The effect of preweaning and postweaning housing on the behaviour of the laboratory mouse (Mus musculus).

Standard housing for laboratory mice severely restricts natural behaviour and the control that the animal has over its environment. Providing the cage with objects is a method that has been used to both increase environmental complexity, promote the performance of natural behaviour and provide greater controllability for the animal. This method of furnishing cages has mostly been studied in adult animals, and little is known about the influence that the preweaning environment has on the behaviour of mice as adults. This study aimed to investigate the effects on mice behaviour of preweaning and postweaning housing environment. In this experiment, 64 pairs of animals of the strain C57BL/6J were used. Half of the animals were born and reared until weaning in standard cages and the other half in cages twice the size of the standard and furnished with nesting material, a cardboard tube, a PVC nest box and a wooden chewblock. After weaning, half the animals in each group were changed to the other type of cage, whereas the other half remained in the same environment; in both cases they were kept in single-sex pairs of littermates. Behaviour during the dark, active period was studied through video recordings. We found no main effects of preweaning environment on behaviour; however, mice moved from furnished to standard cages at weaning showed a decrease in inactive behaviour at four weeks of age. Mice housed after weaning in standard cages spent less time inactive, and more time engaging in activities like feeding and drinking, self-grooming and allogrooming. A sex difference was also found, in that females showed a greater performance of exploratory behaviour as well as a greater prevalence of stereotypies. The use of different objects and locations within the furnished cage was also analysed at both ages. Results show that at eight weeks of age mice spent more time at the top of the cage, and that the use of the nest box (although not for resting) increased between four and eight weeks. Mice were found to use the nest box as a nesting site/sleeping place only at age four weeks, whereas they always used the nesting material for sleeping.