Klinefelter syndrome in a Holstein-Friesian bull: a case report.

BACKGROUND: This report describes the clinical, laboratory, and post-mortem findings in a 16-month-old Holstein-Friesian bull diagnosed with Klinefelter syndrome, a rare sex chromosome disorder characterised by testicular hypoplasia and infertility. CASE PRESENTATION: During the routine genotype quality control process, the bull was flagged as a suspected XXY (Klinefelter syndrome) based on its genotype data. Analysis of parental genotype data revealed the bull inherited one X chromosome from each parent, indicating a paternal nondisjunction event. Karyotyping subsequently confirmed the 61,XXY chromosome complement. Clinical examination revealed the bull had normal libido with normal testosterone concentration (13.1 nmol/ml) but had a small scrotal circumference (18.5 cm). Post-mortem examination revealed that the bull had bilateral testicular hypoplasia and azoospermia. These findings were consistent with other reports of Klinefelter syndrome in bulls. CONCLUSION: This case highlights the importance of the national genotyping screening program to identify infertile bulls (and females) that should not be considered for breeding. The clinical and post-mortem observations add to the limited veterinary literature on bovine Klinefelter syndrome presentations.