Histological, cytogenetic and endocrine evaluation in twenty-five unilateral cryptorchid horses

Data from 49 horses (25 unilateral cryptorchid and 24 as control group) are reported to determine macroscopic and microscopic characteristics of the testes, as well as to characterize their karyotype and hormonal levels. Histology showed that only Sertoli cells were found in the lumen of the seminiferous tubules of the cryptorchid testes, while spermatogenesis in the scrotal testes resulted normal. Cytogenetic evaluation showed that all cryptorchid horses were normal males (2n = 64, XY). In addition, the lower testosterone production observed in cryptorchid horses was associated to the smaller size of the retained testicle as well as to the lower number of Leydig cells adjacent to the seminiferous tubules. This study confirmed that a simple determination of plasma testosterone levels was enough to differentiate between non-breeding stallions, cryptorchid and castrated animals, avoiding the administration of hCG.