Embryonic development after intra-follicular transfer of horse oocytes.

This study describes a technique where immature horse oocytes (eggs before maturation) were obtained from slaughterhouses, transferred into the pre-ovulation follicle of a mare in vivo (inside the body), leading to their maturation, ovulation, fertilization, and eventually, embryonic development.

Methods

• The research involved the collection of immature horse oocytes from slaughterhouse specimens. This action was carried out on mares standing in a tranquil state, and the extraction focused on those follicles which were greater than 3mm in size.
• The researchers classified these oocytes as either immature, maturing, expanded or denuded.
• The pre-ovulatory follicle, a female reproductive structure which releases a mature oocyte, was carefully grasped through the rectum. A trochar and cannula, surgical instruments, were introduced through the abdominal wall, towards the flank area which is on the same side as the grasped ovary.
• A needle was then introduced through the cannula in order to puncture the outer wall of the follicle, while the position of the ovary was continuously adjusted per rectum. The oocyte transfer was performed at this point.
• The mares were inseminated a day after the procedure. A total of twenty such oocyte transfers were performed.

Results

• Out of the twenty transfers, there was one mare from which 15 immature oocytes were transferred to the pre-ovulatory follicle. 24 hours later, 12 oocytes with expanded cumuli were recovered from the follicle. Expanded cumuli refers to a state where the cluster of cells surrounding and nourishing the oocyte has properly expanded, indicating a positive maturation.
• There were three mares where the follicle filled with blood following the oocyte transfer, and they did not ovulate.
• Out of the twenty, sixteen mares ovulated post the oocyte transfer.
• One mare was sacrificed three days after ovulation and the flush from the removed oviduct yielded one embryo, two ovulated oocytes, and three degenerating oocytes.
• In the remaining fifteen ovulating mares, uterine flush for embryo recovery was performed between 7 to 11 days following ovulation. The rest of the mares flushed, and embryos were recovered in seven out of the fifteen flushes.
• Interestingly, in four of the cases, the number of embryos recovered exceeded the number of ovulations observed in the mare (2, 3, 4, and 7 embryos respectively).

Overall, the research presents a technique of transferring immature horse oocytes to mares that can lead to successful maturation, ovulation, fertilization, and eventually embryonic development.