OPU and ICSI
OPU and ICSI
There are several new techniques that are being utilized in the field of equine reproduction, and many people may have come across OPU and ICSI as acronyms. But what are they and how do they work?
OPU- Ovum Pick Up
Also known as Oocyte Collection this is the process where oocytes (eggs) are removed from the ovary, and is the first step in the process.
ICSI - Intra-Cytoplasmic Sperm Injection
This is the procedure whereby a single sperm is injected through the outer surface of a mature oocyte, following which an embryo may develop. It is an advanced form of IVF, and is now routinely used in the production of human embryos. If the oocyte is fertilized successfully by the sperm, an early embryo develops. These are grown (cultured) in special conditions in the laboratory for 7-9days- by which time they are equivalent to a ‘normal’ 4-5day embryo. These embryos are very small, and can therefore be successfully frozen and transported.
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How is this technique and procedure performed?
The mare is prepared, and given sedation, anti-biotics, and an intestinal relaxant. Often a urinary catheter is placed, and sometimes the mare is given an epidural. The ovary is located by the veterinarian with a hand in the rectum, and gently moved so that it lies next to the vagina. A specialized vaginal probe with a needle guide attached is inserted into the vagina. The follicles (which contain the oocytes or eggs) are individually punctured, drained, and scraped multiple times. The procedure is repeated for both ovaries. The retrieved fluid is then taken to the laboratory to be filtered and examined under a microscope. The oocytes are then assessed, washed, and packaged for transport to the company Avantea in Italy. Once at Avantea, the oocytes undergo further maturation, the injection of the sperm, and the early culture of the embryos. If required, the embryos can be biopsied (to allow genetic assessment e.g. for sexing) and then frozen.
What Are The Advantages of OPU and ICSI?
It can be performed at any stage of the reproductive cycle of the mare (and therefore at any time of year.)
Embryos can be stored in liquid nitrogen indefinitely and transferred when suitable recipients become available.
Recipients do not have to be synchronised at the same time as the donor mare.
Donor mares do not have to have their competition schedules interrupted as part of an embryo transfer breeding program.
Donor mares that do not produce embryos via conventional embryo transfer may be able to produce embryos via OPU and ICSI.
In the case of sudden death or euthanasia of a mare, oocytes can still be recovered post mortem and sent for ICSI.
Only one sperm cell is needed for each injected oocyte, and hence is very useful when the supply of semen is limited, for use with sub fertile stallions, or with extremely costly or exclusive frozen semen.
A single straw of frozen semen can be used for up to 8-10 ICSI sessions.
What Results Can Be Expected?
The average oocyte recovery rate is usually 60-65%- ie an oocyte is recovered out of 60-65% of punctured follicles.
NB These results may vary- some mares give a lower yield, and some higher.
After maturation, 60% of the oocytes will be injected with a sperm cell.
The overall chance of one or more frozen embryos after a single OPU session is 60%.
The average number of embryos per successful OPU session is 1.9.
In summary, on average out of 10 different OPU-ICSI sessions, 4 attempts will be unsuccessful, although the other 6 successful attempts will have yielded 12 embryos in total.
Chance of Pregnancy
After thawing and transferring the ICSI embryos into a recipient mare approximately 70-75% will result in a pregnancy.
Things to Consider
Enrollment Criteria for an OPU/ICSI Program
The mare needs to have swabs and bloods done in order that the oocytes can be sent to Italy.
The mares ought to have at least 15 follicles on both ovaries- multiple smaller follicles is the most desirable situation.
The presence of one/more large pre-ovulatory follicles will be a disadvantage.
Frozen semen ready for export to Italy must be available from the desired stallion.
Side- Effects of OPU
It is important to realize that there are risks associated with many veterinary procedures- and the same is true of OPU.
Possible complications include: Bleeding (rectal, vaginal or ovarian), rectal tears, rectal or ovarian abscesses, and peritonitis- which in the worst case scenario can lead to death of the mare.
There is a higher early embryonic mortality following transfer of ICSI embryos than with normal ET.
Equibreed UK only works with experienced professionals who assess these risks, and if necessary will stop the procedure.
Post Procedure Care
Mares will be required to remain at Equibreed UK overnight following their procedure so that they can be intensively monitored.
The day after the treatment, some mares can be quiet with a reduced appetite, and possibly have an increased temperature.
Occasionally they are lethargic for a few days.
We recommend that they are not over exerted for several days.