Animal Care and Use Program
Policies & Procedures
Mouse Housing Densities
and Overcrowded Mouse Cages
Research Integrity Office
Mail code L106-RI
Portland, Oregon 97239-3098
Phone: 503-494-7887
Fax: 503-494-5081
Version 2.0
Date Effective: draft
Background: OHSU has assured the Office of Laboratory Animal Welfare (OLAW) that all aspects of animal
care and use at OHSU will be conducted following the Guide for the Care and Use of Laboratory Animals:
Eighth Edition (2011).
Based on the recommendations of the Guide, the Department of Comparative Medicine (DCM) and the
Division of Animal Resources (DAR) has posted the numbers of mice allowed per cage in all mouse rooms. The
principal investigator of each approved protocol is charged with assuring that all lab members working with
animals are made aware of these cage density guidelines and that they follow them. Investigators are
responsible for managing their own breeding colonies including separating animals when appropriate and
properly identifying each cage with complete information.
Cages that are out of compliance are marked by placing an action card on the cage instructing research staff to
correct the problem. DCM/DAR staff notifies the Investigator’s lab on the day the problem is identified so that
the lab member can correct the problem immediately. The research staff is typically given 3 days to correct the
problem unless it is an issue that warrants immediate action. If after 3 days the cage(s) are still in need of
separating, DCM/DAR Technicians will separate them into the appropriate number of cages and mark them
with separation cards. The PI’s account will be charged for this service. It is not included in Per Diems.
Below are the cage density standards based on the Guide. In addition, the following guidelines should be
adhered to when breeding mice:
Small mouse cages can hold only 5 adults of the same sex, or one (1) breeding pair with one litter. You may
not house more than 1 breeding female in these small cages because as soon as a litter is born, the cage is at
capacity.
Large mouse cages can hold 8 adults of the same sex, or a breeding harem of 2 females and 1 male with one
litter per female. You may not house more than 2 breeding females in these large boxes because as soon as
litters are born, the cage is at capacity. Limited numbers of large cages are available and must be scheduled in
advance with DCM/DAR.
All litters must be weaned by 21 days of age. This is especially important when breeding pairs are maintained
and another litter is expected at about 21 days. Cages may not contain one newborn litter and another litter
over 21 days of age.
Any exception to these guidelines must be scientifically justified in your protocol and approved by the IACUC.
Investigators are responsible for communicating these exceptions to DCM/DAR. The exception must be posted
in the animal roomand on the appropriate cages.
Individual
Mouse Weight
<10 g
Floor area/animal
6 sq in
MINIMUM SPACE REQUIREMENTS
Height must be 5 inches for all
10-15 g
15-25 g
25 g
8 sq in
12 sq in
15 sq in
Female +
litter
Floor area for
housing the
group = 51
sq. in
Number of mice allowed/box
weight
<10 g
10-15 g
15-25 g
25 g
Small shoe box * 12
9
6
5
Large Thoren
20
15
10
8
shoe box**
Duplex Thoren
9
6
4
3
cage
Large Oblong
26
19
13
10
microisolator
Metal Racks+
10
7
5
5
*Can hold only 1 adult female or breeding pair with one litter.
**Can hold only 2 adult females and 1 male with litters.
+Can't house mice less than 6 weeks of age on wire flooring.
Shoe box measurements - (total floor space)
Small shoe
Large
Duplex
Large oblong
To find the maximum number
box72.0.0 sq in
Square
Thoren cage microisolator
of mice allowed per shoe box,
Thoren
55.0 sq in
157.5 sq in
divide the total cage floor
shoe box
space by the individual floor
121.0 sq in
space required per animal
AUTHORITY
PHS Policy
The PHS requires institutions to use the Guide for the Care and Use of Laboratory
Animals (Guide) as a basis for developing and implementing an institutional program for activities involving
animals.
REFERENCES
Guide for the Care and Use of Laboratory Animals, 8th ed. 2011, page 56.