Abstract
Golden hamster embryos were recovered from aged multiparous dams (15 to 16 months old), and young nulliparous females (3 to 4 months old) after mating with fertile males. The numbers of embryos and fetuses were counted at 1-cell, morula or blastocyst, and 8-day stages, respectively. The average number of normal eggs per dam was without significant difference, although slightly larger in young nulliparous females (young group) than in senescent multiparous females (aged group). However, the average number of anomalous eggs per dam increased significantly in the aged group. The average number of the embryos at morula or blastocyst stage per dam was significantly large in the young group. The average numbers of deciduae and fetuses, which were recovered from females at 8 days after mating, decreased significantly in the aged group. The frequency of appearance of mitotic metaphases in first-cleavage embryos decreased significantly in the aged group. These results indicate that the aging of dams causes delay of fertilization, or asynchronous development of embryos and degeneration of the resultant embryos through the embryo development. In senescent golden hamster females, large numbers of unfertilized eggs, "shell eggs" without cytoplasm, which were previously ovulated and then degenerated, were recovered. They were accumulated in oviducts or uterotubal junctions.
