Physical, behavioral, endocrinologic, and cytogenetic evaluation of two Standardbred racehorses competing as mares with an intersex condition and high postrace serum testosterone concentrations.

Case Description: 2 Standardbred racehorses that had been winning races while competing as mares underwent postrace drug testing and had serum testosterone concentrations above the acceptable limit for female racehorses.

Clinical Findings: Initial physical examinations by the referring veterinarian revealed ambiguous external genitalia and suspected intra-abdominally located testes leading to a preliminary diagnosis of male pseudohermaphroditism. Horses were referred for further evaluation of sex. Physical examination of the external genitalia confirmed the findings of the referring veterinarian. Transrectal palpation and ultrasonography revealed gonads with an ultrasonographic appearance of testes. On cytogenetic analysis, both horses were determined to have a 64,XY karyotype and 8 intact Y chromosome markers and 5 SRY gene markers, which were indicative of a genetic male and confirmed an intersex condition. Additionally, both horses had some male-type behavior and endocrinologic findings consistent with those of sexually intact males.

Treatment And Outcome: Taken together, these findings confirmed that both horses were male pseudohermaphrodites. Both horses returned to racing competition as males.

Clinical Relevance: As of October 1, 2008, the Pennsylvania Horse and Harness Racing Commissions implemented a postrace drug testing policy that included analysis of blood samples for anabolic and androgenic steroids and set maximum allowable concentrations of testosterone for racing geldings and females. Within 8 months of initiation of this drug testing policy, the 2 horses of this report were identified as having an intersex condition. This raises the possibility that intersex conditions may be more common in racing Standardbreds than was previously suspected.