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Embryo Transfer

Embryo Transfer in Horses

by Robert N. Oglesby DVM

Introduction

Introduction » The Numbers Game » Superovulation » Synchronizing Donor and Recipient » Collection, Storage, and Transfer » Summary » More Info & Discussions

Embryo transfer (ET) is widely practiced in other species and humans but remains a fairly rare practice in horses. The reason is because of both practical problems that remain unsolved and the lack of acceptance by some breed registries, most notably Thoroughbreds. None the less it remains the best option is some cases. The advantage of ET include:
  • breeding mares that have medical or physical reasons they cannot carry a foal to term,
  • breeding mares that need to continue to compete during the normal gestation,
  • the possibility of creating multiple foals from a mare during a single season.
With improved techniques ET will gain greater acceptance and become a more important equine reproduction technique. This article discusses the current status of ET, the technical problems, success rates, and techniques. Included are a number of scientific research summaries.

The Numbers Game

Introduction » The Numbers Game » Superovulation » Synchronizing Donor and Recipient » Collection, Storage, and Transfer » Summary » More Info & Discussions

If you were to decide to breed your mare using embryo transfer what are the chances of producing a live foal? Numbers vary greatly depending on the factors discussed in greater detail below but assuming a optimum situation you can expect a success rate of about 35% for each egg ovulation where a transfer is attempted. This number breaks down into 2 separate factors:
  • For each ovulation that is appropriately inseminated a healthy embryo is harvested about 50% of the time.
  • Once you have a healthy embryo from a reproductively health mare a successful transfer occurs about 70% of the time. Note the emphasis on the reproductive health of the donor mare.

Costs

Though prices can vary tremendously depending on techniques and circumstances costs for a ET attempt, whether successful or not, range from 3,500 to 10,000 USD. A primary factor effecting expense is the availability of recipient mares. If these need to be purchased this will greatly increase costs. The successful recepients will need to be managed for a year, further increasing the cost of ET over traditional breeding.

Breaking the success factors down

Just like traditional breeding the results depend on a number of factors, one of the most important being the experience of the personnel doing the work. There are technical aspects that improve with practice. This is pretty much a factor that is hard to quantify so let's assume you will not proceed unless you have found an experienced reproduction practice to make the attempt.

The next factor is the reproductive health of the donor and recipient mare. Considering the investment and time required you will want to insure you start with a healthy recipient mare. Your choice should be healthy young mares with a history of having successfully foaled once or twice. ET is often invoked because the donor mare is special, so you will not likely have control over the reproductive health of the donor. You should be aware that older mares that have had difficulty settling have been more challenging to get healthy foals by ET.

It was once hoped that mares with declining fertility could be more successfully bred using ET but this has not been the case. It appears that either there is a problem with older ovum themselves or some important factor in the donor mares uterus for the first week following conception is not optimum. As a result successful ET in these mares falls to below 25% per ovulation attempted.

Technical Challenges

There are a few reasons that ET has not been as successful in horses as other species:
  • difficulty getting mares to ovulate more than a single ovum per cycle
  • difficulty getting donor and recipient mares at the same stage in the reproductive cycle
  • difficulty developing techniques that consistently result in healthy frozen embryos

Superovulation

Introduction » The Numbers Game » Superovulation » Synchronizing Donor and Recipient » Collection, Storage, and Transfer » Summary » More Info & Discussions

                       
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