Preimplantation genetic testing in horses: biopsy of Piezo-ICSI embryos for sex, coat color, and disease alleles.

This research article reveals a noteworthy advancement in equine reproduction, demonstrating the successful use of preimplantation genetic testing (PGT) on horse embryos. The study confirms the efficacy of a non-invasive biopsy technique for determining sex, coat color, and certain disease alleles in pre-transplanted embryos resulting from Intracytoplasmic Sperm Injection (ICSI).

Background and Methodology

• The researchers used a combination of ovum pick-up, Intracytoplasmic Sperm Injection (ICSI), and in vitro embryo production, techniques that offer myriad benefits, such as overcoming infertility issues, producing high yields of blastocysts, enabling embryo cryopreservation, and facilitating preimplantation genetic testing (PGT).
• PGT allows for careful selection of embryos prior to implantation, and is highly valuable in horse breeding circles that have preferences for particular genders, coat colors, and genetic disease outcomes.
• This study focuses on demonstrating and validating an innovative, non-invasive biopsy method for ICSI-derived horse blastocysts (early stage embryos). The safety and efficacy of this technique are confirmed through maintaining the integrity of the embryo during the biopsy.

Results and Observations

• The biopsied cells allowed the researchers to successfully conduct PGT for factors such as gender determinations, white spotting (Tobiano genotype), and clinical DNA screening for certain disorders such as Warmblood Fragile Foal Syndrome Type 1 (WFFST1) and Glycogen Branching Enzyme Deficiency (GBED).
• The methods used for PGT involved PCR-based assays being validated by Sanger sequencing.
• The research achieved a high success rate of 92.76% in sex determination among the 746 ICSI blastocysts that went through biopsy. The results displayed a mean of 56.21% male and 43.79% female, with no substantial differences recorded among different horse breeds.
• Additional findings showcased that over 90.91% of the 22 biopsy analyses done on horse embryos (A mix of heterozygous and homozygous horses) exposed the presence of Tobiano genotypes (white spotting on the coat).
• The method was also successful in diagnosing potential disease alleles, with 19 out of 20 embryos from a GBED carrier stallion correctly identified, with 21.05% confirmed as heterozygous. This validates the potential of the method in controlling the incidence of genetic diseases.

Conclusions and Implications

• This research confirms the reliability of using non-invasive PGT of OPU-ICSI embryos in horse breeding programs. The method promises to give breeders a more nuanced control over genetic disease incidence and contribute to future improvements in assisted equine reproduction.
• The validated biopsy method is safe, non-invasive, and enables informed decisions regarding embryo selection, which could have far-reaching effects on the diversity, health, and quality of future horse populations.