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

Mares with preovulatory follicles >33 mm in diameter were administered hCG and were randomly assigned for aspiration of the dominant follicle at 24 h or 35 h after hCG administration. Oocytes recovered at 24 h were cultured for 12 h before transfer and oocytes recovered at 35 h were cultured for 1 h. Oocytes were transferred by flank laparotomy to the oviduct of the same mare, or to the oviduct of another oocyte donor. Recipient mares were inseminated before and after transfer. The oocyte recovery rates at 24 h and 35 h after hCG administration were not significantly different (10/15 (66%) and 11/15 (73%), respectively) and resulted in an overall recovery rate of 70%. The overall pregnancy rate after transfer was 9/17 (53%) and there was no significant difference between groups (5/8 (63%) for the 24 h group and 4/9 (44%) for the 35 h group). The presence of uterine fluid in recipient mares > 2 days after transfer was associated with a significantly lower pregnancy rate (3/10 versus 6/7 for mares that had no fluid after day 2). This study indicates that the timing of oocyte collection after administration of hCG is not a major determinant of the pregnancy rate after oocyte transfer. Medication associated with follicle aspiration and oocyte transfer may increase susceptibility of recipient mares to endometritis, which can lower pregnancy rates if not resolved.

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