Submitted to: Joint Abstracts of the American Dairy Science and Society of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: 11/1/2003
Publication Date: 3/15/2005
Citation: Guthrie, H.D. 2005. The follicular phase in pigs: follicle populations, circulating hormones, follicle factors and oocytes [abstract]. 37th Midwestern Sectional Meeting of the American Society of Animal Science and The American Society of Dairy Science Association. Paper No. 228.
Technical Abstract: Selection of the ovulatory cohort of follicles from a population of similar sized follicles is a critical event in follicular development. During the estrous cycle the number of 3-6 mm follicles ranges from 30 to 45 per gilt between days 7-15. Of this population, 35-50% are atretic and during this period of luteal dominance, even the non-atretic follicles have low levels of steroidogenesis. The maintenance of a proliferating population of 1-2 mm and 3-6 mm follicles is critically dependent on circulating FSH. Natural or experimentally induced reduction in circulating FSH levels or FSH treatment results in a rapid decrease or increase in numbers of 1-6 mm follicles, respectively. 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 by causing a decrease in FSH secretion and by increased expression of the LH receptor and LH binding capacity relative to non-ovulatory follicles. Selection and maintenance of ovulatory follicles are associated with increased production or activity of intraovarian factors such as estradiol, the IGF system, and inhibin/activin peptides. Treatment regimens such as eGC or PG600 are beneficial for treatment of anestrus and, in conjunction with hCG or GnRH analogues, provide better control of the time of ovulation and increased ovulation rate; however litter size has not been increased. The use of various FSH preparations to better control ovulation rate and improve fertility have not been successful. Genetic improvement of ovulation rate and fertility traits has been made through direct and index selection, but genes specifically responsible selection of ovulatory follicles have not been identified. Functional genomics approaches that integrate genetic and physiological aspects of ovulatory follicle selection have the potential improve fertility and provide new basic knowledge of genetic regulation of the physiological mechanisms involved.