{"id":61237,"date":"2025-12-02T12:42:45","date_gmt":"2025-12-02T17:42:45","guid":{"rendered":"https:\/\/www.bu.edu\/research\/?page_id=61237"},"modified":"2026-01-23T13:43:34","modified_gmt":"2026-01-23T18:43:34","slug":"rodent-breeding","status":"publish","type":"page","link":"https:\/\/www.bu.edu\/research\/ethics-compliance\/animal-subjects\/animal-care\/breeding\/rodent-breeding\/","title":{"rendered":"Rodent Breeding"},"content":{"rendered":"

Boston University is committed to observing federal policies and regulations and AAALAC international standards and guidelines for the humane care and use of animals.<\/p>\n

Mice and Rats have short gestation times and large litters. Therefore, cages may become overcrowded quickly if the individual responsible for managing the breeding colony and separating animals at the proper times does not do so in a timely fashion.<\/p>\n

When overcrowding of cages happens, the animals may become stressed and pups can die from being trampled. In static micro barrier cages, the air quality quickly deteriorates with a high density of animals and may predispose them to respiratory disease. Overcrowding of cages is an animal welfare concern and can have a deleterious effect on research.<\/p>\n

This policy provides guidelines for mouse and rat breeding colonies and defines standards and responsibilities for housing and breeding cages. This policy assigns responsibility for action when mouse and rat breeding cages are overcrowded. This policy also establishes when newborn rodents are to be counted for protocol tracking and regulatory compliance purposes.  Adherence to this policy is mandatory unless a specific exception has been approved by the IACUC.<\/p>\n

Responsibilities<\/h2>\n

Investigators<\/h3>\n

Investigators are responsible for:<\/p>\n

    \n
  1. Coordinating with Boston University Animal Science Center (BU ASC) for space allocation of their mouse and rat breeding colonies.<\/li>\n
  2. Managing their own breeding colonies unless arrangements for technical support have been made with BU ASC.<\/li>\n
  3. Designating a colony manager (someone who has received specific training on managing mouse breeding colonies, and who will be the primary contact person for the lab). More than one colony manager may be designated by the PI, but it is preferable that this number be minimized to facilitate communication between the BU ASC and the rodent users.<\/li>\n<\/ol>\n

    Colony Manager<\/h3>\n

    The designated colony manager (research staff or BU ASC staff) is responsible for separating animals according to allowed cage space as described in the Breeding Schemes, Weaning Pups, and Numbers of Rodents Per Cage sections, below.<\/p>\n

    BU ASC Staff and Investigators<\/h3>\n

    Both the BU ASC staff, and investigators managing their own rodent breeding colonies, must abide by procedures as outlined in this policy.<\/p>\n

    Any recurring problems with rodent breeding colony management will be brought to the attention of the IACUC.<\/p>\n

    Breeding Schemes and Procedures<\/h2>\n

    Two different breeding schemes are generally acceptable. In either, the designated colony manager (research staff or BU ASC staff) is responsible for carefully monitoring pregnancies.<\/p>\n

    A. Monogamous Pairs<\/h3>\n

    Postpartum estrus occurs within 24 hours of parturition: If the male is left in the cage, the female is likely to become pregnant again while lactating and nursing the new litter.<\/p>\n

    For Mice<\/h4>\n

    One male (only one male per cage is allowed) and one female are housed together for mating. Nesting material is provided in the cage. The mice need not be separated when the female becomes pregnant or delivers the pups. This model takes advantage of postpartum estrus and allows the female to become pregnant and nurse at the same time. Litters are born approximately 21 days apart. The three-week-old litter must be weaned prior to the birth of the new litter as the presence of two litters may cause stress to the dam and may result in suboptimal care or cannibalism of the new pups.<\/p>\n

    For Rats<\/h4>\n

    Nesting material is provided to the cage. The male may be removed either before the litter is born when the female is noticeably pregnant or at the first cage change after parturition to make more space for the pups. The second method allows for the use of post-partum estrus, as does leaving the male in the cage.<\/p>\n

    B. Harem Mating<\/h3>\n

    This method houses two females in a cage with one male (only one male per cage is allowed). For mice, three females may be allowed in some circumstances. During routine health\/breeding checks, each noticeably pregnant female is removed and placed in her own individual cage. When the pregnant female is separated from the harem cage, she is given nesting material in her delivery cage to make a nest for her pups. The female delivers her pups and nurses them for 21 days, or up to 28 days with IACUC or veterinary approval, following the procedure below in Weaning Pups. Only one nursing female and litter is allowed per cage. After the pups are weaned, the female may be returned to a harem cage.<\/p>\n

    C. Checking Pregnancy and Birth<\/h3>\n

    The Designated Colony Manager has primary responsibility for checking for pregnancy and birth and for recording these events on the cage card(s). When the litter is born, the cage is flagged with a New Litter Card and the date of birth (DOB) and projected weaning date is documented. However, if BU ASC staff find births of litters when checking and changing cages, they will place a New Litter Card and the DOB.<\/p>\n

    D. After Birth<\/h3>\n

    After pups are born, the cage is left undisturbed for at leas t5 days except for replenishing of food and water as needed. If the bedding gets very dirty or wet, and the cage must be changed sooner, the following procedure will be followed:<\/p>\n