Dixie – the Intersexed Mare

Dixie – the

Intersexed Mare

By Dr. Jennifer Fowlie, DVM, MSc, DACVS and Dr. Annie King, DVM • Moore Equine Veterinary Centre

When a mare presents to a veterinarian due to behavioural issues, particularly if they are described as having stallionlike behaviour, an endocrine (hormonal) source is always a consideration. A tumour of the ovary, known as a granulosa thecal cell tumour (“GCT” or “GTCT”), is the most common culprit of stallionlike behaviour in a mare. Thus, generally the steps in working up a mare with behavioural concerns is to ultrasound the ovaries, +/- running a hormone panel (measuring testosterone, progesterone, inhibin and AMH hormones), and then consider removal of the ovary if it is deemed abnormal.

On the left is the testicle that was removed from where the right ovary normally would be and on the right is the very small amount of testicular tissue that was present where the left ovary normally would have been.

Dixie

For Dixie, a 10-year-old Quarter Horse mare, who had been surrendered to a rescue due to stallion-like behaviour, it was hopeful that removal of her ovaries would help correct her behavioural issues. She was known to have long-term behavioural concerns and was acting stallion-like. Pre-operatively on exam it was noted that her uterus was very small on ultrasound, and the vagina abnormally narrowed down to a very small tubular structure. Her right ovary appeared abnormal on ultrasound and the left ovary was very difficult to definitively see on ultrasound. Blood work showed normal progesterone and testosterone, but elevated inhibin (which can be seen with a GCT). Thus, it was elected to perform a laparascopic ovariectomy.

This was performed with the horse standing under sedation with a special camera known as a laparoscope that is used to look into a horse’s abdomen through small incisions in their flank. This view right into the abdomen allows the surgeon to seal the blood vessels to the ovary using cautery (a “Ligasure”), ultimately allowing for the safe removal of the gonads.

What is normally a routine procedure became a little more interesting, rather than having two ovaries Dixie possessed one very small gonad on the left side and a TESTICLE on the right side. These were both in the normal locations for ovaries, but did not look like ovaries! Histopathology revealed that both gonads contained testicular tissue. It is definitely not every day that we remove testicles from a mare! In fact this was the first time we can recall this procedure being performed at Moore Equine. Thus, Dixie was diagnosed as a “Male Pseudohermaphrodite,” as she appeared outwardly like a mare, but had a rudimentary uterus/vagina and testicles.

Pseudohermaphrodite is a rare intersex condition, and is particularly rare in horses. This condition is congenital – meaning it is present from birth. This disorder can be due to chromosomal abnormalities or may be due to a lack of target organ response to testosterone (defect in the hormone receptor or in hormone production). Intersex animals may present differently depending on the individual; often times the clitoris of the horse looks abnormally enlarged (like a rudimentary penis), something that can be seen externally. Since Dixie’s external genitalia appeared normal on examination, the diagnosis of pseudohermaphrodite was not made until the surgical procedure was performed, though the abnormal uterus/vagina was suspect of something unusual going on.

Removal of the testicles has resulted in a dramatic improvement in Dixie’s behaviour and is doing very well post surgery. As with stallions that are gelded later in life, they can sometimes retain some stallion-like behaviours, as their brain has developed with the presence of testicles, but generally a huge change in behaviour is still noted.

Horses always keep us on our toes as veterinarians… when a mare is showing behavioural concerns it may be that they have normal ovaries, have a tumor in their ovaries, or have testicles! In all cases, surgical removal of the gonads can resolve the behavioural concerns.