Pre-implantation Mortality Research Articles

The significance of light chronodestruction in the development of the embryotoxic effect in the experiment

Objective. To assess the significance of light chronodestruction in the development of the embryotoxic effect in the experiment. Materials and methods. The experiment was conducted on 60 female rats of the Wistar line. To assess the significance of chronodestruction in the development of embryotoxic effect, the uterus was isolated in the experiment, in which the number of implantation sites, the total number of embryos, the number of live and dead embryos, and the number of resorptions were estimated. The number of corpus luteum in the harvested ovaries was estimated. In addition, the mean embryo weight (g) and mean craniocaudal size (mm) were recorded. Indicators of embryotoxic effects of light deprivation were determined by pre- and post-implantation death, which was calculated in accordance with methodological recommendations. Results. Exposure to light deprivation reduces the number of implantation sites as of 7th, 14th and 21st days by 1,5-1,8 times, the total number of embryos by 1,6-1,8 times, the number of living embryos by 2,2-9 times and increases the number of dead embryos as of 14th and 21st days by 4-5,5 times, the number of resorptions – 1,6-11 times. The average craniocaudal size (mm) of embryos in experimental animals was recorded below control values by 1,5 times, 1,3 and 3,7 times by 7th, 14th, 21st days respectively. In females exposed to light deprivation, there was a significant increase in pre-implantation mortality by 35-41,8 times and post-implantation mortality by 7,2-20,4 times compared to the control. Conclusion. Light deprivation may have a negative effect on pregnancy and fetal development in female rats, which is confirmed by an increase in pre- and post-implantation mortality.

Toxicity of cadmium salts on indicators of embryogenesis of rats

Cadmium is a toxic heavy metal which is considered a dangerous environmental pollutant and has a detrimental effect on the organs of the reproductive system, the period of implantation and the development of embryos. The experiment presented in this article established the effect of cadmium salts (chloride and citrate) on the general progress of embryogenesis. For this purpose, 60 rats were randomly divided into three groups: control, experimental group with cadmium chloride exposure and experimental group with cadmium citrate exposure. Cadmium chloride solvent, cadmium citrate solvent at a dose of 1.0 mg/kg and distilled intragastric water were injected from the first to the thirteenth (first subgroup) and from the first to the twentieth days of embryogenesis (second subgroup). When cadmium chloride was injected, total embryonic (by 4.24 and 3.67 times), pre-implantation (by 6.50 and 14.03 times) and post-implantation mortality (by 3.07 and 2.49 times) increased with a reduction of the number of surviving fetuses by 24.0% and 25.9% compared with the control group on the 13th and 20th days of embryogenesis respectively. At the same time, during exposure to cadmium citrate, indicators of total embryonic mortality increased by 4.02 and 3.52 times, pre-implantation mortality by 6.04 and 13.03 times, and post-implantation mortality by 3.09 and 2.26 times, and indicators of the number of live fetuses decreased by 18.3% and 22.2% in relation to the control group. When determining the accumulation of cadmium in embryos on the 20th day of gestation, polyelement analysis of biological materials using the atomic emission method with electric arc atomization revealed a 15.83-fold increase in cadmium chloride and 9.00 times in cadmium citrate relative to the control group. Embryolethality rates increased in animals of both experimental groups while the number of live fetuses per female decreased, which indicated an obvious embryotoxic effect of cadmium compounds. It is would be useful to conduct histological studies, which will help detect changes at the tissue level and possibly explain the level of embryonic mortality.

Зміна ембріотоксичних впливів цитратів металів в залежності від тривалості їх введення

Given the increase in cadmium in the environment (air, soil, water) through modern industrial processes, the absorption of significant amounts from cigarette smoke is relevant to studying the effect of cadmium compounds on embryogenesis. The purpose of the study: experimental study and comparison of embryolethality and embryotoxicity of metal citrates depending on the duration of their intragastric administration (during 13 and 20 days of gestation). Materials and methods. The study was performed on 120 white adult female Wistar rats that weigh 170-200 g. They were divided into 6 groups due to the intragastric administration of solutions of the studied metals – rats treated with citrates: cadmium at a dose of 1.0 mg/kg – 1st group (nfemale = 20, nemb = 166); cadmium at a dose of 1.0 mg/kg and cerium (1.3 mg/kg) – 2nd group (nfemale = 20, nemb = 185); cadmium in a dose of 1.0 mg/kg and germanium (0.1 mg/kg) – 3rd group (nfemale = 20, nemb = 184); cadmium at a dose of 1.0 mg/kg and zinc (1.5 mg/kg) – 4th group (nfemale = 20, nemb = 179); cadmium at a dose of 1.0 mg/kg and nanocomposite (iodine + sulfur + selenium) at a dose of 2.0 mg/kg – 5th group (nfemale = 20, nemb = 180), 6th group – control (nfemale = 20, nemb = 212) – proportional volume of sterile saline in the same way. Females were divided into 2 subgroups of 10 animals each, depending on the duration of administration of test substances. The embryotoxic and embryolethal effects of the test substances were evaluated according to generally accepted criteria, which were calculated according to well-known formulas. Results and discussion. Cadmium compounds harm the embryogenesis of rats in the experimental groups and increase the rates of embryolethality. The most pronounced differences in these parameters concerning the control were found in animals with isolated exposure to cadmium citrate: the rates of total embryonic mortality increased by 4.0 times in both study periods of embryogenesis and 20% from the 13th to the 20th day; increased pre-implantation mortality by 6.0 times with an increase in post-implantation mortality by 3 times on the 13th day and by 15.0 times and 2.8 times on the 20th day of embryogenesis, respectively. Depending on the duration of introduction, the indicators of pre-implantation mortality increased by 25.0% with an increase in post-implantation mortality by 22.2% in the same period. The experimental group of exposure to cadmium citrate at a dose of 1.0 mg/kg recorded the lowest indicators of the number of live fetuses and intrauterine survival with the highest resorption rate studied of embryonic development. At the same time, in the groups of combined exposure to cadmium citrate with metal citrates, a decrease in the indicators of total embryonic mortality was 50.0% - 30.0%, pre-implantation mortality – 50.0% - 25.0%, post-implantation mortality – 60.0% - 44.4 % and increase in the number of fetuses per female – 12.7% - 25.3%. Conclusion. Analysis of the results shows a pronounced embryotoxic effect of cadmium citrate at a dose of 1.0 mg/kg on the processes of embryogenesis, which is a significant increase in overall embryonic mortality, preimplantation, and postimplantation mortality compared with the control group in all studied terms. In the groups of combined action of cadmium citrate with metal citrates, the data obtained indicate a decrease in the accumulation of cadmium under the influence of the studied citrates, which allows them to be considered as potential bioantagonists of cadmium citrate

Експериментальна оцінка ембріотоксичних ризиків кадмію хлориду при ізольованому введенні та у поєднанні з солями цитрату і нанокомпозитом на його основі

Cadmium compounds that enter living organisms pose the potential for serious health effects as they exhibit mutagenic, carcinogenic, gonadotoxic, teratogenic, allergenic and embryotoxic effects. It is important to study the mechanisms of their toxic effect on embryonic development and structural and functional formation of organs of living organisms and to search for their bioantogonists. The purpose of the study was to highlight the results of intragastric administration of cadmium chloride (1.0 mg/kg) with isolated administration and in combination with metal citrates (cerium, germanium, zinc, and nanocomposite (iodine + sulfur + selenium citrates)) on the overall course of rat embryogenesis. Materials and methods. For the study, young female Wistar rats weighing 170-200 g were used. They were divided into 6 groups, depending on the test substances, which they received from the 1st to the 19th day of gestation. Results and discussion. The analysis of the results of the experimental study showed the negative effect of cadmium chloride on the analyzed indicators of embryogenesis (preimplantation mortality, postimplantation mortality, total embryonic mortality), indicators of intrauterine survival, morphological (anatomical) malformations, as well as general delay in fetal development), both on the 13th and 20th days of pregnancy relative to the control group. In particular, the indicators of total embryonic mortality significantly increased by 4.2 times (13th day) and 3.7 times (20th day), with significant increase preimplantation mortality by 6.5 times, postimplantation mortality by 3.0 times on the 13th day of embryonic development, and on the 20th day, the preimplantation mortality indicator was by 14.0 times higher (p <0.01), and the postimplantation mortality indicator was insignificantly by 2.5 times higher than the control group. In the groups of the combined effect of cadmium chloride with metal citrates, there was a proven decrease in the indicators of total embryonic mortality (18.18% - 38.10%), preimplantation mortality (21.43% - 53.85%), postimplantation mortality (20.0% - 66.7%), an increase in the number of fetuses per female (12.66% -36.0%). Conclusion. In groups of the combined effect of cadmium chloride with metal citrates, the obtained data indicate a decrease in the accumulation of cadmium under the influence of the studied citrates, which allows them to be considered as potential bioantagonists of cadmium chloride

Оценка репродуктивной способности самцов крыс при остром токсоплазмозе

Toxoplasmosis is a parasitic disease of humans and animals caused by Toxoplasma gondii. Toxoplasma is an intracellular parasite that belongs to the simplest and has a complex development cycle. Infection with Toxoplasma is possible orally, transplacentally, percutaneously (if the integrity of the skin is damaged). This invasion is often the cause of problems with bearing pregnancy, as well as the development of congenital anomalies in children. The purpose of the study was to study the reproductive ability of male rats in acute toxoplasmosis. Materials and methods. The experiment was performed on 90 female and 45 male Wistar rats with a body weight of 180-200 g. The intact control males were orally injected with 2 ml of 0.2% starch gel. Experimental groups of males were infected with an invasive Toxoplasma gondii culture at a dose of 25 tachyzoites per 1 g of body weight (5000 tachyzoites per rat) and 50 tachyzoites per 1 g of body weight (10000 tachyzoites per rat). Then the males of all groups were coupled with the females for 3 days. The effect of toxoplasmas on the reproductive ability of male rats was assessed by the development of pregnancy and changes in the levels of pre- and post-implantation embryo death in female rats on the 7th, 14th, and 21st days after pregnancy. To account for changes in the pre- and post-implantation death of embryos in female rats after removal from the experiment, the uterus and ovaries were isolated, the uterine horns were opened, the number of implantation sites, the total number of embryos, the number of living and dead embryos, the number of resorption, and the number of yellow bodies in the ovaries were determined. Results and discussion. In the females of the 4th, 5th and 6th groups (coupling with males infected at the dose of 25 tachyzoites per 1 g of body weight), a decrease in the number of implantation sites in the uterus, the total number of embryos and the number of live embryos was recorded by 1.8-1.9 times compared to the control parameters. In female rats of the 7th, 8th and 9th groups (coupling with males infected at the dose of 50 tachyzoites per 1 g of body weight), there was a decrease in the number of implantation sites in the uterus, the total number of embryos and the number of live embryos by 5.6-6.8 times compared to the control. When compared to the results obtained from the females of the 4th, 5th and 6th groups, a decrease in these indicators was recorded by 3.1-3.5 times. Conclusion. Toxoplasma gondii has an effect on reproductive capacity in male rats expressed in changes of the levels of preimplantation mortality in female rats. The obtained effect depends on the dose of infection and the period of parasitosis development in males

Защита сперматогенеза β-каротином при радиационных воздействиях. Сообщение 2: обогащение каротиноидом рациона при однократном остром внешнем γ-облучении

Purpose: Experimental evaluation of the efficiency of β-carotene by single acute γ-irradiation of spermatogenesis correction radiation-induced disorders in males (♂) of Wistar rats during prolonged carotenoid enrichment of a diet. Material and methods: Single external gamma irradiation ♂ was performed at the IGUR facility (137Cs, dose rate 0.029 Gy/s). The carotenoid used up on feeding ♂ in a mixture with cottage cheese for 2 months before irradiation, then – throughout the study period three times a week. During the days that ♂ were in cells with intact ♀ β-carotene was administered ♂ orally by a probe in the form of a suspension in vegetable oil. The damage and effectiveness of protection of spermatogenesis of irradiated ♂ were judged by the state of their reproductive function. Results: β-carotene in intact ♂ rats reduced the overall, pre- and postimplantation embryonic mortality, respectively, from 29 to 14, from 22 to 9, and from 10 to 5 %. At the stage of mature sperm following irradiation ♂ dose of 3 Gy – total and pre-implantation mortality from 45 to 29, and from 23 to 9 %. After irradiation at a dose of 5 Gy – total, an pre- and postimplantation induced embryonic death, respectively, from 67 to 56, from 23 to 13 % and from 56 to 43 %. At the stage of spermatids after irradiation in dose 1 Gy – pre-implantation mortality from 23 to 9 %; in the dose of 3 Gy – the number of dead embryos in pregnant ♀ from 12 to 3; at a dose of 5 Gy total embryonic mortality from 57 to 49 %. Carotenoid enrichment of a diet of ♂ irradiated at doses of 3 and 5 Gy, has not corrective impact on the state indicators of their reproductive function, evaluated at fertilization of ♀ sperm irradiated at the stage of spermatocyte. At the stage of spermatogonia after irradiation at a dose of 3 Gy β-carotene increased fertility of ♂ 7 to 12 living embryos and reduced the overall, before – induced postimplantation mortality, respectively, with 63 and 43, from 42 to 25 and from 35 to 19 %. No statistically significant effect of β-carotene on the weight loss of the gonads irradiated ♂ was revealed. Compared to short-term regimen, long-term enrichment of a diet of irradiated ♂ β-carotene more effectively reduced embryonic mortality of their offspring. Conclusions: Correction effects of β-carotene enrichment of the diet in radiation-induced disturbances by single acute external γ-irradiation at doses of 3 and 5 Gy of spermatogenesis in Wistar rats at stages of mature spermatozoa, spermatids and spermatogonia have been established.

Защита сперматогенеза β-каротином при радиационных воздействиях. Сообщение 1: однократное острое внешнее γ-облучение. Краткосрочное назначение каротиноида

Purpose: Experimental evaluation of β-carotene correction of radiation induced by single acute γ-irradiation of spermatogenesis disorders in male (♂) F1 CBAxC97Bl mice and non-linear rats with short-term carotenoid prescription. Material and methods: Single external gamma irradiation ♂ was performed at the IGUR facility (137Cs, dose rate 0.029 Gy/s). The β-carotene suspension was administered ♂ orally 19 and 4 hours before, 4 and 24 hours after irradiation. The damage and effectiveness of protection of spermatogenesis of irradiated ♂ were judged by the state of their reproductive function. Results: The effects of correction of the short-term prescription of β-carotene radiation-induced by a single acute external gamma irradiation at doses of 3 and 5 Gy of spermatogenesis disorders in mice and rats at stages of mature spermatozoa, spermatids and spermatogonium have been established. β-carotene in ♂ mice reduced total embryonic mortality in 8–14 and 77–84 days after irradiation at a dose of 3 Gy from 46 to 36 and from 41 to 28 %, preimplantation – after 8–14 and 15–21 days – from 24 up to 13 and from 31 to 22 %, postimplantation – after 0–7 and 77–84 days – from 24 to 15 and from 25 to 7 %. In ♂ rats 0–7 days after irradiation at a dose of 5 Gy β-carotene reduced total, pre-, post- and induced postimplantation embryonic mortality from 62 to 41, from 34 to 17, from 41 to 30 and from 38 to 26 %, respectively. After 13–20 days – preimplantation mortality from 27 to 11 %. At the stage of spermatozoa after irradiation at a dose of 3 Gy increased the breeding efficiency from 70 to 100 %, fecundity – by 23–31 %; reduced total and preimplantation mortality from 49 to 39 % and from 41 to 27 %, respectively. At the stage of spermatids –sterilization was prevented and the efficiency of breeding was normalized, reduced post- and induced postimplantation mortality from 25 to 20 and from 17 to 12 %, respectively. The therapeutic and prophylactic effects of β-carotene at the spermatocyte stage are not revealed. In the spermatogonium stage, the carotenoid increased the total number and number of live embryos in pregnant female (♀) from 36 to 55 and from 20 to 50 %, reduced total and pre-implantation mortality from 81 to 56 and from 69 to 42 %, respectively. Conclusions: The prospects of β-carotene use for correction of gonadal radiation injuries in the risk groups of exposure to ionizing radiation and the inclusion of β-carotene in the scheme of drug prevention of acute radiation injuries of spermatogenesis are shown.

Adaptive possibilities, fertility and viability in posterity of female rats under the ethanol influence for the different duration

The investigation was carried out on the white outbred female rats (n = 80) which were being under the influence of15 % solution of ethanol during pregnancy, from the first to the sixth months before its approach and on their viable posterity (n = 440). Anatomic, macro-microscopic and statistical methods of research were used. Two periods of increasing mortality in rats were revealed: the first fell on 1st month of the experiment (mortality reached 25 %) and the second - on 5th and 6th months of the experiment when this indicator rose up to 10 %. The rats' pregnancy duration was increased: the most considerable prolongation of pregnancy (for 5 days) was determined in the female rats which were under the ethanol influence within six months before its approach. The pre-implantation mortality was prevailed in structure of the general antenatal mortality. The highest rates of these indicators were noted in the rats under the ethanol only during pregnancy, and also within two and six months before its approach. The maximum post-implantation mortality was registered in the animals which were affected by alcohol throughout five months before pregnancy. The indicator of mortality of posterity in the early post-natal period reached 100 % in posterity of female rats under the ethanol within three months before pregnancy and for its duration.

Geminin is essential for the development of preimplantation mouse embryos

Replication of DNA is strictly controlled to ensure that it occurs only once per cell cycle. Geminin has been thought to serve as a central mediator of this licensing mechanism by binding to and antagonizing the function of Cdt1 and thereby preventing re-replication during S and G2 phases. We have now generated mice deficient in geminin to elucidate the physiologic role of this protein during development. Lack of geminin was shown to result in preimplantation mortality. A delay in the development of homozygous mutant embryos was first apparent at the transition from the four- to eight-cell stages, concomitant with the disappearance of maternal geminin protein, and development was arrested at the eight-cell stage. The mutant embryos manifest morphological abnormalities such as dispersed blastomeres with nuclei that are irregular both in size and shape as well as impaired cell-cell adhesion. DNA replication occurs but mitosis was not detected in the mutant embryos. The abnormal blastomeres contain damaged DNA and undergo apoptosis, likely as a consequence of the deregulation of DNA replication. Our results suggest that geminin is essential for cooperative progression of the cell cycle through S phase to M phase during the preimplantation stage of mouse development.

Annual Reproductive Patterns of Female House Shrew, Suncus murinus, in Taiwan

Reproductive patterns of female house shrew (Suncus murinus) inhabiting central Taiwan were studied from September 1990 to February 1992 with animals collected monthly. The annual average body weight was 37.4 g for adults (N=198), and 23.2 g for juveniles (N=18), respectively. The reproductive females (pregnant and lactating) were found all the year round with higher percentages (more than 80%) in spring-summer. The average litter size was 2.9 (range: 1–6). The levels of plasma estradiol-17 β in adult females were higher in March-June (140 pg/ml), and decreased gradually to 98 pg/ml in January-February. Plasma levels of estradiol-17 β in pregnant and lactating females were significantly greater than those of non-pregnant adults and of juveniles. Ovarian weights, plasma levels of estradiol-17 β, and pregnancy rate were correlated with day length. The pre-implantation mortality and post-implantation mortality of the embryos were 6.9% and 1.6%, respectively. The present study has demonstrated that the female S. murinus inhabiting central Taiwan breeds all year round with higher reproductive activity in spring and summer.

Reproduction in the Raccoon Dog in Finland

Reproduction in the raccoon dog ( Nyctereutes procyonoides ) was studied on the basis of 632 female carcasses in Finland in 1986–1990. In Finland, raccoon dogs usually mate from February to April, with a peak in March. Differences occurred both regionally and with respect to age, with older females breeding earlier than younger ones. Fecundity (number of corpora lutea per breeding female) averaged 11.5, with variation in fecundity occurring both annually and regionally, but not in relation to age of females. Embryonic litter size averaged 9.6 and was highest among females 3–5 years old. Litter size at birth averaged 8.8 and also peaked at 3–5 years of age. Loss of ova and preimplantation mortality averaged 15% in southern Finland, but was as high as 30% in the northeastern part of the study area. Because fetal mortality averaged an additional 5–10%, total prenatal mortality may surpass 20%. The proportion of reproducing females averaged 78%, increasing with age, as did productivity (number of young per female), increasing from 5.5 at 1 year of age to 8.2 at ≥3 years. Reproductive value was highest among 2-year-old females. Reproduction in raccoon dogs is strongly affected by climate and weather, and the availability of food (voles and berries) in relation to population density. The abundance of food and population density influence growth (including sexual maturation) of young raccoon dogs and their condition (fat reserves). In adult females, condition mostly affects annual variation in litter size at birth, whereas, in young females, it affects the regional variation in the proportion of reproducing females.

Fertility of the early postpartum, lactating domestic rabbit

Sixty-four crossbred primiparous lactating does each suckling six pups were allocated at random into four groups and were mated on either Day 1, 2, 3, or 4 post partum (where Day 0 = the day of parturition). They were subsequently killed on Day 10 post coitum (where Day 0 = the day of mating) to assess fertility. There were no significant differences between treatment groups in their mating response (97% overall), ovulation response (77% overall), implantation response (83% overall), implantation rate (8.7 overall), or preimplantation mortality rate (24% overall). Ovulation rate was significantly increased in does mated on Days 3 and 4 (13.3 and 13.1, respectively), compared with those mated on Day 1 (10.2, P<0.05) and Day 2 (9.6, P<0.01) post partum. From these results we conclude that fertility is high throughout the early postpartum period in the lactating rabbit.

Effects of selecting for litter size and body weight on the components of litter size in mice

Divergent selection for the total number of young born in the first three litters (TNY-3) and for 6-week body weight in mice resulted in different changes in the components of first litter size. Selection for large TNY-3 increased the number of ova shed while pre-natal losses were not modified. Selection for small TNY-3 caused both a decrease in ovulation rate and an increase in post-implantation mortality. Divergent selection for body weight modified ovulation rate in the same direction as body weight. Embryo survival declined in both lines selected for body weight. That decline was caused by an increase in pre-implantation mortality in the case of the high line, and by an increase in post-implantation mortality in the low line.

Body Weight, Sex Ratio and Seasonal Reproductive Changes in the Indian Mole Rat, Bandicota bengalensis in the Punjab

A study has been made of seasonal changes in the body weights of males and females, and of ovarian and uterine weights, in the Indian mole rat, Bandicota bengalensis, between July 1976 and June 1978, from areas surrounding Ludhiana (30�56'N.,75�52'E.). An attempt has been made to correlate them and peaks in reproductive activity with environmental factors such as daylength, temperature, rainfall and availability of food. During both years of study, the percentage of males was 45.2. The body, ovary and uterus were lighter during winter, and then gained weight, with peaks during April and August-September. Males were generally heavier than females. On the whole, 34.7% of females were either pregnant or lactating. The breeding season extended from mid-February to mid-October. Two peaks in breeding activity (April and August-September), with a decline during June, were separated by a period of reproductive inactivity from November to mid-February. The average litter size was 8.88 (range 5-13). Embryos occurred with almost the same frequency in the left and right uterine horns. The pre-implantation mortality was 9.6% and post-implantation mortality 4.8%; thus the total prenatal mortality was 13.7%. The percentage of embryos found resorbing was 4.1. The results have been discussed in the light of the literature on the reproductive biology of rodents in this region.

MATERNAL INFLUENCE ON POSTIMPLANTATION SURVIVAL IN INBRED RATS

Department of Pathology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, U.S.A. (Received 6th January 1975) The derivation and maintenance of inbred strains of animals is frequently difficult or impossible due to reductions in litter size and viability of the offspring. Reductions in litter size might be expected from adverse genetic or environmental effects on components of the reproductive cycle including the ovulation rate, the rate of preimplantation mortality of the zygote and the rate of postimplantation mortality of the embryo. In some strains of inbred mice, the reduction in litter size is largely due to postimplantation losses (Lyon, 1959; Krzanowska, 1960; McCarthy, 1965, 1967). When female mice from inbred strains were mated to males of another strain, the incidence of postimplantation mortality was significantly reduced (McCarthy, 1965). It has been suggested (Lyon, 1959; McCarthy, 1965) that this wastage is the result of an increased number of recessive lethal

Nutritional stress and pre-implantation mortality in Merino sheep, (1964–7). General discussion and conclusions

SUMMARYCollation and re-analysis of the results obtained in separate experiments investigating prenatal mortality in Merino ewes over a period of 4 years have made it possible to draw the following general conclusions:Data from the control groups indicated that in 3 out of 4 years basal prenatal loss averaged approximately 25%, which agrees with a number of other estimates in the literature. Higher losses of ova in 1965 than in the other 3 years could not be partitioned accurately between fertilization failure and prenatal mortality.Submaintenance nutrition apparently caused embryo mortality in 1964, and possibly in 1967, when underfeeding from day 7 to 37 was followed by an unusual number of long cycles; however, there was no evidence of increased mortality in 1965 and 1966.Losses of ova shed as twins were significantly greater than amongst those shed as singles in 1964 and 1967. The higher loss of twin ova was clearly associated with the treated groups in 1964.In each of the 4 years the left ovary produced more ova than the right, and when the 4 years' data were combined, survival of ova shed by the left ovary was significantly better than of those shed by the right. The type of twin ovulation, i.e. whether the two ova came from one ovary or two, had no consistent effect on prenatal mortality.In 3 years there was no significant regression of prenatal mortality on body weight at mating. However, in 1965, when body weights were relatively low, there was a significantly negative regression. It is possible that there is a critical body weight below which poorer prenatal survival can be expected.Ewes which suffered embryonic loss followed by a delayed return to service subsequently conceived less readily than those having a cycle of normal length following fertilization failure or early embryonic death. It is postulated that in some cases this may be because ovulation occurs while resorption is still incomplete. For some ewes having long cycles after embryonic death, anoestrus or removal of the fertile rams precluded subsequent conception in that season. This was an added reason for the season's lambing performance of ‘long cycle’ ewes being much worse than that of ewes re-mated after normal length cycles.

The effects of inbreeding on the components of litter size in mice.

Twenty-four lines were bred from a base population of outbred Q mice by continued full-sib mating. Inbreeding depression in litter size at birth was observed. This decline in litter size was analysed in terms of ovulation rate, the incidence of preimplantation mortality and the incidence of postimplantation mortality. Pregnant females were dissected at 17½ days' gestation and the numbers of corpora lutea, or eggs, and of live and dead embryos were counted. Matings were arranged so that separate estimates of the effects of inbreeding in the mother and in the litter on the components of litter size could be obtained.In the first generation of inbreeding when the inbreeding coefficient of the litter was raised from 0 to 25% decline in litter size was attributable to an increased incidence of preimplantation mortality.In the second and fourth generations decline in litter size was attributable to (1) a reduction in the number of eggs ovulated by the inbred mothers, (2) an increased incidence of preimplantation mortality which resulted from inbreeding in the mother. No evidence of significant effects on mortality of inbreeding in the litter was obtained in the later generation of inbreeding.These findings are discussed in the context of previous work on the effects of inbreeding and crossing on litter size and its components in mice and pigs.