Comprehensive Rodent Service

Mouse Housing and Cage Density Policy

The Association for Assessment and Accreditation of Laboratory Animal Care and the Public Health Service require that institutions base their animal care and use programs on the "Guide for the Care and Use of Laboratory Animals". The Yale University Institutional Animal Care and Use Committee (IACUC) must comply with the national standards and recommendations contained within the "Guide for the Care and Use of Laboratory Animals" when establishing mouse cage populations. Yale Animal Resources Center (YARC) is required to uphold the following density requirements:

Holding Cages:

A standard "shoebox" cage, 67 sq. in., (11 X 7 X 5"), holds a maximum 125gr total of body weight, typically four to five adult mice. YARC technicians will continue to house new shipments at a maximum of five mice per cage. When YARC staff observe a cage containing more than five adult mice or a cage of mice with total body weight exceeding 125gr total of body weight, they will move the excess mice to additional cages. The original cage will be labeled with the date, number of animals moved, and an identifying number or letter. New cages will be labeled with the name of Principal Investigator, protocol number, the date, the identifying number,  and the number of mice.

 Breeding Cages: (cages that contain male and female mice, or pregnant mice)

 The standard "shoebox" mouse cage can hold one breeding pair with a litter. The male may remain with the female during parturition through weaning. A cage is considered overcrowded if a new litter is born before the older litter is weaned or a litter remains with the parents beyond their weaning age. The standard weaning age is 21 days.  (Refer to SOP for “Rodent Weaning Guidelines”).

 Progeny must always be separated from the mother before she gives birth to a new litter.

Breeding colonies using harem (one male with two or more females) schemes, must be managed in a manner that does not compromise animal well-being or create overcrowding, e.g. either the pregnant mouse is separated prior to parturition or the pregnant mouse remains with the male for post-partum estrus mating and the remaining harem females are separated prior to parturition.

 The following examples are conditions where YARC staff will automatically separate mice in breeding cages:

1. A newborn litter born in a harem breeding cage.
2. A newborn litter born in a cage that already has an older litter.
3. A litter reaches 28 days of age(Refer to SOP for “Rodent Weaning Guidelines”)

 All separated cages will be identified as noted above.

 The Principal Investigator will be charged the standard tech time rate for separating mice that have gone beyond the weaning age or are housed in overcrowded conditions.

 Any exceptions to the above policy must have IACUC and Veterinary approval.

Approved by Yale University IACUC September 2002

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Copyright © 1999 Yale Animal Resources Center, Yale University
Last modified: April 22, 2003