Originally, ICSI was developed to allow mares that were no longer able to carry a foal or to produce an embryo to continue to produce offspring by bypassing the uterus and oviduct.  The mares oocytes could be retrieved from her ovaries directly and fertilized mechanically in a laboratory and the subsequent embryo transferred into a surrogate mare.

ICSI also was used to increase production of stallions. Stallions who were no longer very fertile, or stallions who were deceased and had a limited amount of frozen semen could benefit from the procedure.

First of all, ICSI and the associated oocyte retrieval is a delicate, invasive procedure of high difficulty, and it takes a long time and a lot of practice to become proficient. Therefore, the procedure is only going to be as good as the veterinarian or technician doing it. The goal is to retrieve the oocytes from the follicles in the mare’s ovaries with the use of a long needle inside a transvaginal guided ultrasound probe. While one technician holds the ovary against the l vaginal wall rectally, the ultrasound probe is inserted vaginally. The needle passes through the vaginal wall, into the ovary, and follicles are detected via ultrasound and aspirated through the needle, collecting the oocyte inside.  The oocyte is put into a special media and matured for a short amount of time (longer if immature oocytes are collected) until ready to be fertilized.

With the use of a micro-manipulator and a specialized microscope, a single sperm cell is selected from a sample (fresh or thawed) via micropipette and, under the microscope, injected into the oocyte. If fertilization occurs, the dividing cells are matured in another special media in an incubator until it develops into an embryo suitable for transfer.

In the early days, the young cell mass was transferred into the oviduct of the surrogate mare, surgically.  This resulted in good pregnancy results, but the fact that it had to be done surgically (through the flank of the surrogate) made it more invasive, and surrogates could often only be used twice at best. Further research and development resulted in the fertilized oocyte maturing in an incubator long enough to be transferred non-surgically, like a normal embryo transfer. ..

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