Abstract
Simple SummaryThe 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 dose of gonadotrophin-releasing hormone (GnRH), concomitant with the insertion of a progesterone-loaded controlled internal drug release (CIDR) device, caused regression of gonadotrophin-dependent follicles in all test sheep, with 70% of them initiating a new follicular wave and the remaining showing non-dominant follicles.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.
Highlights
In sheep, as in other ruminant species, the use of assisted reproductive technologies like artificial insemination (AI) and multiple ovulation and embryo transfer (MOET) constitute the most effective and efficient strategies to improve the number of offspring from valuable animals and, Animals 2020, 10, 1208; doi:10.3390/ani10071208 www.mdpi.com/journal/animalsAnimals 2020, 10, 1208 to increase genetic gain
The ultrasonographic observation performed on the following day showed that controlled internal drug release (CIDR) insertion caused the regression of large follicles in 81.1% of the sheep in the control group, with all of them showing a significant decrease in plasma estradiol concentrations, from mean values of 4.6 ± 0.7 pg/mL to mean values of 1.8 ± 0.6 pg/mL (p < 0.05)
Our results indicate that the insertion of a progesterone-loaded CIDR device caused the regression of large follicles in around 80% of the treated sheep
Summary
Animals 2020, 10, 1208 to increase genetic gain The success of both reproductive technologies is largely dependent on the interaction between the ovarian status and the hormonal treatments needed for allowing their application (progesterone for inducing and synchronizing estrus occurrence and gonadotrophins for inducing follicular growth and ovulation) [1,2,3]. The objective was to use exogenous progesterone to imitate the role of the corpus luteum in the control of the estrous cycle, avoiding the occurrence of ovulations during progesterone supplementation and allowing them at progesterone removal Such protocols neglected to take into account the follicle—destined to release an oocyte able to result in a pregnancy and to develop in a corpus luteum supporting such a pregnancy.
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