I try to replace the hens that die out each year with new ones that I either raise or buy, but last year I didn't hatch any or buy any new ones. One of my hens will turn 11 years old in May if she keeps going. She's doing well right now. Last year she even laid a few eggs.
Deb, If you know a source of fertile eggs you can hatch some if one of your hens goes broody.
