Our Cat is Ginormous

I knew that our cat was not a small kitty. Even when we first got him, he was a pretty big cat... But lately hi has been putting on some weight. I think it's because he's moving out of adolescence and firmly into adulthood. We've put him on some weight control formula, but it seems to have no effect. We've tried feeding him less food, but it hasn't worked. Any way, it has gotten far out of hand. Hopefully, making him go outside will be good for him...