OPU and ICSI

Advanced Reproductive Technologies involve the use of Ovum (or Oocyte) Pick Up (OPU). This is followed by in vitro fertilisation to establish an embryo or embryos which are either transferred shortly after creation or stored by vitrification (ultra-rapid freezing) to be thawed and transferred at a later date. Vitrification and later transfer is preferrable if embryos are created during autumn, winter or early spring when cycling recipients may not be available. 


Firstly, oocytes (eggs) are collected from the donor mare. These are obtained in two ways:


1) OPU (Ovum Pick Up): The mare is seated and prepared for the procedure (cleaned, and her bladder catheterised). The procedure involves flushing and aspirating the contents of each suitable follicle with a double lumen needle. An ultrasound probe with an attached channel to allow the pass of the needle is introduced into the vagina while the operator controls each ovary per rectum. 


2) Genetic Salvage: A catastrophic event such as a major limb fracture or serious colic in which a mare may have died during or after surgery, and which requires euthanasia. The ovaries can be removed and shipped/transported to the facility as soon as possible. (Details of shipment requirements can be obtained by contacting Robyn or Susanne at Equivet Breeding Centre.) 


Upon arrival at our lab, the follicles in ovaries are scraped to recover the oocytes. They are then placed in a specific solution and examined. Degenerating oocytes are then discarded. Acceptable oocytes are then placed in another media until they reach a desired level of development. 

Secondly, an embryo is created. A single sperm is captured and ‘drilled’ into the viable oocyte using a procedure called ICSI (Intracytoplasmic Sperm Injection), in order to produce an embryo. This procedure gives the best results in horses. Semen can be fresh, chilled or frozen, but specific requirements are essential to render it suitable to enable fertilization to occur. (Conventional in vitro production is the method used in cattle. Some encouraging results have occurred in this area. Please contact Robyn or Susanne about this area.)


Thirdly, the embryo is placed in an appropriate recipient mare or vitrified for later use (see explanation above).


Are there any risks associated with the OPU procedure?

The risks are very small, but mare owners need to be aware of the possibilities. During and after the procedure, the mare is closely monitored for any signs of discomfort. These can vary from mild but brief colic signs, haemorrhage, to – in very rare cases – peritonitis or even death (less than 0.01%).


Why consider in vitro fertilisation (OPU and ICSI)?

Many of the reasons are the same as conventional Embryo Transfer (ET). (Please see Embryo Transfer for a detailed explanation.)

Other reasons include:

  • Better use of frozen semen of poor quality or where there is a scarcity of frozen semen remaining, as one 0.5mL straw can be cut under liquid nitrogen many times
  • Mares do not have to be cycling, but a good number of follicles (at least 6), preferably >10mm, needs to be present
  • As we cannot superovulate mares as we can with cows, this system gives an opportunity to create several embryos
  • Mares with fertility issues such as blocked oviducts, uterine and/or cervical problems or valuable aged mares have more opportunities than with conventional ET. However, it must be remembered that the quality of oocytes declines with age. In addition, mares with serious infective disorders of the uterus are not good candidates due to the increased risk of peritonitis with the procedure.


What are the negatives to be considered with OPU / ICSI?

  • Due to the facilities and technical expertise required, this procedure is much more costly than other conventional embryo transfer.
  • Possible risks to the mare have been outlined.