The motivation of group-housed laboratory mice to leave an enriched laboratory cage

Abstract

Animals used in research are often housed in small, barren cages. Providing environmental enrichment should improve their welfare, and a consequence of this might be a reduction in the animal's motivation to leave an enriched cage. I examined this possibility by housing laboratory mice, Mus musculus, in a cage that provided cagemates, food, water, large floor area, nesting material, a running wheel, shelter, cardboard tube, food stick and chew sticks. The strength of motivation to leave this cage was assessed in an operant consumer demand test. By pressing repeatedly on a switch, one trained mouse within each of six groups could exit the enriched cage to enter a small, empty cage. As the number of required switch presses was increased, the number of visits to the empty cage decreased, although this was unlikely to be caused by habituation. The mice continued to exit the enriched cage and enter the empty one at all the costs imposed. The slope of the demand function for the empty cage indicated that the mice did not perceive this to be a particularly important resource. I argue that the motivation to exit the enriched cage and enter the empty cage was due to monitoring, patrolling or information gathering, independent of any attraction or aversion to either of the cages. Alternatively, the motivation to leave a presumably attractive environment to enter a presumably less attractive one could be the result of factors beyond our anthropocentric-based understanding of how the mice perceived their environments. The implications for consumer demand studies and their application are discussed.