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NC3Rs: National Centre for the Replacement Refinement & Reduction of Animals in Research
Office-led project

Impact of rodent age on study outcome

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Rodent models produce data which underpin biomedical research and non-clinical drug trials, but translation from rodents into successful clinical outcomes is often lacking. There is a growing body of evidence showing that improving experimental design is key to improving the predictive nature of rodent studies and reducing the number of animals used in research. 

Age, one important factor in experimental design, is often poorly reported [1,2] and can be overlooked. The developmental stage or degree of senescence of a rodent can have a profound effect on the functioning of a biological system, and use of an inappropriate age of rodent could result in variable or irreproducible data being collected.  

The NC3Rs convened an expert working group to examine this issue. The group designed and conducted a survey to assess the age used for a range of models, and the reasoning for age choice. The survey was distributed via learned societies and research charities across a broad range of disciplines.

From 297 respondents providing 611 responses, researchers reported using rodents most often in the 6-20 week age range regardless of the biology being studied. The age referred to as 'adult' by respondents varied between six and 20 weeks. Practical reasons for the choice of rodent age were frequently given, with increased cost associated with using older animals and maintenance of historical data comparability being two important limiting factors.

These results highlight that choice of age is inconsistent across the research community and often not based on the development or cellular ageing of the system being studied. This could potentially result in decreased scientific validity and increased experimental variability. In some cases the use of older animals may be beneficial. Increased scientific rigour in the choice of the age of rodent may increase the translation of rodent models to humans.

News item: Does age matter? (June 2016)

Does age matter? inforgraphic


  1. Kilkenny C, Parsons N, Kadyszewski E, et al. (2009) Survey of the quality of experimental design, statistical analysis and reporting of research using animals. PLoS One. 4(11):e7824 doi:10.1371/journal.pone.0007824
  2. Flórez-Vargas O, Brass A, Karystianis G, et al. (2016) Bias in the reporting of sex and age in biomedical research on mouse models. eLife. 5:e13615 doi:10.7554/eLife.13615


Jackson SJ, Andrews N, Ball D, Bellantuono I, Gray J, Hachoumi L, Holmes A, Latcham J, Petrie A, Potter P, Rice A, Ritchie A, Stewart M, Strepka C, Yeoman M, Chapman K. (2016) Does age matter? The impact of rodent age on study outcomes. Lab Anim. 2016 Jun 15. doi:10.1177/0023677216653984