Disorders of sexual development in the domestic horse, Equus caballus.

This research article offers a historical overview and summarization of the investigations conducted on disorders of sexual development in horses that can cause infertility. Predominantly relying on cytogenetic analysis, this study also outlines the more recent molecular technologies that have been developed to determine sex genetic mutations responsible for abnormal sex determination.

Historical Developments

• Since the early 1970s, disorders involving sexual development, which result in infertility, have been a significant subject of study in the field of Equus caballus or domestic horse research.
• Cytogenetic analysis, primarily through karyotyping—a method that visualizes an organism’s chromosomes—has been utilized as the main tool in these investigations.

Range of Abnormalities

• These abnormalities cover a broad range, from phenotypically normal mares that possess gonadal dysgenesis (a condition causing improper development of the gonads) to horses with ambiguous external genitalia along with both male and female internal organs.
• While cytogenetic analysis aids in determining the genetic sex of these horses, it falls short in identifying mutations or deletions of genes involved in the sex determination pathway, hence leaving a portion of the mystery underexplored.

Molecular Technologies

• In recent times, the introduction of molecular technologies has supplemented cytogenetic analysis. These technological advancements have proven beneficial in confirming the results observed through cytogenetic analysis.
• More importantly, these technologies have offered assistance in identifying the genetic causes of abnormal sex determination in horses, thus addressing the prior limitation of not being able to detect gene mutations or deletions.

Summary of Past Cases

• The study also provides a review and summary of the reported cases concerning abnormal sexual development in horses over the last four to five decades. This serves as an overview of the progress made in the field so far.