The 3Rs have been a feature of scientific research since the 1950s when Russell and Burch introduced the concepts of Replacement, Reduction and Refinement to improve animal experimentation welfare . The aims were to reduce the numbers of animals used in scientific experiments by finding alternate methods, streamlining experimental procedures to involve fewer animals and to minimise the welfare impact on those that were used.
Despite significant scientific advances since the 1950s, many millions of animals are still used for scientific experiments. In the UK alone in 2016, 3.94 million procedures were carried out. These included 2.02 million experimental procedures and the breeding or creation of a staggering 1.91 million genetically altered animals that were not used in any further experiments, a total increase between 2007 and 2016 of 23% in animal experimentation largely due to the rise of breeding genetically altered animals .
When transgenic animals are bred, not all animals will have the desired genetic material and often further crossbreeding must take place to create reliable strains of animals for experimentation so many animals are surplus to requirements . The numbers of animals bred but not used in the field of transgenics has been receiving attention with the industry itself looking at ways of working with the 3Rs to minimise the numbers of animals created . Recognised innovations include the use of refinements in techniques to create the need for smaller colonies of transgenic animals to provide the same numbers of usable specimens for experimentation .
However, this reduction in numbers may be seen as a drop in the ocean given the numbers of animals involved and attention is also focussed on whether experimentation on animals can be replaced with other methods. The development of the ‘organ on a chip’ takes cell tissue research and combines with a computer chip to create organ cells in miniature using human tissue . These tiny working models of organs can replicate responses to experimental drugs without the need to use animals. Indeed, as it has been acknowledged that transgenic animals can respond to illness in a different way from humans such as in cancer trials , the use of human tissue can also be seen as a significant step in creating reliable models of disease and treatment.
Suggestions have been made that more animal research trials using invertebrates may also be a way forward in replacing suffering to vertebrates, as invertebrates (with the exception of cephalopods) are not recognised in law as having the same need for welfare protection . This notion is challenged by emerging research into the capabilities of invertebrates of feeling pain and stress  and campaigns for the welfare rights of lobsters, crabs and other crustaceans to come into line with those already accorded to these animals in New Zealand, Norway and Switzerland .
As the likely trend of our understanding of suffering and welfare consequences for more groups of animals grows, perhaps the time is right for the focus of the 3Rs away from the utilitarian idea of refinement of experiments on fewer animals and instead a greater emphasis on the replacement of animal experiments with other methods.
 Russell, W.M.S. and Burch, R.L. (1959) The Principles of Humane Experimental Technique. London: Methuen.
 Home Office (2017) Annual Statistics of Scientific Procedures on Living Animals. Great Britain 2016. London: Home Office.
 National Human Genome Research Institute (2015) Knockout Mice. Available at: https://www.genome.gov/12514551/knockout-mice-fact-sheet/ [Accessed 05.12.2017].
 NC3Rs (2017) When the 3Rs and transgenic technologies meet. Available at: https://www.nc3rs.org.uk/news/when-3rs-and-transgenic-technologies-meet. [Accessed 03.12.2017].
 Transgenic Technology 2017 (2017) And the inaugural prize winner is… Available at: http://www.tt2017.org/and-the-inaugural-istt-3rs-prize-winner-is/. [Accessed 05.12.2017].
 The Scientist (2017) Organs on chips. Available at: https://www.the-scientist.com/?articles.view/articleNo/50097/title/Organs-on-Chips/. [Accessed 05.12.2017].
 Doke, S.K. and Dhawale, S.C. (2013) Alternatives to animal testing: A review. Saudi Pharmaceutical Journal. 23: 223–229.
 Horvath, K., Angeletti, D., Nascetti, G. and Carer, C. (2013) Invertebrate welfare: an overlooked issue. Ann Ist Super Sanita. 49, 1: 9-17.
 The Ecologist (2017) Crustacean Compassion campaigns for welfare rights for lobsters & crabs. Available at: https://theecologist.org/2017/mar/06/crustacean-compassion-campaigns-welfare-rights-lobsters-crabs. [Accessed 05.12.2017].