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

tThe study of emotions in animals is of increasing importance to a number of disciplinessuch as animal welfare science and affective neuroscience. Pigs are a common farm animalspecies, most often reared in intensive systems. Moreover, they are increasingly being usedin laboratories. To accurately understand the welfare needs of these animals, we need tobe able to study emotion, the assumption being that positive emotional states contributeto good welfare, while negative states result in reduced welfare. A variety of methods havebeen proposed to study emotions in animals through behaviour, many of which have beenapplied to pigs. This review will focus on the methods by which behaviour can be usedto study emotion in pigs. First, we discuss the variety of behavioural tests that have beenapplied to study emotion and mood in pigs. We propose a list of criteria with which toevaluate the behavioural tests and discuss each test with respect to these criteria as wellas any behavioural, physiological or pharmacological validation. Second, we look at spe-cific behaviours or behaviour patterns that may also be indicative of emotion and moodin 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 standard-isation of design which would facilitate comparison of results across studies. Furthermore,behaviours measured are often not specific to emotion, or sensitive to subtle differencesin emotion. Suggestions for improvements to the current methods are given with a focuson species relevant behaviour and the potential for assessing both positive and negativeemotions.