The 3Rs

What are the 3Rs? I Definitions | Our impacts

What are the 3Rs?

The principles of the 3Rs (Replacement, Reduction and Refinement) were developed over 50 years ago as a framework for humane animal research. They have subsequently become embedded in national and international legislation regulating the use of animals in scientific procedures. Opinion polls consistently show that in the UK support for animal research is conditional on the implementation of the 3Rs.

Today the 3Rs are increasingly seen as a framework for conducting high quality science in the academic and industrial sectors with more focus on developing alternative approaches which avoid the use of animals. There are a number of reasons for this including the need for better models and tools that more closely reflect human biology and predict the efficacy and safety of new medicines.

The need to improve the design, conduct and analysis of research using animals is also gathering momentum, with greater emphasis from the scientific community on minimising use and improving animal welfare. Knowledge about animals' physical and behavioural requirements is expanding rapidly and translating this into practical information is critical to minimise pain and suffering as well as ensuring the robustness and reproducibility of the experiments they are used for.


Replacement - Methods with avoid or replace the use of animalsReduction - Methods which minimise the number of animals used per experimentRefinement - Methods which minimise suffering and improve animal welfare

We use the following detailed definitions of the 3Rs:


Methods that avoid or replace the use of animals defined as 'protected’  under the Animals (Scientific Procedures) Act 1986, amended 2012 (ASPA) in an experiment where they would have otherwise been used. Protected animals are all living vertebrates (except humans), including some immature forms, and cephalopods (e.g. octopus, squid, cuttlefish). Replacement include the use of:

  • Human volunteers, tissues and cells
  • Mathematical and computer models
  • Established animal cell lines, or cells and tissues taken from animals killed solely for this purpose (i.e.not having been subject to a regulated procedure)
  • Immature forms* of vertebrates, or invertebrates, such as Drosophila and nematode worms.

*Protected forms are embryonic and fetal forms of mammals, birds and reptiles during the last third of their gestation or incubation period, fish and amphibians once they can feed independently, and cephalopods at the point they hatch. Embryonic and fetal forms are protected from an earlier stage of development if they are going to live beyond the stage described above and the procedure is likely to cause them pain, suffering, distress or lasting harm after they have developed to that stage.


Methods that minimise the number of animals used per experiment or study, either by enabling researchers to obtain comparable levels of information from fewer animals, or to obtain more information from the same number of animals, thereby avoiding further animal use. Examples include improved experimental design and statistical analysis, sharing data and resources (e.g. animals and equipment) between research groups and organisations, and the use of technologies, such as imaging, to enable longitudinal studies in the same animals.


Methods that minimise the pain, suffering, distress or lasting harm that may be experienced by the animals. Refinement applies to all aspects of animal use, from the housing and husbandry used to the scientific procedures performed on them. Examples of refinement include, using appropriate anaesthetics and analgesics, avoiding stress by training animals to cooperate with procedures such as blood sampling, and providing animals with appropriate housing that allows the expression of species-specific behaviours, such as nesting opportunities for mice.

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Our impacts


Our 3Rs impacts are wide ranging, from policy and regulatory change to the development and uptake of new technologies and approaches.

Here we provide case studies from the research we have funded at UK institutions to illustate the breadth of the science we support and the benefits delivered. 


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We lead the discovery and application of new technologies and approaches to replace, reduce and refine the use of animals in scientific procedures. We fund research, support training and development, and stimulate changes in policy, regulations and practice.