Breeding Policy for Mice and Rats
IACUC Policy: 007-08, Effective Date: 11/18/2005, Last Revision: 06/20/2025
Overview/Purpose
The purpose of this policy is to ensure compliance with the Guide regarding space requirements for mice and rats utilized for breeding activities in an approved Institutional Animal Care and Use Committee (IACUC) protocol.
Definitions
- Adult mouse: Any mouse or rat that is 21 days or older and able to eat and drink on its own.
- Weaning extension: The IACUC expects pups to be weaned at 21 days of age. If pup development is delayed, weaning may be delayed, but the weaning extension must be noted on the cage card and pups must be assessed regularly and weaned promptly once they are able to eat and drink on their own.
Requirements
- Breeding must be listed as an animal source in the IACUC protocol. Weaning should occur at 21 days of age for normally developing pups.
- Acceptable breeding schemes:
- Mice:
- Monogamous pairs: One female/one male. Required scheme if delayed weaning is necessary due to delayed maturation of pups. Pups should be weaned as soon as they are able to eat/drink on their own. Anticipated weaning age should be noted on the green breeding card if not standard.
- Trio breeding: Two females/one male. Pups should be weaned at 21 days of age and prior to the arrival of a third litter. This scheme is not appropriate for animals needing a weaning extension or for strains with large litters/pups.
- Harem breeding: Up to four females/one male. Pregnant females must be moved into another cage before parturition with no more than two pregnant females per cage.
- Rats:
- Monogamous pairs: One female/one male.
- Colony management (setting up breeding cages, documenting date of birth for litters on breeding cards and weaning) is the responsibility of the Principal Investigator/research team. Weaned animals must be removed at appropriate times to prevent overcrowding that could impact performance and animal welfare.
- Pups that are present in the breeding cage 3 days past the standard weaning age will be weaned by ULAR staff and the PI charged a technical service fee. The research team will not be contacted or reminded of weaning dates.
- Cages with litters of significantly different ages (i.e. newborn pups and weanlings) including animals that are at least 21 days of age and of adequate size to eat and drink on their own must be separated immediately.
- If pup development is delayed, a weaning extension (ie 28 days) must be noted on the breeding card. Individual pups should be assessed regularly once they reach 21 days of age and weaned promptly once they are able to eat and drink on their own. Normal-sized pups within the litter should be weaned at 21 days of age. Pups present in the breeding cage beyond the extension period that are large enough to eat and drink on their own will be weaned by ULAR for a technical service fee.
Additional Information/Guidance
The Guide recommends 51 in2 for a female mouse plus litter with a comment that “other breeding configurations will depend upon considerations.” Current IVC (individually ventilated) mouse caging provides 77.5 in2 of floor space http://www.allentowninc.com/rodent-housing/nexgen/. The IACUC recognizes that trio breeding for mice may be an exception based on The Guide recommendations for floor space. Performance criteria including ammonia levels, pre-and post-weaning mortality, soiling of bedding, the difference in age of pups of different litters, and growth rate have been evaluated and the use of IVC cages for trio breeding of mice is acceptable when pups are weaned at approximately 3 weeks of age. The Guide recommends 124 in2 of floor space for a female rat plus litter. Current IVC (individually ventilated) rat caging provides 142 in2 of floor space http://www.allentowninc.com/rodent-housing/nexgen/. Paired breeding cages of rats with a litter may exceed the Guide recommendations for floor space. Breeders will remain paired to allow for continual social housing of the male based upon performance criteria including pup survival and lack of fighting.
Revision History
- 007-00 – New policy approved. 11/18/2005
- 007-01 – Standard breeding cage was defined. Instructions on breeding cage cards deleted. Approved 02/20/2009
- 007-02 – Cage size added. Weaning set at 21 days. Required justification for weaning added. Instructions for PI’s regarding administrative items deleted. Approved 04/22/2011
- 007-03 – Descriptions of monogamous pairing, breeding trio and harem breeding added. Cage density section added. Overcrowded cages section added. General guidelines for weaning mice deleted. Approved 10/21/2011
- 007-04 – Reformatted into new template. Condensed purpose, expanded adult mouse definition, removed reference to green acetates and minor wording changes throughout. Removed the requirement for weaning extension to be approved by the IACUC. Approved 03/27/2015
- 007-05 – Revisions reflect definition changes, clarifying each breeding schemes, and the requirement that weaning extensions must be noted on the breeding card. Approved 01/20/17
- 007-06 – Revisions reflect definition changes and the requirement that weaning should occur at 21 days of age. Approved 02/21/2020
- 007-07 – Revision to trio breeding scheme adding to definition of what is not appropriate. Approved 05/15/2020
- 007-08 – Revision to anticipated weaning age changed from a must to a should be noted on the green breeding card if not standard. Also, pups present in the breeding cage beyond the extension period that are large enough to eat and drink on their own will be weaned by ULAR for a technical service fee. Approved 03/17/2023.
- 007-09 – Revision to include rat breeding in addition to mice.
Article ID: 28
Created: April 23, 2024
Last Updated: July 22, 2025
Online URL: https://ohiostateresearch.knowledgebase.co/article/breeding-policy-for-mice-and-rats-28.html