• 2.

    Kent MG, Schneller HE, Hegsted RL, et al. Concentration of serum testosterone in XY sex reversed horses. J Endocrinol Invest 1988; 11:609613.

    • Search Google Scholar
    • Export Citation
  • 3.

    Kent MG, Shoffner RN, Hunter A, et al. XY Sex reversal syndrome in the mare: clinical and behavioral studies, H-Y phenotype. Hum Genet 1988; 79:321328.

    • Search Google Scholar
    • Export Citation
  • 4.

    Bartmann CP, Lorber KJ. Laparoscopic gonadectomy in two half-sister horses with male pseudohermaphroditism of the testicular feminisation type. Equine Vet Educ 2003; 15:299303.

    • Search Google Scholar
    • Export Citation
  • 5.

    Kuiper H, Distl O. Intersexuality in horses. Dtsch Tierarztl Wochenschr 2007; 114:5056.

  • 6.

    Wilhelm D, Palmer S, Koopman P. Sex determination and gonadal development in mammals. Physiol Rev 2007; 87:128.

  • 7.

    Raudsepp T, Santani A, Wallner B, et al. A detailed physical map of the horse Y chromosome. Proc Natl Acad Sci U S A 2004; 101:93219326.

  • 8.

    Bugno M, Klukowska J, Słota E, et al. A sporadic case of the sex-reversed mare (64,XY; SRY-negative): molecular and cytogenetic studies of the Y chromosome. Theriogenology 2003; 59:15971603.

    • Search Google Scholar
    • Export Citation
  • 9.

    Abe S, Miyake Y, Kageyama S, et al. Deletion of the Sry region on the Y chromosome detected in a case of equine gonadal hypoplasia (XY female) with abnormal hormonal profiles. Equine Vet J 1999; 31:336338.

    • Search Google Scholar
    • Export Citation
  • 10.

    Bowling AT, Millon L, Hughes JP. An update of chromosomal abnormalities in mares. J Reprod Fertil Suppl1987;(35):149155.

  • 11.

    Buoen LC, Zhang TQ, Weber AF, et al. SRY-negative, XX inter-sex horses: the need for pedigree studies to examine the mode of inheritance of the condition. Equine Vet J 2000; 32:7881.

    • Search Google Scholar
    • Export Citation
  • 12.

    Cammaert S, Coryn M, De Kruif A, et al. Three full sister mares with stallion-like behavior and a high blood testosterone concentration. Equine Vet Sci 1993; 13:220222.

    • Search Google Scholar
    • Export Citation
  • 13.

    Smith LJ, Perkins JD. Laparoscopic-assisted castration of a monorchid male pseudohermaphrodite pony. Equine Vet Educ 2009; 21:295299.

  • 14.

    Power MM & Leadon DPP Diploid-triploid chimaerism (64,XX/96,XXY) in an intersex foal. Equine Vet J 1990; 22:211214.

  • 15.

    Dunn HO, Smiley D, Duncan JR, et al. Two equine true hermaphrodites with 64,XX/64,XY and 63,XO/64,XY chimerism. Cornell Vet 1981; 71:123135.

    • Search Google Scholar
    • Export Citation
  • 16.

    McIlwraith CW, Owen RA, Basrur PK. An equine cryptorchid with testicular and ovarian tissues. Equine Vet J 1976; 8:156160.

  • 17.

    Bugno M, Zabek T, Golonka P, et al. A case of an intersex horse with 63,X/64,XX/65,XX,del(Y)(q?) karyotype. Cytogenet Genome Res 2008; 120:123126.

    • Search Google Scholar
    • Export Citation
  • 18.

    Sultan C, Paris F, Terouanne B, et al. Disorders linked to insufficient androgen action in male children. Hum Reprod Update 2001; 7:314322.

  • 19.

    Mendonca BB, Domenice S, Arnhold IJP, et al. 46,XY disorders of sex development (DSD). Clin Endocrinol (Oxf) 2009; 70:173187.

  • 20.

    Crabbe BG, Freeman DA, Grant BD, et al. Testicular feminization syndrome in a mare. J Am Vet Med Assoc 1992; 200:16891691.

  • 21.

    Howden KJ. Androgen insensitivity syndrome in a Thoroughbred mare (64,XY—Testicular feminization). Can Vet J 2004; 45:501503.

  • 22.

    Meyers-Wallen VN, Schlafer D, Barr I, et al. Sry-negative XX sex reversal in purebred dogs. Mol Reprod Dev 1999; 53:266273.

  • 23.

    Pailhoux E, Vigier B, Vaiman D, et al. Ontogenesis of female-to-male sex-reversal in XX polled goats. Dev Dyn 2002; 224:3950.

  • 24.

    Sìwitonìski M, Jackowiak H, Godynicki S, et al. Familial occurrence of pig intersexes (38,XX; SRY-negative) on a commercial fattening farm. Anim Reprod Sci 2002; 69:117124.

    • Search Google Scholar
    • Export Citation


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

Marc G. Knobbe DVM, MPH, DACT1, Cindy Maenhoudt DVM, DACT2, Regina M. Turner VMD, PhD, DACT3, and Sue M. McDonnell PhD4
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  • 1 Department of Clinical Sciences, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, PA 19348.
  • | 2 Department of Clinical Sciences, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, PA 19348.
  • | 3 Department of Clinical Sciences, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, PA 19348.
  • | 4 Department of Clinical Sciences, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, PA 19348.


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.

Contributor Notes

Dr. Knobbe's present address is 237 Queen St, Philadelphia, PA 19147.

Dr. Maenhoudt's present address is Ecole Nationale Vétérinaire d'Alfort, Centre d'études en reproduction des Carnivores, 7 Av du Général de Gaulle, 94704 Maisons-Alfort, France.

The authors thank Drs. Bhanu P. Chowdhary, Terje Raudsepp, and Pranab J. Das for performing the molecular genetics testing.

Address correspondence to Dr. McDonnell (suemcd@vet.upenn.edu).