OT, but after reading all this I watched Super Size Me 2. I don’t have chickens, I keep quail, so maybe this is a dumb question, how did Murray Mcmurray hatchery gender those day old, seemingly identical all white (yellow) chicks by sight?
They are vent-sexed by experts who can see the small differences between male and female hatchlings.
IIRC, vent sexing can only be done on VERY young chicks.