Reduction Reduction in number of laboratory animals in experiments. Reduction is being achieved by: an appropriate design of the experiment a choice of appropriate species and strains a choice of adequate statistics sharing of experimental animals genetic and microbiological standardization of experimental animals. Microbiology Gnotobiotic animals – positive determination of micro-flora (germ-free, one-germ associated...) Specified pathogen free – negative determination of microflora. Conventional Genetics Outbred – every animal is genetically unique Inbred – all animals are genetically identical, multiple brother x sister breeding Coisogenic strains – two strains differ each other just in one chromosomal locus Transgenic animals – addition or deletion of one gene Replacement Replacement of animal by in vitro methods (cell and tissue culture), invertebrates, plants or micro-organisms, computer simulations or men. Refinement Refinement of experimental methods, caging and breeding. Handling, adequate size of the cage, light/dark cycle, temperature (usually 20 – 24 oC), humidity (40 –70 %), toys... Adequate anaesthesia and analgesia, minimal tissue damage.