Basis: Recommendations for housing laboratory rodents are based on the 2010 edition of the NIH Guide for the Care and Use of Laboratory Animals (the Guide, pp. 56-58).

Protocol Requirements

If animals will be bred for the purposes of research, an application must be submitted and approved by the ARC. If you will be breeding animals and do not already have an approved breeding protocol on file with the ARC, you must submit an Application to Establish and/or Maintain a Breeding Colony. Following approval, a triennial Breeding Colony continuation must be submitted. In cases where breeding is an integral part of research activities (e.g., pregnant dams are administered an experimental diet and pups followed), a separate breeding protocol may not be necessary. Please contact the ARC administrative staff to discuss your breeding activities to determine whether they may be added to your research protocol.

There is no need to complete a separate breeding colony protocol for each strain of animal or housing facility to be used; generally, these can all be accommodated under a single protocol. However, if you plan to breed multiple species of animal, submission of a separate breeding protocol for each species is recommended.

Some special considerations for breeding colony management:

Recommended Minimum Space for Commonly Used Laboratory Rodents Housed in Groups

DLAM has developed a standard operating procedure (SOP) entitled “Rodent Cage Population Limits,” which details the minimum space requirements for the different cage types for non-USDA-covered rodents (primarily mice and rats) that are housed under the care of DLAM at UCLA. The SOP also describes the procedures established by DLAM for notifying laboratory staff of overcrowded conditions and for separating cages.

Important note: cages that might appear to conform to Guide standards when litters are born may have insufficient space as pups grow; the DLAM SOP has been written to consider this. Departures from the minimum space requirements, as detailed in the Guide and reflected in the DLAM SOP, for reasons of convenience, cost, or other non-animal welfare considerations are not acceptable. The ARC will, however, evaluate objective measures of outcome-based performance for cage density and allowed exceptions to the DLAM SOP must be detailed in the animal-use protocol. Examples of objective measures which may be considered as part of a justification for an exception include:

  • average litter* size of the strain(s) of rodents;
  • whether multiple litters* are present in the cage;
  • difference in the age of the pups of different litters*;
  • growth rate;
  • need for cross-fostering (i.e., use of two or more dams in the cage to improve health and survival of pups);
  • overall management and husbandry practices such as cage sanitation or bedding change frequency.

*Note the definition of “litter” in the DLAM SOP as “offspring in one cage up to fourteen (14) individuals, all born within four (4) days of each other.”

Harem Breeding

Mouse harem breeding groups (defined as one male and more than one adult female) are often used for the propagation of inbred, transgenic, or other strains of mice which generate small numbers of pups or are difficult to breed. Outbred crosses, hybrid crosses, intra-specific crosses, or any other crosses that produce larger litters are best propagated by a monogamous (i.e., one male and one female) breeding strategy.

Investigators who decide that harem mating would be a beneficial breeding strategy for their research must accept responsibility for any overcrowding in their colony and follow these guidelines:

  1. For DLAM standard caging systems, four (4) adult mice per cage is considered maximum capacity; for ventilated cages (including disposable cages), five (5) adults of average weight is the maximum. Once a litter, as defined in the DLAM SOP, appears in the cage, the maximum number of adult mice that can be in any size DLAM mouse cage is two (2).
  2. Investigators using a harem breeding strategy must be aware that they have increased responsibilities to ensure "the adequacy of cage space" for all animals, including (a) prompt weaning of mature pups at twenty-one (21) days or less and (b) prompt separation of animals if the cage density becomes greater than that established by the facility or program. In addition, difference in the age of the pups of different litters, growth rate, cage dimensions, and husbandry practices may require an Investigator's prompt attention and intervention if there are multiple litters of pups in one cage that are greater than four (4) days of age apart from each other.
  3. When breeding ratios are 1 male to 3 or more females, the cage space is at maximum capacity, depending on cage type. At this point, the investigator must assure that pregnant females are removed and placed into another cage before parturition.

Extended Weaning Periods

The ARC adopts the standard practice of weaning mice at day twenty-one (21). Individual exceptions to this policy may be permitted after consultation with a DLAM veterinarian. Requests to routinely extend the weaning period must be approved by the ARC and be described in the approved protocol.

Extended weaning periods enhance chances of multiple litters appearing in the same cage, a situation that can compromise the health and welfare of animals by resulting in overcrowded cages and decreased survival of younger animals due to injury or inability to suckle.

Approved 1/27/2014; Revised 6/11/2018
Replaces ARC Policy: Extended Weaning Periods