A design for studies on cognitive bias in the domestic pig

Cognitive tasks as measures of pig welfare: a systematic review

Cognitive approaches are increasingly used to assess animal welfare, but no systematic review has been conducted on pigs despite their cognitive capacities. Our aims were two-fold: first, to assess the popularity and heterogeneity of this approach by quantifying the different cognitive tasks used and welfare interventions studied. The second was to assess how often results from cognitive tasks supported treatment effects. The search yielded 36 studies that met our criteria. Eleven different cognitive tasks were applied (three most common: judgment bias, learned approach/aversion, and holeboard). Welfare interventions investigated were also diverse: the impact of 19 other different events/conditions/states were reported (most common: housing enrichment). We defined "supportive" as the observation of a significant difference between treatment groups consistent with an author's expectation or hypothesis. Supportive findings were reported in 44% of papers. Interventions yielded no significant difference in 33% of studies. In another 21% of reports, outcomes were mixed and a single study refuted the author's predictions. When considering specific cognitive tasks, authors' predictions of welfare differences were supported most often when using learned approach/aversion (55% of these studies). Similar supportive results were observed less commonly (40% each) when using judgment bias and holeboard tests. Analysis of additional concomitant measures of welfare (health, physiology or behavior) revealed that behavioral measures were most frequently supportive of author's expectations (41%) as well as often matching the actual outcomes of these cognitive tasks (47%). This systematic review highlights the growing popularity of cognitive tasks as measures of pig welfare. However, overall rates of supportive results, i.e., changes in performance on cognitive tasks due to welfare interventions, have been limited so far, even for the most employed task, judgment bias. The numerous different combinations of experimental paradigms and welfare interventions reported in the literature creates challenges for a critical meta-analysis of the field especially in evaluating the efficiency of specific cognitive tasks in assessing animal welfare. This work also highlights important knowledge gaps in the use of cognitive tasks that will require both further validation as well as novel innovation to ensure that their potential is fully realized in the measurement of pig welfare.

New Perspectives In The Objective Evaluation Of Animal Welfare, With Focus On The Domestic Pig

Animal welfare can be viewed as the result of integrating repeated affective evaluations of success in coping with environmental challenges, i.e., subjective challenge adequacy.  The present work summarizes why established physiological and behavioral welfare parameters are inadequate to assess challenge adequacy. Behavioral tests based on the mood-congruent judgment effect and physiologic parameters based on components of the somatotropic axis are proposed as an alternative. Here, the judgment bias measures an animal's subjective confidence to cope successfully with a challenge, which is in turn modulated by the animal's previous experience. The somatotropic axis incorporates the insulin-like growth factor (IGF) and its binding proteins (IGFBP), which are involved in the regulation of metabolism and growth. First results indicate that in particular IGF-1 and IGFBP-3 react with higher latency and higher inertness to short-term stressful events than established physiological stress parameters. Before these indicators can be utilized for overall welfare assessment, further validation studies are necessary that provide more insights into how repeatable the measurements are under different conditions and which other factors may confound the measures.

A theoretical approach to improving interspecies welfare comparisons

The number of animals bred, raised, and slaughtered each year is on the rise, resulting in increasing impacts to welfare. Farmed animals are also becoming more diverse, ranging from pigs to bees. The diversity and number of species farmed invite questions about how best to allocate currently limited resources towards safeguarding and improving welfare. This is of the utmost concern to animal welfare funders and effective altruism advocates, who are responsible for targeting the areas most likely to cause harm. For example, is tail docking worse for pigs than beak trimming is for chickens in terms of their pain, suffering, and general experience? Or are the welfare impacts equal? Answering these questions requires making an interspecies welfare comparison; a judgment about how good or bad different species fare relative to one another. Here, we outline and discuss an empirical methodology that aims to improve our ability to make interspecies welfare comparisons by investigating welfare range, which refers to how good or bad animals can fare. Beginning with a theory of welfare, we operationalize that theory by identifying metrics that are defensible proxies for measuring welfare, including cognitive, affective, behavioral, and neuro-biological measures. Differential weights are assigned to those proxies that reflect their evidential value for the determinants of welfare, such as the Delphi structured deliberation method with a panel of experts. The evidence should then be reviewed and its quality scored to ascertain whether particular taxa may possess the proxies in question to construct a taxon-level welfare range profile. Finally, using a Monte Carlo simulation, an overall estimate of comparative welfare range relative to a hypothetical index species can be generated. Interspecies welfare comparisons will help facilitate empirically informed decision-making to streamline the allocation of resources and ultimately better prioritize and improve animal welfare.

The Acute Pharmacological Manipulation of Dopamine Receptors Modulates Judgment Bias in Japanese Quail

We have studied the effects of dopamine antagonists and agonists on Japanese quail behavior in the spatial judgment task. Twenty-four Japanese quail hens were trained in the spatial discrimination task to approach the feeder placed in the rewarded location (Go response, feeder containing mealworms) and to not approach the punished location (No-Go response, empty feeder plus aversive sound). In a subsequent spatial judgment task, the proportion of Go responses as well as approach latencies to rewarded, punished, and three ambiguous locations (near-positive, middle, near-negative, all neither rewarded nor punished) were assessed in 20 quail hens that successfully mastered the discrimination task. In Experiment 1, each bird received five treatments (0.1 and 1.0 mg/kg of dopamine D1 receptor antagonist SCH 23390, 0.05 and 0.5 mg/kg of dopamine D2 receptor antagonist haloperidol, and saline control) in a different order, according to a Latin square design. All drugs were administered intramuscularly 15 min before the spatial judgment test, with 2 days break between the treatments. Both antagonists caused a significant dose-dependent increase in the approach latencies as well as a decrease in the proportion of Go responses. In Experiment 2, with the design analogous to Experiment 1, the hens received again five treatments (1.0 and 10.0 mg/kg of dopamine D1 receptor agonist SKF 38393, 1.0 and 10.0 mg/kg of dopamine D2 receptor agonist bromocriptine, and saline control), applied intramuscularly 2 h before the test. The agonists did not have any significant effect on approach latencies and the proportion of Go responses in the spatial judgment task, as compared to the saline control, except for 10.0 mg/kg SKF 38393, which caused a decrease in the proportion of Go responses. The approach latency and the proportion of Go responses were affected by the cue location in both experiments. Our data suggest that the dopamine D1 and D2 receptor blockade leads to a decrease in the reward expectation and the negative judgment of stimuli. The effect of dopamine receptor activation is less clear. The results reveal that dopamine receptor manipulation alters the evaluation of the reward and punishment in the spatial judgment task.

Judgement bias of group housed gestating sows predicted by behavioral traits, but not physical measures of welfare

Judgement bias testing has emerged as a potential tool for assessing affective states in animals. Researchers infer an animal's affective state based on an animal's response to an ambiguous stimulus that is intermediate to both the rewarded and punished conditioned stimuli. Animals can be classified as "optimistic" or having a positive affective state if the animal displays behaviors that suggest an increased expectation of reward in the face of ambiguous stimuli. Alternatively, animals can be classified "pessimistic" or having a negative affective state if the animal displays behaviors that suggest an increased expectation of punishment in the face of ambiguous stimuli. Recent reports in multiple species question what factors influence performance in judgement bias testing, and which may allow for erroneous conclusions regarding individual affective state. In order to better understand this concern, 25 female swine were subjected to behavioral assessments at critical rearing stages to determine response variability. These same individuals were then assessed for physical measures of welfare and judgement bias using the "go/no-go" task as breeding adults. Sows which were more aggressive approached the ambiguous, but not the positive, stimulus significantly faster than others. Both optimistic and pessimistic biases were observed despite all sows living in enriched housing, and, sows with more positive physical welfare measures (fewer skin lesions and healthy body condition) did not exhibit more optimistic judgement biases. Our data demonstrate that behavior traits, such as aggressiveness, can affect a sow's performance in a judgement bias test, while measures of physical health did not. We suggest that individual differences in behavior (e.g., bold-aggressive behavioral syndrome, or, proactive coping style) generate different emotional responses and can contribute to the animal's overall affective state more so than physical ailment. Our findings highlight the complexity of how different factors impact an animal's overall affective state and support the need for complementary measures in future JBT studies, including personality assessment.

Multimodal characterization of Yucatan minipig behavior and physiology through maturation

Brain injuries induced by external forces are particularly challenging to model experimentally. In recent decades, the domestic pig has been gaining popularity as a highly relevant animal model to address the pathophysiological mechanisms and the biomechanics associated with head injuries. Understanding cognitive, motor, and sensory aspects of pig behavior throughout development is crucial for evaluating cognitive and motor deficits after injury. We have developed a comprehensive battery of tests to characterize the behavior and physiological function of the Yucatan minipig throughout maturation. Behavioral testing included assessments of learning and memory, executive functions, circadian rhythms, gait analysis, and level of motor activity. We applied traditional behavioral apparatus and analysis methods, as well as state-of-the-art sensor technologies to report on motion and activity, and artificial intelligent approaches to analyze behavior. We studied pigs from 16 weeks old through sexual maturity at 35 weeks old. The results show multidimensional characterization of minipig behavior, and how it develops and changes with age. This animal model may capitulate the biomechanical consideration and phenotype of head injuries in the developing brain and can drive forward the field of understanding pathophysiological mechanisms and developing new therapies to accelerate recovery in children who have suffered head trauma.

The effect of age on discrimination learning and self-control in a marshmallow test for pigs

Both humans and nonhuman animals need to show self-control and wait for a larger or better reward instead of a smaller or less preferred but instant reward on an everyday basis. We investigated whether this ability undergoes ontogenetic development in domestic pigs (similar to what is known in human infants) by testing if and for how long nine- and 16-week-old pigs wait for a larger amount of their preferred reward. In a delay-of-gratification task, animals first learned that a small reward was hidden under a white cup and a large reward under a black cup, and then the delay to deliver the large reward was gradually increased. The results show that older pigs could wait longer for a larger reward than younger pigs (10.6 ± 1.3 s vs. 5.2 ± 1.5 s), thereby confirming our hypothesis of ontogenetic development of self-control in pigs. This self-control is likely to be regulated by the behavioural inhibition system and associated systems. Self-control or, more specifically the lack of it may be involved in the development of abnormal behaviours, not only in humans but also in animals. Therefore, research on self-control in decision-making might provide a new perspective on abnormal behaviours in captive animals.

Evaluation of miRNA as Biomarkers of Emotional Valence in Pigs

Simple Summary

It is widely recognized that the assessment of animal welfare should include measures of positive emotional (affective) state. Existing behavioral and physiological indicators of a positive affective state frequently lack sensitivity, objectivity or are unsuitable in a production environment. Therefore, there is a need to develop new approaches to accurately and objectively measure a positive emotional state in animals, including novel molecular markers such a miRNA. These biomarkers must be measurable in the peripheral circulation and provide an accurate account of the physiological and molecular activity in regions of the brain associated with emotional processing. Further, such markers require validation against established behavioral and physiological indices. Here we investigated the efficacy of circulating miRNA as biomarkers of emotional state in the pig.

Abstract

The ability to assess the welfare of animals is dependent on our ability to accurately determine their emotional (affective) state, with particular emphasis being placed on the identification of positive emotions. The challenge remains that current physiological and behavioral indices are either unable to distinguish between positive and negative emotional states, or they are simply not suitable for a production environment. Therefore, the development of novel measures of animal emotion is a necessity. Here we investigated the efficacy of microRNA (miRNA) in the brain and blood as biomarkers of emotional state in the pig. Female Large White × Landrace pigs (n = 24) were selected at weaning and trained to perform a judgment bias test (JBT), before being exposed for 5 weeks to either enriched (n = 12) or barren housing (n = 12) conditions. Pigs were tested on the JBT once prior to treatment, and immediately following treatment. MiRNA and neurotransmitters were analyzed in blood and brain tissue after euthanasia. Treatment had no effect on the outcomes of the JBT. There was also no effect of treatment on miRNA expression in blood or the brain (FDR p > 0.05). However, pigs exposed to enriched housing had elevated dopamine within the striatum compared to pigs in barren housing (p = 0.02). The results imply that either (a) miRNAs are not likely to be valid biomarkers of a positive affective state, at least under the type of conditions employed in this study, or (b) that the study design used to modify affective state was not able to create differential affective states, and therefore establish the validity of miRNA as biomarkers.

Effects of Birth Order on Performance and Affective State of Pigs

In pigs, higher birth order is associated with higher pre-weaning mortality. However, knowledge on the effect of birth order on welfare of surviving piglets is limited. The aim of this study was to explore the possible link between birth order and both newborn piglet performance and later affective state. Firstly, the following data were collected in 393 piglets from 27 litters: stillbirth, intactness of the umbilical cord and birth weight. Subsets of piglets were used to measure suckling latency (n = 67) and teat order (n = 21). Secondly, a subset of first-born (n = 9) and last-born (n = 7) piglets were trained to perform an active-choice judgement bias task (JBT). During discrimination training preceding the JBT, the pigs learned to associate two tone cues with the availability of either a large (4 M&M's® Milk Chocolate candies) or small (1 M&M's) reward, provided at two different locations. After training, ambiguous intermediate tones were introduced and the pig's choice of location was scored as either optimistic or pessimistic. Results showed that last-born piglets had a higher birth weight than middle-born piglets, while first-born piglets did not significantly differ from last- or middle-born piglets. They also latched to more caudal teats than first-born piglets. The last-born and first-born piglets showed a similar learning rate during discrimination training, and a similar latency to approach reward locations, and had a similar optimistic bias in the JBT.

Effects of different social experiences on emotional state in mice

A comprehensive understanding of animals' emotions can be achieved by combining cognitive, behavioural, and physiological measures. Applying such a multi-method approach, we here examined the emotional state of mice after they had made one of three different social experiences: either a mildly "adverse", a "beneficial", or a "neutral" experience. Using a recently established touchscreen paradigm, cognitive judgement bias was assessed twice, once before and once after the respective experience. Anxiety-like behaviour was examined using a standardised battery of behavioural tests and faecal corticosterone metabolite concentrations were measured. Surprisingly, only minor effects of the social experiences on the animals' cognitive judgement bias and no effects on anxiety-like behaviour and corticosterone metabolite levels were found. It might be speculated that the experiences provided were not strong enough to exert the expected impact on the animals' emotional state. Alternatively, the intensive training procedure necessary for cognitive judgement bias testing might have had a cognitive enrichment effect, potentially countering external influences. While further investigations are required to ascertain the specific causes underlying our findings, the present study adds essential empirical data to the so far scarce amount of studies combining cognitive, behavioural, and physiological measures of emotional state in mice.

The Impact of Social and Behavioral Factors on Reproducibility in Terrestrial Vertebrate Models

The use of animal models remains critical in preclinical and translational research. The reliability of the animal models and aspects of their validity is likely key to effective translation of findings to medicine. However, despite considerable uniformity in animal models brought about by control of genetics, there remain a number of social as well as innate and acquired behavioral characteristics of laboratory animals that may impact on research outcomes. These include the effects of strain and genetics, age and development, sex, personality and affective states, and social factors largely brought about by housing and husbandry. In addition, aspects of the testing environment may also influence research findings. A number of considerations resulting from the animals' innate and acquired behavioral characteristics as well as their social structures are described. Suggestions for minimizing the impact of these factors on research are provided.

Pair housing makes calves more optimistic

Individual housing of dairy calves is common farm practice, but has negative effects on calf welfare. A compromise between practice and welfare may be housing calves in pairs. We compared learning performances and affective states as assessed in a judgement bias task of individually housed and pair-housed calves. Twenty-two calves from each housing treatment were trained on a spatial Go/No-go task with active trial initiation to discriminate between the location of a teat-bucket signalling either reward (positive location) or non-reward (negative location). We compared the number of trials to learn the operant task (OT) for the trial initiation and to finish the subsequent discrimination task (DT). Ten pair-housed and ten individually housed calves were then tested for their responses to ambiguous stimuli positioned in-between the positive and negative locations. Housing did not affect learning speed (OT: F1,35 = 0.39, P = 0.54; DT: F1,19  = 0.15, P = 0.70), but pair-housed calves responded more positively to ambiguous cues than individually housed calves (χ21 = 6.79, P = 0.009), indicating more positive affective states. This is the first study to demonstrate that pair housing improves the affective aspect of calf welfare when compared to individual housing.

Judgement bias testing in group-housed gestating sows

Societal concerns about animal welfare have triggered the movement of gestating sows from individual stalls to group housing in many countries. Common methods of assessing sow welfare focus on overt physical ailments, and potentially neglect psychological stressors. A judgement bias task may allow researchers to evaluate an animal's subjective mental or affective state to provide a more comprehensive welfare assessment. Thus, group housed sows were trained to a spatial differentiation task to evaluate their ability to be assessed for individual judgement bias. A total of 45 sows were trained to the task across two replicates, with 24 successfully meeting the learning criteria required to be tested for a judgement bias. In the first replicate, 60% of sows displayed positive bias while 40% displayed negative biases. In the second replicate, 52% of sows displayed positive biases while 33% of sows displayed negative biases. A linear mixed effects model revealed that feed rank affected the latency to approach the ambiguous stimulus (χ² (1) = 9.47, p = 0.002) with more dominant animals being more likely to exhibit a positive bias. Given that all sows in the present study were group housed, as well as fed and managed similarly, these findings highlight the complexities underlying judgement bias outcomes.

A cross-species judgement bias task: integrating active trial initiation into a spatial Go/No-go task

Judgement bias tasks are promising tools to assess emotional valence in animals, however current designs are often time-consuming and lack aspects of validity. This study aimed to establish an improved design that addresses these issues and can be used across species. Horses, rats, and mice were trained on a spatial Go/No-go task where animals could initiate each trial. The location of an open goal-box, at either end of a row of five goal-boxes, signalled either reward (positive trial) or non-reward (negative trial). Animals first learned to approach the goal-box in positive trials (Go) and to re-initiate/not approach in negative trials (No-go). Animals were then tested for responses to ambiguous trials where goal-boxes at intermediate locations were opened. The Go:No-go response ratio was used as a measure of judgement bias. Most animals quickly learned the Go/No-go discrimination and performed trials at a high rate compared to previous studies. Subjects of all species reliably discriminated between reference cues and ambiguous cues, demonstrating a monotonic graded response across the different cue locations, with no evidence of learning about the outcome of ambiguous trials. This novel test protocol is an important step towards a practical task for comparative studies on judgement biases in animals.

Can the way pigs are handled alter behavioural and physiological measures of affective state?

Research on human-animal relationship in animal production has been mainly focused on its effect on stress, productivity and meat quality. Only few studies have assessed its effects on the animals' affective state. In the present study, the influence of positive and negative handling (pH and NH, respectively) on affective state and fear as assessed by the cognitive bias test, the novel object test and the defence cascade test was studied in 56 pigs. Serum, saliva and hair were sampled during the study for the analysis of cortisol concentration. Results showed no differences between pH and NH pigs in the behavioural tests, which may be either due to the lack of previous handling effect on the test results, the lack of validity or the low sensitivity of these tests or a combination of them. Moreover, no differences were found in cortisol concentrations between handling groups. However, correlations between tests were found (p<0.05) suggesting that there are individual factors such as the fear level, the motivation or the coping style, that have a similar effect on the response to these tests. Moreover, pigs who were more fearful had higher (r=0.37; p=0.014) levels of serum cortisol at slaughter.

A Review of Pain Assessment in Pigs

There is a moral obligation to minimize pain in pigs used for human benefit. In livestock production, pigs experience pain caused by management procedures, e.g., castration and tail docking, injuries from fighting or poor housing conditions, “management diseases” like mastitis or streptococcal meningitis, and at parturition. Pigs used in biomedical research undergo procedures that are regarded as painful in humans, but do not receive similar levels of analgesia, and pet pigs also experience potentially painful conditions. In all contexts, accurate pain assessment is a prerequisite in (a) the estimation of the welfare consequences of noxious interventions and (b) the development of more effective pain mitigation strategies. This narrative review identifies the sources of pain in pigs, discusses the various assessment measures currently available, and proposes directions for future investigation.

Making Decisions under Ambiguity: Judgment Bias Tasks for Assessing Emotional State in Animals

Judgment bias tasks (JBTs) are considered as a family of promising tools in the assessment of emotional states of animals. JBTs provide a cognitive measure of optimism and/or pessimism by recording behavioral responses to ambiguous stimuli. For instance, a negative emotional state is expected to produce a negative or pessimistic judgment of an ambiguous stimulus, whereas a positive emotional state produces a positive or optimistic judgment of the same ambiguous stimulus. Measuring an animal's emotional state or mood is relevant in both animal welfare research and biomedical research. This is reflected in the increasing use of JBTs in both research areas. We discuss the different implementations of JBTs with animals, with a focus on their potential as an accurate measure of emotional state. JBTs have been successfully applied to a very broad range of species, using many different types of testing equipment and experimental protocols. However, further validation of this test is deemed necessary. For example, the often extensive training period required for successful judgment bias testing remains a possible factor confounding results. Also, the issue of ambiguous stimuli losing their ambiguity with repeated testing requires additional attention. Possible improvements are suggested to further develop the JBTs in both animal welfare and biomedical research.

A preliminary study of the effects of individual response to challenge tests and stress induced by humans on learning performance of weaned piglets (Sus scrofa)

This study investigated whether individual behavioural characteristics of piglets and stress induced by experience with humans can influence learning performance. After weaning, piglets received a chronic experience with humans to modulate their emotional state: rough (ROU), gentle (GEN), or minimal (MIN) experience. Simultaneously, they were trained on a discrimination task. Afterward, their behaviour during challenge tests was assessed. The first learning step of the task involved associating a positive sound cue with a response (approach a trough) and success of piglets depended mostly on motivation to seek for reward. Although the experience with humans did not have direct effect, the degree of fear of handler, measured based on their reactivity to a human approach test, was related to motivation to seek rewards and learning speed of this first step in stressed ROU piglets, but not in MIN and GEN piglets. In contrast, the second learning step was more cognitively challenging, since it involved discrimination learning, including negative cues during which piglets had to learn to avoid the trough. Locomotion activity, measured during an open-field test, was associated with performance of the discrimination learning. To conclude, fearfulness towards humans and locomotion activity are linked with learning performance in relation to task complexity, highlighting the necessity to take into account these factors in animal research and management.

Overnight Social Isolation in Pigs Decreases Salivary Cortisol but Does Not Impair Spatial Learning and Memory or Performance in a Decision-Making Task

Pigs in modern farming practice may be exposed to a number of stressors, including social stressors such as mixing or isolation. This may potentially affect both cognitive abilities and stress physiology of the animals. We tested the hypothesis that overnight social isolation in pigs impairs performance in a cognitive holeboard (HB) task (Experiment 1) and the Pig Gambling Task (PGT) (Experiment 2), a decision-making task inspired by the Iowa Gambling Task. In addition, we tested the effect of overnight social isolation on salivary cortisol levels. A within-subjects approach was used in which performance in the two behavioral tasks and cortisol levels were first determined during normal social housing, followed by performance and cortisol levels after experiencing stress induced by overnight social isolation. A total of 19 female pigs with a birth weight closest to their respective litter average was selected from 10 different litters and placed in two pens after weaning. Following habituation, pigs were trained in the HB task, starting at 10 weeks of age. Then, the pigs were isolated overnight, five individuals per night, at 15, 16, and 17 weeks of age. Between these three isolations, social housing and training in the HB continued. Starting 6 weeks after the end of the HB experiment, at approximately 23 weeks of age, the pigs were trained in the PGT. The effects of overnight social isolation on performance in this task were assessed once, when the pigs were 25 weeks old. Salivary cortisol was measured from samples collected 15 min after the start of isolation and at the end of the isolation period and compared to baseline values collected before the start of social isolation. Our results did not confirm the hypothesis that isolation impaired HB performance and decision-making in the PGT. Unexpectedly, overnight social isolation decreased cortisol levels below baseline values, an effect that was not associated with changes in performance of the behavioral tasks. We hypothesized that the housing and testing conditions may have prepared the animals to cope efficiently with stress.

The Way Humans Behave Modulates the Emotional State of Piglets

The emotional state can influence decision-making under ambiguity. Cognitive bias tests (CBT) proved to be a promising indicator of the affective valence of animals in a context of farm animal welfare. Although it is well-known that humans can influence the intensity of fear and reactions of animals, research on cognitive bias often focusses on housing and management conditions and neglects the role of humans on emotional states of animals. The present study aimed at investigating whether humans can modulate the emotional state of weaned piglets. Fifty-four piglets received a chronic experience with humans: gentle (GEN), rough (ROU) or minimal contact (MIN). Simultaneously, they were individually trained on a go/no-go task to discriminate a positive auditory cue, associated with food reward in a trough, from a negative one, associated with punishments (e.g. water spray). Independently of the treatment (P = 0.82), 59% of piglets completed the training. Successfully trained piglets were then subjected to CBT, including ambiguous cues in presence or absence of a human observer. As hypothesized, GEN piglets showed a positive judgement bias, as shown by their higher percentage of go responses following an ambiguous cue compared to ROU (P = 0.03) and MIN (P = 0.02) piglets, whereas ROU and MIN piglets did not differ (P > 0.10). The presence of an observer during CBT did not modulate the percentage of go responses following an ambiguous cue (P > 0.10). However, regardless of the treatment, piglets spent less time in contact with the trough following positive cues during CBT in which the observer was present than absent (P < 0.0001). This study originally demonstrates that the nature of a chronic experience with humans can induce a judgement bias indicating that the emotional state of farm animals such as piglets can be affected by the way humans interact with them.

Happy hamsters? Enrichment induces positive judgement bias for mildly (but not truly) ambiguous cues to reward and punishment in Mesocricetus auratus

Recent developments in the study of animal cognition and emotion have resulted in the 'judgement bias' model of animal welfare. Judgement biases describe the way in which changes in affective state are characterized by changes in information processing. In humans, anxiety and depression are characterized by increased expectation of negative events and negative interpretation of ambiguous information. Positive wellbeing is associated with enhanced expectation of positive outcomes and more positive interpretation of ambiguous information. Mood-congruent judgement biases for ambiguous information have been demonstrated in a range of animal species, with large variation in the way tests are administered and in the robustness of analyses. We highlight and address some issues using a laboratory species not previously tested: the Syrian hamster (Mesocricetus auratus). Hamsters were tested using a spatial judgement go/no-go task in enriched and unenriched housing. We included a number of controls and additional behavioural tests and applied a robust analytical approach using linear mixed effects models. Hamsters approached the ambiguous cues significantly more often when enriched than unenriched. There was no effect of enrichment on responses to the middle cue. We discuss these findings in light of mechanisms underlying processing cues to reward, punishment and true ambiguity, and the implications for the welfare of laboratory hamsters.

Frontal brain deactivation during a non-verbal cognitive judgement bias test in sheep

Animal welfare concerns have raised an interest in animal affective states. These states also play an important role in the proximate control of behaviour. Due to their potential to modulate short-term emotional reactions, one specific focus is on long-term affective states, that is, mood. These states can be assessed by using non-verbal cognitive judgement bias paradigms. Here, we conducted a spatial variant of such a test on 24 focal animals that were kept under either unpredictable, stimulus-poor or predictable, stimulus-rich housing conditions to induce differential mood states. Based on functional near-infrared spectroscopy, we measured haemodynamic frontal brain reactions during 10 s in which the sheep could observe the configuration of the cognitive judgement bias trial before indicating their assessment based on the go/no-go reaction. We used (generalised) mixed-effects models to evaluate the data. Sheep from the unpredictable, stimulus-poor housing conditions took longer and were less likely to reach the learning criterion and reacted slightly more optimistically in the cognitive judgement bias test than sheep from the predictable, stimulus-rich housing conditions. A frontal cortical increase in deoxy-haemoglobin [HHb] and a decrease in oxy-haemoglobin [O2Hb] were observed during the visual assessment of the test situation by the sheep, indicating a frontal cortical brain deactivation. This deactivation was more pronounced with the negativity of the test situation, which was reflected by the provenance of the sheep from the unpredictable, stimulus-poor housing conditions, the proximity of the cue to the negatively reinforced cue location, or the absence of a go reaction in the trial. It seems that (1) sheep from the unpredictable, stimulus-poor in comparison to sheep from the predictable, stimulus-rich housing conditions dealt less easily with the test conditions rich in stimuli, that (2) long-term housing conditions seemingly did not influence mood--which may be related to the difficulty of tracking a constant long-term state in the brain--and that (3) visual assessment of an emotional stimulus leads to frontal brain deactivation in sheep, specifically if that stimulus is negative.