Hermaphroditic Teaser "Mare"

Q. A stud farm I once visited was using a hermaphrodite mare as a teaser, with none of the problems of having a stallion (i.e., no problem with mares in foal to the teaser stallion should he escape). How can you tell if a mare is a hermaphrodite (what does she look like, and what is her behavior like)?


A. What you are looking for is a "male pseudohermaphrodite." This anomaly is an animal with the outward appearance of a mare, but with testes instead of ovaries. The behavior is that of a stallion. The testes are almost always inside the abdomen, but the external genitalia is the key. The usual pattern is an overdeveloped vulva and clitoris that resemble the glans penis of a male. You might look a long time, as these horses are not very common.

Another good potential teaser is a mare with a granulosa cell tumor of the ovary, which frequently causes stallion-like behavior.

One word of caution; some of these animals become aggressive and can be difficult to handle.

About the Author

A.C. Asbury, DVM

A. C. (Woody) Asbury received his DVM from Michigan State University in 1956, then spent 21 years in California in breeding farm practice and at UC Davis. He joined the faculty at the University of Florida in 1977 and was involved in teaching, research, and administration until 1996. An Emeritus Professor at Florida, he lives in Kentucky, where he and his wife are developing a small farm.

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