Reproductive aging in male dogs: The epididymal sperm defects and expression of androgen receptor in reproductive tissues

The present study aimed at investigating age-related changes in epididymal sperm motility, morphology, DNA integrity and androgen receptor (AR) expression in canine reproductive tissues. Fifty-five healthy medium-sized male dogs were divided into four groups: young (1 - 3 years old, n = 14), adult (>3 - 6 years old, n = 12), old (>6 - 9 years old, n = 14) and senile (>9 years old, n = 15). After routine castration, testes, epididymides (head, body and tail) and vas deferens were collected. Spermatozoa were flushed from epididymal tails and their motility, morphology and DNA integrity were examined. Localization of AR was investigated by immunohistochemistry and the positive immunostaining cells were evaluated using image analysis software (NuclearQuant, 3DHISTECH). We found significantly lower percentages of epididymal sperm motility, sperm vigour and viability in adult, old and senile dogs in comparison with young dogs (p < 0.05). Animal's age negatively correlated with epididymal sperm motility, sperm vigour and viability. The primary, secondary, major and minor epididymal sperm defects were significantly higher in senile dogs compared to young dogs. There were positive correlations between age and epididymal sperm defects (p < 0.01). The percentage of sperm with fragmented DNA did not differ between age groups. Testicular AR was expressed in the nucleus of Sertoli cells, Leydig cells and peritubular myoid cells, except for germ cells. Expression of AR was found in all epithelium, lamina propria and smooth muscle cells of the epididymis and vas deferens. Expression levels of AR in testis, epididymis and vas deferens did not differ between age groups (p > 0.05). In conclusion, the present study clearly demonstrated that senescence in dogs was associated with decreased epididymal sperm quality. An age-related increase in the incidence of poor epididymal sperm quality may promote subfertility, especially in senile dogs.