Utilisation of a physically-enriched environment by laboratory mice: age and gender differences

Abstract

A variety of recent rodent studies have suggested the use of an enriched environment as a strategy to increase the welfare of captive animals. However, a number of standard procedures of environmental enrichment are applied without taking into account the etho-ecological, species-specific, needs of laboratory animals. The aim of the present study was to evaluate the age and sex differences in the utilisation of a physically-enriched environment, consisting of four differently-shaped plastic compartments: a central chamber, a circle, a running wheel and a tower. These compartments are characterised by features (e.g. size, lightness, presence of food, opportunity to perform physical activity) of eco-ethological relevance for the mouse, the most common laboratory species. Presence and activity in each cage compartment during 5 consecutive days were assessed in juvenile (35 days old) and adult (90 days old) CD-1 mice of both sexes. Mice explored all the compartments, spending most of the time in the central chamber and making an extensive use of the running wheel. Juveniles of both sexes and adult males showed a prominent occupation of the central chamber, where food and sawdust were located, and they widely used it to sleep, suggesting that food availability might be a relevant factor in driving their choice of the resting location. Conversely, adult females displayed a more complex utilisation profile and preferentially stayed in the tower while inactive, suggesting that safety needs, that the covered structure of this compartment probably cater for, may be more relevant for them than availability of food and water resource. These findings indicate that in laboratory mice the features of an enriched environment are differentially relevant according to age and sex and, thus, may exert a different impact on their psycho-physical welfare.