Weaning Of Offspring Research Articles

Brief Communication: Orphaned male Chimpanzees die young even after weaning

If a social-living animal has a long life span, permitting different generations to co-exist within a social group, as is the case in many primate species, it can be beneficial for a parent to continue to support its weaned offspring to increase the latter's survival and/or reproductive success. Chimpanzees have an even longer period of dependence on their mothers' milk than do humans, and consequently, offspring younger than 4.5-5 years old cannot survive if the mother dies. Most direct maternal investments, such as maternal transportation of infants and sharing of night shelters (beds or nests), end with nutritional weaning. Thus, it had been assumed that a mother's death was no longer critical to the survival of weaned offspring, in contrast to human children, who continue to depend on parental care long after weaning. However, in theory at least, maternal investment in a chimpanzee son after weaning could be beneficial because in chimpanzees' male-philopatric society, mother and son co-exist for a long time after the offspring's weaning. Using long-term demographic data for a wild chimpanzee population in the Mahale Mountains, Tanzania, we show the first empirical evidence that orphaned chimpanzee sons die younger than expected even if they lose their mothers after weaning. This suggests that long-lasting, but indirect, maternal investment in sons continues several years after weaning and is vital to the survival of the sons. The maternal influence on males in the male-philopatric societies of hominids may be greater than previously believed.

Morphological and functional effects on cardiac tissue induced by moderate zinc deficiency during prenatal and postnatal life in male and female rats

The aim of this study was to evaluate whether moderate zinc restriction in rats throughout fetal life, lactation, and/or postweaning growth results in early changes in cardiac morphology predisposing the onset of cardiac dysfunction in adult life as well as sex-related differences in the adaptation to this nutritional injury. Female Wistar rats received low or control zinc diets from the beginning of pregnancy up to offspring weaning. After being weaned, offspring were fed either a low or control zinc diet until 81 days. Systolic blood pressure was measured. Echocardiographic and electrocardiographic examinations, morphological experiments, and apoptosis by TUNEL assay were performed in the left ventricle. In the early stages, zinc-deficient male and female offspring showed an increase in cardiomyocyte diameter, probably associated with an increase in cardiac apoptotic cells, but smaller myocyte diameters in adulthood. In adult males, this nutritional injury induced decreased contractility and dilatation of the left ventricle, not allowing the heart to compensate the higher levels of blood pressure, and hypertrophic remodeling of coronary arteries associated with increased blood pressure. Adequate zinc intake during postweaning life did not overcome blood pressure levels but reversed some of the detrimental effects of earlier zinc deficiency in cardiac morphology and function. Females were less sensitive to this deficiency, exhibiting normal levels of blood pressure and no structural or functional heart alterations in adult life. The present study demonstrates that the effects of zinc deficiency on blood pressure, cardiac morphology, and function differ between sexes, with males more predisposed to develop cardiovascular diseases in adulthood.

Impaired Hypothalamic mTOR Activation in the Adult Rat Offspring Born to Mothers Fed a Low-Protein Diet

Several epidemiological and experimental studies have clearly established that maternal malnutrition induces a high risk of developing obesity and related metabolic diseases in the offspring. To determine if altered nutrient sensing might underlie this enhanced disease susceptibility, here we examined the effects of perinatal protein restriction on the activation of the nutrient sensor mTOR in response to acute variations in the nutritional status of the organism. Female Wistar rats were fed isocaloric diets containing either 17% protein (control) or 8% protein (PR) throughout pregnancy and lactation. At weaning offspring received standard chow and at 4 months of age the effects of fasting or fasting plus re-feeding on the phosphorylation levels of mTOR and its downstream target S6 ribosomal protein (rpS6) in the hypothalamus were assessed by immuno-fluorescence and western blot. Under ad libitum feeding conditions, PR rats exhibited decreased mTOR and rpS6 phosphorylation in the arcuate (ARC) and ventromedial (VMH) hypothalamic nuclei. Moreover, the phosphorylation of mTOR and rpS6 in these hypothalamic nuclei decreased with fasting in control but not in PR animals. Conversely, PR animals exhibited enhanced number of pmTOR imunostained cells in the paraventricular nucleus (PVN) and fasting decreased the activation of mTOR in the PVN of malnourished but not of control rats. These alterations occurred at a developmental stage at which perinatally-undernourished animals do not show yet obesity or glucose intolerance. Collectively, our observations suggest that altered hypothalamic nutrient sensing in response to an inadequate foetal and neonatal energetic environment is one of the basic mechanisms of the developmental programming of metabolic disorders and might play a causing role in the development of the metabolic syndrome induced by malnutrition during early life.

Studies in Experimental Autoimmune Encephalomyelitis Do Not Support Developmental Bisphenol A Exposure as an Environmental Factor in Increasing Multiple Sclerosis Risk

Multiple sclerosis (MS), a demyelinating immune-mediated central nervous system disease characterized by increasing female penetrance, is the leading cause of disability in young adults in the developed world. Epidemiological data strongly implicate an environmental factor, acting at the population level during gestation, in the increasing incidence of female MS observed over the last 50 years, yet the identity of this factor remains unknown. Gestational exposure to bisphenol A (BPA), an endocrine disruptor used in the manufacture of polycarbonate plastics since the 1950s, has been reported to alter a variety of physiological processes in adulthood. BPA has estrogenic activity, and we hypothesized that increased gestational exposure to environmental BPA may therefore contribute to the increasing female MS risk. To test this hypothesis, we utilized two different mouse models of MS, experimental autoimmune encephalomyelitis (EAE) in C57BL/6J mice (chronic progressive) and in SJL/J mice (relapsing-remitting). Dams were exposed to physiologically relevant levels of BPA in drinking water starting 2 weeks prior to mating and continuing until weaning of offspring. EAE was induced in adult offspring. No significant changes in EAE incidence, progression, or severity were observed with BPA exposure, despite changes in cytokine production by autoreactive T cells. However, endocrine disruption was evidenced by changes in testes development, and transcriptomic profiling revealed that BPA exposure altered the expression of several genes important for testes development, including Pdgfa, which was downregulated. Overall, our results do not support gestational BPA exposure as a significant contributor to the increasing female MS risk.

Age-related reproductive variation in a wild marine mammal population

Life history theory predicts a change in reproduction success with age as energy resources are limited and must be allocated effectively to maximize reproduction and survival. In this study, we use three reproductive performance measures, maternal expenditure, offspring weaning mass, and first-year survival, to investigate the role that maternal age plays in successful reproduction. Long-term uninterrupted life history data available for Marion Island’s southern elephant seals and mass change estimates from photogrammetry data allow for assessment of age-related reproduction performance and trade-offs. Known-aged adult females were photographed for photogrammetric mass estimation (n = 29) and their pups weighed at weaning during the 2009 breeding season. Maternal age and proportional mass loss positively influenced pup weaning mass. In turn, first-year pup return rates (as a proxy for survival) were assessed through the intensive mark–recapture program. Pup survival increased with female age and weaning mass. Pups of young females aged 3–6 years have a lower first-year survival probability compared with pups of older and larger females.

Incidence of jaw lesions and activity and gene expression of hepatic P4501A enzymes in mink (Mustela vison) exposed to dietary 2,3,7,8-tetrachlorodibenzo-p-dioxin, 2,3,7,8-tetrachlorodibenzofuran, and 2,3,4,7,8-pentachlorodibenzofuran

This study assessed the effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,4,7,8-pentachlorodibenzofuran (PeCDF), and 2,3,7,8 tetrachlorodibenzofuran (TCDF) on the incidence of jaw lesions and on hepatic cytochrome P4501A (CYP1A) endpoints in mink (Mustela vison). Adult female mink were assigned randomly to one of 13 dietary treatments (control and four increasing doses of TCDD, PeCDF, or TCDF) and provided spiked feed for approximately 150 d (60 d prior to breeding through weaning of offspring at 42 d post-parturition). Offspring were maintained on their respective diets for an additional 150 d. Activity of hepatic CYP1A enzymes in adult and juvenile mink exposed to TCDD, PeCDF, or TCDD was generally greater compared with controls, but changes in other CYP1A endpoints were less consistent. Histopathology of the mandible and maxilla of juvenile mink suggested a dose-related increase in the incidence of jaw lesions. The dietary effective doses (ED) for jaw lesions in 50% of the population (ED50) were estimated to be 6.6, 14, and 149 ng/kg body weight (bw)/d for TCDD, PeCDF, and TCDF, respectively. The relative potencies of PeCDF and TCDF compared with TCDD based on ED10, ED20, and ED50 values ranged from 0.5 to 1.9 and 0.04 to 0.09, respectively. These values are within an order of magnitude of the World Health Organization toxic equivalency factor (TEF(WHO)) values of 0.3 and 0.1 for PeCDF and TCDF, respectively.

Early cardiovascular alterations induced by zinc deficiency during fetal life and lactation

The aim was to evaluate early cardiovascular alterations in rats exposed to moderate zinc deficiency during fetal life and lactation, and compare the effects in males (m) and females (f).Wistar rats received low (L,8 ppm) or control (C,30 ppm) zinc diet from pregnancy until offspring weaning (day 21). At 21 days, we evaluate mayor (MM) and minor (mM) myocyte diameter (μm); aortic intima (Ai), media (Am) and perivascular collagen (Ac) thickness (μm); cardiac (C) and aortic (A) nitric oxide synthase (NOS) activity (pmol Cit/g.tissue.min); cardiac thiobarbituric acid substances (Tbars, nmol/mg protein), glutathione (G, mg/g protein), glutathione peroxidase (GPX, μmol/min/mg protein), catalase (CAT, pmol/mg protein) and superoxide dismutase (SOD, U/mg protein) activity in Lm, Lf, Cm and Cf rats. Cm Lm Cf Lf MM 14±1 18±1* 15±1 15±1 mM 8,6±0,5 10,7±0,3* 9,4±0,5 10,1±0,3 Ai 23,3±0,2 18,3±0,1* 23,9±0,2 18,9±0,2† Am 280±2 298±2 287±3 280±2 Ac 16±1 24±1* 12±1 23±2† C NOS 249±5 205±5* 247±3 201±3† A NOS 225±5 172±5* 211±6 179±6† G 9±1 3±1* 10±1 6±1† GPX 81±8 65±6* 85±6 68±8† Tbars 0.41±0.05 0.32±0.02 0.22±0.04* 0.18±0.02 No differences were observed in cardiac SOD and CAT activity p<0.01:*vs Cm;†vs Cf; N=6/group These early cardiovascular alterations may participate in the programming of adult diseasesSupported by University of Buenos Aires, CONICET, ANCyT, Argentina

O' mother where wert thou? Maternal strategies in the southern elephant seal: a stable isotope investigation

Maternal effects are widespread in ecology and can alter the dynamics of a population. We investigated the impact of maternal foraging strategies on offspring weaning mass--a proxy of maternal foraging success and of offspring survival--in southern elephant seals on îles Kerguelen. Using 4 years of data, we modelled pup weaning mass as a two-component mixture and used blood stable isotope values to discriminate between maternal foraging strategies previously identified from bio-logging studies. Carbon isotope ratio was a strong predictor of weaning mass, but the relationship was non-monotonic in contrast to a priori expectations. Females foraging in the interfrontal zone weaned pups with a smaller mass compared with females foraging in Antarctic waters. Pup mass was positively correlated with a proxy of global primary production in the interfrontal zone for small weanlings. Maternal effects, via a poor foraging efficiency in the 1970s, may help explain the large population decrease observed at that time on îles Kerguelen because of an overall decrease in pup weaning mass, survival and subsequent recruitment.

Effects of dietary exposure of mink (Mustela vison) to 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin, 2,3,4,7,8‐pentachlorodibenzofuran, and 2,3,7,8‐tetrachlorodibenzofuran on reproduction and offspring viability and growth

This study assessed the effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,4,7,8-pentachlorodibenzofuran (PeCDF), and 2,3,7,8-tetrachlorodibenzofuran (TCDF) on the reproductive performance of female mink (Mustela vison) and the viability and growth of their offspring. Nine adult female mink were randomly assigned to one of 13 dietary treatments (one control and four doses each of TCDD, PeCDF, and TCDF [2.1-8.4, 4.0-15 and 5.2-25 ng TCDD toxic equivalents (TEQ)/kg body wt/d]). Diets were fed from two months prior to breeding through weaning of offspring at six weeks of age. At least nine kits per treatment group were maintained on their diets through 27 weeks of age. There were no effects on litter size or viability of offspring. No consistent effects were observed on body mass or relative organ masses of animals at any age. 2,3,7,8-Tetrachlorodibenzo-p-dioxin and PeCDF accumulated in the liver and adipose tissue, but TCDF cleared rapidly. The lack of significant effects on reproduction and offspring viability contrasts with effects reported for mink exposed to environmentally derived PCB mixtures with equivalent TCDD potencies. This suggests that it may be inappropriate to apply toxicity reference values associated with PCB mixtures to animals also exposed to TCDD, PeCDF, or TCDF, and the World Health Organization TCDD toxic equivalency factors for some congeners may not be appropriate for mink.

Effect of litter size on body and organ weight, blood pressure, adiposity index and glucose levels in adult offspring of dams fed normal or high salt diet during pregnancy and lactation

Objective To evaluate the effect of litter size reduction at birth on weight and morphofunctional parameters in adulthood. Methods and Results (mean±SD, p<0.05, n=6 to 8/group): Female Wistar rats were fed normal- (NS - 1.3%) or high-salt (HS - 8.0% NaCl) diet from eight weeks of age until offspring weaning (15 weeks of age). Offspring were divided into control (C) and small (S – 8 newborns/litter) groups. All male offspring were fed NS until 12 weeks of age, when body weight (BW, g), tail cuff blood pressure (BP, mmHg), glucose levels (G, mg/dL), left ventricle (LV), white and brown adipose tissue (BAT) masses (g/100g) were determined. Adiposity index (AI) was calculated (% of BW). BW was higher in the S offspring of NS and HS dams (S: NS - 403±15; HS - 416±8) compared to C (C: NS - 291±12; HS - 332±9). BP was not different between S and C from NS dams but was higher in C than in S from HS dams (C - 115±4.3, S - 95±5.1). G were higher in S (NS - 91±2.3 and HS - 109±3.4) than in C (NS - 81±3 and HS - 97±3.6). LV was higher in S (NS - 0.23±0.01 and HS - 0.21±0.01) than in C (NS - 0.19±0.01 and HS - 0.2±0.01). The AI was not different between S and C from NS dams but was higher in S (5±0.2) compared to C (4±0.3) from HS dams. BAT was lower in S (NS - 0.11±0.01 and HS - 0.07±0.01) compared to C (NS 0.25±0.01 and HS 0.13±0.01). Conclusion Litter size reduction at birth alters body weight, left ventricular mass, blood pressure and glucose levels in adult life. Supported by FAPESP

Vinclozolin: A feasibility and sensitivity study of the ILSI-HESI F1-extended one-generation rat reproduction protocol

Feasibility of the ILSI-HESI (ACSA) extended one-generation protocol was tested with vinclozolin (dietary 0, 4, 20, 100mg/kg/day). Parental Wistar rats (n=25/sex/dose) were dosed pre-mating (males 4, females 2weeks) through F1 offspring weaning (postnatal day PND21); F1 dosing continued through PND70. At PND21, 3 subsets (each 1 pup/sex/litter) were selected for neurotoxicology (functional observational battery, motor activity, neuropathology), clinical pathology (hematology, clinical chemistry, urinalysis, thyroid hormone assay) (subsets 1a, 1b; each n=10/sex/dose), immunotoxicology (IgM) SRBC antibody response and natural killer cell assays (subset 2; n=25/sex/dose), and estrus cycle (subset 3; n=25/dose). Vinclozolin reduced parental and offspring bodyweight and prostate, seminal vesicles and epididymides weight, and increased adrenal weight/induced adrenal cortical hypertrophy at 100mg/kg. Mating, fertility, gestation and lactation were unaffected. At 20 and 100mg/kg, F1 males had reduced anogenital distance and retained areolae; at 100mg/kg only, there was hypospadias, purulent prostatitis and seminal vesicle inflammation with atrophy, and Leydig cell hyperplasia, and in F1 females accelerated vaginal opening. These effects are consistent with vinclozolin’s known anti-androgenic developmental effects. Neuro- and immunotoxicology tests were unaffected. F1 Only T4 was reduced at 20 and 100mg/kg. The overall sensitivity of the extended one-generation protocol is comparable to or even greater than the current two-generation study. Thus it reduces animal use while maintaining or enhancing information for risk assessment.

Adaptability of pregnant Merino ewes to the cold desert climate in Nevada1

Grazing ability is difficult to record in animals under free-ranging conditions without sophisticated methods. Alternatively, grazing ability may be indirectly inferred from changes in BW and production characteristics during the grazing period. The present study investigated the effect of grazing on resource-limited rangelands on BW, wool characteristics, and offspring weaning weights in nine hundred five 5/8, 7/8, and fullblood Merino ewes of 2 to 7 yr of age during a grazing period of approximately 2.5 mo (between January and March). A total of 469 ewes gave birth to a single lamb, 248 to twin lambs, and 188 did not give birth. Body weights were measured and wool samples taken before and after the ewes were allowed to graze freely on the rangelands; absolute change in BW and change in BW as a percentage of initial BW were estimated. On average, grazing on resource-poor rangelands resulted in BW loss, a reduction in fiber diameter and its CV, and increased staple length. Animals with finer wool at the start of the grazing period lost phenotypically (r = -0.07, P < 0.05) and genetically (r = -0.23, P < 0.05) less BW during the grazing period and had a greater probability to carry 1 lamb (or 2) to term (P < 0.05). Animals that lost less BW produced more greasy fleece (r = 0.09, P < 0.01). Body weight change did not significantly influence offspring weaning weights. Change in BW was moderately heritable at h(2) = 0.29; fiber diameter was strongly heritable at h(2) = 0.51. Animals with the least inclusion of Merino genetics lost more BW (P < 0.01) during the grazing period and had a more uniform fiber diameter (P < 0.05) but shorter staples (P < 0.05) and less fleece (P < 0.0001) than animals with a greater level of Merino genetics. Our results indicate that animals with finer wool appeared to be better adapted to the cold Nevada desert. Thus, selection for finer wool may positively influence adaptability to resource-limited cold climate conditions; alternatively, BW change may be selected for directly. Because nutritional deficiencies during pregnancy can have adverse consequences for the offspring, indirect selection for grazing ability would foremost result in healthier ewes that can produce lambs and wool without compromising their welfare.

Early weaning and alcohol disorders in offspring: biological effect, mediating factors or residual confounding?

This study explores associations between early weaning and alcohol use disorders in youth and mechanisms by which these associations may operate. We used data from the Mater University Study of Pregnancy and its outcomes, an Australian birth cohort study based in Brisbane. This study is based on a subsample of 2370 participants for whom complete data were available at age 21 years. Length and method of breastfeeding were assessed at 6 months. Alcohol use disorders were assessed at age 21 using the life-time version of the Composite International Diagnostic Interview-computerized version (CIDI-Auto). We adjusted for maternal age, marital status, education, alcohol, tobacco use, anxiety, depression and maternal attitudes towards the baby. Attention Deficit and Hyperactivity Disorders (ADHD) and Intellect Quotient (IQ) were measured with the Child Behaviour Checklist (5 years) and the Ravens SM (14 years), respectively. Those who had been weaned within 2 weeks of being born and breastfed at regular intervals were at increased risk of meeting criteria for alcohol use disorders at age 21 [odds ratio (OR) 1.71, 95% confidence interval (CI):1.07, 2.72]. This study confirms a small but robust association between early weaning and increased risk of alcohol use disorders.

90-Day feeding and genotoxicity studies on a refined arachidonic acid-rich oil

The safety of a refined arachidonic acid-rich oil (RAO) was evaluated for reverse mutation, chromosome aberration and gene mutation, and in a 90-day Wistar rat feeding study with in utero exposure. The results of the genotoxicity assays were all negative. The in utero phase of the 90-day study involved dietary exposure to 0.5%, 1.5% and 5% RAO and two controls diets, a standard feed low-fat diet and a high-fat diet supplemented with 5% corn oil. This exposure covered four-weeks prior to mating, through mating, gestation and lactation until offspring (F 1) weaning. A subsequent 90-day feeding study in the F 1 rats evaluated the same test and control diets. Statistically significant effects were seen for selected histopathology, clinical chemistry and organ weight endpoints; however, other than increased absolute and relative monocytes seen in both sexes of high-dose rats, the observations were not attributed to treatment for one or more reasons. Based on these findings, no adverse treatment-related effects for RAO were seen at up to 5% in the diet, equivalent to an overall average RAO intake of 3170 mg/kg bwt/day. These and similar findings for other refined ARA-rich oils establish a strong body of evidence for the safety of this RAO.

Developmental programming of sex-dependent alterations in lipid metabolism: a role for long-term, sex-specific alterations in LDL-receptor expression. Focus on “Developmental programming of lipid metabolism and aortic vascular function in C57BL/6 mice: a novel study suggesting an involvement of LDL-receptor”

the nobel prize in physiology or medicine was awarded to Brown and Goldstein in 1985 for their discovery of the low-density lipoprotein (LDL) receptor and its importance in the regulation of cholesterol metabolism ([2][1]). Cholesterol, an essential component of the mammalian cell membrane, is

Short hypoxia could attenuate the adverse effects of hyperhomocysteinemia on the developing rat brain by inducing neurogenesis

Gestational deficiency in methyl donors such as folate and vitamin B12 impairs homocysteine metabolism and can alter brain development in the progeny. Since short hypoxia has been shown to be neuroprotective in preconditioning studies, we aimed to investigate the effects of brief, non-lesioning neonatal hypoxia (100% N2 for 5 min) on the developing brain of rats born to dams fed either a standard diet or a diet lacking vitamins B12, B2, folate and choline until offspring's weaning. While having no influence on brain accumulation of homocysteine and concomitant apoptosis in 21-day-old deficient pups, exposure to hypoxia reduced morphological injury of the hippocampal CA1 layer. It also markedly stimulated the incorporation of bromodeoxyuridine (BrdU) in permissive areas such as the subventricular zone and the hippocampus followed by the migration of new neurons. Scores in a locomotor coordination test (days 19–21) and learning and memory behavior in the eight-arm maze (days 80–84) were found to be significantly improved in rats exposed to hypoxia in addition to the deficient diet. Therefore, by stimulating neurogenesis in rat pups, brief neonatal hypoxia appeared to attenuate the long-term effects of early exposure to a deficiency in nutritional determinants of hyperhomocysteinemia.

Effects of the brominated flame retardant hexabromocyclododecane (HBCD) on dopamine-dependent behavior and brainstem auditory evoked potentials in a one-generation reproduction study in Wistar rats

Hexabromocyclododecane (HBCD) is a widely used brominated flame retardant which has been recently detected in many environmental matrices. Data from a subacute toxicity study indicated dose-related effects particularly on the pituitary thyroid-axis and retinoids in female rats. Brominated and chlorinated aromatic hydrocarbons are also reported to exert effects on the nervous system. Several investigations revealed a pronounced sensitivity of the dopaminergic system and auditory functions to polychlorinated biphenyls. Therefore, the present experiment should examine, whether or not HBCD affects these targets. Rats were exposed to 0, 0.1, 0.3, 1, 3, 10, 30 or 100 mg HBCD/kg body weight via the diet. Exposure started before mating and was continued during mating, gestation, lactation, and after weaning in offspring. Haloperidol-induced catalepsy and brainstem auditory evoked potentials (BAEPs) were used to assess dopamine-dependent behavior and hearing function in adult male and female offspring. On the catalepsy test, reduced latencies to movement onset were observed mainly in female offspring, indicating influences on dopamine-dependent behavior. The overall pattern of BAEP alterations, with increased thresholds and prolonged latencies of early waves, suggested a predominant cochlear effect. Effects were dose-dependent with lower bounds of benchmark doses (BMDL) between ≤1 and 10 mg/kg body weight for both catalepsy and BAEP thresholds. Tissue concentrations at the BMDL values obtained in this study were 3–4 orders of magnitude higher than current exposure levels in humans.

Female red squirrels fit Williams’ hypothesis of increasing reproductive effort with increasing age

Williams predicted that reproductive effort should increase as individuals age and their reproductive value declines. This simple prediction has proven difficult to test because conventional measures of energy expenditure on reproduction may not be a true reflection of reproductive effort. We investigated age-specific variation in female reproductive effort in a stable population of North American red squirrels where energy expenditure on reproduction is likely to reflect actual reproductive effort. We used seven measures of reproductive effort spanning conception to offspring weaning. We found that females completed growth by age 3 and that reproductive value decreased after this age likely because of reproductive and survival senescence. We therefore, predicted that reproductive effort would increase from age 3 onwards. The probability of breeding, litter mass at weaning, and likelihood of territory bequeathal were all lower for 1- and 2-year-old females than for females older than 3 years, the age at which growth is completed. That growing females are faced with additional energetic requirements might account for their lower allocation to reproduction as compared with older females. The probability of attempting a second reproduction within the same breeding season and the propensity to bequeath the territory to juveniles increased from 3 years of age onwards, indicating an increase in reproductive effort with age. We think this increase in reproductive effort is an adaptive response of females to declining reproductive values when ageing, thereby supporting Williams' prediction.

Sex of the foetus determines the time of weaning of the previous offspring of captive plains zebra ( Equus burchelli)

We examined if captive plains zebra ( Equus burchelli) mares change the timing of weaning according to the sex of the suckling foal and of the new impending foetus. We observed 19 captive plains zebra foals, in three different formations, at the Dvůr Králové Zoo. The earliest time for weaning of any foal was recorded at the age of only 243 days. The latest suckling that was ever recorded occurred 83 days before the dam's next delivery, when the foal was at the age of 355 days. We found that pregnant mares weaned their foals sooner than the non-pregnant mares. Survival analysis revealed that the sex of the foetus was the most influential factor in determining the weaning age of the current foal. Hence, if the foetus was a male, then weaning occurred sooner than if the dam was carrying a female foetus. This finding is the first of this kind among ungulates. The reproductive state of the mare and the sex of her foetus should be considered when interpreting weaning times of equids.

Perinatal/Postnatal Study of D-003, a Mixture of Long-Chain Fatty Acids, in Rats

D-003 is a mixture of long-chain fatty acids isolated and purified from sugar cane wax with cholesterol-lowering and antiplatelet effects. In order to further characterize the developmental toxicity during the treatment period from late gestation up to weaning of the offspring, pregnant females received 0 (control), 500, and 1,000 mg/kg/day D-003 daily by oral gavage beginning at day 15 of pregnancy and through gestation until day 21 postpartum. Maternal clinical signs, body weight, and food intake were measured at regular intervals during gestation and lactation. Live pups were weighed, sexed, and examined for developmental signs. One female and male of each litter were randomly selected to evaluate the reproductive potential. There were no spontaneous or dose-related maternal deaths during the course of this study. The general health and behavioral condition of offspring was good in all groups. No significant differences among groups were found in comparisons of litter size, survival through the weaning period, sex ratio, and male and female weights. This peri- and postnatal study conducted with D-003 in rats indicated that treatment of the dam during late gestation and lactation did not show adversely effects on reproductive performance or fetal development over two generations.