Scholarly summary

The amount and distribution of prenatal mortality were studied in 126 first and second pregnancies in seventy-three rabbits, weighing 3\m=.\5-4kg. The does were mated naturally, artificially inseminated to ensure against the failure of natural mating, and injected with 25 i.u. luteinizing hormone. The numbers of corpora lutea and implantation sites were counted at laparotomy 7-13 days post coitum (p.c.) and the number of live foetuses was recorded at autopsy 28 days p.c., or after parturition. The diameter of the uterine swellings was measured at laparotomy. In a further eight pregnancies only the litter size was recorded. Ovulation occurred in every case, but in six (4.8%) of the 126 pregnancies all the ova(109, or 8\m=.\1%) were lost before implantation. In the remaining 120 pregnancies there was a total loss of 132 ova (or 154 if corrected for polyovuly), representing 9\m=.\7 % of ovulations. In 64 out of the 120 pregnancies (53\m=.\3%)there was some loss of ova before implantation. The proportion of litters showing loss and the proportion of ova lost before implantation were significantly related to the number of ovulations. After implantation, total resorption occurred in four pregnancies (3\m=.\3%)and in a further eighty-five pregnancies (70\m=.\8%) there was some loss of embryos, which altogether amounted to 18\m=.\3%of the ovulations. The proportion of litters suffering loss after implantation wa