3Rs Information - Rodents


Welfare and scientific considerations of tattooing and ear tagging for mouse identification

A study has outlined the welfare and scientific considerations of tattooing and ear tagging mice and concluded that the total welfare costs of tattooing are not greater than for ear tagging.


Care and use of GA mice

The NC3Rs have collated general information to help with the implementation of approaches to reduce and refine the use of genetically altered (GA) mice. Resources include: guidance on re-establishing colonies after a pause (e.g. COVID-19 lockdown); improving reproducibility and avoiding genetic mosaicism using CRISPR/Cas9 technology; improving animal welfare; genetic drift; the importance of neonate assessment; comparing the technical performances of background strains; the importance of background strains; and opportunities for refinement and reduction.

Laboratory mouse housing conditions can be improved using common environmental enrichment without compromising data

A study, published in PLOS Biology investigated the effect of commonly used environmental enrichment on 164 physiological parameters in mice. The researchers found that environmental enrichment can successfully be added to the cages of mice without interfering with or compromising scientific data. We strongly advise that rodent researchers concerned about the use of environmental enrichment should read this paper.

Variation between inbred and outbred mice

paper published in Nature Methods comparing the phenotypic variation between inbred and outbred mice. These researchers have concluded that even though inbred mice are assumed to display less trait variability, there is no evidence for this and outbred mice, contrary to popular belief, may actually be better for most biomedical research. We recommend that researchers read this paper before planning a study to ensure that the correct mouse model is chosen for their particular needs.

Aggression in group housed male mice

Aggression in group housed male mice is a common problem in laboratory animal facilities, and is often cited as a reason for avoiding the use of male mice, or individually housing experimental animals. The Swedish 3Rs Center has recently published recommendations on preventing aggression in group housed male mice, thus improving welfare and consequently the quality of research. These recommendations, originally written in Swedish, are now available in English.

Breaking up is hard to do: does splitting cages of mice reduce aggression?

study, published in the journal of Applied Animal Behaviour Science, evaluated best practices in separating mice following aggression-related behaviours and the likely outcomes of cage separation. This paper is an essential read for those working with rodents where aggression tends to be an issue.

Measuring endogenous corticosterone

Evaluating stress in laboratory animals is a key principle in animal welfare. Measuring corticosterone is a common method to assess stress in laboratory mice. There are, however, numerous methods to measure glucocorticoids with differences in sample matrix and quantification techniques. In this article, recently published in Altex, the authors present a mapping review and a searchable database, giving a complete overview of all studies measuring endogenous corticosterone in mice up to February 2018.

Self-organising ‘gastruloids’ mimic early development of mouse embryos

Researchers from the University of Cambridge, the University of Geneva and the Federal Institute of Technology Lausanne (EPFL) have developed a 3D embryonic stem cell culture system capable of self-organising into the three major axes of the body. This has potential to replace the use of mice to study the early development of the human embryo. The NC3Rs has released a set of videos where Dr David Turner of the University of Cambridge discusses the research group’s publication on the work.


Housing temperatures in mice

Elsevier data scientists have used data mining, NLP and neural networks to discover that researchers are not keeping mice at the best temperatures for accurate results. This research corroborates a 2015 study where researchers confirmed that mice become resistant to certain cancer therapies at lower temperatures. The vast majority of researchers house their mice between temperatures of 20-22 degree Celsius which is too cold for mice, who respond better to a thermoneutral 30 degrees Celsius.


Mouse Cubby to reduce aggression in group housed male mice

An editorial in ALN magazine (a resource for the design and operation of research animal facilities globally) describes the Mouse Cubby, a refinement designed to reduce aggression in group-housed male mice. This insert allows complete visualisation of the mice in the cage, while dividing the cage from floor to ceiling. This appeals to the thigmotactic nature of mice and provides them an opportunity to manipulate their environment. As there are burrows and a large shared space, mice do not need to compete for limited territory and resources. The HPRA strongly advises all personnel involved in the housing and husbandry of mice to review this and the above resources in relation to mice.

Factors influencing aggression in male CD1 mice

A paper in Nature describes the effect of group size, age, and handling frequency on inter-male aggression in CD-1 mice. This study found that trio-housed mice showed less bite wounds than pair housed mice. In general, mice in larger groups were found to eat less but weigh more, and individually housed mice were found to have high nest scores, low body weights, and increased sucrose and food consumption. These results suggest that even when nesting material is provided, individual mice may be experiencing thermal stress. Based on this data, CD-1 mice can successfully be housed for up to 14 weeks and groups of three may be the best for reducing even minor levels of aggression (i.e. wounding).  

Webinar on refined handling techniques in mice

webinar outlining refined techniques for handling and picking up mice is now available to watch online. This webinar outlines the evidence base supporting refined handling techniques in mice as well as practical advice and tips that can be implemented within institutions.


Group housing male laboratory mice 

An interesting review investigating whether to group-house male laboratory mice, given the welfare concerns relating to territorial behaviour and aggression, has been published. The conclusion is that group or single housing is highly context-dependent according to several factors (e.g. strain, age, social position, etc.) and should be evaluated on a case-by-case basis. The open-access paper can be accessed at the following link:



Results of mouse studies affected by the way the animals are handled

A study, funded by the NC3Rs, has shown that how mice are picked up can substantially change their behaviour in cognitive tests, with the benefits of non-aversive tunnel handling highlighted. This paper should be of interest to anyone working with mice. 


The NC3Rs has expanded the information available on its website on the subject of handling mice. There is now a webpage specifically dedicated to this topic that includes a video tutorial, frequently asked questions document, posters, relevant research papers and a webinar.

Home cage aggression in mice

An interesting article has been published in Lab Animal, regarding a series of experiments testing potential explanations and interventions for post-shipping aggression related injuries in C57BL/6 mice:



NC3Rs neonate assessment

The NC3Rs have published a useful article on the assessment of the welfare of neonatal mice in breeding programmes and provides tips on how to do this with minimal disruption to the litters.

Minimising aggression in group housed male mice

The results of a large NC3Rs study carried out across 44 facilities on aggression-related injuries in mice has been published in Scientific Reports. The report compares the prevalence of aggression across strains as well as the effects of housing and husbandry variables, and makes a number of practical recommendations.

Ageing animals in scientific research

A review article has recently been published on the care, husbandry and management of ageing mice used in scientific studies. The global population of older persons is growing at a rapid rate, and this is increasing the need for aged animals in scientific research. Many systems (e.g. musculoskeletal, cardiovascular and digestive) researched in rodents can become adversely affected as a result of ageing. This paper outlines considerations to mitigate potential adverse effects, including enhanced welfare monitoring, supplementary bedding, different food or alternative food placement, etc. This is essential reading for establishments that use aged rodents.


Tunnel handling in mice

A piece of research has been published in Scientific Reports which shows that mice which are tunnel handled continue to experience positive welfare benefits even when undergoing certain procedures (repeated immobilisation and subcutaneous injection). In contrast, tail-handled mice display as much aversion and anxiety when they are only picked up by the tail as when they are also immobilised and injected. This work adds to the substantial evidence base supporting refined handling methods.


Tickling rats: a social enrichment to improve rodent welfare

Tickling is an effective means of generating a positive mental state in rats. A systematic review by LaFollette et al which was published in PLoS One in August 2019 examines current rat tickling preference and predictors among laboratory animal personnel in the USA and Canada. For those interested in learning the technique, AALAS host an online webinar.

RSPCA rat cage height survey

The RSPCA have published their rat cage height survey in Animals, which reports on investigations on the barriers to implementing higher caging in animal research establishments in the UK. Most adult rats can actually rear up to 30cm, so cages higher than the minimum allowed by the Home Office Code of Practice (20cm) and Directive 2010/63/EU (18cm) would allow animals to rear fully on their hind legs, which is thought to improve welfare. They found that the main factors hindering the implementation of higher caging were health and safety, financial, animal welfare, scientific, and ‘human’. Suggestions to overcome these barriers are provided, as well as alternative animal welfare changes that can be put into place.

Rat playpen guidance

A playpen, or playroom, is a designated enriched space that is usually provided as an addition to the standard enclosure of animals. Access to a playpen has a positive impact on research animal health and wellbeing, which can consequently benefit animal technicians and researchers. The NC3Rs has a dedicated resource page on rat playpens, which provides practical advice on how to set up a rat playpen, and includes a webinar and FAQs.

Emulsified gels as a refinement to oral gavage

Oral gavage is commonly used to administer nutritional substances or drugs to rodents. However, it induces stress and has a risk of mishap. Incorporation into edible gels is difficult for lipid-based preparations. The authors of this study, published in Animal Technology and Welfare, report a new methodology for producing emulsified oil-enriched gels, their effectiveness in pilot studies and subsequent larger experimental studies. They conclude that oil-enriched emulsified gels represent an easily administered highly acceptable, reliable and safe method of lipid delivery to rats, as a refinement to oral gavage.


PREPARE - Group housing of rodents with cranial implants

Norecopa have added a page to the PREPARE guidelines on group housing of rodents with cranial implants. As there are very few publications on this topic, Norecopa have collected anecdotal evidence from members of the CompMed discussion forum.

Forced swim test

paper co-authored by staff at the NC3Rs and the UK Medicines and Healthcare products Regulatory Agency (MHRA) has clarified that the forced swim test is not a regulatory requirement for the development of new antidepressants. The paper, published in ScienceDirect, outlines the pros and cons of the FST in antidepressant drug development, makes the case for research into less stressful tests, and proposes further evaluation of brain-derived neurotrophic factor as a promising alternative to the FST. More information is also available on the NC3Rs website.

Blood sampling

The NC3Rs has produced decision trees for blood sampling in mice and rats. They are designed to assist in determining the amount of blood to sample from the animal, and depending on that volume, the most appropriate techniques to use.

Refined scruffing technique in small laboratory animals

The scruffing technique is an essential immobilisation technique used with small animals to allow for proper implementation of certain procedures, such as oral gavage, and to prevent the operator from being bitten. Norecopa, in collaboration with the Norwegian University of Life Sciences, has produced a short video illustrating a refinement of the scruffing technique in mice. This technique uses three fingers, as opposed to the usual two. It creates a transverse skin fold on the animal, relieving any pressure on the throat and trachea that has the potential to cause the animal stress. This resource would be useful for any technicians or researchers who use small rodents such as mice.


Guidelines on severity assessment of genetically altered rodents

Detailed guidelines on how to perform welfare assessments on genetically altered mice and rats in order to determine the presence of a harmful phenotype, and its severity, have been produced by the Working Group of Animal Welfare Officers in Berlin and published in Laboratory Animals. These guidelines should provide a structured approach to welfare assessment of genetically modified lines, and thus will be beneficial to scientists, veterinarians and animal care staff.

Archiving and sharing GA strains

Archiving genetically altered mouse strains reduces animal wastage and maintains genetic integrity, maximising data reproducibility. Cryopreserved resources are also often the best means of sharing genetically altered strains, providing further opportunities for reduction in animal use and minimising the need for strain duplication. Working with colony management experts, the NC3Rs has updated existing guidance to provide an overview of current best practice, highlighting the reduction and refinement opportunities from archiving and sharing.

Asepsis in rodent surgery

World renowned laboratory animal veterinarian, Prof Paul Flecknell, has written a blog for the NC3Rs about ensuring asepsis in rodent surgery. This is interesting reading for anyone undertaking surgery. 


Temperature transponders

A publication by Hams et al in Frontiers in Immunology, demonstrates the use of subcutaneous transponder chips to monitor temperature in a model of LPS-induced endotoxic shock. This method provides a non-invasive method to monitor body temperature, which enables easier adherence to refined humane endpoints for studies of this nature.


Alternative to metabolic caging for rodent urine collection – hydrophobic sand

Hydrophobic sand has been developed as an alternative to restraining laboratory rodents in order to obtain a urine sample. The use of this sand is not considered a procedure by Directive 2010/63/EU, and so users are legally obliged to implement this refinement.


Mouse and Rat Grimace scales

Norecopa have a dedicated webpage on grimace scales (with a growing collection of references), and the NC3Rs have free A3 posters of the grimace scales available for order. 


Refining arthritis models

There is an interesting report published by the RSPCA on refining rheumatoid arthritis research using mice and rats. If arthritis models are used in your establishment, this link should be circulated to the relevant researchers and technicians as well as the animal welfare body and the ethics committee.


Rodent handling

Although it is common knowledge that picking up rats by the tail is stressful and should be avoided, recent research has shown that picking up mice by the tail induces aversion and anxiety and should also be avoided. The NC3Rs website has been updated to provide information on non-aversive methods for picking up mice. We encourage establishments to become familiar with these methods and use them where possible.

Affective state in rodents

An overview article was published in Animals, where the authors present common and emerging methods to assess emotions in laboratory rodents. They focus on the use of these methods in applied refinement research to identify achieved progress as well as the potential of these tools to improve animal welfare in animal-based research.

FELASA Guidelines on quality assurance and genetic monitoring

 A FELASA working group has published an article describing the objectives of and available methods for genetic Quality Assurance (QA) programmes in rodent facilities. The article focuses on mouse and rat genetic QA, but the principles may apply to other rodent species.

Administering drugs by micropipette

Oral gavage, in particular frequent administration via oral gavage, has the potential to cause distress and injury to rodents. This paper describes the successful use of micropipette-guided drug administration as a non-invasive and minimally stressful alternative to oral gavages.



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