I'm brand new to chickens and in the process of building a coop - no hens yet but planning and learning. The priorities are eggs, manure, and meat in that order. I've read hens are productive at laying eggs for about three years and so after that I'm planning to butcher them and of course get new birds. At first I was thinking to get new chicks at about the 2 1/2 year mark so they'll be ready to take the old hens' places when the mature birds have served their purpose, but I'll only have the one coop (8'X8') w/20'X8' run and I've been reading a few threads on here where people have had bad experiences mixing young and old birds. So my question is, do you normally butcher the mature birds before adding any new birds to the coop, and then do so all at once, or can you add pullets a few at a time? I'm guessing like most things it depends on individual birds' temperament, but I'm hoping to keep this as simple as possible and if it's easier to replace the entire flock at once I'll do it that way. The hens I'm planning to get are Dominiques and Barred Rocks if that matters. I've read RIR's tend to be somewhat aggressive toward younger birds so I'd probably want to stay away from them. Any info would be appreciated.