Definition :Testicular hypoplasia implies an incomplete development of the germinal epithelium of the seminiferous tubules, due to inadequate numbers of germinal cells within the testis. Lack of germinal cells may arise throughpartial or complete failure of the germinal cells to develop in the yolk sac, failure to migrate to the genital ridge, failure to multiply in the developing gonad, or widespread degeneration of embryonic germinal cells within the primitive gonad.
General information: Mild cases may exhibit moderate oligospermia or poor sperm morphology, but severe cases may be aspermic. A hereditary form of hypoplasia exists in Swedish Highland cattle affecting the left testis more commonly than the right. Formerly, in the UK, many cases were detected when bulls were licensed at 10 months of age; however, the abandoning of such licensing means that the frequency of animals with relative hypoplasia is likely to increase.
A high incidence of hypoplasia occurs in the Welsh Mountain pony, in which the right testis is most commonly affected, and in which an inherited aetiology is probable.
Sporadic cases of hypoplasia occur in all species, occasionally, but not often, with a clear familial predisposition.
Klinefelter’s syndrome (karyotype XXY): is a sporadic cause of testicular hypoplasia in bulls, and has been reported in rams, boars and dogs. It is also particularly associated with male tortoiseshell and calico cats.
· The spermatogonia of such animals fail to develop,
· Seminiferous tubules are virtually devoid of spermatogenic cells.
· The semen of such animals is therefore aspermic,
· The Leydig cells being unaffected,
· Libido is normal.
· By measurement of scrotal circumference, a value below acceptable limits for the species and breed being diagnostic.
· Palpation of the testes reveals one or both to be small and flabby.
· Semen analysis may reveal aspermic or oligospermic ejaculates, sometimeswith markedly abnormal morphology or motility characteristics of such sperm as are present.
· By contrast, libido is generally normal and, for this reason, the condition may escape the owner’s attention until the failure to achieve satisfactory pregnancy rates is noticed.
Treatment: Because of the probable inherited basis of testicular hypoplasia, attempting to breed from an affected animal should be avoided. Attempts at treatment with exogenous hormones are invariably unsuccessful, so castration and (for meat animals) slaughter for recovery of the carcass value should be recommended.
Fig. Testicular hypoplasia in a ram. The scrotal
circumference of 22 cm was well below the 30–35 cm
expected for a ram during the breeding season.