Abstract
Because of mammalian genetics, in laboratory animal facilities animals are born that do not carry the traits needed for research. The number of these animals that cannot be used in experiments can be minimized, but it is impossible to completely avoid producing such animals. If no experiments are planned in the longer term, genetically modified lines can be cryopreserved. The use of inducible and tissue-specific gene modifications helps to avoid harmful phenotypes, but also regularly results in higher numbers of surplus animals. Giving animals to other research groups or into private hands or using them in laboratory animal science education are ways to make good use of animals that cannot be used in own research projects. The alternative use of genetically modified animals, that cannot be used for scientific purposes because of their genotype, as feed animals is practically limited to wild-type animals or to such genetically modified animals that have not been created by genetic engineering methods (spontaneous mutants). Passing on genetically modified animals as feed is virtually impossible for regulatory reasons. There is an urgent need for legislative action in this regard at EU level.