I keep my breeding groups together always. I start new groups together and when they get a little worn out I retire the whole group together. When I've tried to move new mice into an already established group I've had problems with them killing the newcomers. Not always, and frankly not even most of the time, but more often then I like to see. I just think it's disruptive to an established group.

I do like the idea though of having tubs of females with lots of males to produce pinkies. My main goal in breeding mice is to produce mainly weanling to adult sized mice for my colubrids and baby ball pythons, so when I wean the young mice I set them up separated by sex to grow for a few more weeks. It might be a good idea to throw a few males in a couple of the female grow out tubs and pull all the preggers when feeding day comes around.