SUCCESSFUL TRANSFER OF BIOPSIED EQUINE EMBRYOS

Embryo biopsy has been used to detect inherited disorders and to impro ve 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 succ essful. Recent discovery of the polymerase chain reaction (PCR) has ma de possible the detection of specific DNA sequences from only a few ce lls. We investigated whether the removal of a small biopsy would allow for successful PCR and normal embryonic development. In the study rep orted here, 14 microblade-biopsied Day 6 to 7 equine embryos were tran sferred nonsurgically into recipient mares. The sex of each embryo was determined from the biopsy by means of restriction fragment length po lymorphism analysis of the ZFY/ZFX loci after PCR amplification. The e mbryos were sexed as 8 females and 6 males on the basis of PCR assay r esults. 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 biop sy and control groups, respectively. All of the microblade biopsy grou p pregnancies were females. One was aborted for cytogenetic analysis. Two were born after normal gestation. With improved pregnancy rates,;h is technique could be used for preimplantation diagnostics of equine e mbryos. As gene mapping advances and associations between particular D NA sequences and inherited traits become established, a rapid PCR tech nique could be used to select embryos before transfer. (C) 1997 by Els evier Science Inc.