The Equine Placenta: Mare and Foal Interactions

Abby L. Fowden, University of Cambridge, UK, discussed nutritive and endocrine functions of the equine placenta at the first Equine Placenta Workshop held at the Gluck Equine Research Center at the University of Kentucky on Dec. 5-6. She said the functions of the placenta are as a barrier, for transport of nutrients and waste, nutrient production, and hormone production.

Placental efficiency of the horse is good. She defined that by looking at grams of fetus that can be produced based on grams of placenta. She said the horse comes out on top when comparing various mammals, with 20 grams of fetus produced per gram of placenta based on maximum values. For comparison, humans only produce six grams of fetus per gram of placenta.

Oxygen transfer across the placenta is important. Her research has shown that while sheep reach a plateau where the ewe can't transfer higher levels of oxygen, the horse can transfer ever-increasing amounts of oxygen. She said a similar result is seen in looking at glucose levels from the mare to the fetus--there isn't a plateau. Fowden suggested that knowledge might help practitioners aid a fetus that is undergoing some sort of stress or when a placenta is compromised.

Fowden said that horses have low placental amino acid transport compared to other animals. She said that perhaps shows a low need of horses for amino acids.

She reminded that as the fetus grows, its demand for nutrients also rises. The equine placenta keeps on growing throughout gestation by increasing the length of the villi and increasing their number of branches. This increases the surface area for exchange of nutrients. Villi are the projections of epithelial cells that connect with the corresponding maternal crypts. Any increase in length of villi has a huge effect on exchange of nutrients and oxygen because of the expanded area of the tissues.

She said while the horse placenta is very efficient in transferring nutrients, it needs high amounts of nutrients itself. The placenta is continually producing hormones and growth factors, and the production of hormones changes as the fetus ages.
There is a complex pathway of hormones back and forth from the mare to the fetus, and vice versa, that changes with gestational age. Some of these hormonal concentrations can provide an index of placental well-being.


About the Author

Kimberly S. Brown

Kimberly S. Brown was the Publisher/Editor of The Horse: Your Guide To Equine Health Care from June 2008 to March 2010, and she served in various positions at Blood-Horse Publications since 1980.

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