An embryo is an organism in development. It is the stage between fertilized egg and active life form, in mammals called the fetus. Embryo transfer is a technique where embryos are harvested before they are attached to the uterus.7 days old embryo This technique allows the production of a greater number of offspring from a given female, the "donor", without requiring her to carry these offspring to term.

To briefly describe the process, the donor is conditioned with hormone treatments to induce multiple ovulations. After she has released several eggs, she is then bred, either naturally or by artificial insemination. Depending on the species, the embryos produced in this way are recovered from the donor by washing her uterus between the 5th and 7th day after insemination. The recovered embryos are transferred into other females, called "recipients", which normally have a lower economic value than the donor. This allows the donor to continue to be used for embryo production.

The first embryo transfer reported was done using rabbits, by Walter Heape of the University of Cambridge in 1890. It was 40 years later, in 1930, before others succeeded in using this technique. Embryo transfer has been used in several species of domestic animals, namely cows, horses, goats, and sheep. It has also been used for certain non-domestic species, such as deer, elk, bison and wildcats.

For goats and sheep, the embryo transfer technique most often used is a surgical procedure, both for collecting the embryos and for transferring them into the recipients. In cows, where this breeding technique is quite popular, as well as for horses, embryo transfer is performed via the genital tracts. The average number of embryos collected from one cow at one time can vary from zero to 50 with an average of six viable embryos. These embryos can either be transferred immediately into recipients or frozen for later use or possibly for export purposes. The embryos may also be micromanipulated to split them into two usable halves, or, with the use of new biotechnology procedures for DNA testing, the sex of the embryo may be determined with a greater than 90% accuracy. In cows, where embryo transfer is most often used, 1 calf is born for approximately every 2 embryos produced, hence about 3 calves per recovery. A donor can undergo an embryo recovery about once every two months.

Photo of a donor cow and six  heifers issued from embryo transfer in recipients.
There are several advantages to using embryo transfer. Following much research as well as the experience of many breeders, the recipients have no genetic effect on the calf they deliver: therefore, this technique is an excellent means of maximizing the genetic potential of a high value female, bred to a bull which also exhibits desirable characteristics for that breed. Another advantage is that this technique can contribute to the survival of a breed, by allowing embryos produced to be transferred into females of different breeds within the same species or a compatible species.

There has been an intercontinental market for domestic animals over the past 100 years and it continues to be very active. Embryo transfer has provided some better alternatives for importing and exporting cattle. Particularly in terms of protecting importing countries from new diseases, embryos are a much safer option than live cattle, while still offering these countries the chance to introduce new genetic lines and new species. This has been very important in Canada which, thanks to embryo transfer, has managed to keep a low level of contagious disease while permitting the introduction of new, marketable genetics.

Finally, suspected genetic defects which are usually hereditary may be identified more quickly by producing a certain number of offspring from a given cross: if the defect is identified within the group of offspring, the responsible parent will be eliminated from the breeding program, in order not to propogate this defect within the breed. This can avoid significant economic loss for breeders of the race.

Dr Roger Sauvé, m.v.
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