Location: Range and Livestock ResearchTitle: Follicular Determinants of Pregnancy Establishment and Maintenance Author
Submitted to: Cell and Tissue Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/23/2012
Publication Date: 3/18/2012
Publication URL: http://handle.nal.usda.gov/10113/59388
Citation: Pohler, K.G., Geary, T.W., Atkins, J.A., Perry, G.A., Jinks, E.M., Smith, M.F. 2012. Follicular Determinants of Pregnancy Establishment and Maintenance. Cell and Tissue Research. 349:649–664. Interpretive Summary: Many factors affect pregnancy success in beef cattle. Among those factors are the environment in which the egg develops and the effects of hormones produced by the ovulating follicle on other tissues. Control of ovarian development and ovulation are common with assisted reproduction in both cattle and humans. Final maturation of the egg and ovulating follicle are required for pregnancy. Specific hormones must also be produced before and after ovulation to aid in pregnancy establishment. The fertility of the egg requires complete maturation before it is released. Learning more about the factors affecting maturity of the egg will improve success with assisted reproduction in all species. This review discusses the many factors affecting pregnancy success with an emphasis on cattle.
Technical Abstract: Synchronization of dominant follicle development and control of ovulation/oocyte retrieval are commonly used assisted reproductive technologies in both cattle and humans. The final maturation of the dominant follicle is intimately tied to the final maturation of the oocyte, preovulatory secretion of estradiol, preparation of follicular cells for luteinization, postovulatory secretion of progesterone, and endocrine control of the oviductal and uterine environment for gamete and embryo development. The physiological maturity of a dominant/ovulatory follicle can affect the establishment and maintenance of pregnancy. Premature induction of the ovulatory process can reduce pregnancy rates and increase late embryonic/fetal mortality in cattle, which is likely mediated through inadequate oocyte competence and a compromised maternal environment. Oocyte competence increases with follicular maturity and is dependent upon acquisition of a complete complement of mRNA transcripts and establishment of the appropriate epigenetic marking of the oocyte genome before the preovulatory gonadotropin surge. Preovulatory secretion of estradiol is a reflection of follicular maturity and affects the oocyte, follicular cells, oviduct, and uterus. The corpus luteum is a continuation of follicular maturation and rate of progesterone secretion following ovulation is linked to fertility. Advancements in our understanding of how the follicular microenvironment affects pregnancy establishment and maintenance will improve the efficiency of assisted reproductive technologies in all species. The purpose of this review is to discuss how follicular microenvironment, oocyte competence, preovulatory secretion of estradiol, and postovulatory secretion of progesterone can affect pregnancy establishment and embryo/fetal survival, with an emphasis on cattle.