OPU (Ovum Pick Up) & ICSI (Intracytoplasmic Sperm Injection)


OPU is the collection of eggs (oocytes) directly from the mare’s follicles in her ovary for the purpose of carrying out intra-cytoplastic sperm injection (ICSI).

Procedures:  The ‘donor’ mare is placed in the stocks and sedated; additionally an epidural/intestinal relaxants may be administered and a urinary catheter may also be placed.

An ultrasound probe with a needle guide is inserted into the vagina and the ovary is held against the probe via a hand in the rectum to enable the follicles to be seen.  The follicles (ideally of 1cm diameter or more) are then punctured individually, aspirated flushed several times and scraped to ensure the retrieval of the oocytes (eggs). The fluid obtained is taken to the lab, filtered and searched under the microscope. The oocytes found are then packaged and transported overnight to Avantea (Italy) where ICSI  will be performed.

ICSI is the technique used for fertilisation of the oocytes where one sperm cell is injected into each mature oocyte. Following this an embryo may develop.

Procedures:  Before ICSI can take place the oocytes need to have matured (for about 24h).  It can be expected that 60-80% of oocytes will reach the right stage to undergo ICSI.  Following ICSI the fertilised eggs are grown for 7-9 days and allowed to develop into embryos (blastocysts).  Unfortunately not 100% of the injected oocytes will produce an embryo.  When embryos develop they are smaller compared to the ones produced via conventional ET and freeze more successfully. The frozen embryos can then be stored, shipped back to Twemlows or transferred into a recipient.  If required, the embryos can be biopsied to know the sex of the foal before freezing.



  • ideal for subfertile mares unable to produce an embryo for embryo transfer or unable to carry a pregnancy to term.
  • can be carried out outside the normal breeding season as mares do not have to be cycling
  • little interruption to competition work
  • frozen embryos can be transferred to a recipient mare, stored until a later date or sold when the owner desires
  • use of a very small amount of semen allows subfertile stallions or exclusive/expensive semen to be used more effectively.  One straw of frozen semen can be used for multiple ICSI sessions.
  • in case of sudden death/euthanasia oocytes can be recovered as soon as possible post mortem and undergo ICSI (Genetic Salvage)


What to expect/What are the chances of having a pregnancy:

Oocyte retrieval rate can vary and could be between 50 – 65%, however this will depend on the individual mare.  Overall, the likelihood of getting one or more embryos per OPU session is 55%, and the chances of getting a pregnancy after transfer of a frozen embryo are around 70%.  It has to be noted that whilst many mares are successful at producing embryos via OPU-ICSI, some mares will fail.

Other comments/requirements for Donor mares:

  • Health papers need to accompany each oocytes shipment. This means that:
  • CEM swabs and EIA blood test should be completed ahead of the OPU procedures
  • The mare must not have been outside the UK 30 days before the OPU or between her health tests and the OPU
  • Mares should have at least 15 follicles of around 1 cm diameter, ideally without the presence of a large preovulatory follicle, to maximize the chances
  • Frozen semen for the ICSI should be available/be shipped ahead of the OPU to Avantea
  • OPU can be repeated at 21-28 days intervals assuming enough follicles have developed in the meantime


Possible complications of OPU/ICSI

It is important to consider the potential complications that may occur during or following OPU.

Commonly mares may show signs of discomfort from the day of OPU for a few days afterwards.  An increase in body temperature is also possible.

Mares will receive non-steroidal anti-inflammatories and antibiotics as precautionary measure.

Other severe complications reported include rectal tears, severe bleeding, rectal or ovarian abscess, infection, peritonitis.  When an epidural is administered infection in the epidural space may happen as well as temporary paralysis of the hindquarters.

Some of these complications in their severe form could potentially lead to a life threatening condition and death.


We recommend the mare stays overnight following the procedure in order to be monitored.  The mare may be able to go home the same day if the owners are happy to monitor her and if not too painful after the procedure.  It is recommended that she is not overly exerted for a few days after the procedure.