title: Age dependent changes in the sperm population and fertility in the male rat.
abstract: The entire reproductive tract was devoid of spermatozoa during the first 42 days of life. The first appearance of spermatozoa was detected in the caput epididymidis of 45-day old rats and in the cauda epididymidis of 52-day or older rats. The number of spermatozoa in the reproductive tract increased with age. The sperm population reached its maximum in the caput epididymidis by day-72 and in the caud epididymidis by day-100. These high levels were maintained beyond 450 days of age. Fifty-two day old male rats failed to impregnate the female. Although male rats of 62-500 days were able to sire litters, the peak reproductive period was found to be between days 100-270, during which the number of young per litter ranged between 11-16. Towards advanced age the litter size dropped to 8. The lower fertility in the males of advanced age might be due to a lower proportion of fertile spermatozoa, a change in the physiology of epididymis or an altered sperm transport in the reproductive tract.
mesh_terms: D000375:Aging; D000818:Animals; D004822:Epididymis / Q000033:anatomy & histology; D005298:Fertility; D008297:Male; D009929:Organ Size; D051381:Rats; D012741:Sexual Maturation; D013076:Sperm Count; D013737:Testis / Q000033:anatomy & histology