I keep up to 8 females with a male, from the time they're initially introduced till the time they're retired & subsequently fed off (usually a 6-month timeframe). I don't introduce new females or males once the group is set up, but have had excellent results letting them birth & raise babies together up to the point of weaning the babies. I'm currently weaning between 200 - 500 mice a week with this setup (well, 200 setups).

There's certainly more than one way to skin a cat...er...raise a mouse.

Just my $.02

K