Azoospermia and Y Chromosome-Autosome Translocation in a Friesian Stallion.

This case report describes spermatogenic arrest and azoospermia in a stallion with a unique Y chromosome-autosome translocation. Clinical diagnosis of azoospermia was based on history of infertility and evaluation of ejaculates collected for artificial insemination. Clinical and ultrasonographic evaluation of the external and internal genitalia did not reveal any abnormalities except for smaller than normal testicular size. Azoospermia of testicular origin was confirmed by determining alkaline phosphatase concentration in semen. Histological evaluation of testicular tissue after castration confirmed early spermatogenic arrest. Cytogenetic evaluation showed the presence of translocation between the Y chromosome and chromosome 13. To the authors' knowledge, this is the first case of azoospermia with a cytogenetically detected Y chromosome abnormality, suggesting that the horse Y chromosome may carry sequences critical for normal spermatogenesis.