Physiological basis for anovulation in high-producing dairy cattle

Abstract

The objective of this research proposal is to identify risk factors and factors that influence establishment and maintenance of pregnancy in anovular dairy cows. Six thousand dairy cows, primiparous and multiparous, lactating, will be synchronized with Presynch-Ovsynch protocol. Ovaries will be scanned by ultrasonographic examinations at the first and second PGF treatments of Presynch protocol, and again on the day of the first GnRH of the Ovsynch-56 protocol. These three evaluations will be used to determine the occurrence of ovulation. Cases will be defined based on the absence of a corpus luteum in all three examinations. Thus, cows will be blocked according to cyclic status and parity, and randomly assigned to one of two treatments: Timed AI (n = 1,500), cows will be received AI 16 h after the last GnRH; or, Timed ET (n = 1,500), 7 days after the last GnRH, cows will receive embryo. Embryos used on the experiment will be produced by superovulation. Blood will be sampled at the second PGF treatment of Presynch and at the first GnRH of Ovsynch protocol, for analysis of estradiol-17b, and at the first GnRH and at the first PGF treatment of Ovsynch protocol, for analysis of progesterone. Interferon stimulated genes expression and quantity of pregnancy-specific protein B will be analyzed on 20 (d 19) and 27 (d 26) days after the last GnRH (d -1), respectively. Pregnancy will be diagnosed on d 33 and d 60 of gestation, and morphometric on d 40 by ultrasonography. Based in information of transition period and of records diseases of cows will find risk factors for anovular condition. The goal is to improve dairy cattle fertility via identification of physiological mechanisms that generate the anovular condition, and development of methods to improve reproductive efficiency of dairy cattle, particularly anovular cows.