Home improvement: C57BL/6J mice given more naturalistic nesting materials build better nests

Abstract

Environmental enrichment of laboratory mice can improve the quality of research, but debate arises over the means of enrichment and its ability to be used in a sterile environment. One important form of enrichment is nesting material. Mice in the wild build dome-shaped, complex, multilayered nests, but this behavior is not seen in the laboratory, perhaps due to inappropriate nesting material rather than the nest-building ability of the mice. Here we focus on the use of naturalistic nesting materials to test whether they improve nest quality through the use of a 'naturalistic nest score' system; we also focus on materials that can be sterilized and easily used in existing housing systems. We first determined whether C57BL/6J mice build naturalistic nests when given shredded paper strips. We then compared these shredded paper strips with other commonly used nesting enrichments (facial tissues and compressed cotton squares). Nests were scored for 6 d. We found that the shredded paper strips allowed the mice to build higher quality nests than those built with any of the other materials. Nests built with tissues were of intermediate quality, and nests built with compressed cotton squares were of poor quality, similar to those built by the control group. These results suggest that C57BL/6J mice given appropriate nesting materials can build nests similar to those built by their wild counterparts.

Figure 1.

The naturalistic nest score system. Scores are based on the shape of the nest as well as on how much the walls are built up around the nest cavity in order to form a dome. Both a top view and a side view are shown.

Figure 2.

Sample nests and their corresponding scores.

Figure 3.

Example of a nest built with a combination of tissue and the shredded paper strips. Note how the tissue is intertwined with the shredded paper strips, creating a 2-layer nest.

Figure 4.

Mean nest quality scores in experiment 1. Tukey post hoc comparison shows that the mean nest score for tissue was significantly lower than that of the shredded paper strips or a combination of the two. Superscripts indicate means that do not differ.

Figure 5.

Mean nest quality scores for experiment 2. Tukey post hoc comparison shows that controls and the compressed cotton squares group (8 g) had significantly lower nest scores than did the group with shredded paper strips (8 g). Tissues (8 g) had nest scores that were not significantly different from any other group. Superscripts indicate means that do not differ.