Establishing Mouse Breeding Groups

Policy

Background

This policy outlines guidelines for establishing and maintaining mouse breeding groups in accordance with the 2011 version of the Guide for the Care and Use of Laboratory Animals (the Guide). The Guide recommends a minimum of 51 in² (330 cm²) for a female mouse with a litter and 12 to over 15 in² (77 -97 cm²) for a group-housed mouse, depending on body weight. This equates to at least 63 to 66 in² (407 – 426 cm²) of cage space for two adults and one litter. Our standard mouse cage provides 70 in² (452 cm²) of floor space, which only allows for two adult mice and one litter.

Background

The maximum capacity for our mouse cages includes up to five adult mice or two adult mice with one litter. To avoid overcrowding, mouse breeding may be performed utilizing either continuous monogamous pairs or harem mating under the following conditions:

1. Monogamous pairs:

   1. One female is housed with one male mouse for breeding. The mice do not need to be separated when the female is pregnant or nursing.

   2. Postpartum estrus occurs within 24 hours of parturition. With the male still in the cage, the female may become pregnant again while nursing the new litter.

   3. Litters may be born 21 days apart. The current litter should be weaned by 21 days, before the next litter is born, to prevent overcrowding.

2. Harem mating:

   1. One male is housed with two or three females for breeding.

   2. The females should be monitored for visual signs of pregnancy every three to four days starting two weeks after pairing.

   3. Each female must be moved to a separate cage once visually pregnant to ensure that she is removed from the harem cage before giving birth.

      1. The maximum capacity for the cage is two adults and one litter.

      2. After the pups are weaned, the female may be returned to a harem breeder cage.

   4. For inbred strains that produce smaller litters (six pups or less) a harem breeding scheme of one male with two females may be used in which the male is removed before any pups are born.

      1. This results in two females with two small litters (that equates to the size of one normal outbred-sized litter) and enables the females to share nursing responsibilities.

Responsibilities

The principal investigator is responsible for ensuring that the breeding colony management complies with these guidelines. If there are decreases in breeding performance indices (decreased pup size, decreasing numbers of pups surviving to weaning) or noncompliance with weaning practices, mating systems may be re-evaluated in consultation with the Animal Care Program.