I have several chickens all running together, several different kinds of standard chickens and silkies. Since the silkies are the only bantams I have, I can easily tell their eggs apart from the standard sized eggs. I am going to take the standard Roo out and leave the silkie roosters in, so the silkie's eggs will be purebred. How long until I can safely consider the silkie's eggs purebred, and be sure that they aren't still going to be mixed with the standard roo? Thanks!