Reproduction - Embryo Transfer

Dr Smith has been involved with equine embryo transfer since 2004. Each year in Australia the demand for horse embryo transfer increases. Embryo transfer in the horse involves collection and transfer of an embryo from one mare (donor) into another (recipient). The donor mare and stallion contribute their genetics to the foal, not the recipient. The recipient will help determine the size of the foal at birth but its subsequent growth is determined by its own genetics and nutrition.

The donor mare can be bred by fresh, cooled or frozen semen and breeding techniques are identical to breeding mares destined to carry their own foal. The day of donor ovulation (day of egg release) is termed day 0. Embryos may be removed from the mare by non-surgical flushing on day 7 ,8 or 9. When an embryo is obtained it is washed and graded and transferred into the recipient mare. The recipient mare should have ovulated within one or two days of the donor.

The first pregnancy test on the recipient can be determined as early as 5 to 6 days after embryo transfer (day 11 to 12).
On occasion embryos can be cooled for transport to another facility or may be frozen for long term storage prior to being
inserted into the recipient.

Advantages to Embryo Transfer

  1. Obtaining pregnancies from Show mares. The most common reason for using the technique is to obtain pregnancies from Competition/Show mares. We are routinely asked to collect embryos from mares that are still actively competing in both Campdrafts and Cutting competitions.
  2. Obtaining multiple pregnancies per season. The ability to obtain multiple pregnancies from a mare in one season ensure that;
  3. Obtaining pregnancies from 2 or 3 year old mares. This request is not as common here in Australia but quite common in the USA. We are reluctant to flush 2 year old mares but are often asked to obtain pregnancies from those promising youngsters that already show incredible potential early.
  4. Obtaining pregnancies from mares that cannot maintain their own pregnancies, i.e. uterine disease or mare injury. This is a common reason for using embryo transfer.
  5. Obtaining pregnancies from mares foaling late in the breeding season and thus enabling them to conceive earlier next season.

Disadvantages to Embryo Transfer

  1. Costs. On average it costs our clients between $ 4,000 - $ 5,500 per pregnancy. The largest cost associated with horse ET is the maintenance of the recipient mare herd. We frequently keep these mares for two or more years without using them. The mares are well fed and need to be carefully screened for reproductive soundness throughout the season.
  2. Veterinary Expertise - Considerable experience is necessary.
  3. Embryo recovery from infertile mares is low. Normal mares will give about 70% embryo recovery per cycle. Infertile old mares may be as low as 20%.
  4. Superovulation is usually unsuccessful (unlike Cattle /bovine ET) Mares usually only release one or sometimes two eggs for fertilisation per cycle. Even though considerable research into increasing the mares ovulation rate has been done is usually expensive, mostly unsuccessful and only results in one extra embryo.

Success Rates - Embryo Recovery

Embryo recovery is best from young, fertile mares and approximately 70- 90% of cycles may yield an embryo. An
important influence on embryo recovery is the fertility of the stallion. Mares that consistently multiply ovulate (Warmbloods,
etc.) have a better embryo recovery rate. The worst embryo recovery rate is from old, barren mares that have
persistent uterine infections (< 20%).

Success Rates - Embryo Transfer

The quality of the recipient mare is the most important determinant of pregnancy rate after embryo transfer. Because of this, most embryo transfer facilities (like Weatherford Equine) prefer to buy and manage recipient mares and do not accept offers from clients to supply their own mares. Non-surgical embryo transfer results in approximately 60-80% pregnancy rate per attempt.