Use of GnRH for Synchronization of the Follicular Wave in Assisted Reproductive Technologies in Sheep: A Preliminary Study

Abstract

The present study aimed to set up a short-term protocol for synchronization of follicular wave emergence in sheep, concomitant with estrus synchronization, which would improve ovarian response in assisted reproductive technologies. Administration of a single GnRH dose, concomitant with the insertion of a progesterone-loaded CIDR device, caused regression of gonadotrophin-dependent follicles ≥4 mm in all the GnRH-treated sheep and in around 80% of the controls treated only with CIDR (p < 0.05). Similar percentages of ewes lost all follicles (around 70%) or only the largest one (around 30%) in both groups. Hence, 54.1% and 70% of the sheep lost all large follicles and initiated a new follicular wave in the control and GnRH groups, respectively (p < 0.05). The remaining sheep showed follicles that were still not dependent of luteinizing hormone (LH). So, in fact, all the sheep had non-dominant follicles after treatment. In conclusion, a treatment including GnRH at CIDR insertion would offer a time- and cost-efficient protocol for inducing follicular turnover and synchronizing a new follicular wave at any stage of the estrous cycle.

The Effects of Model IVS 2 MAP Progesterone, eCG, GnRH, and PGf2? on Pregnancy of Tail Fat Ewes Strain Sapudi Islands Subjected to A Short-term Synchronization of Estrus

“…Here we dare ourselves that GnRH is less efficient if it turns out that T1 compared to T2 seems to be no significant difference. Another reason that hormones stimulate the release of gonadotropins (GnRH) is a key neuro-peptide that controls the reproductive function of vertebrates, especially in ewe expected to experience spontaneous ovulation, ovarian steroids released by mature ovarian follicles controlling pulsatile patterns of GnRH release from the hypothalamus, in turn, stimulates the preovulatory secretions of the luteinizing hormone (LH) by the anterior pituitary gland 17 .…”

Comparison of HCG and GNRH for Synchronization of the Follicular Wave in Saanen Goats During the Breeding Season

“…This could also be a reason why most of the studies have focused on the manipulation of the first wave, which emerges on the ovulation day of the previous cycle, as it is very difficult to predict when other waves would emerge (6,8). Therefore, our study, as in researchers' studies, has been designed to regress large follicles on the ovaries with the insertion of intravaginal devices containing progesterone or its analogues, thus creating a new follicle wave after the withdrawal of intravaginal devices (Day 0 Protocol) (8,20). Also, it has been reported that a new wave of follicles does not emerge unless the large follicles on the ovaries regress (5,8,21).…”

“…Also, it has been reported that a new wave of follicles does not emerge unless the large follicles on the ovaries regress (5,8,21). In a previous study, Año-Perello et al (20) reported that 81.1% (30/37) of large follicles regressed 24 h after insertion of a controlled internal drug releasing device (CIDR) in Segureña meat ewes, and plasma E2 concentrations decreased significantly between days 0 and 1. Despite using the same synchronization protocol in our study, no change in serum E2 concentrations was observed between days 0 and 1 in the control group.…”

Pharmacokinetics of letrozole and effects of its increasing doses on gonadotropins in ewes during the breeding season

“…However, commonly used methods are estrous‐focused methods, and follicular development is less prominent. In applications such as fixed‐time insemination or MOET, follicular development‐focused methods are used (Año‐Perello et al., 2020). In these methods, it is essential to know the number of follicles developed, the certain time when follicular waves commence or the time of ovulation.…”