American Fancy Rat & Mouse Association

This article is from the Fall 2000 AFRMA Rat & Mouse Tales news-magazine.


Hermaphroditic Rat?; RE: Skin Mass/Mass Pops Out

By Carmen Jane Booth, D.V.M.

Hermaphroditic Rat?

Sarah Simon, Colorado, e-mail
Q Question for you, maybe you’ve already heard this one a million times, but . . . I went to the Colorado Springs Humane Society to rescue a “male” rattie named “Ethel.” (You can see the identity problems arising already.) Anyhow, while the vets swore “Ethel” was a boy, I turned Ethel upside down and closely examined “her” only to find . . . Ethel possessed physical traits of both sexes! To be blunt, Ethel had a penis and a vulva and tiny little testes noticeable not to the eye, but only by very gently squeezing. Ethel was a sweet, loving rat, but I sadly had to leave “him/her” at the dog pound due to the fear of the possible ramifications of placing him/her in a giant ferret-size kingdom full of large bull ratties. (I currently have six lovable, big boys.)

Did I overreact? Is this a common result of overbreeding by humans?

Answer from Lorryta Harms
Hermaphrodites are not the product of overbreeding, they are simply a genetic phenomenon. Hermaphrodites are usually “more” one sex than the other, being more female or more male. It sounds to me as though Ethel may have been more female, due to the small testes, but that’s just my opinion If he/she was, in fact, more female, it is more than probable that she could reproduce. The info I found said that “female” hermaphrodites can reproduce, but litter sizes are small. As for the “males,” it said that they will go through the mating process, but produce no sperm, therefore they are sterile. This had to do with the testes being small and underdeveloped. Also, generally being located inside the body cavity, body heat inhibits the production of sperm. I don’t think you overreacted in any way. Actually, it was very responsible of you not to want to take the chance of “her” reproducing. Any responsible breeder/pet owner will not breed or take chances with breeding an animal with a genetic defect. Don’t feel guilty, you definitely did the right thing in this case.

Answer from Carmen Jane Booth, D.V.M.
The presence of external genitalia with both a male and a female feature is definitely abnormal. The diagnosis is ambiguous sexual differentiation and the rat would be called intersex. Intersex is a term that denotes those developmental abnormalities in which there is disagreement between the genetic (chromosomes), gonadal (testis, or ovary), and/or phenotypic (external genitalia). To determine if this rat is a true hermaphrodite or pseudohemaphrodite, the gonads would have to be examined. True hermaphrodites have both ovarian and testicular tissue and varying degrees of internal reproductive tract and external genital ambiguity. These animals are usually infertile, although on rare occasions if they have one functioning ovary and an intact uterus, they may ovulate and become pregnant if bred. Pseudohemaphrodies have the gonads of only one sex, and the external genitalia have features of the opposite sex. Male pseudohemaphrodites are more common than female. They usually have testis (no sperm), a partial to complete uterus, and vulva with a clitoris that looks more like a penis. It would be my guess that this animal is a male pseudohemaphrodite and likely infertile. The cause of intersex is errors in gonadal differentiation (gonadogenesis) during embryogenesis.

Skin Mass/Mass Pops Out (Re: Vol. 16 No. 3 issue, pg. 17)

Debbie “The Rat Lady” Ducommun, The Rat Fan Club, Chico, CA
Q I wanted to comment on a medical question that appeared in Vol. 16 No. 3 of AFRMA Rat & Mouse Tales. Nancy Ferris wrote about a hard mass that popped out of the skin on her rat’s back. Dr. Booth wrote that without histopathology it was impossible to tell what the mass was, but I disagree. This mass was undoubtedly a sebaceous cyst, a minor benign problem that is fairly common in rats, especially males.

A I disagree with this statement. I have looked at both grossly (macroscopically) and microscopically at hundreds of masses and thousands of tissues in the years that I have been studying pathology. Many different tumors can look very similar grossly but can be very different when viewed under the microscope. This tumor, whatever its cell type of origin, had mineralized. Was it originally a sebaceous cyst, a follicular cyst, or how about a calcifying epithelioma, acanthoma, or trichoepithelioma. Who knows? I sure can’t say with accuracy without seeing it on a slide. I don’t have a crystal ball or mental telepathy. All I can say is that it was probably benign. In pathology we can only guess what something might be by macroscopic examination. It is only by microscopic examination that a definitive diagnosis be given.

Let me put it another way, how would people feel if it were them who had this mass and their human doctor gave them a diagnosis without confirming it histologically? It would be malpractice, in my humble opinion.

There are numerous texts (both veterinary and human) on dermatopathology. I could list all the possible things that this could have been, but what purpose would that serve? I cannot disagree that it could have been a sebaceous cyst, but I will counter in that it could have been something else and without histopathology, we will never know. Which is what I said originally. *

Back to top

Updated March 20, 2014