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.
Highlights
Multiple ovulation and embryo transfer (MOET) technologies are applied in sheep in order to increase the progeny from selected ewes
It is likely that the suppression of FSH release caused by E2 is lower in cyclic ewes, which would require larger doses, such as those used in this experiment, to cause atresia of the largest follicle and emergence of a new follicular wave
The results of our study showed that on the day expected for follicular emergence, i.e., day 3 following the administration of 0.5 mg of E-17β, the number of small follicles was similar to that of the control group, which were at random phase follicular growth
Summary
Multiple ovulation and embryo transfer (MOET) technologies are applied in sheep in order to increase the progeny from selected ewes. The superovulation protocol typically entails 14 d of progesterone administration, with FSH treatment beginning approximately 3 d before the removal of the progesterone-releasing device (Cognie et al, 2003; Lagares et al, 2021), i.e., at random stages of follicular wave development. An important limiting factor still affecting the success of MOET programs is the variability of the ovarian response and embryo yield (reviewed by Menchaca et al, 2010 and Bartlewski et al, 2016). This variation is caused by extrinsic and intrinsic factors such as source and purity of hormones, administration protocols, breed, age, nutritional and reproductive status (González-Bulnes et al, 2004). Differences in follicular wave status at the beginning of ovarian superstimulation treatments
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