Oxytocin does not contribute to the effects of cervical dilation on progesterone secretion and embryonic development in mares.

The research article investigates the role of oxytocin in progesterone secretion and embryonic development in mares. The study concluded that the administration of oxytocin or its long-acting analogue carbetocin did not influence progesterone secretion and embryonic growth, challenging the suspected negative impacts of cervical dilation on these processes.

Research Design and Methods

• The study subjected mares to four treatments seven days after ovulation in a crossover design, with endogenous stimulation of oxytocin release under comparison with oxytocin and its long-acting analogue carbetocin administration.
• The treatments were control, oxytocin administration, carbetocin administration, and cervical dilation.
• Pregnancy was then assessed on Day 13 in all the treated groups.

Findings

• All eight mares in the control, oxytocin, and carbetocin groups were pregnant, while only six out of eight in the dilation group were pregnant.
• Among the dilation group, two instances stood out: one mare developed uterine fluid accumulation and uterine edema from Day 6 to 13 and exhibited early embryonic death by Day 11. Another mare, which did not conceive, developed a similar condition from Day 10 to 14.
• The growth rate of conceptuses (embryonic development state) showed no significant difference among all treatment groups. However, individual growth rates varied widely. The mean diameters of conceptuses on Day 13 also did not show a statistically significant difference across all groups.
• The secretion of progesterone was not influenced by any treatments.

Administration of Oxytocin and Carbetocin

• Oxytocin and carbetocin administration both resulted in similar maximum plasma concentrations of oxytocin, but the timing and duration of peak concentrations differed.
• Peak concentrations after the intramuscular application of carbetocin were obtained nearly 20 minutes later compared to the intravenous administration of oxytocin. The peak duration after injection of the long-acting oxytocin analogue was over three times longer than after administering the native oxytocin.

Conclusion

• The study concluded that oxytocin or carbetocin administration seven days after ovulation did not affect progesterone secretion, pregnancy rates, and embryonic growth.
• Two distinct effects of cervical dilation were observed: in a majority of mares, dilation up to a certain diameter had no negative consequences on progesterone secretion and pregnancy outcomes. However, it triggered uterine inflammation and luteolysis in two mares, also causing early embryonic death in one.
• Contrary to the past belief, manipulating the cervix did not negatively impact the success rates of transcervical transfer of embryos in mares.