Three Rs Microsite

About the Three Rs

Three Rs

R.L. Burch and W.M.S. Russell

R.L. Burch and W.M.S. Russell

Three Rs: Replacement, Reduction and Refinement

Animal welfare and the potential for pain and distress to be experienced by animals used in science have concerned the general public and thoughtful researchers for a long time. It was these concerns, together with increasing use of animals in fundamental and applied research that motivated W.M.S. Russell and R.L. Burch to examine how decisions should be made about such use of animals. In the book The Principles of Humane Experimental Technique, first published in 1959, Russell and Burch proposed the concept of the Three Rs. The Three Rs stand for Replacement, Reduction and Refinement. Over the past 40 years the Three Rs have become widely accepted ethical principles, and are now embedded in the conduct of animal-based science in Canada and throughout many countries in the world.


The term "alternatives" was coined by the distinguished physiologist David Smyth in his 1978 book Alternatives to Animal Experiments. It is used to describe any change to established scientific procedures that will result in the replacement of animals, a reduction in the numbers used or a refinement of techniques that may minimize harms to the animals. Therefore, Smyth's term "Alternatives" is synonymous with Russell and Burch's "Three Rs".

The CCAC's ethic of animal experimentation is based on Smyth's definition of Alternatives, i.e. Replacement, Reduction and Refinement.

Replacement alternatives refers to methods which avoid or replace the use of animals in an area where animals would otherwise have been used. This includes both absolute replacements (i.e. replacing animals with inanimate systems, such as computer programs) and relative replacements (i.e. replacing more sentient animals, such as vertebrates, with animals that current expert peer advice and interpretation of scientific evidence indicate have a significantly lower potential for pain perception, such as some invertebrates).

Reduction alternatives refers to any strategy that will result in fewer animals being used to obtain sufficient data to answer the research question, or in maximizing the information obtained per animal and thus potentially limiting or avoiding the subsequent use of additional animals, without compromising animal welfare.

Refinement alternatives refers to the modification of husbandry or experimental procedures to minimize pain and distress, and to enhance the welfare of an animal used in science from the time it is born until its death.

Implementation of the Three Rs

The CCAC requires principal investigators to implement the Three Rs when they are preparing to use animals for a scientific purpose. Investigators must consider whether animals are required or whether suitable replacement alternatives exist. When animals are used, the investigator must consider how best to decrease the number of animals used to a minimum and/or how to maximize the amount of information obtained per animal (Reduction alternatives), and must identify potential harms and ways to minimize these (Refinement alternatives). Consideration of the Three Rs will start during the early stages of research planning, together with development of the experimental protocol (rather than as a last minute addition).