Morphological, histological and histochemical studies of the gonads of ovine freemartins.

Freemartins are XX/XY chimaeras that develop as a result of the fusion of the placental circulation of at least one male and one female fetus. Of 19 freemartin ewes, 13 had testis-like structures, seven of them in an abdominal position and six in an inguinal position. Histologically, their gonads had structures resembling seminiferous tubules and interstitial cells, and grossly, most had structures derived from the mesonephric ducts (vasa deferentia, epididymides and vesicular glands). The other six freemartin ewes had small, undifferentiated gonads that lacked either follicles or seminiferous tubule-like structures. They also lacked any structures derived from the mesonephric ducts. No derivatives of the paramesonephric ducts were detectable in any of the freemartin ewes. The gonads of the male-type freemartins stained immunocytochemically for 3beta-hydroxysteroid dehydrogenase (3beta-HSD) and histochemically for alkaline phosphatase (AP) in a similar way to, but more extensively and intensely than, the gonads of normal rams, and the staining was confined to interstitial cell-like structures. The staining in the undifferentiated-type freemartins was weak, but both 3beta-HSD and AP were present in unidentified cell types.