Embryo Pulsing: Repeated Expansion and Contraction of In Vivo and In Vitro Equine Blastocysts.

The research article focuses on a phenomenon observed in the development of horse embryos, identified as ‘pulsing,’ which involves repeated expansion and contraction of both in-vivo and in-vitro produced blastocysts. The exact cause of this pulsing is unknown, but it’s thought to be associated with embryo quality and implantation rates.

Study Approach

• The researchers conducted a morphokinetic evaluation of the embryo development, focusing on the events during blastulation – the process where an embryo becomes a blastocyst.
• They used time-lapse imaging to monitor and document the process of ‘pulsing’ or repeated expansion and contraction in the early development stages of blastocysts, both developed inside a mare (in-vivo) and those produced in a lab (in-vitro).

Key Findings

• The study showed that pulsing begins during the early blastocyst development stage in horses. The median contraction period observed was 0.22 hours (with a range from 0.08 to 2 hours) resulting in an approximate 12.0% reduction in the size of the embryos.
• Following contraction, the embryos were observed to expand over a median time of 3.3 hours (range from 0.75 to 9 hours), with an increase in size of around 16.9%.
• Pulsing was also observed in in vivo-produced embryos from mares 6.5 days after ovulation, and it continues during the expansion of the blastocysts.

Implications and Future Studies

• The phenomenon of embryo pulsing is thought to have an association with embryo quality and implantation rates as per studies in human IVF procedures, indicating its potential importance in equine in vitro production procedures.
• The pulsing observed in in vivo-produced embryos may explain the variability in morphology often seen in collected or transported embryos.
• The researchers suggest the need for further investigations to fully understand the underlying mechanisms of embryo pulsing, its correlation with embryo quality, and its impact on embryo transfer outcomes in horses.