Mating should occur within the first day of introduction. Mice are observed for abdominal enlargement and can be palpated abdominally to determine if they are gravid. It should be emphasized that these are extremely imprecise methods of pregnancy diagnosis. Animals are monitored daily for parturition. Alternately the litter may be derived surgically and farmed out.
Mice tend to adapt to being surrogate dams quite easily.
A new litter is placed with a female who has just had its litter removed. This may be done at any time during lactation, but is best done within the first 24 hours of parturition by the surrogate. Observe the surrogate and pups to make sure the surrogate is not aggressive to her new litter. It may be necessary to briefly anesthetize the surrogate before placing the pups in her cage to allow the new litter to acquire the odor of the cage. RAR will perform routine random cross breeding for investigators for the purpose of building colony size.