Wild-Derived Mice Strains - Tips on Their Care and Handling
JAX® NOTES Issue 460, Winter 1995
Sharon Chamberlin, Technical Support Coordinator-Customer Service
Special Handling
Wild-derived mouse strains are valuable mapping tools. The large number of genetic differences in progeny from interspecific crosses with common inbred laboratory mice permits the mapping of many genes in a single cross. Researchers using a wild-derived strain for the first time may not always be prepared for the special handling these characteristically hyperactive mice require, but following a few simple guidelines may help.
Ordering
Order more than one pair of breeders because sometimes wild-derived mice fail to breed with the first mate provided.
Upon Arrival
Wild-derived mice tend to burrow and can completely disappear from sight in the bedding. If the shipping container appears to be empty or have fewer mice than expected when it arrives it is very important to check the bedding in the bottom thoroughly. Have a new cage and forceps ready to facilitate picking up the mice as the shipping box is opened.
One way to unpack the wild-derived strains is to place the entire shipping container in the bottom of a sterilized garbage can or other large container. Any mice that get away from you will be much easier to catch in the larger container rather than running around in a mouse room.
Have an extra cage lid handy to place over the opening of the shipping box. As you open the box, slide the lid into place over the opening and maneuver as needed to create smaller openings from which to remove mice. Unlike most common laboratory strains, wild-derived mice look for exits rather than running from light.
Colony Care
Once your wild-derived mice are in your animal facility there are a number of factors involved in maintaining a successful breeding program. Place pairs together in a quiet room, away from areas of heavy traffic and noise. Handle as little as possible. Your Animal Technicians should be trained to handle wild-derived mice and should allot enough time when dealing with them to work slowly and patiently. Wild derived strains are more sensitive to stress from shipping, new surroundings and new handlers. When pairs are placed together, give them 8-12 weeks to settle down and produce a litter. If after 8-12 weeks a pair has not produced a litter, you can switch the males around to different females. Sometimes females will breed with different males.
At 6-8 weeks of age males may fight. Separate them or pair them with females to avoid possible aggression. Strains to watch for this in particular are the CZECH II/Ei mice and progeny from all crosses involving M. m. castaneus.
Handling
The key to breeding wild-derived mice successfully is to disturb them as little as possible. Handling these mice by forceps rather than by hand is recommended. Sticking forceps down into a cage is less traumatic than an entire hand, and importantly, forceps do not deposit human scent on newborn pups. Scent is one factor that could induce a mother to cannibalize her litter. If you do use hands, cover them with a clean pair of rubber gloves each time. Additionally, to decrease the incidence of cannibalism, some colony managers recommend not to change a cage if it contains a litter that is less than 3 days old. When changing cages with very young litters in them, move the nest and pups as a unit by using rubber gloved hands. Also avoid taking the cage off the shelf repeatedly to look at the mice.
Nesting
Nestlets or Kimwipes placed in the cage will often encourage nesting and improve overall productivity. If, however, a female develops a history of abandonment or of cannibalizing her litters, then fostering the pups to a laboratory strain female is usually the best alternative.
Fostering
If you suspect that a female is not taking care of her newborns( i.e., general failure to thrive, absence of milk spots in newborn stomachs, females are getting pregnant but no litters are seen, chew marks on pups, pups just left randomly all over the shavings and pups found dead while others are left alive), then foster the pups out to a female who is a different color and has had a litter of her own within the last 24-36 hours. Newborn litters can be fostered with another litter of 1-3 days old. Place the pups that are to be fostered in the nest with the foster mother's litter and mingle the pups together. Two or three of the foster mother's pups should be left in the nest to provide scent, but the remaining pups should be removed to ensure adequate milk supply.
General References
Foster HL, Small JD, Fox JG. v.1. History, genetics and wild mice, In: The Mouse in biomedical Research. Academic Press, N.Y. 1981.
Bohomme F, Guenet JL. The Wild House Mouse and its Relatives. In: Lyon MF, Searle AG, (eds) Genetic Variants and Strains of the Laboratory Mouse, 2nd ed. Oxford University Press, N.Y. 1989.
Pool TB, (ed). The UFAW Handbook on the Care and Management of Animals, 6th ed. Bath Press, Great Britain, 1987.
