Mine are never locked in only in the winter they have several yards and 1 that is huge 60x60ft.I wonder if it has something to do with them accidently pecking it open as they scratch through the straw looking for seeds in it?I just started a couple of weeks ago.I noticed a couple eggs were yellow and I thought it was some running poo.Last nite I found 1 egg with a little hole in it thought maybe it got stepped on.Today I found one with the whole top off and most of the inside gone.I just have them on layer maybe I need to raise the protien level.I think I will do that.