The motivation of group-housed laboratory mice, Mus musculus, for additional space

The limited amount of space that we provide for research animals can adversely influence the validity of behavioural data and animal welfare. Consumer demand studies have examined the strength of motivation that animals have for additional space; however, one problem of these studies is that the animals tested were generally of a gregarious species, but were tested in isolation. I trained a single mouse from each of six groups to perform an operant task to gain access to an additional 319, 777, or 1600 cm2 while group-housed. As the cost of visits increased, the mice continued to gain access to the additional space, although the numbers of visits and the time in the additional space decreased. The slopes of the demand functions for the three amounts of additional space ranged between 0.64 and 0.44, indicating that the mice perceived additional space to be an important resource. The slopes of the demand functions, the areas under the demand functions and the Y-axis intercepts were not significantly different between the three sizes of additional space, thus corroborating previous similar work. These results indicate that group-housed laboratory mice in standard laboratory cages were highly motivated for additional space, but did not discriminate between the amounts offered.