IACUC Policy on the Maintenance of Mouse Breeding Colonies
- Overview
- Breeding and Weaning Issues
- Policy Statement
- Adherence to this Policy
- Additional Information and Guidance
Overview
UCI’s Assurance of Compliance with PHS Policy (on file with the Office of Laboratory Animal Welfare) and AAALAC, International accreditation standards require strict compliance with federal animal welfare regulations and the Guide for the Care and Use of Laboratory Animals (NRC, 1996). The Guide specifies the minimal amount of cage floor space required for each species based on size and/or weight. According to the Guide, mice less than 10 grams (e.g., pre-weanlings) require 6 square inches each. Strict adherence to this guidance would require separation of animals prior to weaning age for large litters or for cages housing two adult female mice with litters. The IACUC acknowledges that this level of adherence may not be in the best interests of researchers developing specialized genetically-modified animals. The aim of this policy, therefore, is to meet the intent of the Guide while keeping in mind the special needs of investigators maintaining transgenic mouse breeding colonies.
Breeding and Weaning Issues
- A standard-sized filter-top mouse cage can house up to 5 adult mice.
- Accepted breeding schemes include paired (one male, one female), trio (one male, two females), and harem (one male, three or more females) mating.
- Average litter size for mice is between 1 and 10 pups and is highly variable due to genetic and environmental factors.
- Female mice experience a post-partum estrus and can become pregnant within 24 hours of delivering a litter. Consequently, leaving a male mouse in the cage until the time of delivery can result in the production of a subsequent litter when the first litter is 21 days old. This can result in the second younger litter becoming trampled and/or not properly cared for.
- Significant overcrowding and unintended breeding activity may result if the weanling mice are not separated at 21 days of age.
- Research staff is responsible for weaning and separating mouse litters.
Policy Statements
- When a litter of mice is born, there can be no more than 3 adult mice in the cage.
- When there is more than one adult female mouse in a cage with a litter or litters, the maximum number of pups allowed is 14 total.
- When multiple litters of mice are present in one cage, the age difference between litters must be less than 5 days.
- All litters must be weaned and separated at 21 days of age.
- Birth dates of all litters must be clearly noted on each cage card; this information must be provided by research staff.
The IACUC acknowledges that some mouse strains require that procedures in exception to this policy may be required, based on the strain’s unique growth and development characteristics. An example of a procedure that requires exception is delay of weaning until 28 days of age. Requests for exception to this policy must be described in detail in the IACUC protocol associated with the breeding colony and will be considered on a case-by-case basis.
Adherence to this Policy
The Lead Researcher is responsible for adhering to this policy and must ensure that all research personnel responsible for colony maintenance are appropriately trained and experienced. Birth dates of all litters must be clearly noted on each cage card. (NOTE: Researchers are encouraged to keep additional detailed breeding records separate from the cage cards to prevent accidental loss of important data). Research personnel must provide sufficient monitoring of the animals to prevent overcrowding and deal with associated issues such as cannibalism, fighting, excessively soiled caging, etc.
IIf significant overcrowding is noted by ULAR staff or campus veterinarians or if a litter is more than 21 days old, a dated "Please Wean/Separate" card will be placed on the cage. Animals must be separated within two days of the posting; failure to comply may reslut in additional charges to the researcher. In extreme cases, such as when insufficient space in the housing room precludes separation of litters into separate cages, ULAR staff have been authorized by the IACUC to euthanize excess animals following notification to the Lead Researcher.
Additional Information and Guidance
- UCI’s Assurance of Compliance with PHS Policy on Humane Care and Use of Laboratory Animals
- The Guide for the Care and Use of Laboratory Animals
- UCI Transgenic Mouse Facility home page
