Provision of nesting material promotes species-typical behaviors in rodents including deer mice (Peromyscus maniculatus). The purpose of this study was to determine which commercially available nesting material best promotes complex nest building in the subspecies P. m. bairdii yet remains cost-effective for use as enrichment in a laboratory research setting. An existing breeding colony consisting of cages containing all male mice, all female mice, and breeding pairs was evaluated. Five commercially available substrates—compressed cotton squares, cylindrical compressed cotton, cellulose bedding containing small pieces of evenly dispersed compressed paper, brown crinkled paper, and white crinkled paper—were provided according to the manufacturer’s recommendation.

For a change to be considered enriching, the change must enhance animal welfare and improve biological functioning of the animals. A review of the literature shows that a consensus on the definition of changes constituting “environmental enrichment” has yet to be reached. For this reason, the results of studies on the effects of rodent enrichment are inconsistent. In many cases, changes have not been shown to be real improvements. However, enrichment is increasingly appreciated as a way to improve the well-being of rodents, providing them with opportunities for species specific behaviors that might be available to them in the wild.

In laboratories, mice are housed at 20–24°C, which is below their lower critical temperature (≈30°C). This increased thermal stress has the potential to alter scientific outcomes. Nesting material should allow for improved behavioral thermoregulation and thus alleviate this thermal stress. Nesting behavior should change with temperature and material, and the choice between nesting or thermotaxis (movement in response to temperature) should also depend on the balance of these factors, such that mice titrate nesting material against temperature. Naïve CD-1, BALB/c, and C57BL/6 mice (36 male and 36 female/strain in groups of 3) were housed in a set of 2 connected cages, each maintained at a different temperature using a water bath.

Animal welfare requires the adequate housing of animals to ensure health and well-being. The application of environmental enrichment is a way to improve the well-being of laboratory animals. However, it is important to know whether these enrichment items can be incorporated in experimental mouse husbandry without creating a divide between past and future experimental results. Previous small-scale studies have been inconsistent throughout the literature, and it is not yet completely understood whether and how enrichment might endanger comparability of results of scientific experiments. Here, we measured the effect on means and variability of 164 physiological parameters in 3 conditions: with nesting material with or without a shelter, comparing these 2 conditions to a “barren” regime without any enrichments.

Wood-shavings (Clean-chipTM), Cloth (AgrebeTM), Recycled-paper (Paper-cleanTM), Paper (Care-feeazTM)), and on four types of nesting materials (Recycled-paper(Shepherd-shackTM), Cloth (AgrebeTM), Wood (Wood-cylinder), and Polycarbonate (Mouse-iglooTM)). Preference of bedding materials was judged by the time length of staying in acage. The results indicate that mice stayed in the cloth material (AgrebeTM) longer than inother bedding materials (light 51.1 ± 5.3%, dark 51.5 ± 2.6%). In the second experiment,the duration of stay in AgrebeTM was significantly longer than that in the other nestingmaterials in the light phase (70.9 ± 2.4%). In the dark phase, staying time both in AgrebeTMand Shepherd-shackTM were significantly longer.

Behavioural and psychological needs of laboratory animals generally cannot adequately be met in standard laboratory cages. Environmental enrichment, which provides a more structured environment can enhance the well-being of laboratory animals. They may perform more of their species-specific behaviour and may control their environment in a better way.  An easily applicable form of enrichment for laboratory mice is nesting material. Six different types of nesting materials were evaluated in a preference test with male and female animals of two strains (C57BL/6Tor BALB/c, n=48). No significant differences in preference were found
between the strains or between the sexes.