Preferences of individually housed TO strain laboratory mice for loose substrate or tubes for sleeping.

If we are to improve welfare by appropriate environmental design, it is important to determine which characteristics of prefabricated shelters are preferred by laboratory mice. Three investigations were conducted to determine the preferences of individually housed mice for shape, opacity and openness of tubes for sleeping in. During all three investigations, it was evident that the mice preferred to sleep in sawdust when this was available. The mice slept in the tubes only after the sawdust was removed, and then slept in the tubes rarely once the sawdust was replaced. Individual mice were generally consistent in their choice of tube type, even when the position was changed. However, there were no overwhelming group-preference for shape, opacity or openness of the tubes, though a short, wide tube was used more frequently than a long, or short narrow structure. Several mice performed shelter-building activities when using the tubes, indicating that either some characteristic of the tubes was unsatisfactory or that the mice were motivated to perform shelter-building activities despite the presence of a satisfactory structure. Providing pre-formed tubes might not improve welfare if mice are motivated to perform the activities of shelter-building themselves, rather than achieving the functional consequences. However, the repeated use of tubular structures for other purposes, e.g. as a refuge or latrine, indicates that providing such structures is likely to enhance the welfare of laboratory mice.