ThisARC guideline has been written to clearly communicate current standards for thefacility users. Questions should be directed to Nachi Shukla (232-2043) or Dr.Glen Otto (471-2392).

Requirements for Housing Mice

1. No more than five adult mice should be kept in a standard mouse cage.

2. No more than one litter should be present in a standard shoebox-sized cage, in the company of no more than one or two adults. Breeding pairs are relatively easy to manage within these requirements, but if more than one female will be placed with a breeder male (harem breeding) any female that appears pregnant must be removed and housed singly prior to giving birth. If an “accidental” birth occurs in a cage holding more than two adults, all adults other than the mother (and possibly the father if a breeding pair is desirable) should be removed as soon as possible. If the mother cannot be identified, the females and litter(s) may be moved to a large-style cage until weaning (contact the ARC for assistance). One possible exception: If neonatal mice are being produced for experimental use and will be PROMPTLY euthanized by postnatal day 7, it is possible to house a continuous breeding trio.

2. Litters should be weaned promptly by 21 days of age (for most strains), separated by sex, and housed no more than five per cage. Certain mutant and inbred lines may benefit from a later weaning, but in any case it is seldom justified to wean at an age later than 28 days.

3. In the case of male mice, even five per cage may be too crowded, and fighting may result. This is especially true with certain aggressive strains, such as FVB, SJL and BALB/c. If fighting lesions are seen, affected males should be separated, and if severely injured, sacrificed. If injured animals are valuable and will be kept alive, the responsible person should turn in an Illness/Injury Report to the ARC so that any necessary observations or treatments can be arranged.

4. In some areas, large mouse cages are being utilized. These cages can house twice the number of animals as the standard cage (e.g., ten adult mice, or two breeding females and one male in a trio mating scheme using a normal weaning schedule).

5. Unless there are specific standing orders which give the ARC authority to wean, it is the research group‘s responsibility to observe litters and breeder animals frequently to quickly identify and remedy problems or obtain help in dealing with them.

6. ARC staff will also observe colony conditions and communicate with the lab responsible for breeding cages when overcrowding is identified. The ARC has the responsibility and the authority to clean, separate, wean or sacrifice animals if unacceptable conditions persist after the laboratory is notified. The investigator's lab may be billed for the labor should this be necessary.

5/2/06