Repeated transvaginal oocyte aspiration in unstimulated and FSH-treated mares

Transvaginal ultrasound-guided follicular aspiration was conducted repeatedly in 5 cyclic mares. Three techniques were used and the aspirations were performed either > or = 23 d apart (A1, B1, C1) or 6 d apart (A2, B2,C2). During the A1 and A2 aspirations, the follicular cavity was flushed manually 8 to 10 times with flushing medium-filled (60 ml) syringes, while an electrical aspiration pump was used for the B1, B2, C1 and C2 aspirations. Prior to aspirations C1 and C2, the mares were treated daily with porcine FSH (100 mg, im) for 4 d. Aspiration was conducted 24 h after the last FSH injection. A total of 212 follicles with diameters varying between 5 and 23 mm was aspirated. The oocyte recovery rate was significantly higher (P = 0.004) from aspirations conducted with a > or = 23-d interval (35.8%) than from those aspirated 6 d after the previous aspiration (18.4%). Mode of evacuation and flushing (pump or syringe) and FSH treatment of the mare had no detectable effect on the oocyte recovery rate or on the cumulus dimensions of the aspirated oocytes. More than 80 % of the oocytes were at the germinal vesicle or diakinesis stage.