|PERRY, BRANDI - South Dakota State University|
|SCHIEFELBEIN, AMANDA - South Dakota State University|
|Cushman, Robert - Bob|
|PERRY, GEORGE - South Dakota State University|
Submitted to: Animal Reproduction Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/9/2016
Publication Date: N/A
Interpretive Summary: Identifying when to breed cows for maximum fertility is labor intensive and difficult. One approach to reducing this labor requirement is by artificially controlling the time to breed cows using synchronization of ovulation; however, current methods do not result in fertility equal to that obtained with natural breeding. Previous research indicated that the amount of estradiol (a reproductive hormone) produced in response to a typical hormone treatment designed to control the time of ovulation had an influence on subsequent fertility. One possibility is that differences in estradiol caused differences in the function of the cow’s uterus, where the fetus develops during pregnancy. To test this idea, samples of blood and uterine tissue were collected from cows producing high or low estradiol in response to hormonal treatment to control the time of ovulation, and these samples were measured for fertility-related factors of uterine origin. Results indicated that these fertility-related factors were greater in the cows producing more estradiol compared to those producing less estradiol. These results suggest that reduction in uterine function caused by reduced estradiol production after hormone treatment to control the time of mating may contribute to the poor fertility that results from these hormonal programs. This research may identify ways to improve fertility after hormonal control of the time of ovulation, which would reduce labor and improve subsequent pregnancy rates in cattle.
Technical Abstract: Cows that did not exhibit standing estrus around the time of gonadotropin-releasing hormone (GnRH)-induced ovulation had decreased pregnancy success compared to cows that exhibited estrus. Therefore, the objective of the present experiment was to characterize changes in expression of uterine milk protein precursor, inhibin ßA, proenkephalin-A, Period 1, oxytocin receptor, progesterone receptor, and estradiol receptor a and ß between cows with high (highE2) and low (lowE2) concentrations of estradiol at time of GnRH-induced ovulation (Day 0). Beef cows were treated with 100 µg GnRH on Day -9, 25 mg prostaglandin F2a on Day -2, and 100 µg GnRH on Day 0. Uterine horn biopsies were collected on Day 0, 5, 10, or 16 and blood samples were collected on Days 0, 5, 10, and 16. Total cellular RNA was extracted and relative mRNA levels were determined by real-time RT-PCR and corrected for GAPDH. Concentrations of estradiol on Day 0 did not influence expression of progesterone receptor or ERß. Increased concentrations of estradiol on Day 0 increased expression of oxytocin receptor, and increased expression of ERa from Days 0 to 5 of the estrous cycle. Furthermore, cows with increased concentrations of estradiol on Day 0 had increase expression of Period 1, inhibin ßA, and uterine milk protein precursor, and tended to increase expression of proenkephalin-A on Day 10. In summary, preovulatory concentrations of estradiol change expression of some uterine proteins and steroid receptors during the subsequent estrous cycle. Reduced fertility among cows with decreased concentrations of estradiol prior to GnRH-induced ovulation may be associated with effects of changes in uterine gene expression on uterine environment.