I don't know, but I have been wondering about egg shells lately.
In the last few weeks my girls have laid more speckled eggs than normal. (Some girls who normally lay plain brown or slightly speckled are laying very speckled eggs now) They've also layed more rough-surfaced eggs. I did some research on line and found that these (at least the rough ones which are calcium deposits) can be caused by stress in the flock. I wonder if perhaps the change in weather and day length is affecting them.
I'm interested to hear what others have to say!
Stacey