IACUC Policy on Mouse Housing, Cage Density and Temporary Housing (May 2009)

Purpose:

The purpose of this policy is to address the health and well-being of mice by ensuring safe population densities. Limiting breeding cage capacity to a single generation serves to reduce the incidence of morbidity and mortality due to trampling by older animals in the cage. Overcrowding can be a significant animal welfare issue and is in direct violation of federal and University policies on the humane care of animals as well as The Guide for the Care and Use of Laboratory Animals.

Housing in Standard Cages:

Assuming an average adult mouse weighs 25 grams, the standard cages used by LARC can hold up to 5 compatible adult mice; mice that are observed fighting must be separated.

Breeding:

Breeding mice in single pairs is recommended.

Breeding trios (one male, two females) are allowed if the breeding program is closely managed.  A breeding cage may not contain more than 1 trio. The 2 females should give birth no more than four days apart. If the second female has not given birth after four days, she should be moved to a separate cage.
Strains and stocks that routinely have large litters (average 10+ pups) may not be bred in trios.
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.

Weaning:

Litters of mice must be weaned by 21 days of age.
Older litters must be weaned by, or on the day the next litter is born, i.e. there may not be multiple generations in the same cage.

Exceptions:

In the event that a litter cannot be weaned at 21 days, the Investigator should notify LARC staff by appropriately labeling the cage, including the expected weaning date. If the expected weaning date is reached and the litter is still not ready to be weaned, a note should be made notifying LARC staff.

For strains that consistently require delayed weaning, exceptions to the 21 day weaning age may be made. Exceptions are requested by completing section L in the RIO applicaiton. The request should include justification for extended weaning and should include appropriate documentation or scientific justification as to why the density guidelines should be modified. Note: In the case of a strain which is known to require more than 21 days before weaning, the Investigator must separate the dam from the male during pregnancy to avoid breeding at the post-partum estrus. Cages containing a litter which is over 21 days of age cannot also contain a litter of newborns.

Temporary Holding Cages: