Hi there, I've been taking a break from internet and just saw this! That's a good question. To be honest, I don't really manage the culling. Natural selection takes care of a lot of it- any bird that is in less than perfect physical condition is not likely to make it in my predator dense area. I have occasionally sold and given birds away (usually chicks, extra cockerels, and very rarely hens). I started out with 1-2 of each breed and make an effort to add in some new blood every few years from game breeds.Very interesting! How many of each breed did you start with? How do you cull what you don't want?
I think if the goal is to create a sort of "landrace" it can be a pitfall to overmanage. What survives gets to reproduce and that is the best way to ensure vigorous, locally adapted, hearty birds. I like the chickens for their innate talents- a few eggs, tick control, manure for my garden- and have little desire to change their productivity! If I wanted lots of eggs or huge carcasses, I would purchase some production reds and cornish crosses.