I keep most of my breeds pure. The only flock that has different breeds is the layers.
I keep them pure because if you don't they ain't a breed anymore. Even though all breeds start as mutts, it is important to preserve the breeds there are all ready.
If everybody started crossing different breeds, all the pure breeds would go away.
I've got 7 different breeds and 11 different colors of laying hens that I keep in one pen. I then have another pen that I keep just for Welsummers. I thinking that in the spring I might hatch some more and possible sell some fertile eggs.
Right now my Pen setup is everyone is in the same enclosure, but I am not going to start hatching until maybe december/january.
Due to the fact that I have more breeds then I have breeding Pens I have made my own little plan making sure I only hatch purebreds. It goes like this:
Once all my pullets start laying I will seperate all roosters out of the current community enclosure.
Give the pullets 3 or so weeks to get rid of any eggs fertilized by whatever roo got the chance. Then whenever I want to hatch a certain breed of chicken I just put the pullets and rooster of the desired breed in a enclosure of their own for a day so he can do his thing and then put the girls back in the main flock and always put their eggs aside for hatching. That way I don't need a breeding pen for of the 13 + breeds and colour projects I want to have going.
Basically I have 3 enclosures = 1) Hens/community(winter), 2)Roosters, 3)honeymoon suit.
I just have to keep up on recognizing eggs from each breed, or I just get all my hens that lay the same colour egg bred by their matching mates and have a bit of a surprise when I hatch them and see which breeds eggs I have collected.
*edited to add* - I almost forgot to say only crossbreeds I have are the freeranging mutts I got that can do as they please. Nice to watch in the yard and not a big loss if the coyote or hawk takes one.
I'm going to start this spring. I have right now 2 big coops , 2 small pens and 2 tractors. I will be breeding pure Golden Lakenvelders, Welsummers, Blue Andalusians And Barred Rocks. In with my Blues are some mixed hens that lay brown eggs so no problems there I will know the white eggs are pure. In with my welsummers I will have a few leghorn hens and I will know the eggs there.
I will need to work on the barred Rocks as I will have other laying hens with them that lay brown eggs also. But I should be able to know the difference. Once all are laying by egg count and same color. I only have 3 Lakenvelders pullets so they will stay pure with out any other hens with them. And the eggs from all the hens that are in with the pures will be project eggs for any one wanting to hatch out a nice cross.
I currently have 5 pens. one pen of BO, one of BA, one of BR, one with younguns and then the other is mixed breeds. I keep them separate so that I can hatch specific breeds or sell hatching eggs for specific breeds at any time. I'm gonna have to make a new pen next year for the SS I have coming up too.
I raise heritage breeds. The only way we can have this bit of living history to pass along to the generations coming behind us is if we maintain pure flocks. That's why I have a separate coop and run for each breed I raise. My RIRs, for example, are directly descended from a flock my grandfather started in 1942.