Synchronization of follicular wave emergence does not improve embryonic yield in superovulated ewes

Abstract

The present study aimed to investigate the effects of a combination of progesterone with different doses of E-17β on following end points: (1) ovarian follicular dynamics and emergence of a new follicular wave, and (2) superovulatory response and embryo yield. In Experiment 1, 28 ewes were randomly divided into four groups (n = 7) to receive either 2.0 mg, 1.0 mg, 0.5 mg or none E-17β one day after insertion of a progesterone device. The different doses of estradiol similarly delayed the moment of follicular emergence (overall mean = 3.1 ± 1.0 days vs. control group = 0.86 ± 1.0 days; P < 0.01), but the emergence of the new wave showed greater synchronization with the 0.5 mg dosage of E-17β. In Experiment 2, sixty-two donor ewes received an internal progesterone release device (day -1) for 7 d and 1 d after the insertion of this device (day 0) were allocated randomly to receive 0.5 mg of E-17β or only the vehicle (control group). Superstimulation was initiated on day 3 with the administration of 133 mg of pFSH in eight decreasing doses. Contrary to expectations, the protocol with the administration of 0.5 mg E-17β did not improve the percentage of donors with > 2 CL, the number of CL and the production of embryos (P > 0.05). It was concluded that the combination of progesterone and 0.5 mg E-17β was more efficient in synchronizing the emergence of the new follicular wave, however this approach seems to be unnecessary in ewe's superovulation programs.

Keywords: embryos; estradiol-17β; follicle; recruitment; superovulation.

Figure 1. Treatment schedule for cyclic hair sheep receiving a CIDR (day -1) for 7 d. Donor’s ewes were randomly separated into two experimental groups, with one group receiving one dose of E-17β at 24 h after CIDR insertion. All ewes received two injections of FSH i.m. per day over 4 d starting on day 3. Transrectal ultrasonography was performed on day 3 (n = 12). All ewes were inseminated 36 and 48 h after CIDR withdrawal and the previously used CIDR was reinserted 1 d after the second insemination (day 9). Ova/embryos were surgically collected 5 d after the second insemination (day 13).

Figure 2. Follicular characteristics evaluated by ultrasonography on day 3 in ewes of the E-17β group (gray bars) and control group (black bars). (A) number of smaller follicles (1 mm ≤ SF ≤ 4 mm; mean ± SD); (B) median diameter of the largest follicle (mean ± SD); (C) donor ewes with medium/large follicles (MF/LF ≥ 4 mm; percentage). Within sets of data, bars with different lower cases letters show statistical differences (P < 0.01).