Disorders of Sexual Development




Chromosomal DSD.



Chimerism (XX/XY)


David A. Schneider, Ahmed Tibary, Terje Raudsepp, Pranab J. Das, and Katherine I. O'Rourke (2009) Blood chimerism confounds genetic relative susceptibility testing for classical scrapie in sheep J Vet Diagn Invest 2009 21: 295-305. [Abstract] [Full Text] [PDF]  
Haematopoietic Chimerism from sharing fetal vessels occurs infrequently in the general population.

Padula AM. (2005) The freemartin syndrome: an update. Anim Reprod Sci. 2005 87: 93-109.
Brace MD, Peters O, Menzies P, King WA, Nino-Soto MI. (2008) Sex chromosome chimerism and the freemartin syndrome in Rideau Arcott sheep. Cytogenet Genome Res. 2008;120(1-2):132-9.



XX ovarian DSD


Lamm et al 2012 reported on the effects of treatment of pregnant ewes with experimental treatment with Testosterone and DHT as a model for the effects of endocrine disruptors in pregnancy. They described the effects on the developing fetus expecially with masculiniation of the external genitalia and formation of male accessory genital glands.


Lamm CG, Hastie PM, Evans NP, Robinson JE. (2012) Masculinization of the Distal Tubular and External Genitalia in Female Sheep With Prenatal Androgen Exposure. Vet Pathol 2012, 49: 546-551,




XY Testicular DSD


The prevalence of congenital disorders of the male reproductive tract is reported by several authors and summarised in this table

Disorder Foster et al Smith et al    


845 7307*    
Testicular hypoplasia 20 80 (1.1)    
Cryptorchidism 15 75    
notched scrotum 6 34    
hypospadias 0 15    
SAMD 2 4    
SGEH 10 2    
scrotal hernia 3 3    

* 6521 lambs and hoggets, 786 adult rams


Foster RA, Ladds PW, Hoffman D, Briggs GD. (1989) Pathology of reproductive tracts of merino rams in north western Queensland. Aust Vet J 1989; 66: 262-264.

Smith KC, Brown PJ, Barr FJ. (2014) A survey of congenital reproductive abnormalities in rams in abattoirs in South west England. Reprod Domest Anim 2012; 47: 740-745



Testicular hypoplasia

Testicular hypoplasia is where the testis does not develop to its normal size. It is always accompanied by a failure of the epididymis to acquire its normal size. Most cases of hypoplasia are because of cryptorchidism, but in this section, primary hypoplasia is limited to those situations where the testis has descended normally. Hypoplasia is almost always seen as a failure of the prepubertal testis to enlarge, but there may be cases where even the prepubertal testis is smaller than normal. Hypoplasia is best diagnosed clinically by identifying that the testis has not increased in size from puberty.

Microscopic changes of hypoplasia include cessation of spermatogenesis at some stage, with either degeneration or excessive apoptosis of the germinal epithelium. The most severe cases of hypoplasia have a Sertoli cell-only pattern or they have some normal and abnormal tubules intermixed, often with affected tubules being in the more dorsal part of the testis.  

Testicular hypoplasia of rams is consistently the most common reported DSD of the male reproductive tract. It is usually a sporadic disease that is either bilateral or unilateral. The disease is not well studied. A condition resembling Klinefelter’s syndrome, with an XXY genotype, is reported. Zinc deficiency is implicated in some cases.

Various degrees of hypoplasia are recognized, and affected testes may have tubules that, at the extreme are about 90 µm in diameter (normal 160 µm) and lined by mostly fetal Sertoli cells. There is a report of an outbreak of gonadal hypoplasia of multiple rams born within a short time frame. The affected testes were uniformly small and had a “Sertoli cell-only” pattern histologically. An environmental cause was suspected.

Cryptorchidism (Retained testes)

In rams, cryptorchidism often has an autosomal recessive mode of inheritance, but may also be due to a dominant gene with incomplete penetrance. Unilateral maldescent is more common (Fig 5.3) than bilateral involvement, and the right testis is most often retained. Hemicastration is likely in unilateral cryptorchid animals. Some ram lambs, inadvertently, have only their scrotum removed during attemped castration, leaving the testes in an “induced cryptorchid” state. Cryptorchidism in sheep has an increased prevalence in polled animals.