Ok, so do you do back to back breeding through out their whole lives? I think i might try keeping them all together once, and see how it gos. Will the non pregnant/ still pregnant bother other mice babys?
Like I said, I keep them all together, all the time. I pull out the baby mice when they've been weaned. I do cull out the extras though so the tub doesn't get over crowded. Generally no more then 10-12 babies per litter depending on the number of litters. With my tubs I used to have 1.3 adults per tub, but I've found that I actually get better results with 1.2 adults. (my tubs are small and can get overcrowded easily) so I never have more then 20 babies per tub which I thin down to a dozen when they reach large fuzzy-small hopper size (2 1/2-3 weeks) The Adults are always a constant. I put them together when they are young adults of about 6 weeks, then they are never separated until I retire them together when they are about 6-7 months

Mark