Yeah, I'm pretty sure it was a coincidence. I only let the broodies hatch, and I was about 16 for 23 roosters last year. I'm not quite ready to invest in a centrifuge yet. Those girls will sit on anything, and I have a friend that will take any unwanted roosters off my hands, so I'm just going to keep my fingers crossed this yearwell if you are hatching that many roosters - statistically it may be an anomaly, depends on how many you hatched out of how many eggs-and there is some data out there (but i havent looked into it fully) that a temp drop/spike at a specific time will result in a gender difference AT HATCH. note it wont change the gender of the eggs, just which ones survive to hatching. since this is a sort of holy grail for the industry and not much is spoken of it I suspect the claim is bunk. but since genetic gender is determined by which is the heterozygote, and in chickens that is the female...so it's your girls fault. if you could identify the hen(s) then you could exclude them from the breeding. i had thought recently that my one silkie hen (foundation hen for my flock) was producing more females than males, but when i did the numbers it was only out of 11 chicks i made the assumption and it was only one more female than male so ....if only the male was heterozygote then a centrifuge would work....