Mother kept 200-300 layers on the farm for extra income. Every once in a while we would have an old & retired one for chicken soup. About once a year about the time the pullets started to lay we would cull the flock & those no longer producing eggs were sold to someone in town. Never saw a veterinary for the birds, but we did vaccinate for something, I think it was cholera.
We give our chickens antibiotics in their water about once a year but they get electrolytes in their water everyday.
We cull our old stock to the local Hispanics for $5 bird that’s about $1 per year of age.
This past June when the temps were at record high we only lost 2 birds both were elderly. We had another that we were sure was on death’s door, pull out out of it and is doing great. Even though she is older than dirt, if their on my farm we will try to give any animal a fighting chance.