My chickens are 5 months old. They are eating well and appear very healthy. But over the last few days, the appearance of their sides is changing. They are not as full on the lower sides as they used to be. I tried to take photos but don't know if this will come across. It is really apparent on the buffs and the white rock, but all of the chickens have it. Do you see what I mean? I guess I'd describe it as their ribs are showing. There's like a line showing an indentation maybe four or five inches above their legs. I hadn't noticed this before a few days ago and it seems more pronounced every day. Maybe this is normal as they near maturity?