Methods which minimise the number of animals used per experiment

This aim considers whether an appropriate number and species of animals have been selected for a particular experiment. Using too many animals must be avoided whilst using too few may result in an inconclusive result, necessitating wasteful repetition. Reducing the number of animals required involves careful experimental planning and good statistical analysis of data, including, for example, the use of pilot studies.

When calculating animal usage in experiments, it is important to take into account any animals which may have been produced but not used. This includes any additional animals that are inevitably generated when breeding experimental animals that cannot themselves be used in experiments because of their gender or genetic makeup. Minimising sources of variability such as genetic diversity, gender and age can reduce the number needed to generate clear data, although it is also essential to ask whether results obtained in this way have wider relevance, especially to the diverse human population.

As well as ensuring careful experimental planning, Reduction should also be an active process to look at ways in which established experimental designs can be improved with no loss of information quality.



  • The facility uses sentinel mice to confirm the high health status of the facility. These mice are raised and kept within the facility before being killed and analysed for pathogens in order to validate that the mice used in our research are free of unintentional pathogens that might affect the results. To reduce the number of sentinel animals needed we’ve moved to a monitoring system that uses faecal pellets, blood samples, oral and pelt swabs, as well as air filter analysis for pathogens.
  • Computerised record keeping and reporting tools are used to refine and reduce animal use by monitoring colony size and matching breeding performance to usage. Low usage colonies are cryopreserved rather than maintaining live animals.
  • We are also achieving a reduction in the use of animals through considering the best cryopreservation technique to use. Sperm freezing uses fewer mice compared to embryo freezing. Archiving a colony usually requires only two male mice whereas embryo freezing requires several stud males and 20 or more superovulated female mice. Superovulated egg donor females are still required to re-establishing a colony from frozen sperm but sperm freezing and colony reestablishment still uses fewer animals than archiving strains by embryo freezing.
  • Use of techniques to precisely assess the oestrous stage of female mice for mating means that fewer mice are needed to meet experimental requirements for studying mouse embryos at defined stages of development.
  • We promote opportunities for tissue sharing, coordinating mouse use across Institute groups. The Institute is a major contributor to an archive of tissues from aged mice established by SHARM (Shared Ageing Research Models).
  • Using the latest research technologies, for example, multi-parameter flow cytometry and single-cell analysis techniques, allows more data to be gained from fewer cells, thereby reducing the number of donor animals required.
  • Computational modelling of molecular and cellular processes allows to us to reduce the numbers of animals used in research. This includes both making initial discoveries ‘in silico’ and thereby reducing the involvement of animals in research until results need to be validated in a living system, and replacing the use of animals entirely.