Environmental Enrichment for Mice

I. Introduction/Purpose

The goal of environmental enrichment for mice is to maximize activity while increasing species-specific positive behavior and enhancing the animals’ well-being. The components of environmental enrichment for mice include social housing and nesting/hiding materials.

II. Procedures

A. All mice shall be provided with environmental enrichment, unless:

1. The investigator provides scientific justification to the IACUC as to why enrichment is not compatible with the goals of the study and the IACUC approves the variance.
   OR
2. If, in the opinion of the Attending Veterinarian or designee, environmental enrichment will adversely affect the health or well-being of the animals.

A Husbandry Special Services Request form must be completed and turned in by the responsible party (Investigator group or Vet Services) to the facility supervisor if environmental enrichment is to be restricted or absent.

B. Social housing

1. Adult males are to be housed in breeding groups or with other familiar adult males if breeding is not intended. If there is not an available familiar adult male of the same strain and protocol then adult male mice must be housed singly to avoid fighting. Males separated from breeding groups must be housed singly to avoid fighting.
2. Adult females are to be housed in breeding groups or with other familiar adult females if breeding is not intended. Adult females may be housed singly if they have been separated from breeding groups and may be pregnant or if there are no available adult females of the same strain and protocol.
3. Single housed animals will receive extra environmental enrichment (chewing material/toy) at the time of cage change.
4. Some minor fighting between animals is to be expected. However, if fighting occurs that causes injury, the aggressor must be separated from the group immediately and placed into a new cage by itself. Injuries must be reported to Vet Services.

C. Nesting/hiding materials

1. Mice are to be provided with enrichment items for nest building, chewing, and/or hiding such as nestlets, commercially available shredable paper products such as Crink-l’Nest®, nesting sheets, Care Fresh® bedding alone, or mixed with standard corncob or other bedding, or polycarbonate or cardboard tubes or huts.
2. The polycarbonate and cardboard tubes/huts need to be changed every 2 weeks, or when found excessively soiled or chewed beyond use.
3. Nude mice must not receive Nestlets or Care Fresh® bedding for enrichment due to the presence of dust and fiber and the animals’ lack of eyelashes. Instead, they are to be given polycarbonate huts or tubes.

D. New environmental enrichment items can be added with the approval of the Chair of the Environmental Enrichment Committee and the Attending Veterinarian.

III. Approval/Review Dates

SOP Created: 06/05/2003
Last Reviewed/Revised by the IACUC: 05/18/2023