Fred do use the all in all out approach with your Isa Browns? and what do you do with spent layers? Is there any threads on BYC that discuss these topics. Selling eggs in the area where I live is a task seems everyone has a backyard flock.
I do try to keep up with the heritage thread some day I will own good birds....some day.
We surrendered on the egg business, (it was never enormous) a few years back. We'd make more money asking customers if they want to super size their order than selling 10-20 dozen eggs per week. LOL
We did 50% turn over. Half the winter's layers were spring pullets in ferocious lay and 50% were birds were a bit over a year old and still laying well. By year 3, so many birds would contract ovarian, oviduct, water swelling or were barren issues that it made no sense to keep them in the layer group.
Eat them. We did. There's nothing on them, to speak off, but still made excellent soup and you can pull off the meat bits and they're tasty enough, what there is.