How can a Rooster get this Big an continúe to walk? Do You have pics of him whe he was alive?

I think he's around 6 months old in this picture because shortly thereafter I had to take those girls away from him, he was ripping them up. He was actually a really nice rooster, just too big, heavy and clumsy to use for breeding. He got around fairly well, I imagine those humongous legs helped, lol. I didn't really want to butcher him, but he's been taking up one of my breeding pens since last year and I need it.