Maternal transfer of estradiol to egg yolks alters sexual differentiation of avian offspring

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Abstract
Three experiments were conducted to determine whether avian egg yolks contain the sex steroid 17β‐estradiol and whether experimentally produced elevations in maternal estradiol alter yolk estradiol and influence sexual differentiation of the offspring. The yolks of eggs laid by Japanese quail (Coturnix japonica) were found to contain significant amounts of estradiol comparable to those in the maternal circulation. Treatment of laying females with estradiol benzoate (EB) resulted in elevated yolk estradiol and a permanent morphological alteration of female off‐spring in the form of an increased incidence of right oviducts in adulthood. Such maternal transfer of a sex steroid to the egg yolk constitute a potentially significant source of maternal influence over embryonic development and adult phenotype in oviparous species.