Successful transfer of biopsied equine embryos.

Embryo biopsy has been used to detect inherited disorders and to improve the phenotype by analyzing of linkages between marker loci and the desired characteristics. Unfortunately, early procedures required the removal of a large portion (one-half) of the embryo for analysis, and the transfer of bisected equine embryos has not been particularly successful. Recent discovery of the polymerase chain reaction (PCR) has made possible the detection of specific DNA sequences from only a few cells. We investigated whether the removal of a small biopsy would allow for successful PCR and normal embryonic development. In the study reported here, 14 microbladebiopsied Day 6 to 7 equine embryos were transferred nonsurgically into recipient mares. The sex of each embryo was determined from the biopsy by means of restriction fragment length polymorphism analysis of the ZFY/ZFX loci after PCR amplification. The embryos were sexed as 8 females and 6 males on the basis of PCR assay results. Two embryos were biopsied using a needle aspiration technique, but no PCR amplification products resulted from these attempts. Eight intact control embryos were transferred to recipient mares using the same method. Pregnancy rates were 3 14 and 6 8 for the microblade biopsy and control groups, respectively. All of the microblade biopsy group pregnancies were females. One was aborted for cytogenetic analysis. Two were born after normal gestation. With improved pregnancy rates, this technique could be used for preimplantation diagnostics of equine embryos. As gene mapping advances and associations between particular DNA sequences and inherited traits become established, a rapid PCR technique could be used to select embryos before transfer.