Of Horse

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Help!  The Girl Is A Boy!
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Help! The Girl Is A Boy!

I recently heard through a friend about a rather unusual foal that had been born at her stables some years ago. Gender is instantly recognisable in most newborn foals; a quick glance under the tail usually suffices but this foal was different and caused much puzzlement among the other liveries.

The structures in the perineal area under the foal’s tail looked initially like that of a filly, but on closer examination an enlargement at the bottom of the vulva looked distinctly like a tiny penis. All the other foals in that year’s crop were normal and healthy. The foal was turned out with her peers and the brood mares for the next twelve months until weaning. All went well until the rapidly growing youngster was spotted trying to mount one of the mares that had come into season; very strange behaviour for a filly foal!

The foals were duly weaned as yearlings and turned away again. Then things began to change. As the horse matured, she became stocky with a large neck and chest and her behaviour was becoming more like that of a colt.  She was very vocal when one of the brood mares came into season and when the yard stallion was working, although she now had a small udder and to all intents and purposes appeared to be a filly. Things started to get tricky as she grew older.  She was rapidly becoming difficult to handle and could be very aggressive towards the other youngsters and her handler too.  Billy's owner was at her wit's end.  The filly was becoming dangerous and it looked as though having her put to sleep might be the only sensible course of action available.

Finally, a veterinary examination was carried out including ultrasonography. The mystery deepened; where you would usually expect to see ovaries, there were what appeared to be testes and there was no obvious uterus or cervix. Laboratory tests showed that the horse did have small levels of testosterone in its blood and an analysis of the chromosomes revealed that the horse was in fact genetically male.

‘Billy The Filly’ as she/he had become known, was a pseudo-hermaphrodite; male genetically, but with certain female physiological characteristics. The vet explained that the horse was essentially a cryptorchid stallion and as such the undescended testes should be removed surgically as horses like this tend towards unpredictable and aggressive behaviour. They are also at risk from medical conditions like testicular tumours and torsion of the spermatic cord.

This intersex condition is thankfully pretty rare in equines and when it does occur it is usually seen as in this case. Intersex horses are sterile so cannot be used for breeding but they can still be used as performance horses or companions as they are otherwise healthy. Following the operation, the testosterone levels in Billy’s blood dropped, the little penis-like growth shrank and virtually disappeared and her temperament changed dramatically. She went on to become a friendly, docile horse who excelled in jumping and was a much-loved family pet.


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  1. PonyGirl
    One of the trainers I worked for in Dallas had a hermaphrodite horse. The horse was gelded and did not display any weird hormonal tendencies. The Racing Commission told Danny he could race the horse either as a gelding or a filly, but not both. Danny chose to run him/her as a male. They named the horse Sexcetera.
    1. autumnap
      Crikey, that's so confusing; for both the owner and the horse! It seems to depend on the nature of the mixed up gender as to whether it affects the temperament. Great name though!!
  2. Maureen
    Hope he/she is ok now

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