Studies on Prenatal Mortality in the Rabbit, Oryctolagus Cuniculus: The Amount and Distribution of Loss Before and After Implantation

Abstract

SUMMARY The amount and distribution of prenatal mortality were studied in 126 first and second pregnancies in seventy-three rabbits, weighing 3·5–4 kg. 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 8·1%) were lost before implantation. In the remaining 120 pregnancies there was a total loss of 132 ova (or 154 if corrected for polyovuly), representing 9·7% of ovulations. In 64 out of the 120 pregnancies (53·3%) 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 (3·3%) and in a further eighty-five pregnancies (70·8%) there was some loss of embryos, which altogether amounted to 18·3% of the ovulations. The proportion of litters suffering loss after implantation was significantly related to the number of implantations. It was concluded that 7% of the embryos died shortly after implantation, 66% died between days 8 and 17, and 27% were lost between days 17 and 23. Data relating to the diameter of 1728 uterine swellings measured between days 7 and 20 p.c., counts of corpora lutea, the occurrence of corpora lutea atretica and polyovuly, the position of foetuses in utero, weights of placentae associated with resorbed embryos, foetal weights, birth weights, and the incidence of stillbirths are also presented.

Further Studies of The Deep Freezing of Rabbit Spermatozoa In Reconstituted Skim Milk Powder

“…The post-insemination losses in the present experiments are of the same order as those reported by Adams (1960aAdams ( , 1960b for unfrozen semen, and neither time of storage nor freezing increased embryonic mortality.…”

“…Thus insemination of does with semen frozen as described results in some 40-50% of ova developing at 15 days. To compare favourably with fresh semen this should be raised to 60-70% (Adams 1960a(Adams , 1960b Wales and O'Shea 1968). This may be possible by increasing the number of spermatozoa inseminated (Goffaux 1965) or by refinements in the freezing technique.…”

Influence of progesterone supplementation on foetal survival in concurrently pregnant and lactating does

“…Their genital tract was removed and dissected. According to Adams (1960) Early mortality was considered to occur during the first half of gestation and late mortality thereafter (Adams, 1960).…”

Influence of the nutritional deficit of foetal survival and growth and plasma metabolites in rabbit does

“…Therefore, the concentrations of these metabolites were measured in plasma taken from does at 2 stages of gestation (d 17 and 28, experiment 2). The concentration of progesterone was found to be significantly lower in pregnant and lactating does than in non-lactating does (Fortun et al, 1993 Adams (1960), foetuses were divided into 3 classes: 1) live (L), when foetuses were well developed and still moving; 2) dead (D), when the foetus was recognizable, but unmoving and showing marked developmental delay; and 3) resorbed (R), when the foetus was not recognizable and only the placenta was present. Ovulation rate was determined by counting the number of corpora lutea (CL) after the ovarian dissection.…”

“…The following equations were used: total mortality TM = (CL -L)100/CL; early mortality EM = (CL -(L + R + D))100/CL; and late mortality LM = ((R + D)100)/(L + R + D). Early mortality probably occurs during the first half of pregnancy and late mortality thereafter (Adams, 1960 (Pbre, 1987). All the feed was eaten within 20 min.…”