I produce about a thousand rats per month and never seperate the females. As a matter of fact, I make it a point to have at least 2 female per maternity tub. I have seen them from time to time with nips, missing tails, missing toes etc.. on the babies and generally just let the moms figure it out, if I saw something completely out of the ordinary I would seperate the moms and retry them again. If that was unsuccessful I would have a couple of more f/t feeders.
The point I guess is, in the future I wouldnt jump the gun on euthenizing, give them one more go around, sometimes rats just dont get along, kinda like humans, and just do better in a different environment.

Chuck