I have 6 hens and 2 roosters I got 15 weeks ago from tractor supply. A few days ago I noticed what looked like yolk in a soft casing on the droppings board, and yesterday we let them all out of their run and right away one of the girls popped out a yolk and a small piece of shell in the grass. Im putting the nesting boxes in tonight, I had held off to make sure no one got used to sleeping in them. Is this normal behavior? I thought 15 weeks was young to start egg laying? They're still on grower feed, should I switch them all to layer feed now? I have half a bag of grower feed left, can it be mixed? Thank you!