Morphological evaluation of Day 8 embryos developed during induced aluteal cycles in the mare.

The research study sheds light on how the deprivation of progesterone, typically utilized during induced aluteal cycles in horses, has an effect on the growth and development of embryos. The results show embryos collected during these cycles were of lower quality and smaller in size, suggesting progesterone deprivation adversely influences embryonic development.

Study Design and Objective

• The research objective was to study the impact of progesterone-deprivation in horses on the morphology of embryos in the early developmental stages.
• A newly introduced in vivo model was explored, wherein serial administrations of PGF were used to induce aluteal cycles in horses.
• The hypothesis claimed that horse embryos developing during these cycles would be affected in terms of development. It was anticipated that they would be in an earlier stage at collection, possess a smaller diameter, and have a lesser quality grade compared to embryos from control cycles during diestrus.

Methodology

• Seven horses with a median age of 6.5 years were included in a crossover design process.
• These horses were artificially inseminated and randomly assigned to either the control group or the aluteal cycles group.
• The mares received either saline solution (control group) or PGF (aluteal group), administered twice daily for three days and then once daily for the next two days.
• Blood samples were collected daily during estrus and until the eighth day post-ovulation, the day of embryo collection.
• The mares were continuously monitored until they returned to estrus and were inseminated.
• Switching of mares to the opposite group took place only after a successful embryo collection in the previous cycle.

Outcome

• The absence of a significant rise in progesterone was noticed in the PGF-treated group.
• The mean concentrations of plasma progesterone in this group were significantly lower than in the controls, from ovulation until embryo collection.
• Embryos from aluteal cycles also had a smaller diameter compared to control group embryos.
• Compared to control cycle embryos, the majority of embryos from induced aluteal cycles were in earlier stages of development and of lower quality grade.

Conclusion

• The research concludes that frequent administrations of PGF successfully induce aluteal cycles by preventing a significant increase in plasma progesterone levels.
• This creates a progesterone-deprived environment for developing embryos, which subsequently results in smaller, lesser quality embryos.
• This revelation signifies the detrimental effect of progesterone deprivation on embryo development, shedding light on the core importance of this hormone in embryonic development.