Location: Range and Livestock ResearchTitle: Factors affecting preovulatory concentrations of estradiol and its role in establishment and maintenance of pregnancy in suckled beef cows using reciprocal embryo transfer Author
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 5/1/2010
Publication Date: 9/3/2010
Citation: Jinks, E.M., Atkins, J.A., Pohler, K.G., Smith, M.F., Perry, G.A., Macneil, M.D., Geary, T.W. 2010. Factors affecting preovulatory concentrations of estradiol and its role in establishment and maintenance of pregnancy in suckled beef cows using reciprocal embryo transfer. 8th International Ruminant Reproduction Symposium Abstract #118. Interpretive Summary: n/a
Technical Abstract: In postpartum beef cows, GnRH-induced ovulation of small dominant follicles decreased pregnancy rates and increased late embryonic/fetal mortality; however, ovulatory follicle size had no apparent effect on the establishment or maintenance of pregnancy when ovulation occurred spontaneously (Perry et. al 2005). To differentiate between effects of ovulatory follicle size on oocyte quality and uterine environment, a reciprocal embryo transfer study was conducted at Fort Keogh from 2007 to 2009. One objective was to examine the relationship between preovulatory serum concentrations of estradiol in donor and recipient cows and establishment and maintenance of pregnancy. Suckled beef cows (n = 1,166) were administered GnRH1 on d -9, PGF2a on d -2, and GnRH2 on d 0 either with (donor cows; n = 810) or without artificial insemination (recipient cows; n = 354). Single embryos (n = 394) or oocytes (n = 45) were recovered from the donor cows (d 7; ET) and all live embryos were transferred into recipients the same day. Embryos from cows that ovulated a small (< 12.5 mm) or large follicle (= 12.5 mm) were transferred into cows that ovulated either a small or large follicle to remove co-linearity of follicle sizes pre- and post- day 7 of pregnancy. Ovulatory follicle size in both donors and recipients was positively correlated with serum concentration of estradiol at GnRH2 (r = 0.45, P < 0.0001) and estradiol at GnRH2 was greater (P < 0.01) in cows that ovulated in response to GnRH1. Serum concentration of estradiol at GnRH2 was positively correlated with progesterone at ET (r = 0.34, P < 0.0001) and donors with greater estradiol were more likely to yield a fertilized embryo than an unfertilized oocyte (P < 0.0001). There was no effect of donor estradiol at GnRH2 on embryo stage (P = 0.49) or quality (P = 0.14). Using data from the Perry et. al (2005) study, we determined pregnancy rate was significantly decreased when estradiol at GnRH2 was < 8.4 pg/ml. Therefore, we retrospectively divided donor and recipient cows into four groups (low estradiol [< 8.4 pg/ml] or high estradiol [= 8.4 pg/ml]) based on serum concentration of estradiol at GnRH2. Pregnancy rate at d 27 for low-low (n = 78), low-high (n = 80), high-low (n = 91), and high-high (n =101) groups (donor-recipient) was 45a, 65b, 43a, and 61b% respectively (abP <0.02). Estradiol at GnRH2 had no effect on pregnancy maintenance to d 72 in the preceding groups. In summary, serum concentration of estradiol at GnRH2 was positively correlated with ovulatory follicle size, fertilization, and the establishment but not maintenance of pregnancy and its effects were likely mediated through improved uterine environment. Supported by NRI grant 2006-35203-17284 from USDA-CSREES.