Search

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.

The welfare of pigs both on farm and in laboratories can be influenced by the conditions associated with each environment. Modern definitions of welfare emphasize the importance of affective states as essential for understanding welfare needs, and welfare legislation refers to the avoidance of unnecessary ‘suffering’ and ‘distress’ of animals. To objectively measure affective states in animals is therefore a priority for assessing welfare. From human research we know that emotion and mood can influence cognitive processes, such as memory and judgement. In particular emotional valence (positive /negative) can lead to mood congruent judgements of ambiguous stimuli, e.g. people in a positive mood are more likely to make optimistic judgements. It has been proposed that these biases can be used as a proxy measure of the valence of emotion and mood in animals. In this thesis I develop and try to validate novel tasks for pigs which can be used to study emotion-biased cognitive processing. First, we developed a Judgement Bias Task (JBT) whereby pigs were trained to discriminate one tone-cue predicting a large reward (positive cue), from a second tone cue predicting a small reward (negative cue), by choosing the correct goal box. When pigs could sufficiently discriminate between these two cues, responses to three unfamiliar ambiguous tone cues, intermediate in frequency between the positive and negative cue, were measured. An optimistic choice was scored if the pig chose the goal box associated with the large reward. We demonstrated that both a common farm breed and laboratory breed of pig could relatively easily learn the discrimination, and showed a similar pattern of responding to the ambiguous cues. To validate the task we looked at responses of low birth weight (LBW) pigs. LBW in humans is associated with later emotional problems such as anxiety and depression. In pigs, LBW is associated with higher mortality, but also higher stress reactivity in surviving piglets, suggestive of altered emotionality. We hypothesized therefore that LBW pigs ought to make fewer optimistic choices in response to the ambiguous cues. We compared LBW pigs to their normal-birth-weight siblings and, in two studies found, that the LBW pigs did indeed make fewer optimistic choices. In a third study we failed to find a difference. We developed a second task, a probabilistic choice Pig Gambling Task (PGT), to look at decision making under risk, which is also susceptible to emotional influences. Pigs could freely choose between an option offering small but frequent rewards and a second option offering large but infrequent rewards. LBW pigs chose more for the small but frequent rewards suggesting higher levels of risk aversion. Responses on the PGT were independent from responses on the JBT suggesting that the two tasks are measuring different aspects of decision making under uncertainty (risk vs ambiguity). Further, responses on the JBT were independent of memory, learning, and motivation suggesting that our task is indeed targeting emotion-biased judgements. However, our tasks are not yet suitable for the on-farm testing of emotion in pigs due to the complex training involved.

The welfare of pigs both on farm and in laboratories can be influenced by the conditions associated with each environment. Modern definitions of welfare emphasize the importance of affective states as essential for understanding welfare needs, and welfare legislation refers to the avoidance of unnecessary ‘suffering’ and ‘distress’ of animals. To objectively measure affective states in animals is therefore a priority for assessing welfare. From human research we know that emotion and mood can influence cognitive processes, such as memory and judgement. In particular emotional valence (positive /negative) can lead to mood congruent judgements of ambiguous stimuli, e.g. people in a positive mood are more likely to make optimistic judgements. It has been proposed that these biases can be used as a proxy measure of the valence of emotion and mood in animals. In this thesis I develop and try to validate novel tasks for pigs which can be used to study emotion-biased cognitive processing. First, we developed a Judgement Bias Task (JBT) whereby pigs were trained to discriminate one tone-cue predicting a large reward (positive cue), from a second tone cue predicting a small reward (negative cue), by choosing the correct goal box. When pigs could sufficiently discriminate between these two cues, responses to three unfamiliar ambiguous tone cues, intermediate in frequency between the positive and negative cue, were measured. An optimistic choice was scored if the pig chose the goal box associated with the large reward. We demonstrated that both a common farm breed and laboratory breed of pig could relatively easily learn the discrimination, and showed a similar pattern of responding to the ambiguous cues. To validate the task we looked at responses of low birth weight (LBW) pigs. LBW in humans is associated with later emotional problems such as anxiety and depression. In pigs, LBW is associated with higher mortality, but also higher stress reactivity in surviving piglets, suggestive of altered emotionality. We hypothesized therefore that LBW pigs ought to make fewer optimistic choices in response to the ambiguous cues. We compared LBW pigs to their normal-birth-weight siblings and, in two studies found, that the LBW pigs did indeed make fewer optimistic choices. In a third study we failed to find a difference. We developed a second task, a probabilistic choice Pig Gambling Task (PGT), to look at decision making under risk, which is also susceptible to emotional influences. Pigs could freely choose between an option offering small but frequent rewards and a second option offering large but infrequent rewards. LBW pigs chose more for the small but frequent rewards suggesting higher levels of risk aversion. Responses on the PGT were independent from responses on the JBT suggesting that the two tasks are measuring different aspects of decision making under uncertainty (risk vs ambiguity). Further, responses on the JBT were independent of memory, learning, and motivation suggesting that our task is indeed targeting emotion-biased judgements. However, our tasks are not yet suitable for the on-farm testing of emotion in pigs due to the complex training involved.

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.