|Northrop, Emmalee - South Dakota State University|
|Rich, Jerica - South Dakota State University|
|Cushman, Robert - Bob|
|Perry, George - South Dakota State University|
Submitted to: Journal of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: 12/21/2017
Publication Date: 2/5/2018
Citation: Northrop, E.J., Rich, J.J., Cushman, R.A., Perry, G.A. 2018. Regulation of preovulatory estradiol and its impacts throughout the bovine estrous cycle [abstract]. Journal of Animal Science. 96(Supplement 2):22-23.
Technical Abstract: Preovulatory estradiol has been reported to play a critical role in follicular cell growth, initiation of estrus, oocyte maturation, sperm transport, uterine environment, and embryo survival. Furthermore, cattle with elevated preovulatory estradiol (HighE2) concentrations prior to fixed time AI had greater conception rates and pregnancy maintenance compared to cattle that did not experience a rise in estradiol (LowE2). However, the mechanisms by which estradiol exerts these effects is not well-characterized. HighE2 animals had faster follicular growth rates and upregulation of the entire steroidogenic pathway compared to LowE2 animals. When LowE2 animals were supplemented with physiological pulses of GnRH, they had similar LH pulse frequency to HighE2 animals and an increase in circulating estradiol. When a physiological dose of GnRH was administered at CIDR removal during a synchronization protocol estrus expression, interval to estrus, and conception rates to AI were improved. Furthermore, relative abundance of GnRH-I and II within bovine antral follicles was increased in follicles with low concentrations of estradiol compared to follicles with elevated estradiol suggesting GnRH-I and II may act as local regulators of estradiol production. Estradiol can also have a direct impact on the uterus, on d 6 post-AI, HighE2 heifers had increased accessory sperm numbers, and produced embryos that were more advanced and had improved quality compared to LowE2 heifers; however, there was no difference in embryo recovery rates. When embryos were transferred to ovariectomized estradiol supplemented cows, cows in the control treatment lost 75% of existing pregnancies, while cows receiving estradiol lost only 35% of existing pregnancies, during the period between maternal recognition of pregnancy and embryo attachment. But following a fixed-time AI protocol, there were no differences in conceptus survival based on recovery rates, IFNT concentrations, and apoptosis of the trophectoderm on d 16 after AI between HighE2 and LowE2 animals. However, glucose transporter expression in the endometrium, and also glucose and protein concentration in ULF was influenced by preovulatory estradiol concentrations and conceptus presence. In conclusion, increased preovulatory concentrations of estradiol are mediated through an upregulation of the steroidogenic pathway, and HighE2 animals had increased sperm transport and improved embryo quality, but not increased embryo survival to maternal recognition of pregnancy. Thus, increased pregnancy success among HighE2 animals must be regulated by differences in conceptus survival between d 16 and d 29 of gestation.