Mouse Breeding Policy

IACUC Policy: 007-08, Effective Date: 11/18/2005, Last Revision: 03/17/2023

Overview/Purpose

The purpose of this policy is to ensure compliance with the Guide regarding space requirements for mice utilized for breeding activities in an approved Institutional Animal Care and Use Committee (IACUC) protocol.

Definitions

• Adult mouse: Any mouse 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:
    • 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.
• 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 mice 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 plus litter with a comment that “other breeding configurations will depend upon considerations.” Current IVC (individually ventilated) mouse caging provides 77.5 square inches of floor space http://www.allentowninc.com/rodent-housing/nexgen/. The IACUC recognizes that trio breeding 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.