Abstract
Ova were collected from young (9-12-week old) and aged (43-53-week old) golden hamsters at various times before and after fertilization to decide the timing of ovulation, sperm penetration and pronuclear formation. Ovulation was delayed 1 h in the aged animals, although overall ovulation rate did not differ statistically between young and aged animals. Sperm penetration also showed another 1 h delay in aged hamsters. The types of abnormalities during early fertilization were asynchronous development of male and female pronuclei, polyspermy, polygyny and pycnosis. Asynchronous development of the male and female pronuclei, mainly a delay in the development of the male pronucleus, was found more often in the aged females (8.2%), contrasting 3.1% (P<0.01) in the young females. Polyspermy accounted for a small proportion of the abnormalities in both groups (0.5 and 0.4% in the young and aged groups, respectively), whereas abnormalities observed only in the aged group were polygyny (5.5%) and pycnosis (0.4%). It is suggested that increased abnormalities of fertilization observed in the aged hamsters (approximately 15% of the total ova) may be directly related to delayed ovulation and fertilization attributed to defective ova and deteriorated reproductive ability of the aged females. These delays in ovulation and fertilization may be the main factors causing the preimplantation wastage of embryos in the aged hamsters.
