Fertilizability of ova from young or old hamsters after spontaneous or induced ovulation.

Young or aged hamsters, subjected to spontaneous or induced ovulation, were examined for ovulation rate, fertilization rate, and chromosomal normality. The fertilization rate in aged animals was decreased but there were no differences in ovulation rate. Abnormal chromosomes and degenerated oocytes occurred in the aged animals after induced ovulation. The fertilizing ability of sperm incubated in the uteri of young or aging animals showed no obvious differences when used for in vitro fertilization. These results indicated that defective ova represent one of the major factors leading to increased preimplantation loss in aged animals and also that superovulation of aged animals results in no beneficial effect, over spontaneous ovulation, on the fertilization process.