While the zoological community strives to provide the best possible living environment for non-human animals, space limitations constrain where zoos can house particular species. Therefore, an individual may live in proximity to animals that impact its behaviour, physiology, reproductive function or overall welfare status. This article examines how solitary and social species living in managed settings are positively and negatively affected by conspecific neighbours. When making housing decisions, zoos should follow husbandry recommendations outlined by zoo associations, integrate natural history information and attempt to view the environment from the perspective of the species of interest. Furthermore, researchers can collect survey, behavioural and physiological data to examine how variables, such as density, distance between neighbours, the age/sex of conspecifics and types/amount of exposure to others influence welfare. Ultimately, zoos should consider the needs of individuals and investigate whether welfare can be enhanced by modifying enclosures, husbandry routines, enrichment schedules or access to conspecifics. A zoo's willingness to alter an animal's exposure to conspecifics may have a substantial impact on physical, mental and emotional health.

Scientific studies of human-animal interactions (HAIs) and how these develop into human-animal relationships (HARs) now represent some of the most significant contributions to animal welfare science. However, due to the current definition of HAR, studies have only been able to measure HAIs and infer its impact on HARs and animal welfare. Here, we redefine HARs as a series of repeated HAIs between two individuals known to each other, the nature of which is influenced by their historical HAIs and where consideration to the content, quality and the pattern of the interactions is also vital. With a new definition, it is now feasible to empirically measure HARs, however, first, it is important to evaluate current methods utilised in animal industries to allow standardisation across HAR research in zoos. Here, we review the current methods that have been used to assess HAIs in animals and determine their overall suitability for measuring HARs and their use in a zoo environment. Literature searches were conducted using the search terms ‘human-animal’ AND ‘interaction’, ‘human-animal’ AND ‘relationship’, ‘human-animal’ AND ‘bond’. Subsequently, ‘zoo’, ‘companion’, ‘agriculture’, ‘laboratory’ and ‘wild’ were added to each combination yielding five potential methods to evaluate. These methods were assessed according to a panel of indicators including reliability, robustness, practical application and feasibility for use in a zoo environment. Results indicated that the methods utilising ‘latency’, ‘qualitative behaviour assessment’ and the ‘voluntary approach test’ were potentially viable to assess HARs in a zoo environment and could subsequently contribute to the assessment of welfare implications of these HARs for the animals involved. These methods now require empirical testing and comparisons within a zoo environment.

Motivation is a central concept for animal welfare; it has inspired methodological breakthroughs and generated a wealth of crucial empirical work. As the field develops beyond its original mandate to alleviate the suffering of animals in intensive farming systems, the assumptions behind the current models of motivation may warrant closer scrutiny. In this paper, I examine some of the complexities of studying motivation — for example, that what an animal wants can depend on its welfare and that, through genetic selection and housing choices, we can modify what an animal finds to be rewarding versus punishing. The central theme of this paper is, therefore, that we cannot just ask the animals under our care (or even in the wild) what they want and assume that we will receive unadulterated answers, free from human influence. While asking questions about animal motivation with empirical research is invaluable and necessary, our models drive our research questions, methodologies, and results’ interpretation. When the models we employ remain implicit (eg the only motivation questions worth asking are those that could be implemented within the current housing systems), they have ability to stifle progress in understanding animal welfare. Thus, in addition to the empirical work, we also need to expose and evaluate the models that drive the research. Making the models explicit will facilitate our ability to identify their areas of silence, assess their strengths and potential limitations, as well as examine how they conceptualise the relationship between motivation and animal welfare. I end with a discussion of the implications of a few relevant models, both implicit and explicit, noting how such consideration reveals exciting areas for future work, including, for example, research on the motivation to make choices and the motivation to learn.

Human consumption of dog meat continues in some countries as a result of tradition, ritual and claimed medical benefits. In South Korea, it is estimated that over 2,500,000 dogs (Canis familiaris) are eaten annually; however, dog farming is unregulated, as dogs are not classified as livestock, leading to animal welfare concerns. A key component of the physiological stress response is activation of the hypothalamic-pituitary-adrenal (HPA) axis. Cortisol released as a consequence of HPA axis activation is stably deposited in growing biological media, such as hair. Extraction and quantification of hair cortisol can provide a historical record of physiological stress experienced as the hair was growing. By comparison of hair cortisol concentrations in samples collected from dogs surrendered from meat farms with pet dogs, this study demonstrates that hair cortisol concentrations from dogs rescued from meat farms are over twice as high as pet dogs living in and close to Seoul. This difference was independent of sex, breed and coat colour. Within the farmed dogs there were no significant effects of farm identity, number of dogs per farm or dogs per cage. Within the Korean Jindos surrendered from meat farms, hair cortisol was significantly higher in white-compared to black-coated dogs but there were no significant differences within or between dogs of other coat colour variants (agouti, brown). These data provide quantitative evidence that dogs in meat farms are kept in conditions associated with poor welfare and identify the need for better welfare laws to protect farmed dogs.

In nature, animals need to actively engage with the environment in order to prosper in survival and reproduction. Hence, agency is a central adaptive characteristic of animal life. In this paper, I propose that from the adaptive/functional point of view, four levels of agency can be distinguished, namely passive/reactive agency (animal being behaviourally passive or purely reactive), action-driven agency (animal behaviourally pursuing current desirable outcomes), competence-building agency (animal engaging with the environment to gain skills and information for future use) and aspirational agency (the animal achieving long-term goals through planning and autobiographical reflection). Recent progress in affective neurobiology indicates that each tier of agency is supported by a different type of affective functioning, at least in the case of mammals. Furthermore, the particular agency levels can be linked to distinct degrees of awareness as defined by recent selfhood theories. Based on this coupling between agency adaptive functioning, affective neurobiology and animal awareness levels, I examine several links between animal agency and animal welfare, including the notion of animal boredom, and discuss how animal agency might be promoted in the restrictive frameworks of intensive animal farming.

Walking ability is related to motor co-ordination which, in rodents, can be assessed by an established test in pharmacological studies — the rotarod test. The purpose of this study was to evaluate a modified rotarod test for chickens and its relation to the often-used gait score system. At the end of their rearing period, we tested 138 male chickens (Gallus gallus domesticus) from three differing growth performance strains: Ross 308 (fast-growing; n = 46), Lohmann Dual (medium-growing; n = 46) and Lohmann Brown Plus (slow-growing; n = 46). First, the chickens’ gait scores were assessed and, immediately following this, they were placed gently onto a steady rod. The velocity of the rotating rod gradually increased, and the latency to leave the rod was recorded. By using a linear mixed model, we were able to show that the latency to leave the rotating rod was significantly predicted by the gait score. Fast-growing chickens had shorter durations on the rotating rod, and these durations were associated with gait score. We conclude that the rotarod test provides an objective alternative method for assessing walking ability in chickens without the need for intense observer training or the risk of observer biases and propose that this novel methodology has the potential to function as a precise, objective indicator of animal welfare.

Antimicrobial resistance is a major threat to both human and animal health, but reduction of use raises issues of how standards of animal health and welfare can be maintained without them. This turns the spotlight onto the role of good management and higher standards of animal welfare as drug-free ways of improving immune function and increasing resistance to infection. Research is urgently needed into the relationship between animal welfare, immunity, gut microbiota and disease and we are not yet in a position to claim that improving welfare will improve resistance to disease. ‘Boosting’ the immune system is not straightforward and an interdisciplinary approach is needed.

Captive bolts or firearms are unsuitable for euthanasia of livestock when an intact brain is required for diagnostics. Injectable barbiturates can be used, but this method carries risk of poisoning animals eating the carcase. Intravenous saturated salt solutions have been used to euthanase heavily sedated ruminants and are cheap, readily available and not a risk to scavenging animals. However, there is concern that they may be painful or cause distress to animals that are not unconscious. This study aimed to determine the suitability of saturated salt solutions, in combination with xylazine, as a method of euthanasia of ruminants using a sheep model. Thirty-two sheep were sedated with xylazine (0.4 mg kg-1 IM) and euthanased with an intravenous overdose of pentobarbitone (PENT; n = 10), saturated potassium chloride (KCL; n = 11) or saturated magnesium sulphate (MGS; n = 10). Time until end of rhythmic breathing and cardiac arrest, and movement events were recorded. Conscious perception of pain was evaluated by measuring cortical brain activity by electroencephalography (EEG). There was no evidence of perceived pain or unpleasant sensory experience for any treatment as indicated by P50, P95 and Ptot and so all methods were deemed humane. Time until transient EEG was comparable for all treatments. Time until onset of isoelectric EEG was prolonged for KCL. Animals euthanased with KCL consistently exhibited severe reflex movements during infusion (eg kicking, convulsion). No severe movement events were observed in animals euthanased with MGS, hence, physiological and movement data support the preferential use of MGS over KCL.

This systematic review explores the use of on-animal sensors in sheep and their potential application in objective welfare monitoring. The key questions posed were: To what extent can current scientific knowledge inform a sensor-based approach to welfare evaluations? And, how might this knowledge shape development of commercial monitoring systems? These questions were explored through retrospective classification of published sensor applications using The Five Domains (FD) Model as a framework for animal welfare assessment. A total of 71 studies were reviewed. The results indicate studies specifically evaluating the use of sensors for welfare assessment are limited, though many experiments could still be related to some aspect of welfare. The assessment of sensor utilisation revealed the greatest proportion of applications within the ‘Behaviour’ Domain (90.1%; n = 64), and the lowest within the ‘Health’ (25.4%; n = 18) and ‘Mental state’ Domains (25.4%; n = 18). The review also highlights how different sensor types (location, motion or physiological) differ in their applicability for welfare assessment. This paper is the first to classify published sensor applications using the FD Model as a framework and highlights the potential for sensor technology in sheep welfare monitoring. The results suggest that any attempt to create a commercial sensor-based system for objective welfare assessment will require the integration of more than one sensor type, particularly if multiple Domains are to be addressed.

A collaborative effort was undertaken to delineate underwater noise levels within holding enclosures at marine mammal facilities. Ambient noise levels were measured under normal operating conditions in the enclosures of 14 participating facilities. Facility habitats varied from ocean environments to fully enclosed pools. The means and standard errors of the noise pressure spectral densities measured across all pools were similar to those measured in natural coastal environments with relatively low presence of anthropogenic noise. Highest levels of noise in land-based pools were generally at frequencies < 2 kHz and primarily due to the operation of water treatment/filtration systems. Noise levels in land-based pools were comparable to or lower than semi-natural and natural systems at higher frequencies because of the presence of biological noise sources in these systems (eg snapping shrimp [Alpheus spp]). For odontocete enclosures, the whales themselves were often the greatest source of sound at frequencies where the whales have their best hearing (~40-100 kHz). The potential for facility ambient noise to acoustically mask odontocete communication signals and echolocation clicks appears to be low. In general, when noise was elevated it was at frequencies outside the typical frequency ranges of whistles and echolocation clicks, and where odontocetes have poor hearing sensitivity. Occasional noise issues were found; it is therefore recommended that facilities periodically assess enclosure noise conditions to optimise animal management and welfare.

Boredom, while often casually attributed to non-human animals by both laypeople and scientists, has received little empirical study in this context. It is sometimes dismissed by others as anthropomorphic or a trivial concern in comparison to other welfare problems faced in captivity. Recent work on human boredom, however, has led to evidence that, far from being trivial, it can have serious consequences in the form of risky behaviour and reduced physical as well as mental health, and potentially contributes to social problems. Research on mink, supported by older literature on farm and laboratory animals, suggests that monotonous, stimulus-poor environments can induce an increased motivation for diverse stimuli, consistent with the experience of boredom. This experience is likely to be aversive and may lead to problems such as depression-like states or self-injurious behaviour if not addressed. Boredom should therefore be treated as an important welfare concern. Research is needed to find practical ways of identifying this state and to determine how widespread it is across species and which animals are most at risk. Possible ways of alleviating or avoiding this problem include offering animals in our care a choice in the level of stimulation they experience and opportunities to experience appropriate cognitive challenge.

An increasing public concern over the welfare of livestock species is motivating more producers to consider changes to production practices. Providing environmental enrichment for intensively housed animals is one such potentially welfare-enhancing change. The goal of environmental enrichment is to provide biologically relevant environmental stimuli that allows an animal to perform highly motivated, species-specific behaviours. To date, there is no research specific to the applicability of environmental enrichment for commercial boars (Sus scrofa domesticus), nor on commercial boar welfare in general. In this study, eight individually housed, mature boars were observed to prefer interacting with hanging cotton rope enrichment over hanging rubber chew sticks when given the option. There was a significantly negative correlation between the amount of time boars spent interacting with rope and the amount of time they spent performing stereotypic pen manipulation, suggesting that the rope was more effective at reducing stereotypic behaviour than the rubber. Such reductions in amount of time spent performing abnormal stereotypic behaviours could indicate that some of the animals’ behavioural needs are being met by the enrichment object. Thus, the results of this study could help provide producers with more objective, research-based suggestions concerning the efficacy of practical enrichment choices for individually housed boars.

Animal welfare scientists actively seek reliable and practical metrics that can serve as indicators of animal welfare for use with agricultural, laboratory and zoo-housed animals. Behavioural diversity as a welfare concept originated from early welfare scientists linking poor animal welfare with a high proportion of time spent engaged in stereotyped behaviours and little expression of behaviours that would be expected under wild, or natural conditions. Recently, the concept of behavioural diversity as a welfare indicator has been widely adopted and is frequently quantified by the Shannon-Wiener Diversity Index (H-index). However, the H-Index is fraught with theoretical and mathematical limitations when applied to animal welfare. Four key problems with this metric are demonstrated: the metric's responsivity to the size of the behavioural repertoire and the underlying assumption that larger behavioural repertoires reflect better welfare, the sensitivity of the metric to arbitrary decisions about the resolution of behavioural categories, the fact that the calculation of the metric is agnostic to the valence of behaviours, and the metric's susceptibility to the common practice of excluding some behavioural categories. Moving forward, we recommend focusing on validated welfare measures that are sensitive to valence when evaluating animal welfare.

Low atmospheric pressure stunning (LAPS) is a slaughter technique which may be less stressful for pigs (Sus scrofa domestica) than current commercial stunning and slaughter methods. The main methods used currently for slaughtering pigs are electric and carbon dioxide stunning, both of which are widely recognised as stressful for pigs. There is currently no published research on the use of LAPS for stunning adult pigs, however there is a significant body of relevant experience from investigations into the effects of low pressure and hypoxia on humans, hypoxia for killing pigs and the use of LAPS for killing poultry, rats and piglets. In this paper, the basic physics and biology of LAPS is briefly reviewed and relevant experience from research with humans, poultry, rats and piglets is presented. On the basis of this information, some initial parameters for LAPS trials with pigs are proposed, potential welfare issues identified and an approach to achieving LAPS at a commercially viable speed is outlined. While the effects of LAPS on pigs is, at present, uncertain, the evidence from research with humans and other animals suggests that healthy, fasted pigs undergoing LAPS are unlikely to suffer from air hunger or from pain. Any pigs suffering from upper respiratory tract disease, tooth decay or excess gas in the alimentary canal may, however, experience pain. A total killing cycle is likely to require 9 to 14 min. To implement LAPS in a commercial, high throughput processing plant will require the use of multiple decompression cylinders. The evidence available suggests that LAPS could be commercially viable for pig slaughter and that for most pigs it will be less stressful than current commercial slaughter methods.

Academics working on animal welfare typically consider the animal's affective state (eg the experience of pain), biological functioning (eg the presence of injuries), and sometimes naturalness (eg access to pasture), but it is unclear how these different factors are weighed in different cases. We argue that progress can be informed by systematically observing how ordinary people respond to scenarios designed to elicit varying, and potentially conflicting, types of concern. The evidence we review illustrates that people vary in how much weight they place on each of these three factors in their assessments of welfare in different cases; in some cases, concerns about the animal's affective state are predominant, and in other cases other concerns are more important. This evidence also suggests that people's assessments can also include factors (like the animal's relationship with its caregiver) that do not fit neatly within the dominant three-circles framework of affect, functioning and naturalness. We conclude that a more complete understanding of the multiple conceptions of animal welfare can be advanced by systematically exploring the views of non-specialists, including their responses to scenarios designed to elicit conflicting concerns.

Negative experiences during feather growth can result in fault bar formation. Fault bars are malformations perpendicular to the rachis of the feather caused by stressful experiences during feather growth. However, there are little data on the causal effect of psychological stress on the formation of fault bars in chickens. The objective of this study was to examine the effect of acute stress in domestic chickens (Gallus gallus domesticus) on fault bar formation to validate this measure as a welfare indicator. Thirty broiler breeder pullets were housed in six cages at 21 days of age. Three cages were exposed to an acute stress protocol while the other three were the unstressed control. Feathers were marked as close as possible to the growing follicle at 21 (wing feathers) and 60 (all feathers) days of age. Acute stress came in the form of three procedures (unpredictable feed delivery, induction of tonic immobility, and crowding) repeated twice, 3-8 days apart and randomly, from 28 to 60 days of age. Wing, tail, and cover feathers were removed and measured at 60 days of age for weight, length, and number of fault bars. Exposure to acute, unpredictable stress increased the number of fault bars in wing feathers of chicks with a high number of initial fault bars. Feather growth decreased for the stressed group compared to the control. These results suggest that feather traits, including fault bars and feather growth, can be used as indicators of negative welfare in chickens.

Muslims derive their dietary laws from the Quran (Islamic Holy Book) and other Islamic scriptures. These religious scriptures prohibit them from consuming meat from animals that die before they are bled-out. Some Muslim authorities have interpreted this to mean that, in addition to the animal being alive, it must also be conscious prior to neck-cutting. This has led to a section of the Muslim community rejecting pre-slaughter stunning for halal meat production with the belief that all forms of stunning lead to instantaneous death. It must be noted that some jurists have debunked claims that animals must be conscious before they are bled-out because it does not appear to be mentioned anywhere in the scriptures. This paper reviews literature on the role of the brain in the control of conscious perception and death and considers the different scholarly definitions of death and how they impact the interpretation of halal slaughter rules and the impact on animal welfare.

Brachycephalic obstructive airway syndrome (BOAS) is a major welfare problem in short-nosed breeds, such as the French Bulldog and Pug. In addition to respiratory difficulties, exercise intolerance and impaired recovery are major signs of BOAS. To select healthier breeding animals, exercise tolerance tests, such as the 1,000-m walk test, are already used in several countries for brachycephalic dogs, although evidence supporting their use is still scarce. The aims of this study were to assess the daily welfare of young, breeding-age French Bulldogs (n = 44) and Pugs (n = 51) using an owner questionnaire, and to evaluate 6-min walk test (6MWT) and 1,000-m walk test usability for differentiation between non-or mildly BOAS-affected dogs and more severely affected dogs. Only four out of 95 French Bulldog and Pug owners reported that the BOAS signs limited the daily activities of their dogs. However, according to the physical, examination-based veterinary BOAS grading, 31/95 of the dogs had moderate to severe BOAS signs. In both breeds, the more severely affected dogs performed both exercise tests more poorly than those with no or mild BOAS signs. The longer exercise, namely the 1,000-m test, seemed slightly better able at differentiating between affected dogs and less affected ones. The results of this study further support the use of exercise tests as an important part of the breeding selection in French Bulldogs and Pugs. By influencing the breed standards set by Kennel Clubs and by using breeding selection tools, the harmful impacts of brachycephaly can be diminished.

Objective methods for assessing the cumulative lifetime experience of non-human animals would be valuable. We develop the hypothesis that biological age is a common currency that integrates the overall quality of an animal's lifetime experience across a range of types of exposure. Ageing is the result of the accumulation of somatic damage, and its rate is determined by the balance between experiences that cause damage and experiences that mitigate damage or promote repair. Negative affective states are associated with somatic damage via both direct causal and indirect pathways. Based on these premises, we predict that individuals that are biologically old for their chronological age will, on average, have experienced worse lives than individuals that are biologically younger, both in terms of their overall health and affective experience. Biological age is, thus, an attractive measure of cumulative experience because it requires no subjective decisions either about how a given exposure impacts an animal, or about how different dimensions of welfare should be weighted in an overall assessment. Biological age can be measured objectively using biomarkers. We argue that two biomarkers, namely leukocyte telomere length and hippocampal volume, are valid biomarkers of cumulative experience in humans, with potential for use in non-human vertebrates. We discuss how these biomarkers could be used to assess cumulative experience in animals, highlighting some of the limitations. We conclude that biomarkers of biological age offer a viable objective solution to the assessment of cumulative experience and their application in an animal welfare context deserves further exploration.

Artificial rearing involves removing piglets from their mother at seven days of age and feeding them milk replacer until weaning. Early-life rearing conditions can influence piglets’ mental development, as reflected by their emotional state and reactivity. This study compared the post-weaning emotional state and reactivity of pigs which were either sow-reared or artificially reared pre-weaning. Behavioural tests (startle test, novel object test, human-animal relationship test and open door test) were conducted one week post-weaning (weaner 1, 34 [± 0.6] days old), one week after movement to weaner 2 (69 [±1.2] days old) and to finisher (100 [± 1.3] days old) stages. Qualitative Behavioural Assessments (QBA) were conducted on the same days in weaner 2 and finisher stages. QBA descriptors were computed by PCA and all other data were analysed using linear models. Artificially reared pigs were less fearful of human contact in weaner 1 (45.1 [± 8.43] vs 81.3 [± 7.89]%) and finisher (25.8 [± 5.19] vs 45.7 [± 6.00]%) stages; but there was no difference in the other tests. Artificially reared pigs had a higher QBA score (more positive) than sow-reared pigs in weaner 2 (54.49 [± 10.102] vs 17.88 [± 9.94]) but not in finisher (70.71 [± 8.860] vs 52.76 [± 9.735]) stage. In conclusion, artificially reared pigs appeared to have a more positive emotional state transiently post-weaning and a lower fearfulness towards humans, which are likely mediated by their pre-weaning conditions. These data emphasise the need to consider the entire life of the animals to fully evaluate the long-term impacts of a rearing system.