Submitted to: Western Section of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: June 1, 2012
Publication Date: July 15, 2012
Citation: Roberts, C.A., Perry, G.A., Minten, M.A., Roberts, A.J., MacNeil, M.D., Geary, T.W. 2012. Effects of preovulatory estradiol concentration on embryo survival and pregnancy establishment in beef cows. Western Section of Animal Science Proceedings. 63:98-102. Interpretive Summary: Estradiol may be important for pregnancy establishment and embryo survival in beef cows. The objective of this study was to examine the effects of estradiol on embryo survival separately from other factors relating to fertility. For this reason, ovaries were removed from 24 cows. They were allowed to recover from surgery, and then given a series of hormonal implants and injections that simulated the luteal phase of the bovine estrous cycle. Three different treatments were applied during the preovulatory period. Cows were randomly assigned to receive estradiol cypionate (ECP) 36 h prior to ovulation, estradiol benzoate (EB) 12 h prior to ovulation, or no supplemental estradiol (CON). Ovulation was simulated by an injection of GnRH. The study found preovulatory estradiol to be critically important for pregnancy establishment.
Technical Abstract: The role of estradiol during the preovulatory period on embryo survival and pregnancy establishment has not been characterized in beef cows. We hypothesized that preovulatory estradiol is important for embryo survival and pregnancy establishment in beef cows. In order to establish the importance of estradiol during the preovulatory period on embryo survival, ovariectomized multiparous cows (n=24) received estradiol cypionate (ECP), estradiol benzoate (EB) or no treatment (CON) to mimic a preovulatory period. Prior to treatment, all cows received a progesterone- releasing device (CIDR) for 7 d, 25 mg injection of prostaglandin-F2a (PGF) at CIDR removal (d -2), and an injection of GnRH (100 µg; d 0) 2 d later to mimic a follicular phase. Utilizing a 3x3 Latin Square design, cows received either ECP 36 h before GnRH injection, EB 12 h before GnRH injection, or no estradiol (CON). Luteal phase progesterone was mimicked with 2x daily increasing progesterone injections from d 3 to 6 and use of CIDRs from d 7 to 29. On d 7 after GnRH injection, each cow received one embryo and a CIDR. Another CIDR was added 24 h following embryo transfer and every 6 d, the older of the two CIDRs was replaced with a new CIDR. Blood was collected every 4 h between d -2 and d 0 for characterization of serum estradiol profiles. Blood was collected on d -2, -1, 0, 3 to 7, 14, and 17 to 29 to characterize progesterone profiles. Serum estradiol profiles were different (P < 0. 001) between treatments. Mean serum progesterone concentrations were decreased (P = 0.05) for EB and ECP treated cows compared to CON. Transrectal ultrasonography on d 29 indicated that 4% of CON, 29% of EB, and 21% of ECP treated cows were pregnant. Expression of interferon stimulated genes ISG15, Mx2, and Oas1 on d 19 indicated 66.0% of CON, 69.3% of EB, and 71.0% of ECP treated cows were pregnant. Thus, 62, 39.7, and 50% of pregnancies in CON, EB, and ECP treated cows, respectively were lost from d 19 to 29. Overall, results indicate greater embryonic survival and pregnancy establishment in cows exposed to estradiol in the preovulatory period.