Dose-dependent inhibition of spermatogenesis in mature rams with exogenous testosterone

Testicular and accessory sex gland function was examined in 20 mature breeding rams that received graded dosages of testosterone (T) by subdermal Silastic implants or intramuscular injections. Treatments were imposed for 72 days during the normal breeding season. As compared with control rams rams implanted with 20 T-filled Silastic capsules had greatly reduced testes (24%) and epididymides (53%) weights as well as total daily sperm production (3.3%) and epididymal sperm reserves (3.9%). These effects were produced when serum T concentrations were increased four-fold over those of control rams, serum LH was nondetectable and serum FSH was substantially decreased. Testicular weight and total daily sperm production were less dramatically reduced in rams given T (2 x 250 mg/day) by injection. In spite of the high serum T concentrations observed in injected rams, weights of the accessory sex glands were not significantly affected. Treatment with 5 or 20 T-filled Silastic capsules or by injection of T not only suppressed gonadotropin secretion and spermatogenesis but also reduced T concentrations in rete testis fluid. A high correlation (r = 0.94, P < 0.01) between daily sperm production and T concentrations in rete testis fluid was calculated in this study. Results presented herein indicate that 1) treatment of rams with exogenous T affects spermatogenesis in a dose-dependent manner and 2) spermatogenic yield is related to T concentrations in fluid of the rete testis.