UT Southwestern IACUC Policy                                                                     IACUC # 115

Approval Date:_   3/13/2008    _                                                                        Page 1 of 1

MOUSE OVERCROWDING AND
ACCEPTABLE CAGE DENSITY

The Public Health Service requires that institutions base their animal care and use programs on the ILAR "Guide for the Care and Use of Laboratory Animals". The UT Southwestern Institutional Animal Care and Use Committee (IACUC) must comply with the national standards and recommendations contained within the "Guide" when establishing mouse cage populations. UT Southwestern is required to uphold the following density requirements.

Policy:

Density of Non-Breeding Cages

Small Mouse Shoe-Box Cages:

• Standard (6.3 x 10 inch, 63 sq. inch and up to 74 sq. inch cage)

• Ventilated MicroIsolator (7.5 x 10 inch, 75 sq. inch and up to 89 sq. inch)

Large Mouse Shoe-Box cage

• Large Shoe-Box Cages (9x17 inch, 153 sq inch)

• Large Ventilated MicroIsolator (10x18 inch, 180 sq. inch)

Breeding Cages:

Small Shoebox Cages (63-89 sq. inch) 

• Mice are typically bred in male: female ratios of 1:1 or 1:2.
• If bred in a 1:1 ratio, the male, female and litter may remain together until the pups are weaned. 
• If breeding is conducted in a 1:2 ratio (harem breeding), it is recommended that one of the two females be removed to a separate cage when observed to be pregnant. Alternately, it is permissible to keep the male, two females and the pups together providing that when the oldest litter reaches 10 days of age there are no more than 12 pups in the cage.  This condition is based upon standards used at the Jackson Laboratory (Reeb-Whitaker et al., 2001, The impact of reduced frequency of cage changes on the health of mice in ventilated cages.  Laboratory Animals 35:58-73). 
• Date of birth for the litters must be recorded on the cage card by the investigator.
• A cage is overcrowded if a new litter is born before the older litter from the same female is weaned.
• A cage is considered overcrowded if a litter remains with the female beyond 28 days of age. 
• Weaning beyond 28 days of age is a special circumstance and requires either written Veterinarian approval (if done sporadically for health reasons) or prior IACUC approval (if done routinely by the Laboratory).

Large Shoebox Cages (153-180 sq. inch) 

• Mice are typically bred in male:female ratios of 1:2 or 1:3 in a large shoebox cage.
• A harem ratio of 1:3 is allowed but must not exceed a maximum of 2 litters or 24 pups total in the cage.
• A harem ratio of 1:4 or more is not allowed unless some of the pregnant females are removed once noted to be pregnant (E7 to14) to restore a ratio of 1:2 or 1:3 prior to parturition.
• Date of birth for the litter must be recorded on the cage card by the investigator.
• A cage is overcrowded if a new litter is born before the older litter from the same female is weaned.
• A cage is overcrowded if a litter remains with the female beyond 28 days of age. 
• Weaning beyond 28 days of age is a special circumstance and requires either written Veterinarian approval (if done sporadically for health reasons) or prior IACUC approval (if done routinely by the Laboratory).

If an overcrowded cage is found, ARC or PI staff personnel will notify the Principal Investigator or Manager of the colony by placing an overcrowded notice on the cage. If the overcrowded cage is not corrected within 48 hours of tagging, older pups or excess adults will be removed, separated by sex, and placed in another cage.  The original cage will be labeled with the date, number of animals moved, and an identifying number or letter. New cages will be labeled with the name of Principal Investigator, protocol number, the date, the identifying number, and the number of mice. The Principal Investigator will be charged the standard tech time rate for separating mice that have gone beyond the approved weaning age or are housed in overcrowded conditions.   

Note: If the veterinary staff determine that a cage is severely overcrowded, they will separate the animals to ensure their welfare.  The cages will be marked according to ARC SOP #280 and the PI will be notified.

For PI maintained colonies, if ARC personnel determine that an overcrowding problem exists they will notify IACUC and appropriate action will be taken. Repeated violations of the cage density policy may result in the loss of “PI maintained colony” privileges.

Colonies will be designated as having an overcrowding problem and put on an IACUC monitoring list if the percent of overcrowded cages is above 0.4% of the total monthly cage census.

Repeated violations of the cage density policy will result in the following corrective action.

- The first month that a PI's rodent colony is determined to have an overcrowding problem (defined above), a verbal and/or written warning will be issued in addition to the standard ARC tech charge for separating animals.

- The second consecutive month that a PI's colony is found to have an overcrowding problem, the ARC will bill a $25.00 charge per overcrowded cage in addition to the standard ARC tech charge for separating any animals. A letter will be sent to the Dean of the Medical School informing him of the problem.

- The third consecutive month that a PI's colony is found to have an overcrowding problem, the ARC will bill a $50.00 charge per overcrowded cage in addition to the standard ARC charge for separating any animals.  In addition, the IACUC will require a written plan from the PI detailing how the overcrowding problem will be eliminated. If a plan is not provided or is not acceptable to the IACUC, the IACUC will consider restriction of the PI's privileges to conduct animal research and will determine whether the repeated overcrowding problem constitutes continuing noncompliance reportable to OLAW.

Applicability:

This policy applies to all mice used in research at UT Southwestern.

Exceptions:

Exceptions to the Mouse Overcrowding and Acceptable Cage Density policy are considered to be an exception to the Guide and require a written request and subsequent written approval by the IACUC.

Contact Information:

For any additional questions concerning this policy, please contact the IACUC Manager at 5-6420.