Harvesting Oocytes and ICSI

How are oocytes harvested from a mare and what is ICSI?

Oocytes are eggs that come from the follicles on the mare’s ovaries. Harvesting oocytes is the process by which the oocytes are removed from the follicles and are cultured in the lab for maturation. Mature oocytes are subsequently injected with individual sperm from the stallion, a procedure we refer to as ICSI. The resulting oocytes are then cultured in the laboratory for 7-10 days. At this point any viable embryos that have developed can be transferred to recipient mares or frozen for later use.

Advantages of ICSI

  • Some mare’s may be unable to become pregnant themselves (chronic uterine infections, complicating cervical abnormalities, blocked oviducts or other oviductal pathology, abnormal ovulations (anovulatory follicles), or any other conditions that prevent the mare from conceiving or providing a healthy environment for the embryo)
  • Stallions with limited sperm availability. Some stallions may simply have low fertility. Other stallions may be deceased and only a certain amount of semen is available. ICSI should be considered when only 1 or 2 straws of frozen semen remain from a stallion that is no longer alive or additional semen cannot be collected. Sperm injection could theoretically be used to produce multiple foals from a single straw of semen. For example, a small piece of the straw could be utilized, while the rest of the straw remains frozen.

Success Rates

Oocytes can be recovered by transvaginal aspiration once every two weeks. Multiple oocytes are typically recovered through each attempt. Of those immature follicles aspirated, we will recover oocytes from approximately 80% of them. Each aspiration session yields on average 1.2 embryo’s. Transferred ICSI embryos result in a slightly higher early embryonic loss than our naturally produced embryos. The mare’s age and her oocyte quality significantly affects these numbers. Older mares, with poor oocyte quality can take several attempts to result in a pregnancy. Some mares may have decreased numbers of follicles available at the time of aspiration which also affects overall success. Viable pregnancies are highly mare-dependent. Some mares may produce multiple embryos and pregnancies in the first cycle, others may take several more attempts, with the average being around 3 cycles to result in one pregnancy.

Post-mortem Oocyte Recovery

Unfortunately, sudden death or terminal disease or injury may affect your mare. In this case, the ovaries can be harvested from the mare in order to utilize for ICSI immediately following death or euthanasia. Please contact our office for more information on this procedure.


– Click here for New Client Form

– Click here for General Check In

– Click here for the link to Oocyte/ICSI Contract


Feel free to contact us if you have any questions concerning our Oocyte/ICSI Services at PEVS.

We are always available for a consultation.

If you have any questions and would like to speak with a Veterinarian, please call us at 803-641-0644