[ema-leigh]

Over crowding could defiantly cause a mother to abandon her pups..or if the mom knows theres something wrong with them she won't waste her resources feeding them. (although I have seen some really good moms try nurse dead babies!) If she has had a few litters back to back, she made need a few weeks break. Or if she is quite young, she may not be mentally mature enough....
To combat the over crowding issue add lots of card board boxes so they have separate nests and they will feel more secure. Make sure they have lots of food as well, moms likes to build a nest and hoard food into stashes so they feel prepared to raise them.

I don't think there will ever be a nice way to pre kill them. I was having the discussion on another pet rat forum and we were debating a few methods. The best we could come up with, which you may like to put into practice and tell me if its okay, is to set up a dark box with a strong modern metal rat trap. You can put a little treat on the rat trap and just put the lid on the box til you hear the rat trap go off. I feel that will give the most efficient way to break the neck and low stress for the animal. What do you guys think?