Embryo transfer
Due to the costs involved, embryo transfer is mainly used by seed stock producers to accelerate genetic gain. Embryo transfer allows a superior female to have many more offspring than she would have naturally and allows repetition of desired joinings.
In most cases the donor female is treated with hormones so that many more oocytes develop on the ovary than normal. Drugs are used to stimulate ovulation followed by timed insemination. The fertilised embryos are flushed a few days later from the animal and graded. Only quality embryos with a good chance of establishing a pregnancy are kept.
Some cows do not repond well to superovulation but are valuable enough to justify single flushings, where only one embryo is produced and flushed from the animal. Oocytes may also be collected directly from ovaries and then further developed and fertilized in vitro (outside the animal).
The embryos can be either frozen for transferring later or transferred directly into recipient animals. Recipient animals must be synchronised to be at the same stage of the oestrous cycle as the donor animal when the embryos were flushed. Not all recipient animals synchronised will have responded to the synchronisation program. Only those recipients at the correct stage of the oetrous cycle should receive an embryo. The recipient animals represent one of the largest costs to an embryo transfer program.