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.

More resources

• Information on inbred strains of mice and rats
• The Rat Guide
• Rat Behavior and Biology
• Ratbehavior.org
• Sex bias in preclinical research and an exploration of how to how to change the status quo
• Study reveals how sex 'blindspot' could misdirect medical research
• Genetic enhancement of NSG and NRG mice for improved human disease modelling
• The Collaborative Cross panel of inbred mouse strains
• Special issue of the journal Animals with papers on animal emotion
• Welfare and scientific considerationsof tattooing and ear tagging for mouse identification (Roughan et al., 2019)