Equine Disorders of Sexual Development


Sex Chromosome DSD




Gonadal dysgenesis (including ovotesticular)

Villagomez et al (2011) reported six cases of XX DSD. They were all SRY -negative. The majority were probably gonadal dysgenesis with two identified as ovotestes and the others were not examined histologically.All had a female phenotype.



Tories et al 2014) reported on a single horse that had abdominal testes without epididymis and a female phenotype with ambiguous genitalia. An attempt to measure testosterone done but none was found. The genotype was XX, SRY -negative.




Gonadal dysgenesis

Villagomez et al (2011) had six cases of XY DSD but none of them had histological evaluation of the gonads. All were SRY -negative and all had a female phenotype and gonadal dysgenesis was assumed.





Gonadal Dysgenesis




Female phenotype

Villagomez et al (2011) reported on five cases of XY DSD that were SRY -positive. Four had abdominal testes. All had a female phenotype. No measurement of testosterone receptor but it can be assumed that the primary defect is in a failure of masculinisation of the genitalia.

Male Phenotype


Cryptorchid male horses are XY SRY -positive with testes and a male phenotype.

Cryptorchid horses have an equal distribution of the undescended testis - there is an equal number affected on the left and right side. Those that are on the left side I usually intra-abdominal. Those on the right side are located just inside the inguinal ring, within the inguinal ring or just outside the inguinal ring.

There is no convincing evidence of heritability of cryptorchidism in horses.

Almeida et al (2013) found that cryptorchid testes had increased AMH and AMHR2 immunolabelling when compared with normal testes. This suggests a failure of maturation of Sertoli cells and/or lack of testosterone suppression. Failure of Sertoli cell maturation in the cryptorchid testis may also be attributed to AR abnormalities and/or a consequence of lack of testosterone suppression due to decreased 3bHSD. Cyclin-dependent kinase (CDKN1B)was not expressed in Sertoli cells of cryptorchid testes suggesting that Sertoli cells are still proliferating, which is also a characteristic of the immature testis. In addition, Cx43 expression is decreased in the cryptorchid testis, indicating a disruption in intercellular communication.

Gardner et al (2017) reported on a single case of a cryptorchid horse with testicular necrosis. They assumed that the cause of cryptorchidism was testicular necrosis. This unfortunately ignores evidence that cryptorchid testes can undergo degeneration, necrosis, and torsion because they are cryptorchid.


Almeida J, A. J. Conley AJ, Ball BA (2013) Expression of anti-Müllerian hormone, CDKN1B, connexin 43, androgen receptor and steroidogenic enzymes in the equine cryptorchid testis. Equine vet J 2013 45: 538-545

Gardner AK, Santschi EM, Aeffner F, Pigott JH, Russell DS. Testicular ischaemic necrosis as a cause of equine cryptorchidism. Equine Vet Edu 2017; 29: 314-317

Stout TAE, (2013) Can and should we do more to reduce the incidence of cryptorchidism? Equine vet J 2013 45: 531-532

Torres A, Silva JF, Bernardes N, Sales Luı´s J, Lopes da Costa1 L (2012). 64, XX, SRY-negative, Testicular DSD Syndrome in a Lusitano Horse. Reprod Dom Anim 2012,

Villagómez DAF, Lear TL, Chenier T, Lee S, McGee RB, Cahill J, Foster RA, Reyes E, St John E, King WA. (2010) Equine Disorders of Sexual development in 17 mares including XX, SRY -negative, XY, SRY -negative and XY, SRY -positive genotypes. Sex Develop 2011;5(1):16-25.