Management of Embryo Donor Mares with Chronic Infertility was the title of an in-depth presentation by John Hurtgen, DVM, Dipl. ACT, of Nandi Veterinary Associates in New Freedom, Pa., at the 2008 American Association of Equine Practitioners convention, held Dec. 6-10 in San Diego, Calif. He said embryo transfer is a management procedure for producing foals by mares that either are in training or have reproduction problems. In some cases the goal is to allow young performing mares to reproduce while continuing their careers. In other cases the donor mare might be afflicted with a reproductive problem, such as chronic uterine infection or a cervical laceration, that does not allow her to carry a foal to term.

In one challenging case discussed by Hurtgen, a 12-year-old Standardbred mare was referred to his clinic for embryo transfer. The mare had undergone a unilateral ovariectomy (removal) of the right ovary as the result of a granulosa cell tumor (the most common type of ovarian tumor; it secretes hormones). The right uterine horn also was removed at the same time because of a similar condition.

Hurtgen said: "Mares that are missing a uterine horn because of congenital (born with it) anomaly, surgical removal, or occluding luminal adhesions of a uterine horn are unable to carry a foal to term or, with the aid of altrenogest or progesterone, may carry a foal to term but deliver a very undersized foal."

During the five years following the mare's arrival at the clinic, Hurtgen said, embryo transfer was performed in the wake of artificial insemination. During those years the mare suffered from several problems, including uterine fluid accumulation after insemination.

The final scorecard read like this: veterinarians flushed the mare's uterine lumen a total of 11 cycles over a five-year period. Seven embryos were collected, which resulted in the birth of four live foals by recipient mares.

Another embryo transfer success story that still contains an element of mystery involves a Standardbred mare that had delivered a live foal for each year three consecutive years. During the following four years, the mare aborted between seven and 10 months gestation, despite being treated with altrenogest (Regu-Mate--synthetic progesterone, which suppresses estrus and helps a mare maintain pregnancy) three of those years.

A thorough reproductive examination failed to reveal any significant problems. The mare's owner opted for embryo transfer, and for the next six years the mare produced a live foal from the embryo collected and transferred to a recipient mare.

Hurtgen said in some cases aging of the reproductive tract can produce such a strong compromising factor that even embryo transfer is not a solution. He discussed a case involving a 23-year-old Standardbred mare whose reproductive system had shut down to the point where there was little or no ovarian follicular activity. Basically, the mare was unable to produce an egg to be fertilized. She was retired.

Hurtgen proffered this advice to fellow veterinarians: "When presented with mares with chronic infertility in an embryo transfer program, it is important to prepare the mare for the breeding season. The mare's specific health needs, such as chronic arthritis and poor body condition, should be addressed and corrected. It is advantageous to have the donor mare exposed to increased lighting in early December so the mare begins cycling in February even if breeding is planned for later in the spring. This practice will allow ovulation and treatments of reproductive tract problems while the mare is cyclic. Remember, if the donor is exposed to artificial lighting so that breeding can start in February or March, recipient mare candidates should also be included in the artificial lighting program."

About the Author

Les Sellnow

Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and operates a ranch where he raises horses and livestock. He has authored several fiction and non-fiction books, including Understanding Equine Lameness and Understanding The Young Horse, published by Eclipse Press and available at or by calling 800/582-5604.

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