Preimplantation genetic diagnosis in Welsh pony embryos after biopsy and cryopreservation

Preimplantation genetic diagnosis and embryo cryopreservation are important tools to improve genetic management in equine species with marked consequences on the economic value, health, biodiversity, and preservation of the animals. This study aimed to develop a biopsy method at the blastocyst stage that provides viable genotyped cryopreserved Welsh pony embryos. Embryos were collected at d 6.75 to 7 after ovulation. Biopsies were performed with either a microblade or a micropipette. After biopsy, embryos were cryopreserved. The survival rate of biopsied embryos was evaluated on fresh and cryopreserved embryos either 24 h after in vitro culture or after transfer to recipients. Fresh and nonbiopsied embryos were used as controls. Sex, coat color genes, myotony (neuromuscular disorder) diagnosis, and markers of parentage were investigated using PCR on biopsied cells after whole-genome amplification and on remaining embryos. The embryo survival rate after transfer was not affected by the micropipette biopsy (50%, n = 8; 43%, n = 7; and 50%, n = 12, at d 30 for fresh biopsied embryos, vitrified biopsied embryos, and control embryos, respectively) but was significantly reduced by the use of microblade biopsy: 9 (n = 11) vs. 67% (n = 12) for control embryos. Successful sex determination was achieved for 82% (n = 28) of the micropipette biopsies and 100% (n = 50) of the microblade biopsies. Sex determined on biopsied cells was found to correspond completely (100%) with that determined on the remaining embryo (n = 37). More than 90% of the parentage checking markers, coat color, and myotony diagnosis were successfully determined on biopsies obtained with either a micropipette or a microblade. Mendelian incompatibility (7.5 and 5.5%) and embryo genotyping errors (6.6 and 8.6%) were low and not significantly different between the 2 methods. In conclusion, for the first time, pregnancy at Day 30 was obtained after transfer of Welsh pony biopsied and vitrified embryos >300 μm in diameter to recipient pony mares. The biopsied cells collected enabled multigenetic embryo diagnoses to be performed to a high degree of accuracy. The micropipette biopsy is the better method to apply on Welsh pony embryos.