Embryo Transfer

What is Embryo Transfer?
Embryo transfer is the process of removing fertilised embryos from a donor ewe and transferring them into a number of recipient ewes. There are a number of reasons for using embryo transfer. These include:

  • Allowing large numbers of progeny to be produced per ewe, enabling elite female genetics to be rapidly multiplied and integrated into the genetic pool of your flock
  • Rapid multiplication of rare/ introduced breeds where availability is low
  • Cheap form of acquiring individual sheep of rare or introduced breeds when the cost of purchasing individuals is high
  • Ability to transfer genetics across distance, and import or export elite genetics

Embryo transfer involves the administration of a number of different hormones over a period of three weeks to achieve synchrony between donor ewes and their proposed recipient ewes. The hormones also stimulate the ewes to ovulate as many eggs as possible, a term called superovulation. This enables the recovery of a larger number of embryos than would be produced naturally by the ewe.

Breedtech has a very successful embryo transfer program. Each year Breedtech:

  • Flushes 500-20000 ewes,
  • Transfers 5000 - 20 000 embryos,
  • Recovers a consistent average of 10 embryos/ewe,
  • Pregnancy rates 60-90%

We have had single ewes producing up to 45 embryos.
The picture on the right shows 37 embryos from a single donor ewe.

What does an Embryo Transfer Program involve?
An embryo transfer program takes three weeks from beginning to end. The process begins with both donor and recipient ewes having devices, called CIDRs (Pfizer), that contain progesterone inserted into their vagina. It is recommended that the number of recipients required is approximately 10x that of the number of donors. The CIDRs (Pfizer) remain in place for approximately 13 days at the end of which they are removed to stimulate the ewes to begin their seasonal oestrus period again.  In a sense they are being reset, so they all begin at the same time.  At this point, only the donor ewes are begun on a series of injections to begin the process of superovulation. This takes place over 4 days and requires a single injection at both 8:00am and 5:00pm every day. Once this is finished the ewes are artificially inseminated via a laparoscope and are left for the next 5-6 days for their embryos to develop to a certain stage. Recovery of the embryos is then performed surgically where the ewe is completely anaesthetized for approximately fifteen minutes. The embryos are flushed directly from the uterus using specialised equipment and fluids. Microscopes are used to locate, examine and grade the embryos and they are then held in special short-term storage fluid ready for laparoscopic transfer into a recipient ewe or frozen for long-term storage.

Donor ewes recover from surgery very quickly and can be returned to programme within six weeks if required.  The recipient ewes are scanned for pregnancy 60 days after implantation of the embryo.  The percent of ewes pregnant at this time gives a good indication of the expected lambing percentage however abortion may still occur after this time. Great care is taken to ensure that there is minimal stress and discomfort to both the donor and recipient ewes.
 
For a more detailed explanation of the the Embryo Transfer procedure, please click here.

Picture Right: An embryo being transferred directly into the uterus a recipient ewe.

Programme Options
A number of variations in the embryo transfer program are available according to the needs of our clients.

     
  1. Fresh program on centre: Donor & recipient ewes are located at Breedtech and all embryos are transferred directly into recipient ewes at the time of flushing
  2. Fresh Program on farm: Donor ewes are located at Breedtech for hormonal management and recipient ewes are located on farm.  Embryos are collected in the morning and transported to the farm for transfer into recipients in the afternoon (local area only) OR the embryos may be chilled and transported overnight for transfer the next morning (within 24hrs). For more information on transferring embryos at your farm, click here.
  3. Frozen Program on Centre: Embryos may be flushed from donor ewes and frozen in liquid nitrogen for storage and transfer at a later date or for transport to another location.
  4. Frozen Program on Farm: Embryos may be thawed on farm and transferred into recipient ewes.

Figures and Averages

Assuming the ewe is of sound reproductive order, the factors that may influence the embryo recovery include: time of year and breed (some British Breed ewes cycle better at different times of the year); age of ewe; stress in ewe (temperament plays a big role); condition score and nutrition; semen quality (frozen semen is not ideal for an embryo transfer program but good results have been obtained); skilled technicians. Recovery rates vary considerably 1-50 embryos however Breedtech has been consistently recovering averages of 8-12 embryos per ewe flushed. The expected pregnancy rate is approximately 60-80% and this is primarily affected by recipient fertility, condition score, nutrition, stress management and also the quality of the embryo.
 
Husbandry and Management

The husbandry of both donors and recipients is very important in an embryo transfer program. We aim to minimise stress by relocating the ewes to our centre at least 5 weeks before a program as a settling in period. The ewes are drenched with minerals at the time of progesterone implantation and placed on a rising plane of nutrition to increase their fertility.