How old are they? I basically don't worry about obesity at all when they're under 3 years and 1000 grams. I had one 700 gram male that looked pretty round last October... and then he didn't eat again until April. So now I feed him whatever the heck he wants.

I've heard it IS possible for adult males to have obesity problems? But if they're still juveniles or small adults, and you're not throwing rats at them every 5 days, they're fine. Basically if they're still hungry when you feed them, they're not obese.