Rodent Density and Weaning

Cage Density and Weaning Activity for Mice

Purpose

In order to comply with government regulations (PHS and USDA), the Association for Assessment and Accreditation of Laboratory Animal Care International (AAALAC), the Guide for the Care and Use of Laboratory Animals, and the UCONN Health Center's Animal Care Committee (ACC) have implemented a revised policy concerning cage densities and weaning activities for mice.

Action

• The ACC allows a housing maximum of 125 grams to be the total mouse mass to be grouped per standard 67 square inch cage. Post weaned mice are defined as no longer suckling or greater than 21 days old. An exception to the 125 gram rule is granted for large or obese mice (e.g., NOD) where two mice are permitted per cage even if the combined weight exceeds 125 grams. The benefits of social housing takes preference over body mass but such cages must be flagged with the 125 gram exception sticker.
• Monogam Breeding (one male to one female) - The ACC recommends one male to one female in a permanent breeding arrangement as the optimal use of the 67 square inch cage size available in CCM. In this arrangement, cage densities may temporarily exceed the 125 gram combined mouse mass for large parents/litters such as out-bred strains of mice (e.g., CD-1 mice). However, birthdates must be noted on such cages, the 21 day weaning time limit must be observed; and such cages must be flagged with the 125 gram exception sticker if the weight limit is exceeded.
• Bigam Breeding (one male to two females) - The ACC recognizes the necessity for difficult breeders (need for cross fostering and utilizing post partum estrus) to be set-up in a bigam breeding arrangement with a permanent presence of the male with two females. Such cages must be within the 125 gram maximum mouse mass limit at the time of breeding unit set-up. Pups less than 9 grams may stay past the 21 day weaning deadline, but no more than 10 pups from maximum two litters are allowed per cage at any given time. Cages exceeding the maximum 125 gram total mouse mass must be flagged with the 125 gram exception sticker.
• Multigam Breeding (one male to more than two females) - Harem breeding is permitted provided the total mouse mass at the time of breeding cage set-up is less than 125 grams including the males and the non-pregnant females. Due to pregnancies, the total mouse mass may temporarily exceed the 125 gram rule; however, females must be separated prior to parturition even if this means that the post partum estrus will be missed. Cages exceeding the 125 gram total mouse mass must be flagged with the 125 gram exception sticker.
• Investigators and research staff should maintain familiarity with the density policy and CCM's flagging system. CCM staff will flag, with a pink sticker, cages with pregnant females. On the same sticker, CCM staff will record the date of birth (DOB) and the date of weaning (Wean). Once the date of weaning is reached, CCM staff will post a "PLEASE WEAN" sticker as a last reminder. After that, CCM staff will wean without further notice if a cage is in violation of the cage density policy.