The Visual Guide to
Equine Reproduction
Reproductive Technology: Embryos
![Expanding Blastocyst.](images/eq00064.jpg)
Expanding Blastocyst.
The zona pellucida is becoming thinner due to the expansion of the blastocyst. The inner cell mass is a small circumscribed dark area. Trophoblast cells can be seen around the translucent blastocele.
Ball BA (1987)
![Day 7, Expanded Blastocyst.](images/eq00065.jpg)
Day 7, Expanded Blastocyst.
The zona pellucida has become very thin. The diameter of the embryo has also noticeably increased. The embryo sometimes takes on the appearance of a golf ball. Day 7.
Ball BA (1987)
![Unfertilized Ovum.](images/eq00063.jpg)
Unfertilized Ovum.
Unfertilized ovum (UFO) collected on Day 7. Note the fragmentation of the cytoplasm.
Ball BA (1987)
![Day 20 Embryo.](images/eq00126.jpg)
Day 20 Embryo.
Day 20 embryo surrounded by the trophoblast. The embryo itself is 5 mm long.
Bergin WC (1973)
![Degenerating Embryo.](images/eq00133.jpg)
Degenerating Embryo.
Early 6-cell embryo in the process of degenerating. One blastomere at 10 o'clock is still intact.
Bergin WC (1973)
![Degenerating 8-cell Embryo.](images/eq00142.jpg)
Degenerating 8-cell Embryo.
Degenerating 8-cell embryo. The blastomeres have taken on a granular appearance.
Bergin WC (1973)
![Early Degenerating Embryo.](images/eq00156.jpg)
Early Degenerating Embryo.
Six- to eight-cell degenerating embryo. One large original 2-cell blastomere is still intact. Spermatozoa are present in the zona pellucida, on the right.
Bergin WC (1973)