That is a good question. I'm not sure I have the correct answer. I'll give one, but understand it may not be the best one.
If I could only keep say 20 chickens.
I'd hatch at least 100 chicks. Replace half of my breeders every year with the 10 best chicks: cull the rest.
Every 4 or 5 years, maybe less, I'd obtain a new cock of the breed I'm raising from a good breeder: that would help to avoid degeneration.
Does that help? You've asked me a question with which I have never had to deal. With no experience in the area I'm only taking a stab in the dark.
If I could only keep say 20 chickens.
I'd hatch at least 100 chicks. Replace half of my breeders every year with the 10 best chicks: cull the rest.
Every 4 or 5 years, maybe less, I'd obtain a new cock of the breed I'm raising from a good breeder: that would help to avoid degeneration.
Does that help? You've asked me a question with which I have never had to deal. With no experience in the area I'm only taking a stab in the dark.