Intersexuality is a rare congenital abnormality in domestic animals. It is reported in numerous species including the swine, goat, horse, cat, and dog. The present work provides an overview of the variety of intersexual conditions known in different dog breeds. Each case was reclassified based on the described gonadal constitution, reproductive tract abnormalities and karyogram, and categorised according to the stages normal sex development is undergoing resulting in three main categories: (1) sex chromosome disorders, (2) disorders of gonadal sex development, and (3) disorders of phenotypic sex development. Reclassification disclosed that the current classification scheme and terminology are inconsistently used in literature masking the real occurrence and frequency of various intersex conditions in dogs. For establishment of an individual, precise and definite diagnosis, introduction of a new nomenclature is proposed as recently recommended for humans. The new terminology is based on the gonosomal constellation and gonadal constitution, contributes to a systematic classification of canine intersex cases, and replaces the common but confusing diagnoses "true hermaphrodite" and "pseudohermaphrodite". The literature survey was supplemented by adding the results from own investigations in a German Pinscher and Berger Picard dog with bilateral ovotestes and ambiguous external genitalia. The diagnostic approach and clinical, pathomorphological and cytogenetic findings were described in detail.
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