Stage-specific formation of the equine blastocyst capsule is instrumental to hatching and to embryonic survival in vivo.

The research studied the role of a protective “capsule” formed around horse embryos in the early stages of development, finding that it plays a key role in their survival and successful hatching.

Background

• The study focuses on an unusual part of horse embryonic development – the creation of a clear, non-cellular ‘capsule’ overlaying the embryo and underneath the zona pellucida, a protective layer around the embryo.
• This capsule is observable about 6 to 7 days post ovulation and fully wraps around the embryo, remaining in place until about day 23 of gestation.

The Study and Results

• To analyze the role of this capsule, the researchers used a micromanipulator to carefully remove the capsule from fifteen 6-7 day old embryos.
• The embryos, devoid of their capsules, were then surgically transferred into recipient mares to see if they would develop into noticeable pregnancies.
• None of the capsule-free embryos developed into detectable pregnancies. In contrast, four out of six embryos that remained ‘encapsulated’ developed normally into pregnancies.

Importance of Capsule

• These results clearly demonstrate the capsule’s significance in embryonic survival. Without it, the embryo did not develop properly.
• Additionally, the researchers posited a theory about the mechanism of how horse embryos ‘hatch’ from the zona pellucida, implying it may be the expanding capsule’s force causing the zona to literally burst open, allowing the embryo to ‘hatch’ and continue its gestation in the uterus. This hypothesis was formulated from watching the embryos microscopically during the manipulation and collection process.