Background:

As an AAALAC, International accredited institution, the UCR Institutional Animal Care and Use Committee (IACUC) is committed to comply with the national standards and recommendations contained within the “Guide for the Care and Use of Laboratory Animals” (Guide) when establishing mouse cage populations.

Policy:

1. The housing density of laboratory mice (genus Mus) must not exceed those recommended by the current edition of the Guide.  Any exceptions to this policy will need an IACUC approval.

2. Standard mouse ventilated and static cages used at the UCR animal facilities have a floor space ranging from 57 to 75 square inches.  Below are the Guide’s minimum space requirements.

a. Mice weighing up to 25 g:

i. No more than FIVE (5) adult mice can be housed in a ventilated cage (75 in2).

ii. No more than FOUR (4) adult mice can be housed in a static cage. (57 or 70 in2).

b. Mice weighing more than 25 g:

i. No more than FIVE (5) adult mice can be housed in a ventilated cage (75 in2).

ii. No more than FOUR (4) adult mice can be housed in a static cage (70 in2).

ii. No more than THREE (3) adult mice can be housed in a static cage (57 in2).

Breeding schemes:

3. All breeding schemes and practices must be described in the Animal Use Protocol (AUP).  The management of breeding colony is the responsibility of each investigator.

4. To prevent overcrowding, the following procedures must be followed based on breeding schemes and different cage sizes:

a. Monogamous Breeding; one (1) male and one (1) female

i. This breeding scheme can be used for all the three mouse cages.

ii. The male must be removed when the female is visibly pregnant OR

iii. Pups must be weaned on a timely basis (~21 days) *.

b. Trio Breeding; one (1) male and two (2) females

i. For 70 in² and 75 in² cages;

1. One female must be separated when visibly pregnant

2. Pups must be weaned on a timely basis (~21 days) *.

ii. For 57 in² cages;

1. Each female must be separated from the group and individually housed when visibly pregnant.

iii. For >125 in² cages;

1. Two females plus two litters may remain together, provided the litters are no more than 8 days apart in age.  The laboratory is responsible for ensuring that the limit on age difference is observed.

c. Harem Breeding; one (1) male and up to four (4) females

i. Mice weighing up to 25 g:

1. No more than three (3) females can be housed in 57 in² and 70 in² cages.2. No more than four (4) females can be housed in 75 in² cages.

Ii. Mice weighing more than 25 g:

1. No more than two (2) females can be housed in 57 in² cages.

2. No more than three (3) females can be housed in 70 in² cages.

3. No more than four (4) females can be housed in 75 in² cages.

iii. For all the cages, each female must be separated from the group and individually housed when visibly pregnant.

5. It is the investigator’s responsibility to record accurate birth dates on the cage cards for all litters in order to calculate weaning dates.

6.  Two (2) or more adult males must not be housed together in a breeding cage.

7.  When overcrowded cages are identified by the animal care staff, those cages will be marked indicating the date when the overcrowded condition was found and there will be 48 hours granted to separate the overcrowded cage.  If the overcrowded situation is not corrected by the investigator within 48 hours after notification, the cage will be separated by the animal care staff and the PI will be charged a service fee.

8.  When the animal care staff finds a severely overcrowded cage that poses a serious animal welfare concern for the animals housed in the cage, the veterinarian may direct the staff to separate the cage immediately. 

Note:  * In some instances, a litter might not be able to be weaned at 21 days of age due to small size (expected phenotype) or inability to access food or water.  In such case, an exemption to this policy shall be approved by the veterinarian or IACUC.

References

Guide for the Care and Use of Laboratory Animals, (Guide) Current edition

Effective: 2/3/2014; updated 12/16/2019