Breeding for the future

Developments in breeding are providing an alternative to live covering or embryo transfer, with the OPU/ICSI technique. Anna Mitchell MRCVS explains

SIGNIFICANT advances have been made in equine assisted reproductive techniques over the past decade, one of the most notable being the increasingly popular intracytoplasmic sperm injection (ICSI) following ovum pick-up (OPU).

WHAT IS OPU/ICSI?

OPU is the first step in the process and is the procedure by which oocytes (eggs) are collected from the ovary of the donor mare. The oocytes are shipped to a specialist lab where ICSI is performed.

ICSI is an advanced form of in vitro fertilisation (IVF), whereby a single sperm is injected into a mature oocyte, which is then cultured over a period of seven to nine days and may go on to develop into an embryo. The resultant embryos can be frozen and then thawed at a later date and transferred into recipient mares.

THE PROCEDURE

DETAILED preparation of the mare is essential to maximise success. The mare is sedated and given multimodal pain relief, antibiotics and an intestinal relaxant. A urinary catheter is placed to ensure that the bladder is empty.

During the OPU procedure, the veterinarian locates the ovary via the rectum and positions it carefully. A specialised vaginal ultrasound probe with a needle guide is inserted into the mare’s vagina. The ovary is retracted carefully and held adjacent to the vaginal probe, separated only from it by the vaginal wall. The ovary can now be fully visualised.

The follicles (containing the oocytes) are then individually punctured, drained, scraped and flushed multiple times with the help of a long needle attached to the vaginal probe.

The retrieved follicular fluid is taken to the in-house laboratory to be filtered and examined under a microscope for the presence of oocytes. The oocytes are then transported to one of several specialist laboratories in mainland Europe.

Further maturation of the oocytes, the ICSI procedure and the development of the embryos all take place there.