The use and perceived importance of three resources which provide caged laboratory mice the opportunity for extended locomotion

Abstract

Several species of animal are routinely housed in small, barren cages with little opportunity for extended or complex locomotion. Various resources could be provided to overcome this limitation, however, these differ in their practicality, cost and presumably in their suitability as perceived by the animal. This study examined the activity of 5 laboratory mice within three resources which provided the opportunity for extended or complex locomotion, namely, a ‘locomotion-loop’ (a 40 cm torus of plastic tunnel), a complex tunnel environment and a running-wheel. In addition, the perceived importance of these resources was determined by measuring the persistence of their use when the operant cost (switch pressing) of gaining access was increased. When the lowest cost of 1 press/visit was imposed, the mice used the three resources to different extents: the running-wheel was used for the greatest proportion of each 24 h (9.1%), the tunnel system was used for an intermediate amount of time (8.1%) and the loop was used the least (0.3%) (all differences were significant). At the lowest cost the running-wheel was visited 13.7 times each 24 h, the tunnels 14.6 times and the loop only 4.7 times. Over the 15-day duration of the study, the mice reduced the frequency of visits and activity in the loop and tunnel system, but not the running-wheel, i.e. the mice habituated to the loop and tunnels, but not the running-wheel. When the cost of access was increased, the frequency of visits decreased for all three resources. However, activity within visits increased and the duration of visits remained constant for the running-wheel, whereas both decreased for the loop or remained constant for the tunnel system. Therefore, as the costs increased within the range studied here, the mice defended the proportion of 24 h in the running-wheel to a greater extent than time in the tunnel system or the loop. Of the 3 resources, use of the running-wheel was least affected by increasing the cost of access, indicating this resource was perceived as the most important. These results in combination with previous investigations indicate that wheel-running is a higly motivated behaviour. The present results show that caged laboratory mice perceived running-wheels to be an important resource and as such, indicate these might be an appropriate form of environmental enrichment.