For a bottle calf...there can be a wide range of how well they'll gain. Obviously, of course, depends on how they've been fed. Can run from .5lbs/day to 2.5lbs/day, keeping in mind that after a calf passes 500lbs or so it doesn't make much difference if he was raised on a bottle or on a cow. So anywhere from .5 to 2.5 ADG in the 500lb and less class, IMO. My 300-400lb holstein group is running about 2.2lbs/day.
With the potbelly on the black one I'd guess yours are doing closer to 1.8lbs/day, which at 180 days would put him around 400lbs. That's what I'd think looking at the picture, too.
