A Case of Ambiguous External Genitalia in a Thoroughbred Male Horse with 63,XO/64,XY Mosaic Karyotype

Abstract

A Thoroughbred colt with ambiguous external genitalia was presented for clinical and histological examinations. The colt had a short penis, located between his hind limbs and faced backward. The measurements of luteinizing hormone, follicle stimulating hormone, testosterone and ir-inhibin showed a tendency to increase gradually from April. Both sex-determining region of the Y chromosome and amelogenin gene fragments were detected by PCR method. The cytogenetic analysis revealed the 63,XO/64,XY mosaic karyotype (ratio 83:17). In autopsy, immature symmetrical subcutaneous testes were found in the inguinal regions. The testes and the other accessory sex organs were histologically normal. These results add to our knowledge of chromosomal abnormality and information of disorders of sex development in horse.