Effect of timing of follicle aspiration on pregnancy rate after oocyte transfer in mares.

This study investigates if the timing of oocyte (egg cell) collection after administering hCG (a hormone that induces ovulation) affects the pregnancy rates in mares. The results indicate that the timing of oocyte collection doesn’t significantly influence pregnancy rates, but endometritis, an inflammation of the uterus lining potentially caused by the medication linked with the oocyte transfer process, might lower pregnancy rates.

Methodology

• Mares with preovulatory follicles larger than 33mm were administered with hCG to induce ovulation.
• The mares were then randomly assigned for the aspiration, or extraction, of the dominant follicles at 24 hours or 35 hours after hCG injection. This process is known as oocyte aspiration.
• Oocytes recovered at 24 hours were cultured for 12 hours before transfer and the ones recovered at 35 hours were cultured for only 1 hour.
• The harvested oocytes were then transferred to the same mare’s oviduct, or to the oviduct of another oocyte donor.
• In addition, recipient mares were inseminated before and after the transfer.

Findings

• The oocyte recovery rates at 24 and 35 hours after hCG administration were not significantly different (66% and 73% respectively) leading to an overall recovery rate of 70%.
• The overall pregnancy rate after the transfer was 53%, with no significant difference seen between groups (63% for the 24-hour group and 44% for the 35-hour group).
• A presence of uterine fluid in recipient mares more than 2 days after transfer was associated with a significantly lower pregnancy rate.

Conclusion

• The research suggests that the timing of oocyte collection after hCG administration isn’t a crucial factor in determining pregnancy rates after the oocyte transfer.
• However, the potential for endometritis triggered by the medication associated with oocyte transfer may increase the recipient mares’ susceptibility, consequently reducing pregnancy rates if not addressed.