Gail there are alot of things that have to go right before you can get a colony of mice "gelling".
One practice that worked well for me in the beginning was to have a "open colony". I would have 1 male for about 15 females ... as soon as the females got noticeably pregnant they would go to a single holding tub. And I would put a new female in with the male. Although it worked for me most people will find that it is horribly time consuming.
The cannibalism is usually due to wrong protein content in their diet (or limited resources), the male not thinking the babies are his, and first time females or old females with no litters.
When I get in new mice that I may want to breed I sex them out. Males go together ... females go together. Youll lose some animals the first week ... but you probably would have lost them anyhow. During this first week I get them used to drinking from valves or bottles, get them on my rodent pellets (which are 16% protein 5% fat), and cull any that I think are weak or show deformities.
After this first week they are then put into female only colonies. If its a 1:5 rack I put in 5 females ... if its a 1:6 rack I put in 6 females. I then leave them alone in their newly establishing colonies for another week. At the beginning of the third week I introduce the male.
The male, having been kept with other males, wont have as much testosterone for the first few days, and will be easier for the females to get along with. The male should be 4-5 grams bigger than the females. Once the male is introduced leave them alone for a few days (except to feed or water).
When introducing the male to the female do so right after a bedding change ... this way its noones territory.
Females in a colony need to be the same size. If you have 3 large females and 2 weaned females, the 2 weaned females will most likely be dead the next morning. When introducing a female to a colony to replace a dead or culled one make sure she is at least the same size as the other females ... dont introduce an older female that is unproven and make sure it is done at the same time as a bedding change ... even if this means doing a bedding change sooner or keeping the mouse solo for a few days.
Bryan
