Microsurgical methods have been developed to extract individual cells (blastomeres) from early stage embryos. The cells remaining in the biopsied embryo generally survive and develop into a viable offspring. The individual cells removed from both early- and later-stage embryos can be used to determine the sex of each embryo prior to its transfer to a recipient female. Embryo sexing using the DNA amplification procedure known as the polymerase chain reaction (PCR), with specific Y-chromosome DNA probes, is remarkably accurate for sexing cattle embryos. This procedure is now user-friendly, and can be completed within 5 hours after the embryos are harvested from donor animals. Sexing later-stage embryos (6 to 8 days of age) before transplantation is now possible at embryo transplant stations. The capability of sexing embryos gives producers the option of selecting bull or heifer calves for market and for reproductive management purposes.
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