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Journal of Biological Sciences

Year: 2006 | Volume: 6 | Issue: 2 | Page No.: 375-381
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Authors

Manee Archawaranon

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Research Article

Seasonal Changes in Gonadotropins, Prolactin and Sex Steroid Hormones in Captive Hill Mynah Gracula religiosa

Manee Archawaranon
In the present study seasonal changes of gonadotropins, prolactin and sex steroid hormones in captive Hill Mynah were measured from October 1995 to September 1996. During the breeding season, these hormone levels were higher than during the non-breeding one. Plasma levels of FSH in males and females rose in December, prior to the onset of breeding and remained elevated throughout the breeding season except in May. LH, testosterone and estradiol in both sexes were elevated in January, the onset of breeding. The maximum levels of these hormones were coincident with development of the gonads, secondary sex characters, territorial aggression and sexual behavior. Plasma testosterone and estradiol titers in males and females respectively were evidently bimodal with peaks in January and April which corresponded to the norm of two clutches per breeding season of this species. Progesterone levels in females surged in March, April and May which was the period of egg laying and incubation. Circulating prolactin in females was high during the parental phase of the breeding cycle in April and June. In addition, social cues such as sexual partner and external stimuli such as eggs or nestlings influenced the reproductive endocrinology.
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