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United States Department of Agriculture

Agricultural Research Service

Title: Relationship Between Follicle Size at Insemination and Pregancy Success in Beef Cattle

Authors
item Perry, George - U OF MISSOURI
item Smith, Michael - U OF MISSOURI
item Lucy, Matthew - U OF MISSOURI
item Green, Jonathan - U OF MISSOURI
item Parks, Tina - U OF MISSOURI
item Macneil, Michael
item ROBERTS, ANDREW
item GEARY, THOMAS

Submitted to: Proceedings of the National Academy of Sciences
Publication Type: Proceedings
Publication Acceptance Date: November 1, 2005
Publication Date: April 5, 2005
Citation: Perry, G.A., Smith, M.F., Lucy, M.C., Green, J.A., Parks, T.E., Macneil, M.D., Roberts, A.J., Geary, T.W. 2005. Relationship between follicle size at insemination and pregancy success in beef cattle. Proceedings of the National Academy of Sciences v. 102. no. 14. 5268-5273.

Interpretive Summary: Administration of gonadotropin-releasing hormone (GnRH) induces a surge of luteinizing hormone and ovulation in a variety of species, including humans. GnRH-induced ovulation of follicles '11 mm resulted in decreased pregnancy rates and increased late embryonic mortality. This observation is particularly important due to the extensive use of GnRH in many synchronization regimens. The decrease in fertility was associated with decreased circulating concentrations of estradiol on the day of insemination, a lower rate of increase in progesterone following insemination, and decreased circulating concentrations of progesterone. However, ovulatory follicle size had no apparent effect on fertility when ovulation occurred spontaneously. Thus, follicles undergoing spontaneous ovulation do so at a wide range of sizes when they are physiologically mature. Therefore, administration of GnRH to induce ovulation likely initiates a preovulatory gonadotropin surge before a dominant follicle has attained physiological maturity, and GnRH-induced ovulation of follicles that are physiologically immature has a negative impact on pregnancy rates and late embryonic survival. These observations in cattle may have implications to assisted reproductive procedures in the human.

Technical Abstract: Our objectives were to determine the effect of follicle size at the time of ovulation on corpus luteum function and establishment and maintenance of pregnancy in cows in which ovulation was either spontaneous or induced with GnRH. Ovulation was synchronized with an injection of GnRH followed 7 d later with an injection of PGF and 2 d later with a second injection of GnRH in two populations of cows. GnRH-induced ovulation of follicles ' 11 mm resulted in decreased pregnancy rates and increased late embryonic mortality in both herds of cows. This decrease in fertility was associated with lower circulating concentrations of estradiol on the day of insemination (P < 0.01), a decreased rate of increase in progesterone following insemination (P < 0.01), and, ultimately, decreased circulating concentrations of progesterone (P < 0.05). In contrast, ovulatory follicle size had no effect on pregnancy rate (P > 0.40) or subsequent progesterone production (P > 0.53) when ovulation occurred spontaneously following estrus. Follicles undergoing spontaneous ovulation do so at a wide range of sizes when they are physiologically mature. Administration of GnRH to induce ovulation likely initiates a preovulatory gonadotropin surge before a dominant follicle has attained physiological maturity. GnRH-induced ovulation of follicles that are physiologically immature has a negative impact on pregnancy rates and late embryonic survival.

Last Modified: 7/28/2014
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