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What are the 3Rs?

The 3Rs - Replacement, Refinement and Reduction - are a widely accepted ethical framework for conducting scientific experiments using animals humanely.

The 3Rs principles were first introduced in Russell and Burch's 1959 book 'The principles of humane experimental technique'. The NC3Rs has adopted the following definitions:

Replacement refers to methods that avoid or replace the use of animals defined as 'protected' under the Animals (Scientific Procedures) Act 1986 (ASPA) in an area where they would otherwise have been used. 'Protected' animals are all living vertebrates - except man - including some immature forms, and one invertebrate, Octopus vulgaris.

Replacement methods can be absolute replacements - techniques which do not involve animals at any point, such as computer modelling, in vitro methodologies (e.g. tissue engineering), or human volunteers - or relative replacements, which avoid or replace the use of 'protected' animals. Examples include:

Established animal cell lines
Animal cells, tissues and organs collected from animals killed by a humane technique (see Schedule 1 of the ASPA)
Abattoir material
Invertebrates, such as Drosophila and nematode worms
Mammals, birds and reptiles up to half way through gestation or incubation
Larval forms of amphibians and fish, until the stage where they become capable of independent feeding

Reduction refers to methods which minimise animal use and enable researchers to obtain comparable levels of information from fewer animals or to obtain more information from the same number of animals, thereby reducing future use of animals. Examples include:

Improved experimental design and statistical analysis
Modern imaging techniques
Sharing data and resources

Refinement refers to improvements to scientific procedures and husbandry which minimise actual or potential pain, suffering, distress or lasting harm and/or improve animal welfare in situations where the use of animals is unavoidable. It applies to the lifetime experience of the animal. There is evidence that refinement not only benefits animals, but can also improve the quality of research findings. Examples include:

Using non-invasive techniques
Using appropriate anaesthetic and analgesic regimes for pain relief
Training animals to co-operate with certain procedures (e.g. taking blood samples) so the animals are less stressed
Ensuring that accommodation meets the animals' needs (e.g. providing opportunities for nesting for rodents)
Environmental enrichment to improve living conditions for research animals

Species selection has a bearing on each of the 3Rs.

The 'mouse house' is a refinement developed at the MRC National Institute for Medical Research. The transparent, red, plastic house provides mice with an area to nest, hide and climb. The mouse house appears dark to the mice, yet the transparent walls mean that animal care staff can see the mice at all times and so are able to carry out their daily checks without disturbing them.