About 3 years so rotating a couple of new ones in every other year won't hurt. Depends on feed used too as you can force egg production and there are only so many eggs per hen...
I try to rotate new birds in each year. And every year the oldest birds are culled out as needed to keep the flock in peak performance. That being said- my flock took a huge hit this year with predators and culling behavioral issues, so I had to tweak my plans a bit. Next year I should get back on track. I try to keep pullets, 1 y.o. layers and 2 y.o. layers, while culling out 3 y.o. and older. Some hens make the cut to stay permanently, some make the cut to stay past their prime, but the majority are weeded out after 3. That way I always have eggs. Even when 2/3 of the flock is molting I still get pullet eggs from the newest group of birds. I hope this helps. Good luck.
It is up to you! I've had layers that lays well, everyday, until they reached their four to five years. I've had better luck with my Welsummers, one hen is coming six year old, lays daily but shorter months, from ten months laying down to eight to nine months out of the year. That is pretty good. AND none of them are hatchery birds. As for hatchery birds, you can push it to two to three year old before they come down with reproductive problems, mainly egg peridontis which it plagued many of the BYCers hatchery birds. Look under SpeckledHen's threads and another BYCer thread on those information. It is very very informative. Egg production is your main goal? Hatchery birds are the way to go and that is what they are bred for. Breeders and show birds are not well known to be very productive unless they have some production strains in them. RIR, Barred Rocks, New Hampshires seems to be going both ways for showing AND production which some breeders are having very good success with it. If I can remember right, to get some RIRs, some of BamaChicken's stock/lines indeed have the best of both worlds. Good luck!
