What to Expect
One should expect recovery of an oocyte from a dominant follicle on approximately 75% of the attempts. Immature oocytes can often be recovered from smaller follicles at the same time. While the oocyte from the dominant follicle may be higher quality, the greater numbers generally recovered from immature follicles allow further opportunity. Oocytes (eggs) fertilized through ICSI will divide and grow approximately 70-80% of the time. Depending on the age of the donor mare and oocyte quality, 25-70% of these can be cultured to the blastocyst stage for non-surgical transfer. Growth and transfer survival varies with the quality of the embryo, although successful transfer parallels standard embryo transfer. Oocyte quality and vigor decline with the donor mare’s age so that use of eggs from older donors tends to result in somewhat lower pregnancy rates than for young mares. Embryo production is highly mare-dependant, so while some mares may produce multiple embryos and pregnancies in the first cycle, others may take several more attempts, especially if they are older, with the average being around 3 cycles.