I hav e three breeds of chickens...Leghorns, Buff Orps, and Silver Laced Wyn. I have a rooster for each breed. Currently they are all around 10 weeks old. Once they start laying I will be interested in continuing my flock by incubating & hatching my own eggs. So how long do I need to separate the breeds before I know that the eggs the hens are laying are going to be "pure bred" and not sex-link?