Conception rate after sex determination and cryopreservation of D7 bovine embryos

The aim of this study was to evaluate conception rate after sex determination and subsequent freezing of Day 7 (D7) bovine embryos and to compare it with transfer of fresh female embryos. High quality embryos obtained from superovulated donors were biopsied and the embryonic cells (5-10) were analysed by PCR using specific primers for the Y-chromosome determinant. Fresh embryos were blade biopsied (n = 172) and subsequently transferred (ET) ipsilaterally to synchronized recipients. Selected embryos (n = 112) were biopsied by cell aspiration and cryopreserved for later transfer. Sex determination was successfully completed in 91.3% of fresh group embryos (44% female) and in 87.5% of freeze-thawed group embryos (45.9% female). The achieved pregnancy rate was 56.5% after fresh transfer of sexed (female) embryos whereas intact embryos (control 1) implanted in 61.9% recipients. 95.6% (43/45) of embryos survived biopsy and cryopreservation. After transfer of freeze-thawed sexed (female) embryos, pregnancy was established in 48.8% of recipients. A similar conception rate was found in intact embryos (50.7%, control 2). The results clearly demonstrate that the microsurgical technique used and subsequent PCR sex analysis allow the rapid commercial exchange of genetic resources on the basis of fresh or frozen sex-desired embryos in embryo transfer programs.