Embryo transport through the mare’s oviduct depends upon cleavage and is independent of the ipsilateral corpus luteum.

The research conducted experiments on mares to understand the factors influencing embryo transport through the oviduct. It was discovered that ovum cleavage significantly impacts this process, while the presence of an ipsilateral corpus luteum doesn’t affect it.

Plain Language Overview

The study conducted two experiments on 14 mares to determine what affects the transport of embryos through the mare’s oviduct. It was determined that the splitting of the ovum, or cleavage, plays a critical role, while the presence of a corpus luteum on the same side does not.

Experiment 1

• In the first experiment, a group of mares were inseminated with semen treated with TEPA, a compound known in other species to halt ovum cleavage at the 2-4 cell stage.
• The mares’ oviducts and/or uterus were flushed after ovulation; for six mares this was done 7-10 days after ovulation (Group A) and for five mares this was done 2-6 days after (Group B).
• Fresh eggs were found in oviduct flushes of mares from both groups, most of which appeared to have undergone cleavage, though none had developed beyond 16 cells.
• Most eggs contained sperm and showed evidence of fertilization under ultrastructural examination.
• However, Group A mares retained fertilized eggs in the oviduct beyond the normal time for them to enter the uterus (6 days), indicating that development beyond the 2- to 4-cell stage is essential for normal transport.

Experiment 2

• In the second experiment, attempts were made to recover an embryo within 4 days of ovulation and transfer it to the contralateral oviduct.
• A single pregnancy was achieved, indicating that a unilateral interaction with the corpus luteum is not necessary for embryo transport to the uterus.

Conclusion

• The research suggests that embryo transport in mares highly depends on the cleavage of the ovum. In contrast, the presence of a corpus luteum on the same side as the ovary that produced the oocyte does not have a significant impact on embryo transport.