The 3Rs

The 3Rs refer to the terms Replacement, Reduction and Refinement, principles which were originally defined by William Russell and Rex Burch in 1959. The 3Rs aim to improve the welfare of animals used in science or education, while advancing the quality of scientific and medical testing. The 3R principles remain a fundamental concept in laboratory animal science today, underpinning EU and national legislation on the protection and welfare of animals used for scientific purposes. These principles also apply to the conduct of studies used in domestic animals as well as wild animals or birds that might be the subject of research projects.  

Replacement          Reduction          Refinement

Article 4 of EU Directive 2010/63/EU describes the requirements for the 3Rs. 



Article 4 (1): “Member States shall ensure that, wherever possible, a scientifically satisfactory method or testing strategy, not entailing the use of live animals, shall be used instead of a procedure.”
The HPRA understands this to mean that ‘alternative’ methods are to be used where possible instead of live animals. Examples of alternative methods would include in vitro tests such as cell lines, computer simulation and modelling, video material, or the use of invertebrates such as fruit flies or worms. However, in cases where there is no alternative to the use of live animals, the HPRA’s goal is to ensure that the highest standards of animal welfare and care are applied.



Article 4 (2): “Member States shall ensure that the number of animals used in projects is reduced to a minimum without compromising the objectives of the project.”

A common misconception is that Reduction simply refers to decreasing the total number of animals used for scientific purposes. However, the principle of Reduction is to ensure that the appropriate number of animals are used for each project. This allows scientists to obtain statistically robust data without using more animals than are necessary. The use of more animals than necessary in a project is not in keeping with the principle of Reduction. However, using too few animals in a project is not in keeping with the principle of Reduction either, and can be equally detrimental. If too few animals are used in a project, the results obtained may not be reproducible and therefore are invalid and the animals used for this purpose will have gone to waste. Therefore the HPRA believes that Reduction should start with good experimental design and planning.
In addition, Reduction applies to the sharing of resources and tissues between research groups. The use of new technologies can also reduce the need for additional animals. For example, new imaging techniques can facilitate longitudinal studies in the same animal, rather than having to use multiple animals at various points in time through a study.




Article 4 (3): “Member States shall ensure refinement of breeding, accommodation and care, and of methods used in procedures, eliminating or reducing to the minimum any possible pain, suffering, distress or lasting harm to the animals.”
The HPRA understands Refinement to mean that animals used for science are provided with the best possible care and that suffering is reduced to an absolute minimum whilst undergoing procedures. Refinement techniques would include, for example, careful handling by trained individuals, the provision of high standards of housing and husbandry to include enrichment materials (e.g. toys and nesting material) and the appropriate use of anaesthesia and pain relief during procedures.   



For further information on the 3Rs, see the pages below:

Large mammal
Other animals
General 3Rs
Useful 3Rs websites


For other useful links please click here.

If you have any queries about these links, or suggestions for additional useful 3Rs resources that could be included here, please email