Koko’s aggressive female-mounting behaviour raised suspicion
Written by Mike Treadgold
Recent tests completed at the Ontario Veterinary College (OVC) have determined that Koko, a horse that appeared to be a mare (female) was, in fact, a (stallion) male, and part of a family of intersex horses.
Researchers Allan King, Tracy Chenier and Daniel Villagomez discovered that not only was Koko an intersex horse, but so are her sister, Sequoia, and cousin, Pandora. The researchers are the first to identify a rare genetic abnormality in a family of horses called pseudo-hermaphroditism.
Photo courtesy.
Observers originally thought that Koko had an ovarian tumour, which heightens testosterone levels and often causes aggressive behaviour that is more commonly exhibited by stallions. It wasn’t until tests were done on Koko’s reproductive system that internal testes were found. Further chromosome studies concluded that Koko had the male XY genotype.
“It was a very exciting discovery,” said Chenier, in a press release on the university’s website. “To be expecting a tumour but discover an entirely different internal system than anticipated sparked a lot of questions.”
When similar diagnoses were applied to Sequoia and Pandora, the condition was deemed hereditary. Using this discovery, the researchers are continuing their research on genetic mutation.
“Because these horses are from the same family line, the condition is likely a genetically heritable one,” said Chenier in the release.
Upon the discovery of Koko’s internal testes, they were surgically removed; researchers hoped this procedure would lessen her aggressive behaviour. The surgery and outcome went as planned, leaving Koko with a much calmer demeanor.
“Before the surgery, she was so aggressive that it was too dangerous to ride her,” said owner Sam Campbell. “But she is completely different now. She is an incredibly lovely horse.”
Given the success of Koko’s procedure, similar surgical removals of the testes were performed on Sequoia and Pandora at the OVC.
Similar discoveries were later found in two American standardbred horses, which had excessively high levels of testosterone. Initially, it was thought that these testosterone levels were due to steroid use, but this suggestion was later disproved when the internal testes were discovered.
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