There are two broad areas which need to be considered when planning animal studies:

1. The suitability of the species or strain as a model of the target organism, and the ethical issues surrounding their use: ‘choosing the right animal for the right reason’. The large increase in use of genetically altered lines has created increasing concern about the suitability of these animals as models of human conditions.
2. Characterisation of the animals. Items to be considered, in collaboration with the supplier, include:
   • Species, strain, line and phenotype (with an explanation of any genetic modifications)
   • Age, developmental stage, sex and weight
   • Stage of oestrous cycle and any previous breeding history
   • Any necessary pre-treatment (e.g. castration or ovariectomy) and those responsible for this
   • Name and address of the supplier/breeder, or, if wild-caught, the place, time and method of capture and transport
   • Health status (e.g. germ-free, gnotobiotic, SPF, conventional, vaccination status)
   • Re-use of animals, which should be justified and which may be regulated by national legislation
   • Any plans for release or re-homing, which may be regulated by national legislation

Collaboration with other internal or external laboratories should be considered, to reduce the number of animals needed, for example by sharing organs. Steps should be taken to avoid surplus animals, such as those in breeding programmes which prove to be too old, those which respond poorly to treatment (for example by showing a weak immune response) or which are otherwise unsuitable for re-use, re-homing or release.