I keep 1 mom to her babies, thats all. Rats, that is. I have a 5:1 female:male adult ratio for breeding, then when theyre preggo, I put them in their own single tub by their lonesome. So, it's just the mom and her 8-12 babies. I just found 10 4-week olds dead in their mom's today today...this is getting silly now. They have food and water galore...it's not like they just die, they always have brains and stomachs missing from the mom, too.