An intersex (male pseudohermaphrodite) horse with 64XX/XXY mosaicism.

The researchers document a rare case of intersexuality in a horse, exhibiting both XX (female) and XXY (male pseudohermaphrodite) chromosomal types, driving unique physical and behavioral characteristics.

Objective of the Study

• The main objective of this study was to investigate and document the unusual case of a horse exhibiting both male and female physical and behavioral traits. The researchers undertook clinical examinations, pathological studies and chromosomal analysis to understand the underlying cause of this rare phenomenon.

Findings and Clinical Observations

• The horse, which initially appeared to be a female, demonstrated strong male sexual behavior. Morphologically, the horse possessed a small penis that emerged from a rudimentary vagina, an anatomical feature typically associated with females.
• Further investigation revealed the presence of two small testes located in the animal’s abdomen, a characteristic typically found in males. However, the seminiferous tubules within the testes were undifferentiated and harbored only supporting cells, indicating an abnormal sexual development.
• In terms of female reproductive organs, the researchers did not discover any uterus in the horse which further complicated the phenotypic sex classification.

Chromosomal Analysis

• In order to explore the root cause of this intersexuality, the researchers performed a chromosomal analysis. They cultured peripheral blood leucocytes (a type of blood cell involved in counteracting foreign substances and disease in the body) from the horse.
• This culture revealed a chromosomal mosaic condition, where different cells had different numbers of chromosomes. Specifically, they found a combination of 64XX (typical of a normal female horse) and 65XXY (indicative of Klinefelter syndrome, a form of male pseudohermaphroditism). This chromosomal peculiarity explained the mixed male and female characteristics exhibited by the horse.

Conclusion

• The study offers crucial insights about intersexuality in horses, a rare condition linked to chromosomal variations. It enlightens the association between chromosomal mosaicism and the manifestation of mixed male and female characteristics in horses.
• This particular case highlights the potential complexities associated with sex determination in animals, indicating a need for thorough genetic evaluations in inconclusive cases.