Developmental competence of equine oocytes and embryos obtained by in vitro procedures ranging from in vitro maturation and ICSI to embryo culture, cryopreservation and somatic cell nuclear transfer.

The research is focused on the continued development and improvement of assisted reproductive technologies in horses, including methods such as in vitro maturation, Intracytoplasmic Sperm Injection (ICSI), embryo culture, cryopreservation and somatic cell nuclear transfer. The findings indicate that in vitro matured equine oocytes can efficiently develop into viable embryos and offspring.

Context of the Study

• The research addresses assisted reproductive technologies in horses, which hasn’t advanced as quickly as other domestic species, primarily due to limited availability of abattoir ovaries, and horse breeders and breed associations showing little interest.
• However, in recent years, progress has been made in the technology of in vitro oocyte maturation and the use of Intracytoplasmic Sperm Injection (ICSI) for in vitro fertilisation.

Methodology and Findings

• Embryo culture was initially conducted in vivo, in the mare oviduct or in the surrogate sheep oviduct, resulting in top embryo development, between 18-36% of the fertilised oocytes.
• Later development in in vitro oocyte maturation conditions and improvement in embryo culture media led to higher rates of embryo development from in vitro matured and cultured ICSI embryos – from 5-10% in early studies to up to 38% in recent ones.
• Since 2003, with the birth of the first cloned equids, somatic cell nuclear transfer technology has been established and improved, assisted by advancements in the basic steps of in vitro embryo production, including cryopreservation.

Outcomes of the Study

• Pregnancy and foaling rates were calculated based on a small number of in vitro produced equine embryos transferred to recipients.
• The most extensive set of data on non-surgical embryo transfer of in vitro produced embryos, from ICSI of both abattoir and in vitro-matured Ovum Pick Up (OPU) oocytes, and from somatic cell nuclear transfer, was obtained in this research.
• The study revealed that equine embryos produced by OPU and then cryopreserved reached up to a 69% pregnancy rate, with an 83% foaling rate.
• However, these percentages drop to 11% and 23%, respectively, for cloned embryos.

Conclusion

• The study concludes that extensive evidence exists, proving that in vitro matured equine oocytes can efficiently develop into viable embryos and offspring, thereby demonstrating the possibilities of these assisted reproductive technologies in horse breeding.