The present invention relates to a method for promoting production of female embryos in fertilized eggs, comprising steps of: incubating said eggs; generating at least one type of energy with a predetermined energy profile; and simultaneously generating a pre-determined profile of a non-energy parameter by means of an energy generation device, applying both energy profile and the non-energy parameter to the eggs; and, collecting the eggs; wherein said method is non-toxic to the embryos, the application of both the energy profile and the non-energy parameter increases the fraction of females in the hatched chicks.