Physiological basis for anovulation in high-producing dairy cattle

Abstract

Fertility is critical for improved efficiency of dairy production but continues to be suboptimal in lactating dairy cows despite improvements in reproductive management and development of methods to improve insemination rates. One major problem on dairy herds is the incidence of cows that have not resumed ovulation by the end of the voluntary waiting period, termed anovular cows in this proposal. Incidence of anovular cows averages ~24% in high-producing dairy herds. Anovular cows have impaired reproductive performance because of reduced insemination risk in herds breeding to estrus and reductions in pregnancies per AI (P/AI) and increased pregnancy loss. However, a complete understanding of the physiologic and molecular mechanisms that impede high fertility in these populations of cows remains to be defined. The objective of this research proposal is to estimate of the incidence of the anovular condition in dairy herds in Brazil, and to understand the mechanisms involved, to identify risk factors and factors that influence establishment and maintenance of pregnancy in anovular dairy cows. On the experiment 1, 1000 dairy cows will be evaluated and classified as cyclic or anovular. Additionally, when anovular, cows will be classified as no dominant follicle anovular phenotype; small dominant follicle anovular phenotype; large dominant follicle phenotype; or with follicular cysts. On the experiment 2, 6000 dairy cows, primiparous and multiparous, lactating and non-lactating, will be synchronized with Presynch-Ovsynch protocol, (prostaglandin F2± [PGF] - 14 d- PGF - 11 d - GnRH - 7 d - PGF - 1 d - PGF - 32 h - GnRH). 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 CL in all three examinations. Thus, cows will be blocked according to cyclic status and parity, and randomly assigned to one of two treatments: FTAI (n = 1500), cows will be received AI 16 h after the last GnRH; or, FTET (n = 1500), 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. 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, definition of molecular processes associated with reduced fertility in anovular cows, and development of methods to improve reproductive efficiency of dairy cattle, particularly anovular cows. (AU)