Establishment of pregnancies after serial dilution or direct transfer by vitrified equine embryos.

The research explores the in vivo viability of horse embryos, post-vitrification, assessing whether the size of an embryo affects the success of pregnancy. These experiments involve the use of a method called vitrification, a rapid freezing technique to preserve the living cells of an embryo, which is then warmed and transferred into a mare. Outcomes indicate that smaller embryos have a higher chance of resulting in successful pregnancies.

Experiment Design and Procedure

• The study was conducted using two separate experiments.
• The first experiment concentrated on the procedure of embryo vitrification. The equine embryos were subjected to vitrification solutions of ascending ethylene glycol and glycerol concentrations.
• The final solution had 3.4 M glycerol and 4.6 M ethylene glycol concocted in a base medium of phosphate-buffered saline.
• After vitrification, the embryos were warmed employing a two-step dilution method before being transferred into recipients.

Study Findings

• No pregnancies were observed after the transfer of larger blastocyst embryos (those greater than 300 micrometers).
• However, pregnancy was established when smaller embryos (morulae or blastocysts equal to or smaller than 300 micrometers) were transferred, as reflected in the occurrence of four embryonic vesicles out of six (67%).
• The second experiment showed that the rate of embryo recovery per ovulation was similar for collections on Day 6 (28 out of 36, 78%) and Days 7 and 8 (30 out of 48, 62%).
• Embryos that were equal to or smaller than 300 micrometers, and embryos larger than 300 micrometers, were vitrified, thawed, and transferred using the same process as in the first experiment.
• Additionally, some embryos equal to or smaller than 300 micrometers were also transferred using a direct-transfer procedure (DT).
• Embryo development rates to Day 16 revealed no difference between embryos equal to or smaller than 300 micrometers that underwent the first experiment’s procedure and those transferred by DT.
• In contrast, embryos over 300 micrometers resulted in no embryonic vesicles, indicating unsuccessful pregnancies.

Significant Outcomes

• Overall, the study suggests that vitrification is more effective for smaller embryos, and the experiment demonstrates the possible viability of freezing equine embryos to ensure species survival, improve breeding strategies, etc.
• This research is especially important considering breeding timelines in equine reproduction, and effectiveness of the vitrification in maintaining the viability of the embryos.
• The insignificant difference in success rates between the small embryos treated via the first experiment’s method and those transferred directly shows that vitrification and direct transfer are equally viable techniques for smaller embryos.