I had 3 chickens die today out of no where. They wasn't sick or anything. So in the process of trying to figure out what could be the problem. I decided to dissect one of the birds to see if there was anything visibly wrong inside. When I did the chicken looked normal. Except for that the liver was extremely large, and hard as a rock. What could have caused this? These chickens are kept inside a coop, and are 4 months old. All 3 were roosters. No visible injuries or missing feathers laying around.