Capacity of fertilized ova from mature and middle-aged rats to undergo preimplantation development in vitro.

The ability of ova collected from mated middle-aged rats (9-10 months of age) to undergo preimplantation development in vitro was compared to that of younger controls (3-4 months of age). The majority of ova from young rats underwent at least one cleavage division for every 24 h of the 96 h culture period. Seventy-two percent reached the morula/blastocyst stage at the termination of the culture. Aged ova had a reduced capacity to undergo preimplantation development in vitro with the number of fragmented and/or degenerated ova increasing after each day in culture. At the end of the culture period, 81.6% of the ova had degenerated. It is concluded that middle-aged rats ovulate defective ova and that these defective ova account, in part, for the preimplantation losses that characterize middle-aged rats.