Housing Policy on Male Mice
Group-housed rodents typically develop dominance hierarchies. Male mice of certain strains (e.g. BALB/c, CD-1, and C57) are reported to have an increased incidence of fighting that can inflict severe wounds on their opponents. 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 cases significant stress as the animals establish a new social dominance hierarchy.
Even with the precautions, inter-mouse aggression may subsequently develop in previously “stable” groups of male mice.
In order to mitigate the occurrences of fighting, reduce experimental variables, and preserve the humane housing of research animals, BUASC requires all BU Researchers and ASC Staff to adhere to the below policy when considering housing male mice in all our vivaria.
Housing Male Mice upon Arrival to BUASC
Newly received male mice will be housed by ASC staff in the same grouping(s) as shipped by the sending institution/vendor.
- Males shipped in separate compartments of the same shipping box or in individual boxes will not be combined upon entry into ASC facilities.
- Should the investigator require special housing arrangements different from how the mice were grouped at arrival, he/she must provide scientific justification to do so. There must be an IACUC approved exemption to the BUASC housing policy within the protocol under which the animals are covered.
Housing Male Mice Born within BUASC
Male siblings and conspecifics (aged 3-4 weeks) weaned from their parent cage may be
housed together. After 3-4 weeks of age, male mice separated from their siblings may not be re-housed with siblings and/or any other males.
- It is permissible to house a male mouse with any female(s), up to 3 females per harem, for breeding purposes.
- Should a cage of male siblings be flagged as a health concern for fighting, the male aggressor/s will be removed from the cage and housed individually. This cage (or cages if multiple aggressors are found) will be labeled as an “aggressor” and is no longer permitted to be housed with its siblings or with any other male mice.
- Should a male mouse in a breeder cage be flagged as a health concern for fighting, the male will be removed from the cage and housed individually. This cage will be labeled as an “aggressor” and is no longer a suitable candidate for breeding with that female mouse.
- Should the investigator require any “aggressor” mice to be re-housed with previous female mice, he/she must provide scientific justification to do so. There must be an IACUC approved exemption to the BUASC housing policy within the protocol under which the animals are covered.
Animal Cages Flagged for Fighting
Cages flagged for fighting by the ASC Animal Care Staff will be examined by the ASC Veterinary Staff. The “aggressor” male will be separated by ASC staff at no charge to the investigator. Injured animals will be treated by the Veterinary staff at the discretion of the Attending Veterinarian or designee. The investigator(s) will be notified via email or phone of the health concern and of the separation, including treatment plan and new cage card information.
Once the injured animal/s have healed, it is NOT permissible to re-house the “aggressor” animal with its former cage mates. For instances where the “aggressor” is not easily identifiable (the animal without any wounds), all non-injured animals will be housed individually and the injured animals will remain together. In the event that all animals in a cage are found to have fight wounds, all animals will be housed individually.
- Should the investigator require any “aggressor” mice to be re-housed with other mice, he/she must provide scientific justification to do so. There must be an IACUC approved exemption to the BUASC housing policy within the protocol under which the animals are covered.
Disclaimer: Should any previously separated animals, which are not covered by an IACUC approved exemption, be housed back together by the investigator and/or lab members, and be found by ASC staff, they will be separated for a service fee and the BU IACUC will be notified.
*Information provided by Jackson Laboratories and Boston University Animal Science Center Rodent Housing Policy