|IACUC Policy:||Rodent Breeding & Space Requirements|
|Policy #||IBT-207.00||IACUC Approval:||February 27, 2014|
Texas A&M Health Science Center’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, 2010). The Guide specifies the minimal amount of cage floor space required for each species based on size and/or weight.
The Institutional Animal Care and Use Committee (IACUC) and the Program for Animal Resources (PAR) acknowledge 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 genetically modified rodent breeding colonies.
All modifications to research in live vertebrate animals are subject to oversight by Texas A&M Health Science Center IACUC.
It is the responsibility of the Principal Investigator (PI) or designate to:
- Adhere to this policy and ensure that all research personnel responsible for colony maintenance are appropriately trained and/or experienced.
- Wean and separate mouse/rat litters as described in this policy.
- Ensure birth dates of all litters are 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).
- Ensure research personnel provide sufficient monitoring of the animals to prevent overcrowding and deal with associated issues such as cannibalism, fighting, excessively soiled caging, etc.
I. Mouse Specific Breeding and Weaning:
1. A standard-sized filter-top mouse cage (75in2) can house up to 5 adult mice.
2. Accepted breeding schemes include paired (one male, one female), trio (one male, two females), and harem
(one male, three or more females) mating.
3. Average litter size for mice is between 1 and 10 pups and is highly variable due to genetic and
4. 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 between 19-21 days old. This can result in the second younger litter
becoming trampled and/or not properly cared for.
- When a litter of mice is born, there can be no more than 2 adult mice in the cage.
- Prior progeny must be separated from the mother before she gives birth to a new litter.
5. It is recommended to not touch or manipulate the mother or pups until the pups are at least 3 days of age
unless there is a problem or unless an IACUC approved protocol requires it.
6. All litters should be weaned and separated at 21 days of age. If the weaning date falls on a Friday, weaning
may be delayed until the next Monday. However, these cages must be tagged and dated. It is essential these
cages be weaned promptly the next workday.
7. Birth dates and weaning dates of all litters must be clearly noted on each cage card; this information must
be provided by research staff.
II. Rat Specific Breeding and Weaning:
A standard-sized conventional rat cage (143in2) can house one breeder male and up to two females (less than 400g).
- Accepted breeding schemes include paired (one male, one female) and trio (one male, two females) mating.
- Pregnant females must be housed individually prior to parturition.
- All litters should be weaned and separated at 21 days of age. If the weaning date falls on a Friday, weaning may be delayed until the next Monday. However, these cages must be tagged and dated. It is essential these cages be weaned promptly the next workday.
- Birth dates and weaning dates of all litters must be clearly noted on each cage card; this information must be provided by research staff.
III. Other Considerations:
Weaning is a critical period in an animal’s life. Without maternal care, newly weaned rodents must be able to survive. Transgenic and knockout animals often require special attention during weaning as they may be smaller and less vigorous than the normal animal. Some suggestions for successful survival of weaned rodents:
- A water source must be readily available for newly weaned rodents. Use a water-gel supplement to ensure adequate access. This is not intended to be a food source. Place several pieces in a small container or on a paper towel on the cage bottom as needed.
- Provide easy access to a food source for 1-2 weeks until rodents are capable of eating from the food hoppers by placing food pellets directly on the cage bottom.
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. 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.
- An example of a procedure that requires exception is delay of weaning until 28 days of age.
- Rodents are normally weaned at 21 days of age. However, if animals are small, slow in developing, or otherwise compromised it is acceptable to leave them with their mother for a longer period of time. Prior progeny must always be separated from the mother before she gives birth to a new litter.
- The Program for Animal Resources staff should be notified if animals are not being weaned due to survival concerns
Failure to wean/separate animals as per this policy will result in overcrowding, and may be subject to IACUC review per Rodent Cage Overcrowding policy.
- National Research Council. Institute for Laboratory Animal Research. 2011. Guide for the Care and Use of Laboratory Animals. Public Health Service, Bethesda, MD.
- Public Health Service Policy on Humane Care and Use of Laboratory Animals http://grants.nih.gov/grants/olaw/references/phspol.htm.
- ARENA/OLAW Institutional Animal Care and Use Committee Guidebook. Second edition, 2002.
- Animal and Plant Health Inspection Service, USDA. US Animal Welfare Act (AWA 1990) and Regulations (PL-89-544, as amended, 7USC Ch. 54) 2008. CFR Title 9, Subchapter A - Animal Welfare. U.S. Government Printing Office, Washington, D.C.
- Silverman, Jerald, et.al. 2000. The IACUC Handbook: The Basic Unit of an Effective Animal Care and Use Program. Baltimore, MD.
Version 00 – Initial Approval: February 27, 2014