Animal Cage Capacity Policy

This policy is for the Animal Science Center housing of animals.

The Animal Science Center (ASC) is committed to upholding minimum cage space requirements for all laboratory animals. For most laboratory animal species, the cage size is mandated by federal law.1 The “Guide for the Care and Use of Laboratory Animals” reflects these laws and sets additional standards that are utilized by the American Association for Accreditation of Laboratory Animal Care (AAALAC) in their program review procedure.2

ASC Cage Size by Animal Type and Size


Recommended Space for Commonly Used Group-Housed Laboratory Rodents

Recommended Space for Rabbits, Cats, Dogs, and Birds

Recommended Space for Non-Human Primates

Housing and Animal Aggression

Group-housed rodents typically develop dominance hierarchies. Male mice of certain strains (e.g., BALB/c, CD-1) are notorious fighters that will inflict severe wounds on their opponents during repeated battles. In severe cases, mortality may be directly or indirectly caused by fighting.

It is highly recommended that newly received animals be housed in caging groups that are expected to be appropriate for the duration of the housing period. The mixing of unacquainted animals as new cage-mates frequently causes significant stress as the animals struggle to establish a new social dominance hierarchy.

If experimental variables are to be minimized, animals should not be redistributed into new social groupings during or immediately prior to the experimental period. Creation of a stable social grouping within each cage immediately following shipment will allow the animals to establish their dominance hierarchy during their recovery from the stress of shipment.

Even with these precautions, inter-mouse aggression may subsequently develop in previously “stable” groups of male mice.

ASC Policies


7″x11″ Style Shoebox (MED-W/R/M)8″x13″ (JAG 75)Style Shoebox (670 Albany St., W9, CRC)
4 adult males5 adult males
5 adult females5 adult females
2 adults and 1 litter2 adults and 1 litter


Body weight (grams)Number
>5001 adult Opti-plus cage: 2 adults
1 adult female & 1 litter Opti-plus cage: 1 female & 1 litter
400-499 g (each animal)2 adults Opti-plus cage: 3 adults
300-399 g (each animal)3 animals Opti-plus cage: 4 adults
200-299 g (each animal)4 animals Opt-plus cage: 6 adults
100-199 g (each animal)6 animals
<100 g (each animal)8 animals

Authorized Cage Population, Rodent, Per Cage

Newly received animals will be housed according to the table above or according to the investigator’s specification on the animal order form, whichever stipulates the fewer number of animals per cage.

The ASC staff may request confirmation of an investigator’s request to house mature male mice of aggressive stocks or strains at >1 per cage.

Rats and mice will be weaned and placed into appropriate housing groups at 21 days of age unless special arrangements are made by the investigator and approved by the IACUC.

Overcrowded Cages

The ASC staff will tag overcrowded cages with a green support card. Investigators are responsible for separating the cage within 48 hours to avoid a service fee charge.  After 48 hours the animal care staff will separate the cage and charges will be applied to the lab’s account.


Male mice that have been fighting (as evidenced by bite lesions on the rump and tail) will be separated into successively smaller groups until fighting ceases. Individual housing (one per cage) will be provided for any mouse that has been seriously traumatized by aggressive cage-mates.

Euthanasia may be stipulated if a mouse has serious medical problems as a result of fighting. All occupied mouse cages must be appropriately identified. The separation of overly aggressive mice is the responsibility of the first person (either ASC or research staff) who observes the problem.

Request help from the ASC staff if you have any questions about the condition of mice.


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