I have a batch of female Cornish Rock Crosses that for some reason have not filled out as much as they should for their age. I am feeding straight ground corn, (due to costs) and they were doing great till they got too large for the pen. I then released them into a small pasture, about 30'x40'. They really loved eating the grass and bugs in there. I have kept the corn available at all times, to fit easier into my schedule instead of giving them 12hrs feed, 12 off as I have read. Could that be why they have seemed to top out just around the cornish game hen size and haven't filled out the rest of the way? They are about 13 weeks old at this time. Should I change the feed? or should I just go ahead and start harvesting them now so they don't get too old? I had hoped to have a bunch of chickens already in the freezer at this time, not still feeding them.