An equine cryptorchid with testicular and ovarian tissues.

This research study investigates a rare case of an intersex horse that was initially diagnosed as a cryptorchid, which means it had undescended testes. Upon further examination, the horse was found to have both testicular and ovarian tissues and dual chromosome make-up.

Experiment Process

• The study began with a horse that was clinically diagnosed as a cryptorchid, a condition in which one or both of the testes fail to descend. Cryptorchidism is relatively common in horses, affecting approximately 3% of the equine population.
• The diagnosis was confirmed through surgery, which revealed that the horse was, in fact, a bilateral abdominal cryptorchid. This means both of the horse’s testes were undescended and retained in the abdomen, which is less common than one undescended testis.
• Next, a histological examination was performed on the horse’s left epididymis. This examination revealed the presence of ovarian tissue, indicating that this horse had both testicular (male) and ovarian (female) tissues, a condition known as true hermaphroditism.

Results of Chromosome Analysis

• Researchers then conducted a chromosome analysis of cells from the horse’s testicular and ovarian tissues, as well as skin cells.
• The analysis revealed cells with both 64-XX (female) and 64-XY (male) chromosomal make-up. Notably, the left gonad (the one with the ovarian and testicular tissues) had more XX cells than XY cells, indicating a greater presence of female tissue.
• Despite these findings, the horse displayed external characteristics and behavior consistent with a “routine” cryptorchid. This means it appeared and acted like a typical male horse with undescended testes.

Discussion and Comparison

• The study also involved reviewing other cases of equine intersexes, i.e. horses that exhibit both male and female characteristics or have a discrepancy between their biological sex and expressed (phenotypic) sex.
• The paper discussed theories that could explain the discrepancies observed between the horse’s genetic, gonadal and phenotypic sex. For instance, phenomena such as mosaicism or chimerism could explain the horse’s dual chromosome make-up and presence of both male and female gonadal tissues.

In summary, this study adds valuable insights into our understanding of intersex conditions in equines by providing a detailed examination of a cryptorchid horse found to have both testicular and ovarian tissues and a dual chromosomal make-up.