Effects of aging on the male dog reproductive tract

The impact of aging on the male reproductive tract has been extensively studied in men; however, such information is limited in dogs. The general aim of the thesis was to evaluate and describe the changes occurring with age in seminal and testicular characteristics in dogs. Three age groups were considered: young (0-24 months), adult (25-84 months) and old (>84 months). Study 1 observed that age had no influence on volume, sperm number or motility. Percentage of normal spermatozoa was higher in young animals (60.5 ± 4.9%) than in old ones (41.5±4.3%). The proportion of spermatozoa with midpiece defects increase with advancing age, and, in particular, there were significantly more proximal droplets in old animals (22.1 ± 4.9%) than in young (3.8 ± 2.9%) or adult dogs (5.5 ± 1.5%). In Study 2, the peak systolic velocity (PSV), end-diastolic velocity (EDV), pulsatility index (PI) and resistive index (RI) within the distal supra-testicular artery did not differ in the age groups. In Study 3, the total seminiferous epithelium’s area (TSEA) measured in the evaluated microscopic fields significantly varied according to age: TSEA was lower in young and old dogs compared to adult dogs. The ratio TCA/TSEA, between total collagen area (TCA) and total seminiferous epithelium’s area (TSEA), and the percentage of collagen (%Col) did not change in the three age groups suggesting how the degree of testicular fibrosis is not affected by the age of the dog. Combining the results of the three studies, senescence turned out to affect sperm morphology, especially that of the midpiece (Study 1). Furthermore, also quantitative aspects of the spermatogenesis seem to vary with increasing age, not only qualitative ones. In fact, TSEA increases in the transition between the juvenile and the adult age and it declines in advanced age (Study 3). No modifications were observed in the degree of interstitial fibrosis (Study 3) or in vascular resistance (Study 2). Further studies are necessary to elucidate the physiological mechanisms responsible of the age- related changes observed in this Thesis.