embryotransfer
What is embryo transfer?
The embryo is the name given to the group of cells that will eventually grow into the foal. After insemination, the sperm burrows its way into the egg – this is termed “fertilisation”. This allows the egg and sperm to mix their DNA together in order to create an embryo. It starts off as one cell, and then divides into two, the into four, then eight and so on. The embryo grows rapidly, as it travels down the mare’s reproductive tract.
Seven to twelve days after fertilisation, the embryo attaches itself to the wall of the mare’s uterus, which is called “implantation”. There it will develop for around eleven months until it is a fully formed foal.
Embryo transfer is the delicate process of removing the embryo from the “donor” mare before implantation, and moving the embryo into the uterus of another mare (the “recipient”). Once moved, the embryo should bind to the recipient mare’s uterus wall and develop normally for the next eleven months, until birth. This allows one mare to act as a “surrogate mother” for another mare.
Why use embryo transfer?
- To obtain a foal from a mare with uterine disease or injury that will not allow her to attain and carry a pregnancy to full term.
- To obtain a foal from a mare with cervical scarring/tearing or other injury that will not allow her to attain and carry a pregnancy to full term.
- To obtain a foal from a mare that is less than three years old. Pregnancy is a younger mare may lead to injury, or loss of the foal before pregnancy reaches full term.
- To obtain a foal from a mare that is currently competing in events so that her reproductive history can begin at an earlier age.
- To obtain a foal from a mare with proven bloodlines or show record and eliminating the possibility of injury during foaling.
- To obtain a foal from a mare that may be too small to attain and/or safely carry a pregnancy to term.
- To obtain more than one foal per season from a mare that has proven bloodlines or competition record.
How is embryo transfer achieved?
The donor mare is assessed for reproductive soundness, breeding history, conformation, and several other factors.
The donor and recipient mares’ oestrus cycles must be synchronised, and this is most often achieved through administration of synthetic hormones that stimulate oestrus in the mare. Good quality chilled or frozen semen must be readily available for insemination when the donor and recipient mare are deemed to be ready for the embryo transfer process. Once the donor mare has ovulated, she must be inseminated by a trained artificial insemination technician.
After exactly seven days from the time of ovulation in the donor mare, her uterus must be flushed using a special buffering solution, which helps protect the egg. It should be noted here that although the donor mare may experience some discomfort, under normal circumstances no damage or injury will occur and the process will not effect the animal’s health in any way.
The fluid that is collected from the donor mare and examined under the microscope, to find the embryo. Once found, the embryo is removed by use of a special pipette and is transferred into a small amount of transfer buffer. The embryo is transferred into the recipient mare using a catheter and syringe. The recipient mare is then treated using regumate to help maintain the pregnancy.
This should, barring any major problems, lead to the recipient mare acting as a surrogate mother, and carry the foal to full term. The resulting foal should be no different to how it would have been if it had been carried to full term by the original, donor, mare.
Should I use embryo transfer?
Embryo transfer can be an expensive process, but if any of the reasons above (why use embryo transfer?) apply to you and your mare, then it is an ideal technique to help your breeding and competition program. Speak to your vet, or an equine reproduction facility if you are unsure about any aspects of the process.
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