2. Universidad Cardenal Herrera-CEU

The objective of this investigation was to determine the ovarian response, fertility, and prolificacy of nulliparous sheep when compared to multiparous sheep after a short-term (7 days) CIDR/eCG treatment which was administered during the non-breeding season. All the multiparous sheep, whereas only 54% of the nulliparous ewes, showed signs of estrus. However, 81.8% of the multiparous sheep and 100% of the nulliparous ewes ovulated. Fertility was also low after short-term progesterone treatments during the anestrous season in maiden sheep (30.8 vs. 72.7% in multiparous ewes). Such results indicate significant differences in the response to CIDR/eCG protocols for induction and synchronization of estrus and ovulation between nulliparous and multiparous sheep during the non-breeding season.

This research aimed to evaluate whether the administration of hCG at the time of removal of a progesterone device may be effective at inducing estrus and ovulations in sheep during the natural seasonal anestrous, by comparing reproductive outputs (induction and duration of estrus, follicle development, ovulation, ovulation rate, and pregnancy rates) in ewes treated with eCG or only saline solution at the time of CIDR removal. Whereas results demonstrated no response in the control non-treated group, the largest rate of narrowly synchronized estrus signs and ovulations occurred in the eCG-group. The administration of hCG was effective at inducing estrus, promote follicular growth and a delayed yet significant ovulation (>84%) on day 10 after CIDR removal; moreover, an increased embryonic implantation rate was also observed. Moreover, if the hCG ewes remain exposed to active males for some days, said strategy could be adopted, aiming to induce pregnancies by natural mating in a short period of time.

The foreseen shortage of eCG for estrus synchronization in sheep makes necessary the development of alternative protocols. The aim of the present work was to evaluate the reproductive response of sheep in breeding season to the administration of GnRH using propylene-glycol as a cosolvent and the subcutaneous route for slowing and extending the release of GnRH, as well as the most adequate timing for such administration. In the present study, protocols based on a short-term CIDR treatment and a single subcutaneous dose of GnRH in propylene-glycol at 36 h after CIDR removal induced a similar ovarian response to protocols based on administration of eCG at CIDR removal or intramuscular GnRH in distilled water at 56 h after. In such protocol, 80% of the animals developed estrus in a narrow timing (75% between 36 and 48 h after CIDR removal), and all of them also ovulated in a narrow window (87.5% between 72 and 76 h after CIDR removal, with 62.5% between 72 and 76 h) and showed a similar ovulation rate and plasma progesterone concentrations at the induced estrous cycle. Hence, administration of GnRH in propylene-glycol may constitute an alternative to traditional protocols based on the administration of eCG.

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 o er a time- and cost-e cient protocol for inducing follicular turnover and synchronizing a new follicular wave at any stage of the estrous cycle.