can provide appropriate treatment to manage pain effectively. We acknowledge that many animals are, however, still experiencing pain. Even with the acceptance of animal sentience, recognizing, assessing and evaluating pain in animals is difficult. We briefly detail physiological indicators of pain such as heart rate and cortisol but acknowledge that there are difficulties in their use within veterinary clinics, for example. Behavioral indicators of pain can range from change in eating behavior to aggression. We discuss that there are many tools currently available to identify and assess pain, but that many require extensive training, are time consuming to carry out, and tend to measure the long-term impact on general biological functioning rather than pain per se. We highlight the more recent increase of the use of facial expression scales as an alternate tool that can accurately recognize and assess pain in a variety of species and can indicate what an animal is feeling at that moment in time. We also briefly touch on the use of technology such as Artificial Intelligence and Computer Vision as a novel tool to assess pain, providing a much more objective assessment. There is an urgent need for tools that can effectively and directly detect and measure pain in animals and further research in the use of computer-based modelling will be key for the future.