Production of monozygotic (identical) horse twins by embryo micromanipulation.

This research explores the use of manipulation techniques, involving injecting horse embryos into pig zonas pellucidae, to successfully create identical horse twins. The transferred embryos spent a certain number of days in sheep for further growth before being transferred back to mares, with a higher rate of success found in mares that were not recent embryo donors.

Technique Involved in the Embryo Micromanipulation

• A total of 23 pony mares went under surgery to recover embryos 1-3 days after ovulation.
• The recruitment process involved separating the blastomeres of these embryos.
• These separated cells were then inserted into emptied pig zonas pellucidae, creating 27 “half” and 17 “quarter” micromanipulated embryos.
• This process required detailed micromanipulation techniques to safely relocate the horse egg cells into a receptacle derived from pigs.

Cultivation of Micromanipulated Embryos

• Following the micromanipulation process, the embryos were encapsulated in agar, which is often used as a growing medium in lab studies. This encapsulation likely protected the delicate embryos and provided a controlled environment for their growth.
• The encapsulated embryos were then transferred and grown in the oviducts (tubes that connect a female’s ovaries to her womb) of sheep for a period of 3.5-5 days. This in vivo (in the body) culture allowed the embryos to develop into the late morula or early blastocyst stage, crucial stages of embryo development.

Transfer and Success Rate

• After the in vivo culture period in the sheep, 13 ‘half’ and 17 ‘quarter’ embryos were transferred back into mares, either surgically or non-surgically.
• This process resulted in 10 successful ongoing pregnancies. Impressively, two out of this number resulted in monozygotic, or identical, horse twins. This implies that the micromanipulation process was able to split an individual horse embryo into identical twins, which is a significant milestone in animal reproductive science.
• The study also provides valuable information on the most optimal conditions for embryo transfer. The success rate was higher (10 out of 20) when transferred embryos were implanted into mares that had not recently had their embryos used for the study (recent donors), versus no successful pregnancies in recently operated mares (0 out of 10).