Rating enrichment items by female group-housed laboratory mice in multiple binary choice tests using an RFID-based tracking system

Abstract

Laboratory mice spend most of their lives in cages, not experiments, so improving housing conditions is a first-choice approach to improving their welfare. Despite the increasing popularity of enrichment, little is known about the benefits from an animal perspective. For a detailed analysis, we categorized enrichment items according to their prospective use into the categories 'structural', 'housing', and 'foraging'. In homecage-based multiple binary choice tests 12 female C57BL/6J mice chose between enrichment items within the respective categories over a 46-hour period. A new analyzing method combined the binary decisions and ranked the enrichment items within each category by calculating worth values and consensus errors. Although there was no unequivocal ranking that was true in its entire rank order for all individual mice, certain elements (e.g. lattice ball, second plane) were always among the top positions. Overall, a high consensus error in ranking positions reflects strong individual differences in preferences which could not be resolved due to the relatively small sample size. However, individual differences in the preference for enrichment items highlights the importance of a varied enrichment approach, as there does not seem to be one item that satisfies the wants and needs of all individuals to the same degree. An enrichment concept, in which the needs of the animals are central, contributes to a more specific refinement of housing conditions.

Fig 1. The relative probability of preferences (worth values) and consensus errors (in percent) of all mice (n = 12) for the tested enrichment items from the categories foraging, structural and housing in the single paired comparisons.

The 46-hour period depicts the complete testing cycle whereas the active time depicts the dark phase of the testing cycle and the inactive time depicts the light phase of the testing cycle.

Fig 2. The relative probability preferences (worth values) of the mice from Group 1 (n = 4), Group 2 (n = 4) and Group 3 (n = 4) for the tested enrichment items from the categories foraging, structural and housing in the single paired comparisons over the entire 46-hour testing cycle.

Fig 3. The Mouse Positioning and Surveillance System (MoPSS).