When is a filly not a filly?

The research uncovers a rare genetic anomaly amongst horses whereby an intersex foal, with both diploid and triploid cells, was identified. The article advocates for accepting such animals into racing if they undergo gonadectomy and are marked as geldings, thus easing potential inappropriate attention.

Diploid-Triploid Chimaerism in Horses

• The article reports on the first-ever case of a horse, more specifically a foal, with diploid-triploid chimaerism, a condition where two distinct types of cells with different genetic make-up are found in the same organism.
• A karyotype study of peripheral lymphocytes (a type of white blood cell) from the foal showed the presence of a normal female chromosome constitution.
• Interestingly, the clinical features didn’t align with the findings, prompting further investigation into another cell line, using skin fibroblast culture this time.

Clinical Investigation and Findings

• The further study revealed two cell lines – the minority was normal diploid female cells with an XX chromosome, while the majority were abnormal triploid cells with XXY chromosomes.
• The research suggests that intersex horses, having both male and female characteristics, might be more common than generally assumed, citing a study that verified existence of chromosome anomaly in 2.7% of equine cases, and an intersex rate of 0.02% in some family of horses.

Registration and Classification of Intersex Horses

• The International Studbook Committee, responsible for registering horses, had been asked to consider the registration of intersex horses.
• Although no specific, universal decision has been reached on this yet, individual countries can decide on their registration policies for intersex horses.
• For instance, Weatherbys in Great Britain and Ireland have decided to allow registration for any such animals born in these countries, categorising their sex as ‘ambiguous’.
• They also issue a caution for breeders and potential purchasers, noting that rules, under which such animals may be allowed to race, may differ from country to country and, at times, racing permission may be denied to them.

Management and Future Recommendations

• The report suggests that referring to an intersex foal as ‘ambiguous’ may not be popular among Thoroughbred breeders, potentially making the progeny of intersex horses less attractive for purchase. However, there is no scientific evidence supporting this biased view.
• Developing a system wherein all intersex horses undergo gonadectomy (removal of reproductive organs) before their first race and then racing them under the ‘gelding’ category could minimize media attention.
• A revision in the definition of ‘gelding’ to include post-gonadectomy intersex horses could prevent complications in horse races and studbooks.
• Even though some may argue that these horses should not be registered for racing, the article insists they are as much Thoroughbred racehorses as any other, and castration or their sexual status does not affect their racing competence.