A targeted approach to developing environmental enrichment for two strains of laboratory mice

Previous studies on environmental enrichment have generally placed a purported enrichment in the cage and observed changes in behavioural and physiological indicators of welfare. However, many of these ‘enrichments’ are not purposely designed, or appear to be designed with anthropomorphic or anthropocentric concerns, which have little biological relevance. The aim of this study was to screen the behavioural responses of mice to a range of 24 potential enrichments (PEs) considered by an expert panel to have characteristics most biologically relevant to mice. Female mice (64 C57/Bl/6 and 64 ICR(CD-1)) were housed in groups of four and observed three days per week for 12 weeks whilst provided with a different PE weekly. The overall time-budgets of the two strains differed significantly. ICR(CD-1) mice performed more bar chewing, digging, manipulation of PEs, and rearing in the cage. They were also more likely to be hidden in the cage. C57/Bl/6 mice performed more drinking, cage sniffing and social interaction, and showed three times more bar climbing. The two strains responded differently to the PEs, with the ICR(CD-1) mice making more use of PEs, particularly those that could be manipulated or which provided additional hiding places. The higher trait anxiety of the C57/Bl/6 mice may have reduced their utilisation of novel PEs. We conclude that, whilst enrichment can significantly improve animal welfare, those types of enrichments that work well for all strains need to be identified, or strain-specific enrichment policies devised.