Effect of mother's physical condition during pregnancy and lactation on postnatal growth and reproductive success of offspring in water vole Arvicola terrestris L

Postnatal growth, life span, and probability of reproduction in the adult state depended on the mother's physical condition during pregnancy and lactation in water vole. The white fat weight in the female abdominal cavity was shown to significantly increase in pregnancy and to decrease in late lactation. As an indicators for nutritional state of females, their body weight difference after parturition (or in late lactation) and expected from the regression equation relating individual body weight at the beginning and the end of each reproductive stage were used (physical condition indexes in pregnancy or lactation). The correlation of the physical condition index in pregnancy with the storage fat weight was 0.67. The metabolic resources of the mother's body proved to favor faster offspring development. The female offspring weight at the age of 3 and 10 weeks as well as adult ones positively correlated with the mother's nutritional state in pregnancy, while the male offspring weight demonstrated a similar correlation at the age of 3 and 6 weeks. Increased negative energy balance during lactation proved to decrease the offspring weight in both sexes after separation from mother and at the age of 6 weeks. High nutritional state of mother in pregnancy favored both the probability of reproduction and life span of female offspring. The reproduction of male offspring did not depend on the mother's physical condition. The life span peaked in male offspring of mothers in a nutritional state below average in pregnancy and above average in lactation. Thus, the physical condition of the mother's body is an important sex-dependent factor of phenotypic variation in the offspring body weight, reproductive competence, and life span.     

Effect of mother’s physical condition during pregnancy and lactation on postnatal growth and reproductive success of offspring in water vole <Emphasis Type="Italic">Arvicola terrestris</Emphasis>

Postnatal growth, life span, and probability of reproduction in the adult state depended on the mother’s physical condition during pregnancy and lactation in water vole. The white fat weight in the female abdominal cavity was shown to significantly increase in pregnancy and to decrease in late lactation. As an indicators for nutritional state of females, their body weight difference after parturition (or in late lactation) and expected from the regression equation relating individual body weight at the beginning and the end of each reproductive stage were used (physical condition indexes in pregnancy or lactation). The correlation of the physical condition index in pregnancy with the storage fat weight was 0.67. The metabolic resources of the mother’s body proved to favor faster offspring development. The female offspring weight at the age of 3 and 10 weeks as well as adult ones positively correlated with the mother’s nutritional state in pregnancy, while the male offspring weight demonstrated a similar correlation at the age of 3 and 6 weeks. Increased negative energy balance during lactation proved to decrease the offspring weight in both sexes after separation from mother and at the age of 6 weeks. High nutritional state of mother in pregnancy favored both the probability of reproduction and life span of female offspring. The reproduction of male offspring did not depend on the mother’s physical condition. The life span peaked in male offspring of mothers in a nutritional state below average in pregnancy and above average in lactation. Thus, the physical condition of the mother’s body is an important sex-dependent factor of phenotypic variation in the offspring body weight, reproductive competence, and life span.     

Mass transfer from mothers to pups and mass recovery by mothers during the post-breeding foraging period in southern elephant seals (Mirounga leonina) at King George Island

Mass transfer from mother to pup during the lactation period, and mass recovery for the same females during the foraging period were measured in the southern elephant seal at King George Island, Antarctica. During the 19.2 ± 0.9-day lactation period measured (which represented 87% of the entire nursing), females lost a mean mass of 10.56 ± 1.76 kg/day (n = 27), while their pups gained a mean mass of 5.27 ± 1.1 kg/day. There was a correlation between daily body weight gain in pups and daily weight loss by their mothers. Pup weaning mass was positively related to maternal post-partum mass. Serial samples showed that weight losses by females and gains by their pups were not linear over lactation, but showed lower values at the beginning and at the end of lactation. During the 60.5 ± 6.2-day foraging phase between the end of lactation and molt, females gained 2.21 ± 0.65 kg/day (n = 12), or 54% of the mass lost during nursing. Growth rates reported here are higher than those reported in other breeding sites. However, the ratio of body mass loss by females to gain by their pups was similar, suggesting that higher growth rates and greater weaning mass at South Shetland are due to a higher mean weight of females on arrival at this breeding site. The foraging period was shorter and the mass gained greater than those measured at South Georgia; this could be related to relatively shorter distances to foraging areas. Received: 20 September 1996 / Accepted: 28 April 1997     

Effects of prenatal administration of testosterone and cortisone on the reproductive system of the female rat.

Testosterone propionate, cortisone, or sesame oil vehicle were given to rats during the last week of pregnancy so that effects of the hormones on anogenital distance, breeding capacity and vaginal opening of the female progeny could be contrasted. Testosterone significantly increased anogenital distance and delayed vaginal opening of progeny. When females that had been exposed to testosterone in utero were tested for breeding capacity, a significantly smaller number mated than in the control group. Female rats that had been exposed to cortisone in utero exhibited premature vaginal opening but did not differ from controls in anogenital distance, and, unlike the testosterone-exposed rats, mated. Cortisone-exposed rats carried litters to term and the litters did not differ from those of controls in numbers of pups or numbers of living pups at birth. The pups born to cortisone-exposed rats had greater birth weights and a higher survival rate to 20 days of age than pups of controls. Results indicate that testosterone administration to rats during pregnancy is far more detrimental to the development and subsequent function of the reproductive system of female progeny than cortisone and suggest that similar changes which occur in response to maternal stress or to administration of ACTH during pregnancy are more likely to result from increases in testosterone than from increases in glucocorticoid secretion.     

Energetics of lactation in harp seals (Phoca groenlandica) from the gulf of St. Lawrence,Canada

 This study reports the findings of an integrated, comprehensive analysis of lactation energetics in harp seals conducted using longitudinal measurements of mass, body composition and milk composition from mother-pup pairs in conjunction with water flux measurements in pups. The nursing period of harp seals is a short, intense and relatively efficient period of energy transfer from mothers to pups. The average daily milk intake for pups was 3.65±0.24 kg which is equivalent to 79.5 MJ of energy. Eighty-one per cent of the energy received in the milk was metabolisable and 66% of the energy was stored by the pups as body tissue. The field metabolic rate of pups was 3.9±0.4 time basal metabolic rate. The pups were growing at a rate of 2.2 kg per day during the nursing period. The distribution of this mass gain varied in terms of tissue composition, depending on the age of the pups, but over the whole nursing period approximately half of the tissue was stored as fat. Harp seal mothers lost an average of 3.1 kg per day during lactation which was composed of 37% water, 50% fat, 11% protein and 2% ash. Mothers spent half of their time during the lactation period actively diving and only one-third of their time on the surface of the ice. Milk compositional changes followed the normal phocid pattern with increasing fat content and decreasing water content as lactation progressed. The mean mass transfer efficiency was 73%. However, this value cannot be used without qualification because female harp seals in this study fed to varying degrees, consuming an estimated 0–4.8 kg of fish per day. Feeding does not appear to be required in order to achieve the energy requirements for lactation, given the energy stores possessed by females, and some females do fast through the entire period so feeding may be considered opportunistic in nature. Accepted: 25 April 1996     

Bioenergetics of reproduction and pup development in a subterranean rodent (Ctenomys talarum)

The objective of this study was to evaluate the maternal costs of reproduction and pup development in the subterranean rodent Ctenomys talarum (Thomas 1898). Statistical differences were detected in whole-animal metabolic rates between nonreproductive and pregnant or lactating females. Whole-animal metabolic rates during pregnancy and lactation were 128% and 151% of the resting metabolic rate (RMR) observed in nonreproductive females. The total additional energy cost of reproduction (above the nonreproductive level) was similar for both the gestation and lactation periods. Mass-specific RMR revealed an upregulation of cell or tissue metabolism during lactation but not during gestation. The mass-specific metabolic rate of pups was 237% of the adults' metabolic rates. No differences were observed in body temperature among nonreproductive, pregnant, or lactating females. No differences were detected in body mass at birth among pups from litters with different numbers of nestlings. Pups increased their body temperature, reaching adult temperature at 30 d of age, when they were near weaning. Milk constituted the exclusive food for pups until they started eating solid food at 10 d old. Suckling time decreased with age of pups, and at the same time, mother chases directed toward their pups increased. These reproductive characteristics may contribute to successful existence in a subterranean habitat.     

Limits to sustainable energy budget during lactation in the striped hamster (Cricetulus barabensis) raising litters of different size

A female animal appears to approach an upper limit to the rate of sustained energy intake/metabolic rate (SusEI/MR) during lactation. However, different species of animals may respond differently to the sustainable limit. Here, we measured energy budget during lactation in female striped hamsters raising litters of natural size (Con), and females whose litter size was manipulated during early lactation to support fewer or more pups (minus pups, MP or plus pups, PP). The striped hamsters significantly decreased their body mass and increased food intake from early to late lactation; and MP females had lower weight loss and food intake than the control and PP females. Litter size of the PP group decreased significantly over the period of lactation, and pups were weaned at a similar weight to that of the controls. MP females supported a significantly lower litter mass throughout lactation compared with the control and PP females, but during late lactation the pups from the MP group were significantly heavier. Resting metabolic rate (RMR) did not differ significantly between the three groups and the gross energy intake during peak lactation was 5.0×, 4.2× and 5.0 × RMR for the control, MP and PP females, respectively. Female striped hamsters reached a plateau in food intake at around 14 g/d during peak lactation, which might signify a limit of SusEI at 5.0 × RMR. However, it was not possible to determine whether the limitation on SusEI was imposed centrally by the capacity of the gastrointestinal tract to process food, peripherally by the capacity of the mammary gland to produce milk, or by the capacity of animals to dissipate heat.     

Malnutrition in utero and lactation: relation between the weight gained by the mothers and the development of their offspring

Physiological weight changes in rat dams and their offspring as sequelae of malnutrition during pregnancy and lactation have been studied. Daily monitoring of the body weight as well as the consumption of food (malnutrition dams 14 g during pregnancy and 20 g during lactation) and drink in control and malnutrition dams was conducted. The number of pregnant dams that completed their pregnant period successfully was registered as well as the number and weight of the pups at birth and their evolution over a period of a month. The percentage of mortality of the pups during that period has been studied. The present results indicate a highly significant decrease in body weight in experimental dams, which determines a retardation in the physiological development of the pups, and yields a higher percentage of mortality in the experimental animals than in controls. It can thus be concluded that malnutrition in utero and during lactation affects the ratio between weight gain for dams and the physical development of their pups.     

Maternal food restriction delays weaning in the guinea pig, Cavia porcellus

In mammals, the duration of lactation varies much more than other life history parameters in relation to body mass, both within and between species. The causes of this variation are poorly understood and seem to result from varying conditions of mothers and young. We studied the effect of long-term maternal food restriction on litter mass at birth, duration of lactation and offspring development in the precocial guinea pig. Mild experimental food restriction during reproduction resulted in prolonged nursing behaviour of mothers. Evidence for a threshold mass at weaning was, however, equivocal. In the guinea pig, benefits of prolonged lactation prove hard to understand, because nutritional benefits are minor. Independently of maternal food regime, pups terminated suckling attempts several days after mothers ceased nursing behaviour. The time between the last nursing behaviour and the last suckling attempts was not longer in litters with higher need, that is, in litters of food-restricted females, than in litters of females fed ad libitum. Under food restriction, mothers maintained their own body mass, leading in pups to lower mass at birth, reduced postnatal growth and lower body mass at maturity. Guinea pig mothers appear to be selected to value their own condition more than that of a litter. We suggest that lengthening of the nursing period under poor conditions is a life history response primarily of precocial mammals.     

Influence of maternal mass and condition on energy transfer in Weddell seals

1. Environmental variation influences food abundance and availability, which is reflected in the reproductive success of top predators. We examined maternal expenditure, offspring mass and condition for Weddell seals in 2 years when individuals exhibited marked differences in these traits. 2. For females weighing > or = 355 kg there was a positive relationship between maternal post-partum mass (MPPM) and lactation length, but below this there was no relationship, suggesting that heavier females were able to increase lactation length but lighter females were restricted to a minimum lactation period of 33 days. 3. Overall, females were heavier in 2002, but in 2003 shorter females were lighter than similar-sized females in 2002 suggesting that the effects of environmental variability on foraging success and condition are more pronounced in smaller individuals. 4. There was no relationship between MPPM and pup birth mass, indicating pre-partum investment did not differ between years. However, there was a positive relationship between MPPM and pup mass gain. Mass and energy transfer efficiency were 10.2 and 5.4% higher in 2002 than 2003, which suggests costs associated with a putatively poor-resource year were delayed until lactation. 5. Heavier females lost a higher proportion of mass during lactation in both years, so smaller females may not have been able to provide more to their offspring to wean a pup of similar size to larger females. 6. MPPM had only a small influence on total body lipid; therefore, regardless of mass, females had the same relative body composition. Females with male pups lost a higher percentage of lipid than those with female pups, but by the end of lactation female pups had 4.5% higher lipid content than males. 7. It appears that for Weddell seals the consequences of environmentally induced variation in food availability are manifested in differences in maternal mass and expenditure during lactation. These differences translate to changes in pup mass and condition at weaning with potential consequences for future survival and recruitment.     

Protein content in urine of male and female water vole (Arvicola amphibius) at the period of spring growth and sexual maturation

The study was carried out on the water voles Arvicola amphibius reared in vivarium. For the first decade of January, March, and June, the body length, the anogenital distance, and the body mass were measured, and urine was collected for determination of its protein content. The obtained results have shown that the protein content depends on the animal gender and is connected with the reproductive status of males and their size-weight characteristics. The urinary protein excretion level in females remained stable at different months, whereas in males its sharp rise was noted at the period of spring growth and sexual maturation. The significant sexual differences were established in March and enhanced in June. In March the urine protein content in males was noted to correlate positively with the body mass and length and with the anogenital distance. The males reached sexual maturity at the earlier calendar terms than the females did; in sexually mature males the urine protein content was significantly higher than in the sexually immature ones.     

Dynamics of morphophysiological charateristics in female water voles (Arvicola amphibius L.) during pregnancy

Pregnancy and lactation need increased energy consumption and are accompanied by morphological and physiological changes of various maternal organs and systems. In water voles, connection of female interior characteristics has been poorly studied. Under standard vivarium conditions, we evaluated morphophysiological parameters of non-reproducing females and of females at the early (1–7 days), intermediate (8–14 days), and late (15–21 days) stages of pregnancy. There were established effect of the reproductive state on mass of abdominal and brown adipose tissue, liver, adrenals, spleen and an increment of body mass (without uterus with embryos). In pregnant females, as compared with the non-pregnant ones, the blood thyroxine level was significantly lower (16.2 ± 0.8 and 21.7 ± 1.4 pmol/l) and the blood testosterone level was higher (1.29 ± 0.19 and 0.83 ± 0.09 nmol/l). The blood glucose content fell in the end of pregnancy. Dynamics of morphophysiological parameters at the period of pregnancy reflects the compensatory body reactions providing preservation of embryos and preparation to lactation of offspring.     

Adrenocortical responsiveness in southern elephant seal mothers and pups during lactation and the effect of scientific handling

We examined the cortisol responses to chemical and physical restraint stress in southern elephant seal Mirounga leonina females and their pups at three stages during lactation. In anaesthetised females the serum cortisol levels changed moderately during the 45-min sampling period following restraint, with average peaks at 23 min after anaesthetic administration. Overall, cortisol was relatively low 2 days postpartum and increased throughout lactation. In physically restrained pups serum cortisol increased rapidly after capture; the response was milder at age 2 days than at 11 days and 21 days. Levels were higher in female pups than in males. In order to test whether cortisol levels and/or responses became chronically (i.e. days to weeks) altered due to restraint, we compared the cortisol response at a late stage of lactation between three groups of mother-pup pairs previously given different levels of chemical (mothers) or physical (pups) restraint stress: control (not handled previously), moderate treatment (previously handled twice), and high treatment (previously handled 3-4 times). Pups of the three treatment groups showed similar adrenocortical responses suggesting no chronic effect of repeated physical restraint, despite the clear acute effects. Mothers of the control and moderate treatment groups showed similar cortisol responses; however, mothers of the high treatment group showed significantly attenuated responses. This indicated that elephant seals tolerated moderate degrees of handling disturbance; however, repeated (3-4) chemical immobilisations in lactating females may reduce their adrenocortical responsiveness for a period of days or weeks.     

Effects of body mass and reproduction on the basal metabolic rate of brown long-eared bats (Plecotus auritus)

We measured basal metabolic rate (BMR) of nonreproductive and of breeding (pregnant and lactating) female brown long-eared bats (Plecotus auritus) to investigate the effects of intra- and interindividual variation in body mass and of reproduction on metabolism. The BMR of six nonreproductive females was measured between five and seven times at approximately 2-wk intervals over a period of 2.5 mo. There was a highly significant effect (P<0.001) of body mass on BMR of these nonreproductive females. The pooled within-individual scaling exponent (1.88) significantly exceeded the established mammalian interspecific exponent (0.75). In addition, we made single observations on 14 nonreproductive females to establish the effects of differences in mass between individuals. The mean BMR across all 14 individuals was 82 mW (+/-24 SD). There was a significant positive relationship between BMR and body mass across these individuals (r2=0.39), with a between-individual scaling exponent of 0.75. Inter- and intraindividual effects of mass on BMR were combined in a regression analysis that included mean body mass and deviation from mean mass on any given day as predictors. This regression model explained 55% of the variation in BMR. We made longitudinal measurements of BMR throughout reproduction and compared these with the predicted BMR of nonreproductive bats of the same body mass. Reproductive females exhibited temporal flexibility in BMR. BMR during pregnancy increased on a whole-animal basis but was significantly lower (by, on average, 15%) than BMR predicted for nonreproductive females of the same mass. Over a period of 1-75 d following birth, whole-animal BMR was greater than that during pregnancy, even though body mass declined after parturition. Hence, postbirth BMR was greater than the level predicted for nonreproductive females of the same mass. This study indicates that the scaling of BMR with body mass differs significantly within and between individuals and that there is a reduction of BMR in pregnancy and an elevation of BMR during lactation.     

Effects of perinatal maternal food restriction on pituitary-gonadal axis and plasma leptin level in rat pup at birth and weaning and on timing of puberty

The effects of maternal 50% food restriction (FR) during the last week of gestation and/or lactation on pituitary-gonadal axis (at birth and weaning), on circulating levels of leptin (at weaning), and on the onset of puberty have been determined in rats at birth and at weaning. Maternal FR during pregnancy has no effect at term on the litter size, on the basal level of testosterone in male pups, and on the drastic surge of circulating testosterone that occurs 2 h after birth. At weaning, similar retardation of body growth is observed in male and female pups from mothers exposed to FR. This undernutrition induces the most drastic effects when it is performed during both gestation and lactation or during lactation alone. Drastic retardation of testicle growth with reduction of cross-sectional area and intratubular lumen of the seminiferous tubules is observed in male pups from mothers exposed to undernutrition during both gestation and lactation or during lactation alone. Maternal FR during the perinatal period reduces circulating levels of FSH in male pups without affecting LH and testosterone concentrations. Maternal FR does not affect circulating levels of LH, estradiol, and progesterone in female pups. Female pups from mothers exposed to FR during both gestation and lactation show a significant increase of plasma FSH as well as a drastic retardation of ovarian growth. The follicular population was also altered. The number of antral follicles of small size (vesicular follicles) was increased, although the number of antral follicles of large size (graafian follicles) was reduced. Maternal FR occurring during both late gestation and lactation (male and female pups), during lactation alone (male and female pups), or during late gestation (female pups) induces a drastic reduction of plasma leptin and fat mass in pups at weaning. The onset of puberty is delayed in pups of both sexes from mothers exposed to FR during lactation and during both gestation and lactation. In conclusion, these data demonstrate that a perinatal growth retardation induced by maternal FR has long-term consequences on both size and histology of the genitals, on plasma gonadotropins and leptin levels, on fat stores at weaning, and on the onset of puberty.     

Variation in milk production and lactation performance in grey seals and consequences for pup growth and weaning characteristics

Phocid seals are one of the few groups of mammals capable of sustaining the energetic demands of lactation entirely through body nutrient stores while fasting. Lactation performance of the female in turn influences the rate and pattern of pup growth. We examined variation in and patterns of milk composition and production, maternal energy output, and pup growth and energy deposition over the entire lactation period in 18 grey seal mother-pup pairs using hydrogen isotope (3H2O and D2O) dilution. Milk composition was independent of maternal mass and nutrient stores, indicating dependence on other physiological and genetic factors. Heavier females lactated longer (r2=0.653, P<0.001), had higher total milk outputs (r2=0.652, P<0.001), and produced larger pups at weaning (r2=0.417, P=0.005). While fatter females lactated for longer periods of time (r2=0.595, P<0.001), females with a larger lean body mass at parturition produced more milk (r2=0.579, P<0.001). Total milk energy output was the strongest predictor of pup weaning mass, which, along with the pup's efficiency of energy storage, accounted for 91% of the variation in weaning mass. Nevertheless, there was sufficient plasticity in milk composition and energy output that some smaller females produced relatively large pups. Few females appeared to deplete body nutrients to the point where it might limit the duration of lactation.     

Mass changes of grey seal Halichoerus grypus pups on Sable Island: differential maternal investment reconsidered

Theory predicts that where variance in reproductive success differs between sexes, as in many sexually dimorphic species, mothers should invest more in male than in female offspring. In pinnipeds, parental investment is the sole responsibility of the mother. Both size at birth and subsequent mass gain during lactation are measures of that investment. We studied mass gain of grey seal pups, a sexually dimorphic species, during lactation and mass loss during the first 13 days of the postweaning fast using longitudinal data obtained on Sable Island, Canada. A mixed-effects repeated measures model was used to account for the serial correlation in these longitudinal data. We found no significant difference in the birth mass of male (16.6 ± 0.45 kg) and female (15.6 ±0.74 kg) pups. Rate of mass gain by males (3.0 ± 0.13 kg/d) and females (2.7 ± 0.12 kg/d) also did not differ significantly during the lactation period. Grey seal pups on Sable Island tended to be larger at birth and gain mass more rapidly (70%–100%) during lactation than those in the United Kingdom. Mass loss of weaned pups was curvilinear over time. Over the first 10 days of the fast, pups lost 22% of their weaning mass. In both males and females, large pups lost mass more slowly than small ones during the postweaning fast. Based on our results and a review of previous studies, we found little evidence of differential maternal investment in male and female grey seal pups.     

Reproductive performance in grey seals: age-related improvement and senescence in a capital breeder

1. Three hypotheses have been advanced to account for age-related improvement in performance: the selection hypothesis predicts improved due to the loss of lower quality phenotypes, the constraint hypothesis predicts individuals improve function, and the restraint hypothesis predicts younger individuals forego or reduce effort because of mortality risks. A decline in age-related performance (i.e. senescence) is predicted by mutation accumulation, antagonistic pleiotropy and disposable soma (wear and tear) hypotheses. 2. Using five measures of performance - birth rate, maternal and pup birth mass, pup weaning mass, weaning success and lactation length - we tested these hypotheses concerning age-related change in reproduction in 279 female grey seals (Halichoerus grypus), ages 4-42 years, over a 23-year period between 1983 and 2005 on Sable Island, Nova Scotia. These females produced 2071 pups. 3. Although body mass of primiparous females increased with age (4-7 years) birth mass of their pups did not, but pup weaning mass did. Second- and third-parity females of the same age as primiparous females gave birth to and weaned heavier pups. However, parity and age were dropped from models when maternal body mass was included. 4. The proportion of females giving birth varied significantly with maternal age, increasing in young females and then declining late in life. Weaning success rate also increased rapidly to about 8 years and subsequently declined in females > 32 years. 5. Generalized additive models indicated nonlinear changes in 3 day body mass (i.e. approximately birth mass) and weaning mass of pups as a function of maternal age, after accounting statistically for the effects of maternal body mass. Mixed-effects, repeated-measures models fitted to longitudinal data further supported the conclusion that pup birth mass and weaning mass vary nonlinearly with maternal age and indicated nonlinear changes in lactation duration. 6. We found some support for the constraint hypothesis, but our findings were not consistent with the selection hypothesis or the restraint hypothesis as the basis for improvement in reproductive performance. 7. Senescence was evident in multiple female and offspring traits, indicating the degeneration in function of several physiological systems as predicted by the disposable soma hypothesis.     

Effects of genistein in the maternal diet on reproductive development and spatial learning in male rats

Endocrine disruptors, chemicals that disturb the actions of endogenous hormones, have been implicated in birth defects associated with hormone-dependent development. Phytoestrogens are a class of endocrine disruptors found in plants. In the current study we examined the effects of exposure at various perinatal time periods to genistein, a soy phytoestrogen, on reproductive development and learning in male rats. Dams were fed genistein-containing (5 mg/kg feed) food during both gestation and lactation, during gestation only, during lactation only, or during neither period. Measures of reproductive development and body mass were taken in the male offspring during postnatal development, and learning and memory performance was assessed in adulthood. Genistein exposure via the maternal diet decreased body mass in the male offspring of dams fed genistein during both gestation and lactation, during lactation only, but not during gestation only. Genistein decreased anogenital distance when exposure was during both gestation and lactation, but there was no effect when exposure was limited to one of these time periods. Similarly, spatial learning in the Morris water maze was impaired in male rats exposed to genistein during both gestation and lactation, but not in rats exposed during only one of these time periods. There was no effect of genistein on cued or contextual fear conditioning. In summary, the data indicate that exposure to genistein through the maternal diet significantly impacts growth in male offspring if exposure is during lactation. The effects of genistein on reproductive development and spatial learning required exposure throughout the pre- and postnatal periods.     

Pregnancy of adult caribou (Rangifer tarandus): evidence for lactational infertility

To examine the relations between pregnancy, body condition, and lactation, 106 adult female caribou Rangifer tarandus granti ) of the Porcupine Herd were captured, weighed, measured, and scored for body condition in November 1990–1992. Blood samples were drawn for determination of pregnancy, and body fat content (kg) was estimated from the product of body weight and the body-condition score. Pregnant females were significantly fatter and heavier than non-pregnant females, and non- lactating females were significantly fatter, but no heavier, than lactating caribou. Probability of pregnancy was positively correlated with body weight and fat content, but prediction of pregnancy was improved when multiple independent variables, including skeletal dimensions and lactation status, were included in logistic models. Non-lactating females were more fertile than lactating females at a particular body weight and metatarsus length; but, at the same fatness, they were not more fertile than females that had lactated through the summer and were ceasing lactation in November. However, females that were extending lactation in November were least fertile, and this reduction of fertility was not explained by differences in body condition or skeletal dimensions. We suggest that the extended lactation group is exhibiting lactational infertility. Finally, unexplained differences in the relation between pregnancy rate and body condition exist among years, suggesting that interannual patterns in the nutrition and ecology of caribou affect the physiological relation between pregnancy and body condition.