I just received an order of Pearl White Leghorns from McMurray and find I have a problem. There are fifty pullet chicks and five cockerel chicks, but they weren't marked so I can't tell which is which. I want to keep the cockerels and sell about half the pullets so how do I tell them apart? I know they can be feather sexed but I haven't done this yet so does anyone have a link or resource I can review? And how long can this be done before they become indistinguishable? Thanks much!