I have a very quick question? We have 6 21 week old hens. 2 white leghorns, 2 buff Orpingtons, & 2 Easter eggers. Our 2 leghorns have already started laying but the other 4 have not. My question is, we have had 3 shell less eggs since we got our first egg, what could be causing this? We live in southeast Michigan and the weather here has been cool at night and hot during the day. The 2 leghorns both laid today and we found a shelless under the roosting bars this evening when we went to lock them up. Any answers or comments would be greatly appreciated. Thanks!