Diagnosis of XX/XY blood cell chimerism at low percentage in horse

Disorders of sexual development (DSDs) are common in horses and cause economic loss in horse breeding. Thus, it is important to develop methods for unambiguous and fast identification of affected horses shortly after birth, as well as those that may propagate the condition to the next generation. Genetic causes of DSDs are multivarious and still little known, and thus development of diagnostic tests requires accumulating knowledge about individual cases and their etiologies. In particular, it is necessary to perform clinical, ultrasound, surgical, histological, cytogenetic, and genetic analyses with close attention in all the affected individuals. This report describes the case of a XX/XY chimeric horse with reproductive apparatus abnormalities and a very low percentage of XY cell in blood highlighting that to avoid undiagnosed case of cell chimeras, above all when studying DSD cases, it is essential to perform both genetic and cytogenetic analyses possibly on more than one tissue.