Determining the sex of bovine embryos using polymerase chain reaction results: a six-year retrospective study

Knowing the sex of embryos produced for use in an embryo transfer program can assist the dairy producer in managing his resources more effectively. A reliable procedure for accomplishing this goal is to apply PCR technology to the biopsy of an embryo. A description is provided of how the technique has been applied on a large scale in a commercial setting in western Canada between 1992 and 1997. A total of 4,183 embryos was biopsied over a 6-yr period. The sex was determined with more than 90% of the embryos. The results showed that there was a seasonal variation in the sex ratio, with more females being recorded in the period of least light (October to March), than in April to September. While both sire and embryo quality affected the sex ratio, the differences were too small to be of value in most breeding programs. Pregnancy rates with fresh sexed embryos (58 to 71%) were comparable to those with fresh unsexed embryos. The results following freezing and thawing of sexed embryos were low (37 to 66%) but sufficient to be viable commercially. When the sex assigned by PCR was verified by fetal sexing at 60 d of gestation, the error rate was 7%. This study demonstrates that sexing of embryos can be carried out on a large scale. Demand for quick, reliable determination of sex can be met in a cost effective manner. The pregnancy rates achieved with embryos after biopsy are suitable for use in a commercial setting.