Michael Mendl

• PhD in Animal Behaviour
• Professor (Full) at University of Bristol

Medical detection dogs search for diseases from remote samples (biodetection) and assist patients with chronic conditions (medical alert assistance). There is scarce information on how dogs’ decision-making tendencies relate to task performance. This study explored the relationships between medical detection dog demographics, responses in a behavio...

The concept of animal welfare is evolving due to progress in our scientific understanding of animal biology and changing societal expectations. Animal welfare science has been primarily concerned with minimizing suffering, but there is growing interest in also promoting positive experiences, grouped under the term positive animal welfare (PAW). How...

The emotional valence hypothesis suggests an increased left-brain hemisphere activation during positive situations and vice versa during negative situations. Since facial thermal asymmetries may reflect lateralised brain activity, we investigated this in dairy calves subjected to hot-iron disbudding (Disbudded; n = 12) as a model of negative affect...

Dogs can discriminate stressed from non-stressed human odour samples, but the effect on their cognition is unstudied. Using a cognitive bias task, we tested how human odours affect dogs’ likelihood of approaching a food bowl placed at three ambiguous locations (“near-positive”, “middle” and “near-negative”) between trained “positive” (rewarded) and...

Even when pain control is implemented, calves may experience pain for days after hot-iron disbudding. Whether calves seek pain relief post-disbudding offers a novel approach to assessing pain in these animals. By employing an approach-aversion paradigm, we explored the ability of cold therapy to provide immediate pain relief in disbudded calves. Ca...

Effective and safe foraging requires animals to behave according to the expectations they have about the rewards, threats, and costs in their environment. Since these factors are thought to be reflected in the animals’ affective states, we can use foraging behavior as a window into those states. In this study, rats completed a foraging task in whic...

More widespread farming of species not typically used as livestock may be part of a sustainable approach for promoting human health and economic prosperity in a world with an increasing population; a current example is peccary farming in the Neotropics. Others have argued that species that are local to a region and which are usually not farmed shou...

Dairy calves are typically fed restricted amounts of milk. Although feed restrictions are predicted to result in negative affective states, the relative aversiveness of ‘hunger’ remains largely unexplored in this species. Here, we investigated whether the conditioned place preference paradigm can be used to explore how calves feel when experiencing...

Introduction Depression is a human mental disorder that can also be inferred in non-human animals. This study explored whether time spent inactive but awake (“IBA”) in the home-cage in mice was further triggered by risk factors similar to those increasing vulnerability to depression in humans (early life stress, genetic predispositions, adulthood s...

Dogs can discriminate between stressed and non-stressed odour samples from humans, but the effect on their cognition and emotional state is previously unstudied. Eighteen dogs each participated in three cognitive bias sessions: baseline (no odour), stress odour and relax odour, with the order of the two test odours counterbalanced across dogs. The...

Chronic pain in humans is associated with impaired working memory but it is not known whether this is the case in long-lived companion animals, such as dogs, who are especially vulnerable to developing age-related chronic pain conditions. Pain-related impairment of cognitive function could have detrimental effects on an animal’s ability to engage w...

The illegal primate trade is one of the major drivers of the decline of nonhuman primate populations and a threat to their wellbeing. Thousands of trafficked primates enter rescue centers every year, and their destiny (release back into the wild, long-term captivity, or euthanasia) involves controversial decisions and complex ethical considerations...

Measures of individual behavioural differences (personality) are highly valuable in many areas of ethology, particularly studies of animal emotion and welfare. However, there are limitations to current behavioural tests of personality. Caregiver questionnaires may provide a complementary approach to overcome some of these limitations and provide a...

Simple Summary The spotted paca (Cuniculus paca) has been legally bred by small-scale producers in Brazil as an alternative source of protein. Although captive breeding of this species is considered relatively easy and promising for farmers, little is known about its welfare in captivity. Therefore, using boomer balls to induce object play, we inve...

Objective measures of animal emotion-like and mood-like states are essential for preclinical studies of affective disorders and for assessing the welfare of laboratory and other animals. However, the development and validation of measures of these affective states poses a challenge partly because the relationships between affect and its behavioural...

We aimed to assess whether play behavior can be used as a welfare indicator for farmed spotted pacas (Cuniculus paca) by examining its association with other positive welfare markers including affiliative behavior and low-amplitude vocalizations. We submitted six groups of spotted pacas (one male/two females per group) (N=18) to an ABA experimental...

Monitoring the concentration of glucocorticoid metabolites (GCMs) in faecal samples is a non-invasive tool for physiological stress evaluation, particularly useful when studying wild species. However, both negative and positive stimuli (distress and eustress, respectively) can lead to a rise in glucocorticoids. Thus, besides validating whether GCM...

Chronic pain in humans is associated with impaired working memory but it is not known whether this is the case in long-lived companion animals, such as dogs, who are especially vulnerable to developing age-related chronic pain conditions. Pain-related impairment of cognitive function could have detrimental effects on an animal’s ability to engage w...

The use of 2-dimensional representations (e.g. photographs or digital images) of real-life physical objects has been an important tool in studies of animal cognition. Horses are reported to recognise objects and individuals (conspecifics and humans) from printed photographs, but it is unclear whether image recognition is also true for digital image...

Most studies of the effects of housing and husbandry on animals’ affective states and welfare investigate the impact of stable living conditions, comparing for example, animals living in enriched environments with those living in non-enriched ones. Changes in living conditions, including from more to less enriched environments, have also been found...

Refining the housing and husbandry of laboratory rats is an important goal, both for ethical reasons and to allow better quality research. We conducted a mapping review of 1,017 studies investigating potential refinements of housing and husbandry of the laboratory rat to assess what refinements have, and have not, been studied, and to briefly asses...

Environmental enrichment (EE) is used to promote natural behaviours in captive animals and may hold promise as a form of pre-release training, a strategy for improving coping skills of translocated birds. We investigated the use of EE to enhance foraging and vigilance behaviours of captive Sporophila angolensis, which may be related to post-release...

Rat tickling is a heterospecific interaction for experimenters to mimic the interactions of rat play, where they produce 50 kHz ultrasonic vocalisations (USV), symptoms of positive affect; tickling can improve laboratory rat welfare. The standard rat tickling protocol involves gently pinning the rat in a supine position. However, individual respons...

Vocal emissions in non-human mammals can be used as non-invasive indicators of animal emotion and welfare. Therefore, we aimed to validate the use of acoustic parameters as indicators of affective states and welfare in farmed spotted paca (Cuniculus paca). We recorded the vocalizations of 36 pacas, living in 12 groups (two females and one male/grou...

Rat tickling is a heterospecific interaction for experimenters to mimic the interactions of rat play, where they produce 50 kHz ultrasonic vocalisations (USV), symptoms of positive affect; tickling can improve laboratory rat welfare. The standard rat tickling protocol involves gently pinning the rat in a supine position. However, individual respons...

Our experiences of the conscious mental states that we call emotions drive our interest in whether such states also exist in other animals. Because linguistic report can be used as a gold standard (albeit indirect) indicator of subjective emotional feelings in humans but not other species, how can we investigate animal emotions and what exactly do...

Background: Pet care guidelines play an important role in ensuring that owners are well informed about good husbandry practices, allowing them to provide the best care for their animals. However, the development of such guidelines is difficult when there is little appropriate empirical evidence on which to base guidelines, as in the case of pet ra...

Biomedical research suffers from a crisis of reproducibility and translatability (1), with some studies estimating that more than 50% of preclinical studies are irreproducible (2). The lack of reproducible results has led to annual economic losses of about US$28 billion in the United States alone, delays to new treatments, and unneces- sary use of...

Human patients with chronic pain from osteoarthritis often report impaired sleep, but it is not yet known if sleep is also impaired in dogs with osteoarthritis. This study aimed to compare the night-time sleep behaviour of osteoarthritic (N=20) and healthy control (N=21) dogs over a 28-day period, using an actigraphic device (the FitBark activity m...

Reporting of outcome variables by care-givers in welfare studies is commonplace, but is open to subjective bias and so requires validation. Biases can occur in either direction: familiarity with an animal allows a deeper insight into welfare problems, but also can lead to reticence in admitting that an animal in one's care is experiencing problems....

To assess the welfare of captive animals, validated measures, so-called ‘welfare indicators’, are required. We used a triangulation approach to investigate the extent to which different measures converged to provide corroborating evidence of welfare. Laying hens were exposed to living conditions designed to be generally preferred (GP) or generally...

Background: There are few studies on the physiology and haematology of rescued bearded capuchin monkeys. These are necessary to better understand the health and welfare status of the animals, including when performing reintroductions, and to avoid zoonoses. Methods: We aimed to obtain physiological and haematological values, morphometry and para...

We previously identified in laboratory mice an inactive state [being awake with eyes open motionless within the home cage; inactive but awake, ‘IBA’] sharing etiological factors and symptoms with human clinical depression. We further test the hypothesis that greater time spent displaying IBA indicates a depression-like state in mice by investigatin...

Good translatability of behavioral measures of affect (emotion) between human and nonhuman animals is core to comparative studies. The judgment bias (JB) task, which measures “optimistic” and “pessimistic” decision-making under ambiguity as indicators of positive and negative affective valence, has been used in both human and nonhuman animals. Howe...

Choice tests, which measure animals' preferences for resources, are increasingly used to aid the design of new husbandry systems. However, under farm conditions, these systems are not always used as desired. A possible explanation for this is that laboratory testing and on-farm conditions induce different states of stress or disturbance in animals...

Surveys provide a low-cost means to obtain large amounts of data that are ideal for conducting exploratory research, and they are becoming an increasingly valuable tool in a veterinary context. We investigated whether surveys of pet rat owners might provide useful data that could pave the way for more targeted empirical studies of pet and laborator...

A top priority of modern zoos is to ensure good animal welfare (AW), thus, efforts towards improving AW monitoring are increasing. Welfare assessments are performed through more traditional approaches by employing direct observations and time-consuming data collection that require trained specialists. These limitations may be overcome through autom...

Understanding why some species thrive in captivity, while others struggle to adjust, can suggest new ways to improve animal care. Approximately half of all Psittaciformes, a highly threatened order, live in zoos, breeding centres and private homes. Here, some species are prone to behavioural and reproductive problems that raise conservation and eth...

Domestic dogs are trained using a range of different methods, broadly categorised as reward based (positive reinforcement/negative punishment) and aversive based (positive punishment/negative reinforcement). Previous research has suggested associations between use of positive punishment-based techniques and undesired behaviours, but there is little...

Third-party interventions may regulate conflicts to reduce aggression and promote cohesion amongst group members, but are rarely documented in ungulates. The white-lipped peccary (Tayassu pecari) lives in mixed-sex herds of hundreds of individuals in Neotropical forests, which are likely to benefit from mechanisms that sustain social cohesiveness....

Background: To date, despite the substantial literature investigating how rats prefer to be kept in captivity, no research has been conducted to assess the housing, husbandry and health of pet rats. Methods: To better understand the United Kingdom's pet rat population and the welfare issues they face, we conducted an online survey of pet rat own...

This chapter reviews assessing emotions in pigs, specifically focusing on the ways of determining negative and positive mental states. It begins by examining behavioural indicators of emotion such as behavioural tests, qualitative behaviour assessment, vocalisations, play behaviour, defence cascade responses and facial expression and body posture....

Simple Summary The paca (Cuniculus paca), a Neotropical caviomorph rodent, provides the most sought-after game meat in all its range, and it therefore faces high hunting pressure and consequent poor welfare. The species is categorised as having a conservation status of “least concern” and appears resilient to over-hunting by humans, which may be re...

Links between affective states and risk-taking are often characterised using summary statistics from serial decision-making tasks. However, our understanding of these links, and the utility of decision-making as a marker of affect, needs to accommodate the fact that ongoing (e.g., within-task) experience of rewarding and punishing decision outcomes...

Emotions encompass cognitive and behavioural responses to reward and punishment. Using contests as a case-study, we propose that short-term emotions underpin animals' assessments, decision-making, and behaviour. Equating contest assessments to emotional "appraisals", we describe how contestants appraise more than resource value and outcome probabil...

Variation in executive function and age-related cognitive decline may underlie the emergence of behaviour and welfare problems in dogs. A better understanding of such links, and of dog cognition in general, will be facilitated by the development of cognitive tasks that can be readily implemented, including with publicly-owned dogs that are availabl...

Positive animal emotion (affect) is a key component of good animal welfare [1] and plays an important role in stress-coping and resilience [2]. Methods for reliably inducing and measuring positive affect are critical, but both have been limited in availability. In rats, one promising way of inducing positive affective states is by human-simulated r...

Simple Summary Excessive body mass, i.e., being overweight or obese, is a health concern. Some lemur species are prone to extreme weight gain in captivity, yet for others a healthy body condition is typical. The first aim of our study was to examine possible ecological explanations for these species’ differences in susceptibility to captive weight...

The influence of affective states on decision-making is likely to be complex. Negative states resulting from experience of punishing events have been hypothesised to generate enhanced expectations of future punishment and ‘pessimistic’/risk-averse decisions. However, they may also influence how decision-outcomes are valued. Such influences may furt...

Just as happy people see the proverbial glass as half-full, ‘optimistic’ or ‘pessimistic’ responses to ambiguity might also reflect affective states in animals. Judgement bias tests, designed to measure these responses, are an increasingly popular way of assessing animal affect and there is now a substantial, but heterogeneous, literature on their...

Just as happy people see the proverbial glass as half-full, ‘optimistic’ or ‘pessimistic’ responses to ambiguity might also reflect affective states in animals. Judgement bias tests, designed to measure these responses, are an increasingly popular way of assessing animal affect and there is now a substantial, but heterogeneous, literature on their...

Affective states are key determinants of animal welfare. Assessing such states under field conditions is thus an important goal in animal welfare science. The rapid Defence Cascade (DC) response (startle, freeze) to sudden unexpected stimuli is a potential indicator of animal affect; humans and rodents in negative affective states often show potent...

Links between affective states and risk-taking are often characterised using summary statistics from serial decision-making tasks. However, our understanding of these links, and the utility of decision-making as a marker of affect, needs to accommodate the fact that ongoing (e.g. within-task) experience of rewarding and punishing decision outcomes...

Individual behavioral differences may influence how animals cope with altered environments. Depending on their behavioral traits, individuals may thus vary in how their health is affected by environmental conditions. We investigated the relationship between individual behavior of free-living golden-headed lion tamarins (Leontopithecus chrysomelas)...

Recent clinical and pre-clinical research suggests that affective biases may play an important role in the development and perpetuation of mood disorders. Studies in animals have also revealed that similar neuropsychological processes can be measured in non-human species using behavioural assays designed to measure biases in learning and memory or...

Graphical abstract summarising principles of affect and decision-making model

Food sharing experiments with Eurasian jays have provided some of the most compelling evidence to date for co-operative social cognitive abilities in corvids. Male Eurasian jays have been found to alter their food sharing response in line with the specific satiety of their female partner. However, as food sharing forms part of courtship it may be u...

Male Eurasian jays were previously reported to alter their food-sharing response in line with the specific satiety of their female partner. Here, we tested the flexibility of the same males’ food-sharing behavior by testing whether they can process information from contextual cues that predict the opposite pattern of food shared to that observed in...

The scientific study of animal affect (emotion) is an area of growing interest. Whilst research on mechanism and causation has predominated, the study of function is less advanced. This is not due to a lack of hypotheses; in both humans and animals, affective states are frequently proposed to play a pivotal role in coordinating adaptive responses a...

Theory and empirical findings predict that individuals in a negative affective state are more sensitive to unexpected reward loss and less sensitive to unexpected reward gain compared to individuals in a neutral or positive affective state. We explore the use of sensitivity to reward shifts measured during successive contrast tasks as an indicator...

This second edition of Mental Health and Well-Being in Animals is fully revised, expanded, and comprehensively updated with the most current knowledge about the full array of mental health issues seen in animals. Written by key opinion leaders, internationally-recognized experts and specialists, it is comprehensive covering basic principles to ment...

Affect-driven cognitive biases can be used as an indicator of affective (emotional) state. Since humans in negative affective states demonstrate greater responses to negatively-valenced stimuli, we investigated putative affect-related bias in mice by monitoring their response to unexpected, task-irrelevant stimuli of different valence. Thirty-one C...

Validated measures of animal affect are crucial to research spanning numerous disciplines. Judgement bias, which assesses decision-making under ambiguity, is a promising measure of animal affect. One way of validating this measure is to administer drugs with affect-altering properties in humans to non-human animals and determine whether the predict...

The componential view of human emotion recognises that affective states comprise conscious, behavioural, physiological, neural and cognitive elements. Although many animals display bodily and behavioural changes consistent with the occurrence of affective states similar to those seen in humans, the question of whether and in which species these are...

Validated measures of animal affect are crucial to research spanning a number of disciplines including neuroscience, psychopharmacology, and animal welfare science. Judgement bias, which assesses decision-making under ambiguity, is a promising measure of animal affect. One way of validating this measure is to induce affective states using pharmacol...

Objective: To describe clinically relevant, physiological measurements collected during a 3 hour duration of alfaxalone total intravenous anaesthesia. Study design: Case series. Animals: A total of 112 client-owned middle-aged or older dogs. Methods: Dogs were premedicated with intramuscular acepromazine (0.03 mg kg-1). Anaesthesia was induc...

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Scientific methods for assessing animal affect, especially affective valence (positivity or negativity), allow us to evaluate animal welfare and the effectiveness of 3Rs Refinements designed to improve wellbeing. Judgement bias tasks measure valence; however, task-training may be lengthy and/or require significant time from researchers. Here we dev...

Background: Assessing the affective state of animals is important for a range of research areas, including neuroscience. The use of cognitive judgement and attention biases to determine affective state has been demonstrated in animals, but approaches to assess mood-congruent biases in memory have yet to become established. New method: We describ...

In man, central sensitisation (CS) contributes to the pain of osteoarthritis (OA). Dogs with spontaneous OA may also exhibit CS. Electrophysiological reflex measurements are more objective than behavioural assessments, and can be used to evaluate CS in preclinical and clinical studies. It was hypothesised that dogs suffering from OA would exhibit e...

Affective states influence decision-making under ambiguity in humans and other animals. Individuals in a negative state tend to interpret ambiguous cues more negatively than individuals in a positive state. We demonstrate that the fruit fly,Drosophila melanogaster, also exhibits state-dependent changes in cue interpretation.Drosophilawere trained o...

The concept of ‘coping strategies’ has received increasing attention over the last few years. Benus et al. (1991) reported two major types of strategy in rodents. These were the so-called active and passive strategies. The active strategy consists of being aggressive, forming behavioural routines and showing low responsiveness to changes in the env...

From an animal production and welfare perspective, an important social choice made by farm animals is whether and how vigorously to fight others. The choice to fight (i.e. simultaneous escalated aggression by both contestants) may result in severe injury when unfamiliar animals first meet or compete for highly valued resources. Game theory models o...

This third edition of "Animal Welfare" has 407 pages and is divided into five parts. Part I, Issues, introduces the background and philosophy of the subject. Part II covers problems for animal welfare, starting in chapter 3 with the animal's interactions with its environment. The following four chapters use categories similar to the UK Farm Animal...

In recent years there has been a growing research interest in the field of animal emotion. But there is still little agreement about whether and how the word “emotion” should be defined for use in the context of non-human species. Here, we make a distinction between descriptive and prescriptive definitions. Descriptive definitions delineate the way...

Syringomyelia is a common and chronic neurological disorder affecting Cavalier King Charles Spaniels. The condition is putatively painful, but evaluating the affective component of chronic pain in non-human animals is challenging. Here we employed two methods designed to assess animal affect - the judgement bias and reward loss sensitivity tests -...

Simple Summary Wild mice live in territories inhabited by one adult male, several females, and their offspring. This cannot be replicated in the laboratory, so male mice are usually housed in single-sex groups or individually. However, there can be serious animal welfare problems associated with both these approaches, such as lack of social contact...

In view of the forthcoming UK ban on stall and tether housing for sows, the long-term consequences of housing pregnant pigs in alternative systems were assessed. The objective of the study was to examine the effects of two indoor group-housing systems on measures of the welfare of pregnant pigs, and to compare pigs housed in these systems with pigs...