I feed my rats and mice the proper rat/mice pellets. Had no problems with them at all. I had a couple of males attack another male while I was sorting out tubs and sexes etc. Two males ripped the balls of the third one, don't know why either. He was quickly euthenaised and fed to one of my diamonds. I now grow up the weaners in groups of four ,1m and 3f, and they all get along great, not deaths, no dead pinkies, mothers will share the feeding duties etc. I also do the same for my mice and they are the same. I think growing them all up together helps as the males are the first to breed with the females. It is like their own little harem....LOL