The principles of the 3Rs concerning animal experimentation were postulated in 1959 by William Russell and Rex Burch in a book entitled Principles of Humane Experimental Technique. The principles are today internationally widely recognized by scientists as a moral obligation. They are moreover implemented in many national legislations on animal protection.
Replacement
Methods, which permit a given purpose to be achieved without conducting experiments or other scientific procedures on animals.
Replacement methods can represent full or partial replacement methodologies, based on i) approaches not entailing the use of living animals such as cultured cells (including primary cells), tissues and organs as well as the use of testing strategies that take into account existing in vivo data, in vitro methods, in silico computational methods, physicochemical properties and non-testing data, and/or on ii) use of animals that, based on current scientific evidence, are not considered capable of experiencing suffering such as some invertebrates and immature forms of vertebrates.
Reduction
Methods for obtaining comparable levels of information from the use of fewer animals in scientific procedures, or for obtaining more information from the same number of animals.
Reduction methods include careful design and analysis of animal-based experiments so that fewer animals can be used, such as optimization of breeding programmes, experimental designs, statistical analyses, as well as sharing of animals and animal material (organs, tissues, cells), and, if appropriate longitudinal instead of cross-sectional measurements, and measures to reduce unexplained variation in the data.
Refinement
Methods, which alleviate or minimise potential pain, suffering and distress, and which enhance animal well-being.
Refinement applies to all aspects of animal care and use, including housing conditions, handling methods, anaesthesia and analgesia, habituation to procedures, execution of procedures, monitoring of health and well-being, humane endpoints, and euthanasia. Refinement also includes the development of better (i.e. more accurate, reliable, sensitive) tools to assess suffering and well-being.