Author
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Guthrie, Howard |
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Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 6/15/2004 Publication Date: 4/5/2005 Citation: Guthrie, H.D. 2005. The follicular phase in pigs: follicle populations, circulating hormones, follicle factors and oocytes. Journal of Animal Science. 83(E Suppl.):E79-E89. Interpretive Summary: The purpose of the follicle preovulatory maturation is provide an environment to ensure delivery of a subpopulation of developmentally competent oocytes and capacitated sperm to the site of fertilization. Follicles selected for ovulation may be at the right place at the right time, a window of opportunity, on d 14-16 of the estrous cycle or in prepuberal gilts following an injection of eCG. In order to improve reproductive efficiency in the future, research should be directed toward obtaining more knowledge about genetic and physiological regulation of ovulatory follicle selection and the effect of follicle development on oocyte developmental competence. The FSH treatment protocols were not found to be useful as assisted reproductive techniques in swine for thee following reasons: 1) the failure to increase ovulation rate, 2) association with a low incidence of estrus compared to eCG treatment, and 3) low oocyte developmental competence compared to eCG. In the future we should keep in mind some of the lessons of the mouse KO models and begin using genomics and proteomics technologies to determine novel gene association and expression patterns controlling the selection of ovulatory follicles in swine. Such knowledge will be potentially important in applying reproductive biotechnologies in swine. Technical Abstract: Activation of primordial follicles and their growth to the antral stage of development is continuous process. Once follicles reach the antral stage they grow rapidly to a size of 4-5 mm after which they usually cease growth and cell proliferation, and the granulosa cells undergo apoptosis. The maintenance of a proliferating population of antral follicles is critically dependent on circulating FSH. Natural or experimentally induced increase in circulating FSH levels results in an increase in antral follicles and conversely decreased secretion of FSH is followed by a decrease in the number and in health status of antral follicles. The only time that this pattern is broken is when a small portion of the follicle population is selected for ovulation. The mechanisms that regulate the selection of ovulatory follicles are not well understood. However, the ovulatory cohort appears to shift from FSH- to LH-dependence at the expense of the non-ovulatory follicles as indicated by the following: 1) decreased secretion of FSH, 2) decreased in expression of the FSH receptor, and increased expression of the LH receptor. The selection of ovulatory follicles may be dependent on the interaction of members of the intraovarian IGF system to maintain a high level of IGF-I bioavailability. Gonadotropin treatment with eGC or PG600 triggers selection of ovulatory follicles and while these treatments do not increase litter size they are beneficial for treatment of anestrus and, in conjunction with hCG or GnRH analogues, provide better control of the time of ovulation. The use of porcine FSH has not increased ovulation rate or improved oocyte developmental competence. In order to improve reproductive efficiency in the future, research should be directed toward obtaining more knowledge about genetic and physiological regulation of ovulatory follicle selection and the effect of follicle development on oocyte developmental competence. |
