Abstract
To investigate whether the presence of large numbers of nonviable ova and the delay in embryonic development in senescent female hamsters could result from delayed fertilization the early stages of fertilization and development in young and senescent hamsters were compared. Ova were collected at from 1 hour to 3 1/2 days postovulation from 120 virgins aged 3-5 months and from 172 multiparas aged 14-17 months. It was found that fertilization of ova from aged animals was delayed 2-5 hours beyond time of fertilization in young animals which was attributed to prolongation of the spermatozoons pentration of the zona pellucida and vitellus. 40% of the ova from the senescent group were nonviable at time of implantation which appeared to be in part a result of the delayed fertilization. When the number of ova from 3-day-pregnant young was compared with the number from 3 1/2-day-pregnant senescent animals the former group had 4.2 more ova on the average (p less than .001) indicating the importance of preimplantation loss in senescent animals. A developmental lag in zygotes from senescent animals became apparent at 2 days. It is concluded that preimplantation loss is the most important cause of declining litter size in aging hamsters and that the delay in fertilization is the primary factor contributing to loss of ovum viability.
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