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Exogenous hormonal control of gonadotropin release affecting dominant, persistent, and superstimulated ovarian follicle development in cattle
Abstract
The objective of the research described in this dissertation was to provide a better understanding of the relationships between gonadotropins and their influence on ovarian follicle and oocyte development in cattle. In the first study, a single, large dose of progesterone injected within the first 6 days of emergence of a typical dominant ovarian follicle was not sufficient to induce its atresia. In the second study, treatment with a large dose of progesterone required at least 24 hours to decrease the amount of luteinizing hormone (LH) receptor mRNA and induce atresia of a persistent ovarian follicle. Therefore, large doses of progesterone induce atresia of persistent dominant follicles, but not typical dominant follicles during the selection and early dominance phases. In the third study, the effects of treatment with an antagonist to gonadotropin-releasing hormone (GnRH) inhibited the magnitude of increase in follicle stimulating hormone (FSH) that regulates waves of ovarian follicular development, but had no effect on basal concentration of FSH. Follicular development was also inhibited, but only when FSH was inhibited. GnRH may, therefore, have a role in regulating the magnitude of FSH release during increases of FSH that precede waves of ovarian follicular development, but may have a limited role in regulating basal secretion of FSH. In the fourth study, lengthening the interval between prostaglandin-F 2α administration and ovulation in heifers treated with gonadotropins to stimulate ovarian follicular development, caused neither a reduction nor an increase in intervals to estrus, the preovulatory LH surge, or ovulation, nor mean numbers of unovulated follicles, corpora lutea, ova, or embryos. The fifth study was designed to evaluate how the lack of LH pulses, the preovulatory LH surge, or both, affects follicle and oocyte development. It was concluded that only basal secretion of LH is required for final maturation of oocytes in heifers treated with gonadotropins to stimulate ovarian follicular development. Furthermore, acquisition of developmental competency subsequent to fertilization in oocytes was enhanced by a preovulatory surge release of LH. The surge release of LH, therefore, had a greater effect on embryonic development than on fertilization rates.
Subject Area
Anatomy & physiology|Animals|Livestock
Recommended Citation
Lindsey, Bradley Rex, "Exogenous hormonal control of gonadotropin release affecting dominant, persistent, and superstimulated ovarian follicle development in cattle" (1999). ETD collection for University of Nebraska-Lincoln. AAI9917847.
https://digitalcommons.unl.edu/dissertations/AAI9917847