Assisted Reproductive Techniques in Equine Embryology

Assisted reproductive techniques in equine embryology encompass a suite of interventions designed to overcome limitations of natural breeding, enhance genetic management and support conservation efforts. Core procedures include ovum pick-up (OPU), in vitro maturation (IVM) of oocytes, intracytoplasmic sperm injection (ICSI), embryo culture to the blastocyst stage and transfer into recipient mares. Cryopreservation of oocytes and embryos has further increased logistical flexibility, allowing global distribution of valuable genetics. Recent advances in preimplantation genetic testing permit selection of euploid embryos and screening for monogenic traits, thereby improving foaling rates and reducing transmission of inheritable disorders. Parallel research into the metabolic and microenvironmental requirements of the cumulus-oocyte complex and early embryos has revealed species-specific demands that inform refinement of culture media and holding protocols. Studies of maternal age, dietary supplementation and follicular fluid composition have elucidated factors affecting oocyte quality, embryo viability and lineage specification. Together, these innovations are transforming clinical practice in sport-horse breeding and offer a model for comparative reproductive biology and endangered equid preservation.

Research from Nature Portfolio

Recent studies have established a genome-wide preimplantation genetic testing platform for equine embryos that combines simultaneous haplotyping and copy number analysis. This approach enables concurrent detection of aneuploidies and monogenic variants of interest, allowing selection of embryos free of chromosomal errors and disease-associated alleles. Validation in trophectoderm biopsy–blastocyst pairs demonstrated reliable prediction of euploid status and parental haplotypes, with direct implications for improving foaling success and reducing early embryonic arrest in vitro. Complementing genetic advances, an in depth characterisation of energy metabolism in the equine cumulus-oocyte complex during IVM has revealed a high reliance on oxidative phosphorylation alongside glycolysis, species-specific mitochondrial efficiency and a loss of spare respiratory capacity over culture. These findings highlight deficiencies in current IVM protocols and provide a metabolic blueprint to optimise oxygen tension, substrate supply and media formulation for improved oocyte maturation and embryo development.

Assisted Reproductive Techniques in Equine Embryology publication trend

The graph below shows the total number of articles in assisted reproductive techniques in equine embryology across all publications each year (not limited to Nature Index journals).

Technical terms

Ovum pick-up (OPU): Ultrasound-guided aspiration of oocytes from live mares for in vitro procedures.

In vitro maturation (IVM): Culture of immature oocytes to metaphase II stage outside the reproductive tract.

Intracytoplasmic sperm injection (ICSI): Direct microinjection of a single sperm into the oocyte cytoplasm.

Blastocyst: Preimplantation embryo stage characterised by a fluid-filled cavity, trophectoderm and inner cell mass.

Preimplantation genetic testing (PGT): Molecular screening of embryos for chromosomal abnormalities (PGT-A) or specific gene variants (PGT-M) prior to transfer.

Cumulus-oocyte complex (COC): Oocyte surrounded by cumulus granulosa cells essential for nutrient support and signalling during maturation.

References

1. In Vitro-Produced Equine Blastocysts Exhibit Greater Dispersal and Intermingling of Inner Cell Mass Cells than In Vivo Embryos. International Journal of Molecular Sciences (2023).
2. Equine maternal aging affects the metabolomic profile of oocytes and follicular cells during different maturation time points. Frontiers in Cell and Developmental Biology (2023).
3. Genome-wide equine preimplantation genetic testing enabled by simultaneous haplotyping and copy number detection. Scientific Reports (2024).
4. Success rate in a clinical equine in vitro embryo production program. Theriogenology (2022).
5. Energy metabolism of the equine cumulus oocyte complex during in vitro maturation. Scientific Reports (2020).
6. Monozygotic multiple pregnancies after transfer of single in vitro produced equine embryos. Equine Veterinary Journal (2019).
7. Oocyte metabolic function, lipid composition, and developmental potential are altered by diet in older mares. Reproduction (2022).
8. Study of the Metabolomics of Equine Preovulatory Follicular Fluid: A Way to Improve Current In Vitro Maturation Media. Animals (2020).