Standard cages for laboratory animals are often small, minimalist and barren. Such cages can compromise animal welfare, indicating that there are welfare-based reasons for improving their designs. However, a second issue, that is, whether animals from standard laboratory housing and husbandry conditions provide valid research data, also indicates that cage designs and husbandry methods need to be improved. This paper reviews various influences of standard laboratory cage design and husbandry. These include their effects on the repeatability of studies, models of neuro-degenerative disease, sensory development, physiology, and behaviour, the effects of standard social housing and standard handling, and the effects of maternal experience on the responses of offspring. These studies show that the development and responses of animals from standard laboratory housing and husbandry conditions are often unrepresentative and idiosyncratic, indicating that data are likely to have reduced external validity. An underlying question is whether animals from standard, barren laboratory cages are ‘abnormal’ and therefore might not provide valid baseline data. In terms of animal welfare, these studies indicate that standard laboratory housing may sometimes be associated both with reduced welfare and with reduced benefits gained from research. It is suggested that in a similar manner to the use of production measures when assessing cages for production animals, laboratory cages could be assessed in terms of their suitability to provide valid research data.

Minimising suffering is an ethical and legal requirement in animal research. This is particularly relevant for research on animal models of sepsis and septic shock, which show rapid progression towards severe stages and death. Specific and reliable criteria signalling non-recovery points can be used as humane endpoints, beyond which a study cannot be allowed to progress, thus preventing avoidable suffering. Body temperature is a key indicator for assessing animal health and welfare and has been suggested to have potential for monitoring the status of mouse models of sepsis. In this study, we monitored temperature variations using contactless methods – thermal imaging and subcutaneously implanted PIT tags – in a surgical model of sepsis by caecal ligation and puncture (CLP). We monitored body temperature variation following mid-grade CLP, high-grade CLP and sham surgery. All mice (Mus musculus) were monitored four times per day in the high-grade CLP model and three times per day in the mid-grade CLP model by both PIT tag readout and infrared thermography for ten days post-surgery, or until animals reached a predefined humane endpoint. Thermal data were compared with the clinical score and weight loss threshold used at our facility. Mean body surface temperature (MBST) assessed by thermal imaging and subcutaneous temperature (SCT) measured by PIT tags correlated, albeit not strongly. Moreover, while MBST does not appear to be a reliable predictor of non-recovery stages, SCT showed promise in this regard, even surpassing the widely used weight loss criterion, particularly for the high-grade CLP model of induced sepsis.

Severity assessment in animals is an ongoing field of research. In particular, the question of objectifiable and meaningful parameters of score-sheets, as well as their best combination, arise. This retrospective analysis investigates the suitability of a score-sheet for assessing severity and seeks to optimise it for predicting survival in 89 male Sprague Dawley rats (Rattus norvegicus), during an experiment evaluating the influence of liver cirrhosis by bile duct ligation (BDL) on vascular healing. The following five parameters were compared for their predictive power: (i) overall score; (ii) relative weight loss; (iii) general condition score; (iv) spontaneous behaviour score; and (v) the observer’s assessment whether pain might be present. Suitable cut-off values of these individual parameters and the combination of multiple parameters were investigated. A total of ten rats (11.2%; 10/89) died or had to be sacrificed at an early stage due to pre-defined humane endpoints. Neither the overall score nor any individual parameter yielded satisfactory results for predicting survival. Using retrospectively calculated cut-off values and combining the overall score with the observer’s assessment of whether the animal required analgesia (dipyrone) for pain relief resulted in an improved prediction of survival on the second post-operative day. This study demonstrates that combining score parameters was more suitable than using single ones and that experienced human judgement of animals can be useful in addition to objective parameters in the assessment of severity. By optimising the score-sheet and better understanding the burden of the model on rats, this study contributes to animal welfare.

Institutions using animals for research typically have a veterinarian who is responsible for the veterinary care programme and compliance with regulatory obligations. These veterinarians operate at the interface between the institution’s animal research programme and senior management. Veterinarians have strong public trust and are well positioned to share information about animals used for scientific purposes, but their perspectives on sharing information with the public are not well documented and their perceptions of transparency may influence how institutional policies are developed and applied. The objective of our study was to analyse the perceptions of institutional transparency among laboratory animal veterinarians working at different universities. Semi-structured, open-ended interviews were used to describe perceptions of 16 attending veterinarians relating to animal research transparency. Three themes were drawn from the interviews: (i) reflections on transparency; (ii) reflections on culture; and (iii) reflections on self. Veterinarians reflected on their personal priorities regarding transparency and when combined with barriers to change within the institutions, sometimes resulted in reported inaction. For example, sometimes veterinarians chose not to pursue available opportunities for change at seemingly willing universities, while others had their initiatives for change blocked by more senior administrators. The sharing of information regarding the animals used for scientific purposes varied in how it was conceptualised by attending veterinarians: (i) true transparency; communication of information for the sake of openness; (ii) strategic transparency; attempt to educate people about animal research because then they will support it; (iii) agenda-driven transparency; selective release of positive stories to direct public opinion; and (iv) fearful non-transparency; not communicating any information for fear of negative opposition to animal research. Transparency was not perceived as an institutional priority by many of the veterinarians and a cohesive action plan to increase transparency that involves multiple universities was identified as a promising avenue to overcome existing barriers.

Tests of emotionality conducted outside the home-cage show that rodents from standard laboratory housing are more anxious than animals from enriched housing; however, it is not known if this also indicates increased anxiety within the home-cage. We used a novel method, recording the self-administration of a psychoactive anxiolytic, to examine home-cage anxiety levels of laboratory mice (three per cage) in Standard (n = 10 cages), Unpredictable (n = 10 cages) and Enriched (n = 6 cages) housing. The mice were given a choice of drinking either non-drugged water or a solution of the benzodiazepine Midazolam. There was a significant effect of housing on the proportion of total fluid consumed from the bottle containing Midazolam solution (P = 0.02). Mice from Standard and Unpredictable cages drank a greater proportion than mice from Enriched cages. This indicates that mice from the Standard and Unpredictable laboratory caging may have been experiencing greater anxiety than mice from the Enriched cages. There was also a significant effect of bottle position (P = 0.002). Mice from the Standard and Unpredictable cages drank a greater proportion of total fluid from the bottle containing Midazolam solution when this was toward the rear of the cage rack, ie in a location that was less susceptible to extraneous disturbance. Monitoring self-administration of psychoactive drugs as a method of welfare assessment could be applied to a wide variety of housing conditions, husbandry practices, or experimental procedures that putatively induce negative mental states. The major finding is that standard cages for laboratory rodents may induce greater anxiety than enriched cages. This is discussed in terms of animal welfare and the validity of data from animals housed in minimalistic environments.

Considering the welfare of animals used in research is crucial for both the validity of the results obtained and for the social acceptance of animal research. In Europe, the majority of the 5,784 primates currently used for scientific purposes are macaques (Macaca fascicularis and M. mulatta). Inadequate housing conditions can lead to various physiological and behavioural alterations that indicate poor welfare and can impact upon the quality of the data collected. Although there are a number of documents that summarise scientific knowledge on welfare issues and describe the basic needs of macaques, a specific and comprehensive welfare evaluation tool is lacking for the two aforementioned species when housed in a research context. The objective of the Primate Welfare INdicators (PWIN) project is to develop a welfare assessment tool for macaques used in scientific research, through the adaptation of the existing AWIN protocol for farm animals. PWIN aims to provide an objective lifelong assessment of macaque welfare, with repeated evaluations taking place not only during studies but also before and after experimental procedures. The tool comprises an evaluation of macaque housing, nutrition, health and behaviour, complemented by behavioural observations using 10-min continuous focal sampling. PWIN will support ethical research practices, facilitate compliance with regulatory requirements, and enhance information transparency during inspections and project authorisation processes. Beyond tool development, this research seeks to encourage laboratory teams, including researchers, caretakers, and veterinarians, to regularly monitor macaque welfare at the individual level. The imperative to enhance animal welfare considerations in scientific research aligns with European legislation and the 3Rs principle. By establishing a versatile, species-specific method, this research aims to improve existing practices and support ethical, sustainable primate research.

The use of animals as scientific models is argued to be crucial for producing new scientific and medical knowledge and clinical treatments. However, animal research continues to raise socio-ethical concerns. In recent years, there has been a push for openness amongst the life science community, with the aim of increasing the transparency of animal research to wider publics. Yet, how this push for openness is experienced by those responsible for the care and welfare of research animals requires further study. This paper draws upon qualitative interviews with Named Veterinary Surgeons (NVS) in the UK and explores how they practise openness, avoid openness, and, at times, challenge the way their role is represented within openness agendas. Overall, this social scientific analysis reveals that the current openness agenda has the potential to create tensions for professionals, as they seek to manage regulatory and public imaginaries of the veterinary identity alongside the animal research controversy. The paper concludes by arguing for a culture of dialogue, where openness includes allowing those with responsibilities for animal welfare to express ambivalence or concern about their own role. Finally, the paper calls for sustained academic work on relations between the veterinary profession and wider society, particularly areas that involve contested practices in which care and harm may coincide.

Russell and Burch’s 1959 original definitions of the 3Rs (replacement, reduction and refinement) are widely used today as standards for the ethical use of non-human animals in research, although they have a number of limitations. Authors and institutions around the world have addressed some of these, coming up in certain cases with more accurate, functional, and up-to-date definitions. However, not only do there still remain limitations needing to be addressed, but some that have been addressed resulted in discrepancies, contradictions, and general confusion as to how best apply the 3Rs in practice. In order to clarify the meaning of the 3Rs and enable more optimal implementation of these principles in animal experimentation, this article provides a theoretical discussion for revised definitions of the original 3Rs via examination of some of their main limitations and inconsistencies. First, we offer up the original definitions as presented in the context of Russell and Burch’s book The Principles of Humane Experimental Technique. Then, we examine the main limitations and present clear specifications and requirements for such revised definitions. After presenting our revised definitions, we conclude with various implications for animal welfare within the context of experimentation.

Breeding management in laboratory rodents is challenging, particularly around parturition and the neonatal period, where cage disturbance is often avoided in an attempt to limit neonatal mortality. Nevertheless, cage-side observations and single daily checks frequently underestimate pup numbers born and miss parturition complications. Home Cage Monitoring (HCM) systems are gaining popularity in animal facilities, detecting critical events such as food availability and activity levels. Parturition is a complex event involving specific patterns of behaviour, activity and vocalisations. In this study, audio and video data were collected from parturition events of single-housed C57BL/6J females and breeding pairs housed in a prototype rack with integrated microphones. Vocalisations were detected during parturition in both housing conditions, with minimal vocalisations observed prior to parturition, except for ultrasonic sounds in pair-housed mice (Mus musculus). After parturition, all vocalisations gradually decreased. Despite limitations such as the need for post-event analysis and the focus on a single mouse strain, this study suggests that detecting vocalisations can be a promising basis for developing automated parturition detection. This highlights the potential of HCM systems for improving breeding management and welfare in laboratory rodent colonies.

Environmental enrichment programmes are widely used to improve welfare of captive and laboratory animals, especially non-human primates. Monitoring enrichment use over time is crucial, as animals may habituate and reduce their interaction with it. In this study we aimed to monitor the interaction with enrichment items in groups of rhesus macaques (Macaca mulatta), each consisting of an average of ten individuals, living in a breeding colony. To streamline the time-intensive task of assessing enrichment programmes we automated the evaluation process by using machine learning technologies. We built two computer vision-based pipelines to evaluate monkeys’ interactions with different enrichment items: a white drum containing raisins and a non-food-based puzzle. The first pipeline analyses the usage of enrichment items in nine groups, both when it contains food and when it is empty. The second pipeline counts the number of monkeys interacting with a puzzle across twelve groups. The data derived from the two pipelines reveal that the macaques consistently express interest in the food-based white drum enrichment, even several months after its introduction. The puzzle enrichment was monitored for one month, showing a gradual decline in interaction over time. These pipelines are valuable for assessing enrichment by minimising the time spent on animal observation and data analysis; this study demonstrates that automated methods can consistently monitor macaque engagement with enrichments, systematically tracking habituation responses and long-term effectiveness. Such advancements have significant implications for enhancing animal welfare, enabling the discontinuation of ineffective enrichments and the adaptation of enrichment plans to meet the animals’ needs.

With recent increased focus on positive welfare in animal welfare science, there is demand for objective positive welfare indicators. It is unclear whether changes in body surface temperature can be used to non-invasively identify and quantify positive states in mammals. We recorded continuous measurements of tail surface temperature using infra-red thermography (IRT) and concurrent behavioural observations in male and female Wistar rats (Rattus norvegicus). If tail surface temperature can differentiate between positive and negative experiences, we expect a qualitatively different response compared to negative experiences. Three groups of rats were presented with increasing magnitudes of food rewards (neutral/none, one and three rewards). The rats were placed in an arena to which they were habituated and filmed for 30 s before and 30 min after exposure to different rewards. Tail temperature initially decreased from the pre-reward baseline and subsequently returned towards baseline temperature. The overall pattern of the change was the same as for rats subjected to negative stimuli in previous studies. Nevertheless, dynamic changes in tail temperature, specifically the rate of recovery and the behavioural response (exploration), differed between neutral and rewarded rats but failed to distinguish reward magnitude. Sex differences were found in both thermal and behavioural responses, unrelated to reward magnitudes. Female rats exhibited a greater initial response with a slower recovery than male rats, emphasising the value of using of both sexes in animal welfare research. This study improves our understanding of the effects of positive emotions induced by food reward on peripheral body temperature and behaviour.

Changing long-held practices is hard. Employing change management strategies simplifies the process and makes it attainable. These strategies can be used in the vivarium to introduce changes that improve animal welfare. This manuscript describes how change management can be effectively used to transition a global organisation from traditional tail handling to refined handling of mice and rats across 68 international sites. Refined handling methods offer clear benefits for animal welfare, personnel well-being, and scientific integrity, yet tail handling remains common in many research settings. A combination of the Prosci ADKAR model and the Results Pyramid framework were used to create a structured, values-driven approach focused on awareness building, desire for change, knowledge development, hands-on skill acquisition, and sustained reinforcement. Key initiatives included targeted training for diverse stakeholder groups, global workshops, multilingual educational materials, pilot studies to address operational concerns, and a network of site-level champions to foster local ownership and success. Progress was assessed through follow-up surveys and site-level assessments to ensure meeting the pre-assigned success metrics and change success was reinforced with awards. Four years after the programme was initiated (2021–2025), all sites had successfully adopted refined handling for mice (Mus musculus) and rats (Rattus norvegicus), with reported improvements in human-animal interactions, reduced bite incidents, and no significant long-term increases in task duration or error rates. This work demonstrates that structured organisational change management can effectively drive large-scale refinement initiatives and promote a sustainable Culture of Care in laboratory animal programmes.

The distress experienced by animals during the induction of unconsciousness remains one of the most important and yet overlooked aspects of effective methods of anaesthesia and euthanasia. Here we show that considerable differences exist in the aversive responses elicited by 12 common methods of inhalational anaesthesia and euthanasia in laboratory rats and mice. Carbon dioxide, either alone or in combination with oxygen or argon, was found to be highly aversive to both species. The least aversive agents were halothane in rats and enflurane in mice. Exposing these animals to carbon dioxide in any form, either for anaesthesia or for euthanasia, is likely to cause considerable pain and distress and is therefore unacceptable when efficient and more humane alternatives are readily available.

A global contract research organisation (CRO) aimed to transition to refined handling (RH; cupping and tunnel handling for mice [Mus musculus]; body and tunnel handling for rats [Rattus norvegicus]). Three surveys were used to assess handling methods, attitudes, resources needed, and challenges. Surveys included a 2022 survey to benchmark current handling practices (37 responses; 29 sites), a 2023 survey to assess progress (67 responses; 42 sites), and a 2025 survey to assess handling methods and attitudes following uptake of RH (255 responses; 37 sites). In 2022, 81% of sites primarily tail-handled mice. By 2025, RH methods were the primary methods. For rats, in 2022, body handling was the primary method of handling, but tail handling was common for young adult and older and/or less handled rats. By 2025, RH methods were the primary method for all rats. Personnel reported as never or rarely bitten increased from 52% in 2022 to 68% in 2025 for mice, and from 59% in 2022 to 90% in rats. The resources that were most useful were on-site training (77%) and ability to practice RH (59%). Ease of working with animals (60%) and relationship with animals (67%) improved after implementing RH with mice. Ease of working with animals (64%), job stress (50%), relationship with animals (71%), and job satisfaction (53%) improved after implementing RH with rats. The main challenges entailed getting used to alternative methods (i.e. muscle memory) (55% mice; 67% rats) and increased time (61% mice; 49% rats). Ultimately, benefits were reported for implementing RH for both mice and rats.

Tamoxifen-induced CreER-LoxP recombination is often used to induce spatiotemporally controlled gene deletion in genetically modified mice. Prior work has shown that tamoxifen and tamoxifen-induced CreER activation can have off-target effects that should be controlled. However, it has not yet been reported whether tamoxifen administration, independently of CreER expression, interacts adversely with commonly used anaesthetic drugs such as medetomidine or its enantiomer dexmedetomidine in laboratory mice (Mus musculus). Here, we report a high incidence of urinary plug formation and morbidity in male mice on a mixed C57Bl6/J6 and 129/SvEv background when tamoxifen treatment was followed by ketamine-medetomidine anaesthesia. Medetomidine is therefore contra-indicated for male mice after tamoxifen treatment. As dexmedetomidine causes morbidity and mortality in male mice at higher rates than medetomidine even without tamoxifen treatment, our findings suggest that dexmedetomidine is not a suitable alternative for anaesthesia of male mice after tamoxifen treatment. We conclude that the choice of anaesthetic drug needs to be carefully evaluated in studies using male mice that have undergone tamoxifen treatment for inducing CreER-LoxP recombination.

In rodents, cage cleaning increases cardiovascular and behavioural activity for several hours, which are commonly interpreted as stress responses. In mice, post-cleaning activity also includes aggression, which can cause serious injuries. This study was part of a long-term investigation into the effects of cage cleaning frequency on rat behaviour and welfare. Here we aimed to ascertain whether post-cleaning activity is stress- or aggression-related, thereby leading to recurrent acute reductions in welfare, or simply a result of non-aversive stimulation. Male Wistar (n = 160) and Sprague–Dawley (n = 160) rats, kept in four animal units, had their cages cleaned twice per week, once per week or once per fortnight, and were kept on one of two types of bedding. Behaviours were recorded in detail before and after cage cleaning for 20 weeks, as was the aversion-related Harderian gland secretion, chromodacryorrhoea (‘red tears‘). Cage cleaning caused decreased resting and increased feeding, walking, bedding manipulation and sheltering for at least 30 min after the disturbance. Skirmishing also increased markedly for 15 min after cleaning, but decreased thereafter to below baseline levels. Unlike in mice, all skirmishing was non-injurious and play-like. The frequency of cage cleaning did not affect the magnitude of this skirmishing peak, but rats that had their cages cleaned more frequently settled more quickly after cleaning. Surprisingly, chromodacryorrhoea decreased after cage cleaning; this could mean that rats find soiled cages stressful or alternatively, like many disturbances, cage cleaning might provoke frequent, curtailed bouts of grooming, thereby removing the secretion. Rats also manipulated aspen bedding more than paper bedding. Overall, we found no evidence that cage cleaning caused rats any acute decrease in welfare — a finding consistent with additional data we have obtained on the lack of preference by rats for soiled over clean cages, and a lack of long-term, behavioural and physiological responses to being cleaned frequently or infrequently.

Enhancing the complexity of the environments of captive animals is often referred to as environmental enrichment, and aims to have positive effects on the animals’ well-being. Such enrichments may have consequences both for so-called ‘normal’ behaviour and for the pathophysiology of the animals in question. The effects of a lack of environmental complexity, including social isolation, on home cage behaviour and on pathophysiology in rats is considered in this review. Several preference tests on rats — choice tests and operant tests — indicate a preference for bedding, nesting material and social contact. Contradictory research results concerning the need for gnawing objects per se are more difficult to interpret, and it is argued that excessive gnawing may be indicative of primary frustration and hence reduced welfare. One disadvantage of providing environmental enrichment to laboratory animals is a possible increase in subject variability, resulting in the need to use a greater number of test animals. However, this increased variability seems to be inconsistent and is not very well documented. It is argued that in cases where the behavioural benefits of environmental enrichment justify the use of more animals, better welfare should be more highly valued than a reduction in the number of animals used.

Isolating an animal refers to the situation where the animal is physically fully demarcated from conspecifics without physical, visual, olfactory and auditory contact. Animals housed in separate cages in the same room are, although deprived of physical and visual contact, still in olfactory and auditory contact, and thus not totally isolated. During the fifties and sixties several studies claimed to show physiological and behavioural differences between individually and group housed rats and mice. The so-called ‘Isolation Syndrome’ characterised by changes in corticosterone levels, metabolism, growth, and behaviour was introduced, rather as a model for psychoneurosis than through any concern for animal welfare. Today, it is often stated as common knowledge in laboratory animal science textbooks that individual housing as well as isolation of rats and mice has an effect on physiology and behaviour. It is, however, unclear whether this effect actually impairs animal welfare.

The aim of this paper is to analyse studies on individual housing of mice and rats to evaluate whether there is documented proof that individual housing affects welfare, and, alternatively whether it is possible to house these animals individually without negative impact on welfare, eg by providing special housing improvements.

A range of studies have shown that individual housing or isolation has effects on corticosterone, the open field behaviour, barbiturate sleeping time and the metabolism of different pharmaceuticals in the animals. However, this review of 37 studies in rats and 17 studies in mice showed divergence in test results difficult to explain, as many studies lacked basal information about the study, eg information on genetic strains and housing conditions, such as bedding, enrichment and cage sizes. Furthermore, test and control groups most frequently differed in cage sizes and stocking densities, and behavioural tests differed in ways which may very well explain the differences in results. Overall, there seemed to be an effect of individual housing, although it may be small, and it seems reasonable to assume that, through making small changes in the procedures and housing environments, the effects can be minimised or even eliminated. More well-controlled and standardised studies are needed to give more specific answers to the questions this issue poses.

Criteria for assessing the severity of scientific procedures in laboratory rodents include the loss of body mass. However, guidance is limited for passerine birds and application of criteria developed for mammals risks poor welfare decisions. Here, I ask whether, and how, body mass criteria could be incorporated into laboratory welfare assessment of passerines. Passerine birds strategically adjust their body mass to minimise combined mortality risk from starvation and predation. A systematic literature review found that strategic mass changes can be sizeable (sometimes > 10%) even over short timescales. Many aspects of a bird's current or past environment, including husbandry and experimental procedures, may alter perceived starvation or predation risks and thus drive strategic mass change via evolved mechanisms. Therefore, body mass criteria used for rodents may be too stringent for passerines, potentially leading to over-estimated severity. Strategic mass changes might obscure those stemming from experimental interventions yet could also offer insights into whether birds perceive an intervention or altered husbandry as a threat. Mass criteria for severity assessment should be species- and context-specific in order to balance needs for refinement and reduction. To guide the development of appropriate criteria, a future research priority is for greater data collection and sharing based on standardised routine monitoring of mass variation under a representative range of husbandry conditions and procedures.

Although barbering is common in laboratory mice (Mus musculus), little is known about its effects, both on animal welfare and the research data collected from barbered mice. To gain information on the occurrence of barbering and related risk factors in animal facilities in Germany, we performed an online survey. All the respondents (n = 32 animal facilities) had experienced barbering in their facility. In most cases, less than 10% of the mice were affected, and the age of onset was mostly observed to be 2 to < 6 months. A greater susceptibility was reported in females and in C57BL/6 mice, but this could not be verified as the prevalence of females and the C57BL/6 strain was unknown. One facility reported differences in barbering between commercial animal suppliers. Barbering was also recorded in mice provided with enrichments, such as houses, wood-gnawing blocks, tunnels, running wheels/discs or cage dividers. None of the responding facilities provided swings, structural elements such as an elevated platform or foraging and cognitive enrichment. The questions of whether barbering may have an impact on study results and whether victims of barbering can be used for experiments revealed mixed opinions, most likely due to a lack of data on potential effects. This survey clearly demonstrated barbering to be a widely underestimated problem that is not given enough attention. We suggest that the occurrence of barbering should be systematically documented in every animal facility and reported in research articles, to provide a greater understanding of barbering and its potential effects.