Seminiferous tubule stages in the prairie dog (Cynomys ludovicianus) during the annual breeding cycle.

The male prairie dog (Cynomys ludovicianus) is an annual breeder with complete testicular regression between breeding periods. Knowledge of the seminiferous tubule cycle stages at all phases of the annual cycle is essential for evaluation of testicular effects of endogenous and exogenous hormones. Testis tubule diameter is directly correlated with testicular weight during the annual cycle. Seminiferous tubule stages found during testicular activity start with sperm release and round spermatids in the Golgi stage (I). Then they progress through the cap and acrosome stages (stages II to VI) until elongate spermatids are formed. During these stages preleptotene, leptotene and zygotene cells develop into pachytene cells which mature with the long spermatids (stage VII). Two distinct tubule associations (stages VIII, IX) follow during which the first and second meiotic metaphases occur. These stages are correlated with the middle and late phases of residual lobe retraction and condensation. The last stage (X) has final sperm development and is present with round spermatids that have no Golgi development. During regression changes are initially associated with the seminiferous tubule stages of active testes and end with relocation of Sertoli cell nuclei to a position above the basal layer of spermatogonia. Out of season testes are characterized by few spermatogonial mitoses and absence of viable spermatocytes. In recrudescent testes, Sertoli cell nuclei again become basal, spermatogonia resume mitoses and spermatocytes and spermatids progressively develop. After each cycle of proliferation of germ cells there is sloughing of the most differentiated spermatocytes and spermatids until the final tubule associations of the active testis are present.