I have the same problem. But at least I can give them to the younger crew who aren't yet laying. I waited about 2 weeks on them. I wish someone really knew how long it lingered in the system! I have 3 eggs a day going back into chick food. And I am buying $4 cage free eggs! This must stop!
My chickens seem to keep passing around whatever they have. I then have to give another shot. At least it is the little ones this time.