Rats in particular can be VERY prone to cancer, malignant or benign. It is usually in the salivary glands or mammary tumors, but can turn into an all out lymphatic cancer. Not fun. Also, inbreeding can be a cause for growths or other abnormalities, so use the same pairs, or one dad for the same mom rodents and no breeding moms to sons or dads to daughters, LoL ... And yes, as Smulkin said, there can be cannibalization of the babies if stress is involved, so try to keep the cage(s) as quiet as possible. Also, if you're pretty money-conscious, you really don't have to disinfect the cage with anything special, just soap and water works, or a little bleach, just be sure to rinse REALLY well. I usually just put the cage in the bathtub, spray it with water, get some soap and rinse. Hope this helped a little.