After having pet rats for years well before we ever owned snakes and bred rats, I really think part of keeping them living longer is good nutrition and keeping them from getting fat on treats. Our pet rats were sadly allowed far too many treats and were overweight to some degree or other. Working with the breeder/feeder colony I've learned a lot, changed the way the rats are feed, fed them far more healthy treats and they seem to do so much better overall. Fat rats just never seem to live as long as they should, get more cancers, have more strokes, etc. I like the rats well fleshed and never skinny but definitely more fit than fat.