We have 6 male hairless rats and 3 female hairless rats at my work. (We do a lot of small animal rescue.) One of the main problems we've had with rats is obesity. Our males are pigs, but hate to exercise. Our girls are not pigs, and love to exercise. Other than that we haven't had any problems. We are just careful not to feed them to excess and we are also careful what we feed them. Also keeping their cage clean will of corse keep them helthier. All-in-all rats make wonderful pets. The good defiantly out weighs the bad.