Leah-yes I know I'm crazy :
You could work this to your advantage with pre-planning. I think a rir roo and br hens will give you chicks that are auto sexing. (If I'm wrong someone will correct me in a few seconds...) So you could say have rir's and br hens and end up with some pure breds, some sex links at hatching.
I really admire pre-planning in others and whish I had thought before jumping in.
That is certainly a way to go. With Rhode Island Red roosters, and both RIR and Barred Rock hens, you would not only know which chicks are the pure RIR's but be able to identify the sexes of the other chicks.
pure RIR = red chicks
sex-link pullets = black chicks
sex-link cockerels = black chicks with white dots on their heads
Hens often lay eggs in common nests and it may be difficult to separate the eggs by breed. As soon as they hatch, you would know
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One caution on mixing breeds, I wouldn't want large roosters of one breed and very small hens of another. The other way around works fine, however. Not caring about fertile eggs, about my best combinations have been large breed hens with Ameraucana or Hamburg roos. A 4 pound Hamburg is a large enuf roo with 7 or 8 pound Australorps or Orpingtons. The frumpy, dumpy hens keep the flighty Hamburg around, too
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Steve