Comparative studies on testis, epididymis and serum hormone concentrations in foxes, and hybrids during the...

Silver fox and blue fox belong to different genera, and the hybrid males are reproductively sterile. In the present study, there was a comparison of testicular and epididymal morphology and serum hormone concentrations among silver foxes, blue foxes, and the hybrids during the pre-breeding period, using 20 male silver foxes, 20 male blue foxes, 15 male HSBs (silver fox male × blue fox female hybrids) and 15 male HBSs (blue fox male × silver fox female hybrids), respectively. Hybrids had a smaller diameter of seminiferous tubules than pure-species males, and testes of hybrid males did not differ in mean size and relative weight from pure-species males. There were many Sertoli cells and spermatogenic cells in silver foxes and blue foxes, while numbers of spermatogonia and primary spermatocytes were less with no secondary spermatocytes in the hybrids. Furthermore, mean serum testosterone and estradiol concentrations in the hybrids were less, and FSH, LH, and PRL were greater than that in silver foxes and blue foxes (P <  0.05), suggesting that lesser concentrations of testosterone and estradiol and greater concentrations of FSH, LH and prolactin can inhibit the completion of spermatogenesis during the pre-breeding period. The results indicate that fox hybrid sterility may result from failures at the early stages of spermatogenesis.