Researching the Equine Embryo

At 14 days, it's shaped like a pear and has a clear line dividing its left side from its right. At 16 days, it resembles a shoe sole, and tiny beginnings of the very complex nervous system are popping up everywhere. For the first time in history, scientists are viewing the fine details of the equine embryo at major stages of early development, thanks to the use of the transmission electron microscope (TEM).

Although it was invented in 1931, the TEM has rarely been used to study horse embryos, especially those older than 12 days, according to Ingrid Walter, PhD, professor and researcher at the Institute of Histology and Embryology in the University of Veterinary Medicine in Vienna, Austria, and primary author of this new research. Using a modern TEM, which can magnify images up to 250,000 times with high quality resolution, Walter and her colleagues examined 14- and 16-day-old embryos (about a half an inch in diameter) to better understand the unique aspects of the developing horse.

"Almost all of the information (about equine embryos) in textbooks is based on other species and might not be true for the horse," Walter said. "This technique is essential to better understand equine development and to enhance in vitro fertilization techniques."

One discovery Walter made was tiny vesicles on the surface of the 16-day embryo which act as a sort of "pump" to absorb fluid. As the embryo travels for more than two weeks in the oviducts and uterus before attaching to the uterine wall, these vesicles provide access to the nutritious secretions of the uterine glands, she said. They were also able to more closely evaluate blister-like structures on the surface, which might serve as a stability and orientation system at the time the embryo attaches to the wall.

Now that this study is completed, Walter is currently working on TEM investigations of 17-day-old equine embryos. "It's astonishing how much progress these embryos can make in 24 hours," she said.

More about the researcher: Ingrid Walter has been interested in the science of reproduction since her undergraduate work in biology and zoology at the University of Vienna. After a brief sabbatical as a guest professor in the Tufts University Medical School in Boston, where she worked on zebra fish molecular biology, she has focused her work primarily on the endometrium and the placenta of many species of animals, including horses. In addition to her research and teaching activities, she runs the VetBioBank (, a collection and storage center for biomedical research tissues, which she established at the University of Vienna in 2007.

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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