A review of behavioural methods to study emotion and mood in pigs, Sus scrofa

The study of emotions in animals is of increasing importance to a number of disciplines such as animal welfare science and affective neuroscience. Pigs are a common farm animal species, most often reared in intensive systems. Moreover, they are increasingly being used in laboratories. To accurately understand the welfare needs of these animals, we need to be able to study emotion, the assumption being that positive emotional states contribute to good welfare, while negative states result in reduced welfare. A variety of methods have been proposed to study emotions in animals through behaviour, many of which have been applied to pigs. This review will focus on the methods by which behaviour can be used to study emotion in pigs. First, we discuss the variety of behavioural tests that have been applied to study emotion and mood in pigs. We propose a list of criteria with which to evaluate the behavioural tests and discuss each test with respect to these criteria as well as any behavioural, physiological or pharmacological validation. Second, we look at specific behaviours or behaviour patterns that may also be indicative of emotion and mood in pigs. We find a number of issues with the more commonly used behavioural tests, including the lack of ethologically valid test designs, and the need for greater standardisation of design which would facilitate comparison of results across studies. Furthermore, behaviours measured are often not specific to emotion, or sensitive to subtle differences in emotion. Suggestions for improvements to the current methods are given with a focus on species relevant behaviour and the potential for assessing both positive and negative emotions. (C) 2014 Elsevier B.V. All rights reserved.