Chromosome Deterioration in Ageing Eggs of the Rabbit

Abstract

COITUS-INDUCED ovulation in the rabbit ensures that fertilization of nearly all eggs is initiated within 2 or 3 h of their arrival in the fallopian tube. When ovulation was induced by hormone injection, and coitus permitted at the time of ovulation (10 h after injection), fertilization began about 5 h later and continued for a further 3–5 h, eventually involving a little over 70 per cent of the eggs1. As a result, therefore, of the delay in the time of coitus, eggs underwent 6 or 7 h ageing before fertilization was initiated; fertilization nevertheless occurred in all but about 30 per cent of eggs. Despite this relatively small drop in fertilization rate there is evidence that fertility in the rabbit is seriously impaired by the delay of coitus. Chang2 observed that 60 per cent of eggs failed to implant and that more than half the implanted embryos died before term, and Hammond3 recorded an 80 per cent reduction in the mean number of young born. To some extent, the reduced fertility can be attributed to the occurrence of polyspermy and polygyny, conditions that lead to the highly lethal state of triploidy in the embryo, but this would not account for embryo but this would not account for embryo loss of more than about 16 per cent4,5.