- Personnel Responsible
- This policy applies to all personnel involved in activities involving the care and/or use of mice in Michigan Tech’s Animal Care Facility (ACF) regardless of the funding source.
- “Research Staff” as referred to in this policy is defined as the principal investigator and any staff or students working with them, NOT the Animal Care Facility staff.
- The purpose of this policy is to address the health and well-being of mice by ensuring safe population densities. Animal overcrowding can contribute to significant animal welfare issues and therefore may violate federal and University policies on the humane care of animals if not expediently addressed.
- Breeding Schemes
- Housing in Standard Cages:
- Breeding mice can be done in:
- Pairs (one male, one female)
- Trios (one male, two females)
- Quintet/Quartet (one male, three or four females)
- For pairs and trios, the breeding cages may be set up on a continuous basis, leaving the male with the female(s) after pups are born. Multiple litters of differing ages are NOT allowed. Weaning schedules must be strictly managed to avoid overcrowding cages with animals that are nearly adult-sized along with newborn pups. Please see the section “Sanctions.”
- In continuous breeding cages, the preferred scheme is pairs when the following two
- The strain produces large numbers of offspring (≥10 pups/litter)
- Weaning needs to be delayed beyond 21-23 days due to the small size of offspring and their inability to thrive(as occurs for some inbred strains).
- Breeding trios (one male, two females) should be closely managed to ensure that overcrowding does not occur. If the strain of mice used regularly produces large litters (≥10 pups), the litters should be weaned between 21-23 days.
- For inbred strains that produce large litters (≥10) and also require 28 days for proper weaning, the PI will justify the need for trio breeding with delayed weaning in the IACUC protocol for review on a case-by- case basis.
- When Quintet/Quartet breeding, visibly pregnant females must be moved to their own cage to prevent housing multiple pre-weanling litters with more than 3 adults.
- To ensure the well-being of newborn animals, as well as to provide adequate data regarding birth and weaning dates, cages must be adequately labeled by the investigator with the date of birth of each litter.
- Breeding mice can be done in:
- Housing in Standard Cages:
- The Research Staff is responsible for cage card documentation and for separating and weaning mice. Litters must be weaned according the procedures defined in the investigator’s approved animal protocol.
- Male and female pups must be separated at weaning unless they are being set up as new breeding cages, using one of the schemes defined above (pair, trio, quintet/quartet).
- Weaned pups must have a minimum of 2 mice per cage. In the case of a lone female, she may stay with the mother. In the case of a lone male, he should be paired with a similarly aged litter of the same strain, in the same room. If this is not possible, he should be provided with extra enrichment (multiple tubes or houses/huts) and the ACF Director should be notified (firstname.lastname@example.org).
- Allowing a 3-week old litter to stay in the cage with a lactating female that also has a newborn litter is NOT permitted.
- In the event that a litter cannot be weaned according to the approved schedule specific to the protocol, the investigator should notify ACF staff by appropriately labeling the cage, including the expected weaning date.
- For strains that consistently require delayed weaning, exceptions to the 21- 23 day weaning age may be made. Exceptions must be requested in the IACUC protocol. The request should include justification (scientific, via a performance standard) for extended weaning and should include appropriate documentation or scientific justification. Once approved by IACUC this extended weaning time is acceptable.
- ACF Actions When Cages Have Become Overcrowded
- The ACF Staff checks for overcrowding when changing cages. Any cages that might be considered overcrowded according to standards defined above are marked with an “Overcrowded” or “Please Wean Pups” Card, dated and initialed.
- When overcrowding is noted, the Research Staff is contacted once via email and given
up to 72 hours to correct the problem, depending on the severity of the overcrowding.
Alternatively, if the investigator feels that weaning should be delayed further, the
ACF Director must be consulted.
- If cages are extremely overcrowded (>1/4 of cage floor space is occupied by animals)
to the extent animal welfare is affected, ACF staff will promptly separate cages.
New cage cards will be marked with the “coordinate” number (A1, B2, etc.) of the original
cage, plus “A”, “B”, etc. for each new cage created due to separation. Research staff
are responsible for checking the newly created cages ASAP. ACF staff are not responsible
for accurate sexing.
- Situations where extreme overcrowding occurs may result in sanctions for the research lab. Please see the section “Sanctions” below.
- NOTE – Weekends and Holidays are INCLUDED in the 72 hours and are NOT EXEMPT.
- If cages are extremely overcrowded (>1/4 of cage floor space is occupied by animals) to the extent animal welfare is affected, ACF staff will promptly separate cages. New cage cards will be marked with the “coordinate” number (A1, B2, etc.) of the original cage, plus “A”, “B”, etc. for each new cage created due to separation. Research staff are responsible for checking the newly created cages ASAP. ACF staff are not responsible for accurate sexing.
- If overcrowding is not addressed within the allotted time, please see “Sanctions” below.
- Investigators will be notified that they are out of compliance with IACUC regulations for each incident in which overcrowding has occurred because weaning was delayed past the age prescribed in the approved protocol OR in cases where pregnant females were not separated and there are multiple pre-weanling litters in the same cage. In such cases, the investigator may be subject to further remedial actions as deemed necessary by the IACUC, including a loss of breeding colony privileges.
- Related Information
- University of California San Francisco, Office of Research, Institutional Animal Care and Use Program - Mouse Cage Density
- Heiderstadt KM, Blizard DA, “Increased juvenile and adult body weights in BALB/cByJ mice reared in a communal nest.” J Am Assoc Lab Anim Sci. 2011 Jul;50(4):484-487.
- Hickman DL, MP Swan. “Effects of Age of Pups and Removal of Existing Litter on Pup Survival during Cross-Fostering between Multiparous Outbred Mice.” J Am Assoc Lab Anim Sci. 2011 Sept;50(5):641-646.