Refinement of rodent research through environmental enrichment and systematic randomization

Recently, conventional housing of laboratory rodents has been criticised for inducing abnormal behaviours and poor well-being, which also questions the validity of many animal experiments. Environmental enrichment may prevent abnormal behaviours and improve animal wellbeing, but concerns have been raised that it might also disrupt standardisation, thereby reducing the precision and replicability of animal experiments. In this article, we review the logic and evidence surrounding this debate. We show that animal welfare can be improved by beneficial enrichments without disrupting standardization. However, we also argue that standardization is a flawed concept, which entails the risk of obtaining results of poor external validity and therefore needs to be profoundly revised.