I had read this article from a state research labs magazine regarding producing hens verses roos in which is done through some sorts for special artifical lighting, simular to ott lights for birds and this is accomplished by keeping the hens under them for so many day time hours of their life before the eggs are laid. Does not make a lot of sence to me either however, I'm going to look around for this vets book that I have with hopes to locate this article again. Never can tell what secrets are out there, so many it's not funny for us sense we look stupid compared to researchers! If we all knew about it most breeds of roosters would nearly go extinct since most want more hens than roos, from my experiences anyway.