Regulatory guidelines for housing laboratory mice indicate a need to clearly define maximum cage population densities. Determination of maximum cage densities in this Policy is based on the recommendations outlined in the “Guide” (Page 57 – 8th edition). In order to prevent or eliminate the possibility of overcrowding within cages, the UMBC IACUC has created this policy for use in laboratory mice facilities.
Population Density for Breeding Mice
- If the male is integral to successful rearing of offspring, the male may remain with a single female and her offspring. A second female could also be present if there is to be only a single litter in this cage. Housing two (2) females with litters in the same cage as the male is not permitted.
- Up to two (2) females with litters not to exceed a total of 18 mice/cage (e.g. two females with a total of 16 offspring). Each litter should be 4 or more days apart in age, otherwise they should be kept one litter per cage; this allows the placement of a limit on the total density of mice within 1 cage i.e. a younger litter is much lighter in weight than the older litter which is soon to be weaned. Conversely, we should only singly house 2 litters that are less than 14 days apart (to decrease the likelihood of a 14 day old mouse stepping on a 2-day old). Overall, the litters should range from 4-14 days apart.
- Weaning must occur on day 21 or when pups reach a weight of 8-12 grams unless the strain/line is specifically approved for later weaning by the IACUC. If weaning is to occur after 21 days, only 1 litter per cage may be maintained.
- This policy will be adhered to by investigators in preparing their animal use protocols, and throughout the period that animals are maintained under the protocol; any deviations from this policy must be approved by the IACUC..
Experimental (non-breeding) Mice
- No more than 5 mice (weanling to adults) may be housed in a cage at any time.
- Larger mouse strains (e.g. – MRL/MpJ and LG/J – adult body weights are substantially higher than other strains), whose body weight is in excess of 25 grams, should be housed at no more than 4 mice/cage.
Singly Housed Mouse
Mice should not be housed alone unless IACUC approved or due to medical reasons as assessed by the veterinarian.
Separation of Mice in Overcrowded Cages
It is incumbent the animal care staff and the Principal Investigator (PI) and their respective staff to follow population guidelines. Cages that are identified by the animal care staff as overcrowded will require separation within 48 hours of discovery. Cages that are out of compliance are marked by placing an action card on the cage instructing research staff to correct the problem. Animal care staff will monitor cage density as part of their routine duties and will attempt to notify researchers and/or their designated contact person via email, by phone, or in person if overcrowded cages are discovered on the day the problem is identified to allow the lab member the opportunity to correct the problem within 2 days, unless it is an issue that warrants immediate action. If after 2 days the cage(s) are still in need of separating, animal care staff will separate the animals and notify the attending veterinarian and IACUC Chair. Animal care staff may separate immediately, or change the cage of any animals when animal welfare concerns exist. Non-compliance to this policy and “The Guide” may require a report to the Office of Laboratory Animal Welfare (OLAW).