I have 4 Chickens, 2 Leghorns and 2 Isa Browns. They are all about 7 - 8 months old. A few weeks ago they were laying every day, for some reason they stopped laying for about 3 weeks now, I have no idea what's wrong, they've all been eating, drinking and running around and they look perfectly healthy. I'm just looking for some advice. I've also seen a few lice on one of my leghorns but not the others, could that be the case?