Effects of GnRH and hCG administration during early luteal phase on estrous cycle length, expression of estrus and fertility in lactating dairy cows

Gonadotropin-Releasing Hormone (GnRH) and Its Agonists in Bovine Reproduction II: Diverse Applications during Insemination, Post-Insemination, Pregnancy, and Postpartum Periods

The administration of GnRH and its agonists benefits various aspects of bovine reproductive programs, encompassing physiological stages such as estrous synchronization, post-insemination, pregnancy, and the postpartum period. The positive impact of GnRH administration in overcoming challenges like repeat breeder cows, early embryonic loss prevention, and the management of cystic ovarian disease (COD) is thoroughly surveyed. Furthermore, this review focuses on the significance of GnRH administration during the postpartum period, its role in ovulation induction, and how it enhances the productivity of embryo transfer (ET) programs. An emerging feature of this field is introduced, focusing on nano-drug delivery systems for GnRH agonists, and the potential benefits that may arise from such advancements are highlighted. While this review offers valuable insights into various applications of GnRH in bovine reproduction, it emphasizes the crucial need for further research and development in this field to advance reproductive efficiency and health management in dairy cattle.

Impact of Accessory Corpus Luteum Induced by Gonadotropin-Releasing Hormone or Human Chorionic Gonadotropin on Pregnancy Rates of Dairy Cattle following Embryo Transfer: A META-Analysis

The circulation of progesterone (P4) concentrations of recipients has positive correlations with embryo survival and pregnancy success of embryo transfer (ET) in dairy cows. One strategy to improve P4 concentration is the administration of gonadotropin-releasing hormone (GnRH) or human chorionic gonadotropin (hCG), thereby inducing the formation of accessory corpus luteum (CL). This study aimed at determining the efficacy of GnRH or hCG treatment regarding embryo transfer (ET) and providing a better clinical veterinary practice guidance. A meta-analysis was conducted on the data from 2048 treated recipient cows and 1546 untreated cows. By inducing the formation of accessory CL with GnRH (100 µg), GnRH analogue Buserelin (8-10 µg), or hCG (≥1500 IU) 5-11 days after synchronized ovulation, hCG alone achieved an improvement (RR = 1.39, p < 0.05), while GnRH and GnRH analogue did not result in significant changes (RR = 1.04, p = 0.26). Treatment with GnRH or hCG 5-7 days after synchronized ovulation was associated with increased chances of pregnancy compared with later treatment (11-14 days). Owing to the treatment, the pregnancy rate of cows with very poor fertility (<40%) was improved, while that of cows with good fertility (≥40%) was not affected. Treatment with GnRH or hCG greatly improved pregnancy rates of parous lactating cows (RR = 1.32, p < 0.05) compared with heifers (RR = 1.02, p > 0.05). Additionally, as indicated by pregnancy loss analysis, the treatment had no benefit on late embryo/early fetus survival at days 28-81. In conclusion, the induction of accessory CL with GnRH or hCG may benefit fertility and have important implications for the management of reproductive performance in the dairy industry.

Graduate Student Literature Review: Effects of human chorionic gonadotropin on follicular and luteal dynamics and fertility in cattle

Circulating progesterone concentrations during the growth of the ovulatory follicle and early embryo development have been positively associated with embryo quality and survival and pregnancy success. As a potent luteotropic agent with LH-like activity, human chorionic gonadotropin (hCG) has been tested in different studies to improve pregnancy outcomes by increasing circulating progesterone concentrations during the growth of the ovulatory follicle or early embryonic development. Nevertheless, hCG has produced inconsistent, contradictory, and intriguing results. Furthermore, recent research indicates that hCG, when used before artificial insemination, may affect physiological events necessary for the ovulation of a viable oocyte. In addition, the use of hCG-inducing accessory corpus luteum during the estrous cycle seems to disturb luteolysis and follicle and luteal dynamics during the estrous cycle. This literature review discusses past and current research exploring the effects of hCG on the estrous cycle characteristics and pregnancy per artificial insemination and embryo transfer.

Accessory corpus luteum induced by human chorionic gonadotropin on day 7 or days 7 and 13 of the estrous cycle affected follicular and luteal dynamics and luteolysis in lactating Holstein cows

Our objective was to determine the effect of inducing an accessory corpus luteum (CL) with human chorionic gonadotropin (hCG; 3,300 IU) on d 7 (hCG7) or 2 accessory CL with hCG on d 7 and 13 (hCG7+13) of the estrous cycle in noninseminated lactating Holstein cows. Cows (n = 86) between 39 and 64 DIM were pretreated with an Ovsynch + CIDR protocol, and only synchronized cows were used (n = 64). The day of the last GnRH of Ovsynch was considered d 0 of the estrous cycle. Follicular and luteal dynamics of cows were evaluated daily during an entire estrous cycle by ovarian ultrasonography. Blood samples were collected daily to measure serum concentration of progesterone (P4). Cows were randomly assigned to CON (n = 22, no treatment), hCG7 (n = 20), or hCG7+13 (n = 22) treatments. Two cows from hCG7+13 failed to ovulate after hCG and were removed from the analyses post-hCG treatment. The first day of luteolysis was considered the day that P4 declined to more than 2 SD of the mean for the 4 consecutive P4 concentrations with the greatest mean in late diestrus for each individual cow. The P4 cut-off for complete luteolysis was <1.0 ng/mL. Mean P4 on d 7 (3.23 ± 0.16 ng/mL) did not differ among treatments. Cows treated with hCG had greater total luteal and original CL volume and serum P4 during diestrus than CON. Cows treated with hCG7+13 had greater serum P4 after d 13 of the cycle than hCG7. Cycles were classified as having atypical cycles if the dominant follicle or future dominant follicle at the time of luteolysis did not ovulate (delayed ovulation; CON, n = 2; hCG7, n = 4; hCG7+13, n = 3), had a short cycle (CON, n = 1), delayed (CON, n = 2) or incomplete luteolysis (CON, n = 1; hCG7, n = 4; hCG7+13, n = 5). The remainder of cycles with normal complete luteolysis followed by ovulation were considered to be typical. Based on blood perfusion, the CON cow with incomplete luteolysis had 2 original CL remaining functional after first onset of luteolysis. The rest of the cows with incomplete luteolysis (9/10) had one or more CL regressing and at least one remaining functional after first onset of luteolysis. No specific pattern for CL side (ipsilateral vs. contralateral to a CL with complete regression) was observed for nonregressed CL. Cows with incomplete luteolysis had a second onset of luteolysis to undergo complete functional luteolysis. The proportion of cows with typical cycle was 73% (16/22) for CON, 60% (12/20) for hCG7, and 55% (11/20) for hCG7+13. Cows with typical cycles treated with hCG (hCG7 and hCG7+13) had a later onset of luteolysis, prolonged time to undergo complete luteolysis, and greater proportion of cows with 3 follicular waves than CON, resulting in a longer interovulatory interval for hCG7 and hCG7+13 than CON. In summary, accessory CL induced by hCG during diestrus not only altered follicular and luteal dynamics but also deferred and prolonged the luteolytic process.