Effects of environmental enrichment for mice: variation in experimental results.

This study focused on the effects of different enriched environments for mice in a number of behavioral and physiological parameters in 2 routine laboratory testing procedures: potency testing for tetanus vaccine and stress-induced hyperthermia. The variability in the results was studied by calculating and analyzing mean absolute devi-ations. Mice from enriched conditions weighed more and consumed more food than mice from standard housing conditions. However, mice from enriched conditions lost more body weight after being housed individually. Other physiological parameters showed no differences. Mice from standard conditions were more active in an open field, suggesting a tendency to overrespond to various stimuli in a testing environ-ment. Mice from enriched environments were more tranquil and easier to handle. The enrichment did not influence the variability in any of the parameters measured, al-though earlier results and results of other studies suggest that the effects on the vari-ability in results are parameter dependent. When enrichment does not influence vari-ability, there is no reason for not introducing cage enrichment and by doing so contributing to the animals' welfare.