GIFT (Gamete Intra-Fallopian Transfer) May Be Solution to Mare Infertility

Bruce E. Eilts, DVM,MS
Professor of Veterinary Clinical Medicine
Diplomate, American College of Theriogenology

Establishing pregnancy in the mare is a simple event. Briefly, sperm cells from the stallion move from the mare's uterus and into the oviduct (the tube that connects the uterus to the ovary). The oocyte (egg) is contained within a follicle on the ovary. The follicle grows and the oocyte matures when the mare comes into estrus (heat). The oocyte is released (ovulated) and is fertilized by the sperm cells within the oviduct. Once the oocyte is fertilized in the oviduct, it becomes an embryo.

In the mare, as opposed to most other species, only fertilized oocytes pass through the oviduct and enter the uterus. Therefore, the small oviduct has the task of assisting in oocyte fertilization and selecting and transporting only fertilized embryos to the uterus. The embryo exits the oviduct and enters the uterus approximately six days after ovulation. The embryo then travels around the uterus for an additional 10 days in order to firmly establish a pregnancy. If the uterus or embryo is abnormal, then a pregnancy will not be established. As 'simple' as this process seems, fertility is truly an amazing feat. If something goes awry in this process, then veterinarians often become involved.

If a mare is not pregnant after repeated breedings, further diagnostic or therapeutic measures need to be undertaken. Veterinarians have palpated the uterus per rectum and performed uterine cultures, uterine cytology examinations, and uterine biopsies for many years. Many types of uterine abnormalities can be treated effectively. For example, an infection can be treated using oxytocin (which causes the uterus to contract and evacuate abnormal fluid), uterine flushes, or uterine infusions of antibiotics. If the mare's uterus is abnormal and cannot be treated, then a different technique must be employed to obtain a foal from the mare. The first technique to be used on mares with an abnormal uterus was embryo transfer. Using embryo transfer, a mare can be bred and the fertilized embryo can be flushed from the donor mare's uterus and placed into a recipient mare with a normal uterus, and the recipient mare can then carry the pregnancy.

When the uterus appears to be normal and the mare still does not become pregnant, there may be other problems causing infertility. Extensive research has shown that many mares probably are infertile because there is either an oviduct malfunction or a defect in the oocyte itself. Unfortunately, veterinarians have no direct tests to determine if the oocyte or oviduct is abnormal. There are, however, new therapeutic techniques that can help mares with abnormal oviducts to produce a foal. Research being performed by the Louisiana State University Department of Animal Science St. Gabriel Research Station, with assistance from the Theriogenology section at the School of Veterinary Medicine, has sought a solution for the mare that is infertile because of an oviduct abnormality.

If the oviduct appears to be the problem, it must be bypassed in the fertilization and transport process. This can be done by harvesting the oocyte from the donor mare and then placing the oocyte directly into a recipient mare's oviduct for fertilization. The recipient mare is then bred, so the fertilization of the donor mare's oocyte now occurs in the "normal" oviduct of the recipient mare. All other steps from this point proceed as they would have in the donor mare; the oocyte is fertilized and the embryo enters the uterus and establishes a normal pregnancy. This procedure is commonly called "GIFT" (Gamete Intra-Fallopian Transfer). Actually, this procedure is more correctly called oocyte transfer. In GIFT, the sperm and oocyte are both placed in the recipient mare's oviduct. In oocyte transfer, only the oocyte is placed in the oviduct; the mare is bred either naturally or artificially and the sperm cells make their own way to the oviduct. However, GIFT is the commonly used term.

The exact procedure requires expensive equipment, expertise by the operator, and appropriate planning to synchronize the ovulation of both donor and recipient mares. In a direct oocyte transfer, the donor and recipient mares are brought into estrus at the same time, using either prostaglandin or a progestogen (Regu-Mate¨). It is essential that the mares ovulate on the same day. The oocyte from the mature follicle is removed one day before the recipient mare is expected to ovulate (Figure 1).

This is performed by inserting a special ultrasound probe into the vagina of the recipient mare. While palpating the mare per rectum, the ovaries are manually pulled back against the vaginal wall and the ultrasound probe is pushed against the vaginal wall. The mature follicle on the ovary is viewed using the ultrasound, and a needle is passed through the vaginal wall and into the ovarian follicle. The follicular fluid and the oocyte within the follicle are aspirated through the needle, using a suction device. The recipient mare now has no oocyte to fertilize, but is inseminated so sperm cells will be waiting when the oocyte from the donor is placed in the oviduct. Breeding can be accomplished using natural service or artificial insemination with fresh, shipped-cooled, or frozen semen. On the next day, the same procedure is performed on the donor mare, but the oocyte from the mature follicle is saved and placed in a culture medium for 12 hours in order to allow it to mature to the correct stage for fertilization. After the 12 hours of incubation, the oocyte is ready for transfer into the recipient mare that has been bred and has sperm cells waiting in the oviduct. The transfer of the oocyte into the recipient mare is performed via a surgical incision through the mare's flank. The success rate of collecting the oocyte, using this procedure, is approximately 65 percent and the pregnancy success rate after the surgical implantation to the oviduct is approximately 75 percent.

This may seem like a procedure that would be of great interest to many horse owners, but it is still a relatively new procedure and not widely in practice, but is available at LSU. It also must be considered an expensive endeavor because considerable expertise and special equipment are needed to perform the procedure. With research into new assisted reproductive techniques, there is hope for mares that had been previously diagnosed as infertile.