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Animal Reproduction and Physiology
Asian-Australasian Journal of Animal Sciences 1994;7(1): 75-81.
DOI: https://doi.org/10.5713/ajas.1994.75    Published online March 1, 1994.
Ontogenetic aspects of steroidogenesis by gonads of ducks and its role in sex differenciation
O. Doi, A. Iwasawa, T. Nakamura, Y. Tanabe
To elucidate the relationship between steroidogenesis and sex differentiation in the duck, plasma, testicular and ovarian testosterone, estradiol-17棺 and progesterone concentration in male and female embryo of day 11 to 27 (just before hatching) of incubation and in 1- to 7-day-old male and female duckling were investigated by radioimmunoassays. Plasma estradiol-17棺 concentration in female embryos declined from very high at days 11 and 15 of incubation and remained at low levels after hatching. Male plasma estradiol-17棺 concentration were always lower than those of the female throughout this period. Plasma testosterone and progesterone concentrations in both sexes were low during the embryonic stage, but then increased to peaks 3 days and 1 day after hatching, respectively. Estradiol-17棺 contents were much higher in the left ovary than the right ovary or testes throughout the experimental period. The estradiol-17棺 content of the left ovary was very high at day 15 of incubation, and decreased gradually thereafter. Both in right ovary and testes, estradiol-17棺 contents were always low. Testosterone and progesterone contents in the left ovary were low from day 11 to 23 of incubation, and reached a peak 1 day after hatching. Progesterone content in the right ovary and testes were low levels over time period examined. Testosterone and progesterone contents were much higher in the left ovary than the right ovary and testes. The present results clearly demonstrate that the capacity of the embryonic left ovary of duck to synthesize estradiol-17棺 and testosterone is much higher than that of the embryonic testis. It is suggested that estrogen secreted from the embryonic ovary earlier than day 15 of incubation has an important role in female sexual differentiation in the duck, and the sex of the avian species is basically male with homozygous sex chromosome (ZZ).
Keywords: Sex Differentiation; Ontogeny; Steroidogenesis; Gonad; Duck
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