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1.
This study tests the hypothesis that female house mice (F1 generation of wild caught Mus domesticus) should preferentially invest in own offspring if confronted with young of different degrees of relatedness. The maternal behaviour of females with litters of 4 own and 4 unrelated alien young (cross-fostered at day 1 of lactation) was analysed during a lactation period of 22 days both under ad libitum and under restricted feeding (food was restricted by 20%). Cross-fostering and restricted feeding had no effect on the amount of time spent nursing until weaning. Under both feeding conditions the females did not differ in their maternal behaviour towards own and alien young: there were no significant differences either in the amount of time spent nursing own versus alien pups or in the time spent licking own versus alien young. Weight gain of own and alien = wild littermates did not differ significantly in mixed litters and was similar both under ad libitum and under restricted feeding. Such indiscriminate behaviour might be adaptive if female house mice prefer to communally nest with a relative and thus improve their inclusive fitness by investing in own and related offspring in a communal nest. Under moderate restricted feeding females could not wean the entire litter but reduced litter size by cannibalizing on average 2.7 pups (75% of the pups were killed when they were 4–8 days old). Females with cross-fostered litters killed as many own as alien young. This suggests that females cannot discriminate between own and unrelated young if cross-fostering takes place at day 1 of lactation. Besides testing kin recognition abilities, the experiments also allow analysis of the weaning strategy of females under food shortage. Under restricted feeding, body weight of the females was significantly lower during middle lactation than under ad libitum feeding. Weaning weight of young in reduced litters under food restriction (9–10 g) did not differ significantly from weaning weight of young in litters of 7–10 young, but was lower than that of young in similar sized litters (litter size 6), under ad libitum feeding. The maternal behaviour of cannibalizing some young under food shortage can be interpreted as a weaning strategy which results in the largest number of offspring that can be raised to a minimal weaning weight of 9–10 g. Such a weaning strategy might represent a favourable trade-off between number and size of young produced.  相似文献   

2.
The spiny mouse Acomys cahirinus produces well-developed pups although it is a relatively small mammal (45 g). We envisioned two opposing hypotheses on the effect of early weaning on the growth rate of pups. The first predicts little effect since the increase in energy intake of dams above non-reproducing females is relatively low, suggesting that pups consume a large portion of their energy as solid food, and the pups are very well developed at birth. The second predicts a substantial effect since the 'index of precociality', that is the energy intake for maintenance of a pup as a proportion of that predicted for a rodent of its body mass, falls within values for altricial rodents, suggesting an extended maternal dependence of the young. To test these hypotheses, we measured the growth rate and food intake of pups weaned after either 7, 14, 21 or 28 days. Only three of 12 pups weaned after 7 days survived and, consequently, the latter hypothesis was supported. All pups weaned at 14–28 days survived. There was a significant decrease in growth rate during the first day after weaning in pups weaned at 7, 14 and 21 days but not after 28 days, suggesting that pups did not require parental care by day 28. Peak growth rate in pups weaned at 14 days occurred in the second week but occurred in the third week in pups weaned at 21 and 28 days. In spite of these differences, pups in all treatments had similar body mass at 64 days, indicating compensatory growth. We concluded that pups of A. cahirinus are precocial from a morphological aspect in that they are well developed at birth but altricial from a nutritional aspect in that they require extended maternal support.  相似文献   

3.
Young laboratory rats received a daily subcutaneous injection of thyroxine (T4) and propylthiouracil (PTU) in saline, from birth until the period of spontaneous weaning. The rate of growth and the time of eye opening as well as the spontaneous weaning was assessed. The intake of maternal milk was followed directly, i.e. by the transport of 85Sr in maternal milk from the maternal body to the sucklings. In the young treated with T4 the eyes opened earlier than in the young treated with PTU. The body mass differed in both groups between the 4th and 20th day of life (the T4 pups were heavier). The 85Sr transfer in maternal milk was higher in the PTU young from the 22nd day of life. The PTU sucklings weaned spontaneously one week later than those receiving T4. A hypothesis has been proposed on the primary significance of maturation of oral mechanisms of sucking for spontaneous weaning.  相似文献   

4.
The effect of pregnancy on lactation was studied during the third week of lactational pregnancy in postpartum pregnant rats with a delay in implantation of only 1 day (1d-LP rats). In an experimental design in which the suckling litter was prevented from consuming solid food, lactational performance was estimated by weighing the ten-pup suckling litters on days 16-21 of lactation or by measuring maternal weight loss after a nursing spell on day 21. In 1d-LP rats, food consumption as well as lactational performance was lower than it was in nonpregnant lactating rats (L rats) and pregnant-lactating rats with a normal long delay of implantation of at least 6 days (LP rats). The time spent by the pups sucking at the nipples was not different among the three groups, but the number of milk ejections was diminished in 1d-LP dams. Restriction of daily food supply during days 16 to 21 of lactation diminished lactational performance more strongly in 1d-LP rats than it did in L rats; 1d-LP rats conserved protein stores and mobilized fewer minerals than did L rats. The weight and composition of the litter in vitro were not affected by the food restriction. In pregnant-lactating rats (LP and 1d-LP rats), the number of early resorptions was increased in comparison with pregnant rats, showing that lactation can affect the earlier stages of pregnancy. It was concluded that late pregnancy does not affect nursing behaviour, but suppresses lactation by restricting maternal food intake and mobilization of maternal stores. Measurements in serum indicate a causative role for oestradiol, but not for leptin.  相似文献   

5.
An experiment was conducted to examine whether weaned piglets would display preference for a food containing a pharmacological level of zinc oxide (ZnO). A total of 60 piglets were weaned at 7.8 kg ± 0.14 (s.e.m.) and 27.8 ± 0.11 days of age into eight mixed sex groups of seven or eight piglets per pen. Groups were balanced for litter origin, weaning weight and sex. Piglet feeding behaviour was constantly recorded by a multi-spaced feeding behaviour recording system (Leeds University Feeding Behaviour System) in each pen. Each pen of pigs was offered ad libitum access to two different foods (16.2 MJ digestible energy, 16 g lysine/kg), which differed only in the level of ZnO supplementation: unsupplemented (U) or supplemented (Z; ZnO 3100 mg/kg). Both foods contained a basal level of zinc (100 mg/kg). Feeding time was recorded for each individual at each trough. Piglets were weighed at weaning and at 7 and 13 days thereafter. The experiment ran for 13 days. Any piglet observed with post-weaning scour (Y) was recorded and treated appropriately whereas healthy piglets were categorised as N (no scour). Preference for a food was defined as being significantly different from 50% of total feed intake or time spent feeding. There was no difference between piglet numbers selecting each food as their first meal. However, within the first 24 h, piglets preferred (P < 0.001) food U, spending only 36.3% (32.2 to 40.5; 95% confidence interval) of feeding time at food Z. Throughout the experiment, piglets showed aversion (P < 0.001) to food Z, consumption being 8.9% (5.1 to 13.6) and 15.7% (8.9 to 23.9) of total intake in weeks 1 and 2, respectively. Individual piglets showed their preference for food U with only 16.6% (14.6 to 18.5) and 21.8% (19.6 to 24.0) of feeding time spent on food Z in weeks 1 and 2, respectively. Scouring piglets did not show any difference in feeding behaviour from healthy piglets in either week. Average piglet gain (of all piglets) was low, at 0.039 ± 0.03 and 0.272 ± 0.04 kg/day in weeks 1 and 2, respectively. Given a choice, weaned piglets showed a clear preference for the food U even when exhibiting post-weaning scour. It can be concluded that the newly weaned, naïve, piglet is not able to recognise a food with clear health and performance benefits but selected the food U due to the reduced palatability of the food Z.  相似文献   

6.
Female rats were kept on a diet with a low content of animal protein (5.5%) beginning from the 2nd day after delivery. Beginning from the 10th day after delivery their body weight was persistently lower than that of control females. Also the body weight of their young was lower than that of control animals throughout the experiment, with significant differences appearing on the 17th day of life. Spontaneous termination of maternal milk intake occurred in malnourished young 10 days later than in the controls. Retention of 85Sr in malnourished females was in keeping with their milk production. Irrespective of the differences in body weight and the quality of solid food, the malnourished young began consuming solid food at the same age and in the same relative amounts as the controls. Thus in malnourished young the period of gradual weaning was prolonged by more than to 3 weeks in contrast to 2 weeks in the controls. This is probably due to the slower extinction of the oral sucking mechanism resulting from changes in the maturation of the CNS. No changes were found in maternal behaviour (nest building and efficiency of retrieving) in malnourished females during the suckling period. However, infanticide appeared in some females during the weaning period.  相似文献   

7.
Ghrelin, an endogenous ligand of the growth hormone secretagogue receptor, has been primarily isolated from the human and rat stomach. Ghrelin has been shown to stimulate appetite and fat deposition in adult rats and humans. The aim of this study was to investigate the effect of ghrelin administration on pancreatic growth in suckling, weaned and peripubertal seven week old rats. Rats were treated with saline or ghrelin (4, 8 or 16 nmol/kg/dose) intraperitoneally twice a day: suckling rats were treated for 7 or 14 days starting from the first postnatal day, three week old weaned rats and seven weeks old rats were treated for 5 days. Treatment with ghrelin did not affect animal weight in suckling or weaned rats, whereas in young seven week old rats, ghrelin caused a significant increase in body weight. Ghrelin decreased food intake in weaned rats; whereas in seven week old rats, food intake was enhanced. In suckling rats, ghrelin decreased the pancreatic weight, pancreatic amylase content, DNA synthesis and DNA content. In contrast, ghrelin increased pancreatic weight, DNA synthesis, DNA content and amylase content in weaned or young seven week old rats. Pancreatic blood flow was not affected by ghrelin in any group of rats tested. Ghrelin increased serum level of growth hormone in all rats. This effect was weak in suckling rats, higher in weaned and the highest in seven week old animals. Ghrelin did not affect serum level of insulin-like growth factor-1 (IGF-1) in suckling rats. In weaned and in seven week old rats, treatment with ghrelin caused increase in serum level of IGF-1. We conclude that ghrelin reduces pancreatic growth in suckling rats; whereas in weaned and young seven week old animals, treatment with ghrelin increases pancreatic growth. This biphasic effect of ghrelin in young animals on pancreatic growth seems to be related to age-dependent changes of the release of anabolic IGF-1.  相似文献   

8.
9.
Social relationships among female laboratory-bred rats in a community are influenced by their early life history. When the rats were born and kept until adulthood under conventional breeding conditions, i.e. in single cages, and then used to form a community in which they gave birth, one female assumed the dominant role, with all others subordinate. The dominant female herded all young rats born in the community, irrespective of their age, in a single litter and suckled them. She accumulated food and wood shavings from other parts of the community near the nest and prevented access to the nest to all other community members including other females that had given birth. Subordinate females ceased to show maternal behaviour, including lactation, within 24 h (occasionally within 48 h). The mortality of the young until 15 days of age was high. This type of behaviour in a community was observed both with randomly chosen female rats and with rats selected as dominant and subordinate types in preceding experiments. Female rats born and reared in a community and rats living in a community from 15 to 30 days of age did not differentiate into dominant and subordinate types. All females retained their maternal behaviour, including lactation. Mortality of young rats was minimal. In most cases the females built one common nest; sometimes each female built her own nest. The results point to the decisive role of early experience in the development of maternal behaviour and in the occurrence of communal rearing of the young.  相似文献   

10.
Coprophagy: a supplementary food source for two freshwater gastropods?   总被引:1,自引:0,他引:1  
1. The freshwater pulmonate snail Radix peregra voluntarily and regularly fed on its faeces, whereas Bithynia tentaculata (Prosobranchia) did not.
2. With high-quality faeces as food (faeces with C : N-values below ten) Radix could grow and survived for 11 weeks. Growth was 24–30% of that achieved with control food (lettuce, Chlamydomonas and Tetramin), and body mass was close to the expected value.
3. As with real food, the percentage organic content of faeces was reduced during gut passage, with the exception of very low-quality faeces.
4. Faeces contained living cells of green algae ( Chlamydomonas reinhardii ) and diatoms ( Achnanthes lanceolata, Eunotia pectinalis ), which survived the gut passage of R. peregra and B. tentaculata . Faecal material was also rich in bacteria, with up to 150 × 106 cells mg–1 dry mass. Bacteria increased in abundance in faeces which had been evacuated for 7 days or more.
5. A further degradation of partly digested food in the faeces was indicated by the activity of the extracellular digestive enzymes cellobiase and chitobiase. These enzymes hydrolysed material with an activity of 0.2–14.5 pkat mg–1 faecal dry mass in 1–12-day-old faeces. In faeces of Bithynia fed control food or incubated sycamore leaves, chitobiase activity was correlated with bacterial abundance.
6. Coprophagy is considered to be a suitable strategy for further degradation and utilization of refractory material for which one gut passage is too short and/or too inefficient.  相似文献   

11.
Age at weaning affects the behaviour of piglets weaned in conventional confined environments. The adaptation of piglets to this event, which exposes piglets to important stressors, has not been examined in detail in outdoor systems. The aim of this study was to compare the behaviour of piglets weaned at 3 or 4 weeks of age in an outdoor production system. Six replicates of four piglets born and raised outdoors, originated from different litters but previously acquainted, were weaned at the age of approximately 20 (D20) or 30 (D30) days in 36 m2 outdoor pens and offered high-quality diets. Their behaviour was recorded by direct visual observation during four consecutive days after weaning (days 1 to 4). Data were analysed by repeated measures ANOVA. An effect of weaning age was observed on feeding and rooting ( P < 0.01), and a day-by-weaning age interaction for escape attempts, vocalizing, walking and fighting ( P < 0.01), and playing ( P < 0.03). Compared to D30 piglets, D20 piglets showed a higher frequency of escape attempts on day 1, vocalized more during days 1 and 2, and walked more during days 1 to 3 ( P < 0.05). Feeding behaviour, on the other hand, was higher in D30 piglets on days 1 to 3 ( P < 0.05). On days 3 and 4, D30 piglets spent more time interacting with peers (playing and fighting; P < 0.05) and on day 4 were more active than D20 piglets ( P < 0.05). As previously reported in confined environments, age at weaning affected the behaviour of piglets raised on the outdoors system. Weaning appeared to be more stressful for the piglets at 3 than at 4 weeks of age. The impact of weaning age on welfare cannot be ignored, especially when outdoor breeding of pigs is proposed to address welfare concerns of the public.  相似文献   

12.
Normally weaned females (at 30 days) displayed seasonal cyclic changes in natality and the characteristics of the young. Natality in the spring and summer was high, the litters were large, the proportion of females and males in the litter was equal and deaths among the unweaned young were very few. Natality in the autumn and winter was low and the litters were small and consisted mainly of males. The death rate among the young was higher than in the spring and summer. Prematurely weaned females (at 15 days) displayed no seasonal cycle either in natality or in the characteristics of the young. The studied parameters corresponded to the values found in the spring and summer in normally weaned females. No differences were found in maternal retrieving, but there was a marked difference in nest-building. The normally weaned female tore up paper (building material) into small fragments 24 hours before giving birth and dropped the young into a soft nest of finely shredded paper. On leaving the nest it covered the young up. The prematurely weaned female scattered the paper about the cage 24 hours before giving birth and dropped the young into a depression stamped out among whole pieces of paper. It did not cover the young up on leaving the nest. The cause of the difference in building behaviour is evidently that prematurely weaned females failed to acquire early experience of this behaviour between the 15th and 30th day of life.  相似文献   

13.
P R Walker 《Life sciences》1974,15(8):1507-1514
Controlled feeding schedules have been used to maintain rats during the first thirty days following birth to investigate the role of food in determining the course of liver development. Use of the ‘8 + 16’ feeding schedule and a new ‘16 + 8’ suckling schedule allowed rats to be reared through the neonatal period without access to solid food until the day they were weaned. Food-independent increases in Pyruvate kinase type I isoenzyme, glucokinase and aldolase B take place in the late suckling period. Thus it appears that the change in the nutritional status of the animal at weaning is not a major factor in liver development.  相似文献   

14.
The objective of this work was to study the effect of early weaning on alimentary preference for the macronutrients protein, carbohydrate and fat in adult rats. Male Wistar rat pups were weaned by separation from the mother at 15 (D15) or 30 (D30) days old. Body weight and food intake were measured every 30 days until pups were 150 days old. At 110 days of age, the alimentary preference was evaluated for 1 h on 3 consecutive days. At 120 days of age, the palatable diet test was conducted during 3 consecutive 24-h periods. Body weight and food intake were not altered, but early weaning in rats induced an alimentary preference to fat and hyperphagia of a palatable diet. In conclusion, early weaning, although did not modify body weight or basal food intake, promoted an increased preference for palatable and fatty foods. This demonstrates that early weaning is not capable of promoting perceptible alterations of alimentary behavior under normal laboratory conditions. However, in the presence of a stimulating factor such as a choice of nutrients or a palatable diet, a possible latent effect on dietary preferences may become apparent. Over the long term, this preference for foods with high caloric density can lead to obesity and metabolic perturbations.  相似文献   

15.
Early weaning of rat pups on day 16 to semi-ground Purina chow food and drinking water, ad libitum, delayed growth of body and lungs, and the appearance of adenylate cyclase activator (ACA) in lung after day 22. However, early weaning of pups to either milk or a gel diet containing semi-ground Purina chow food, agarose gel, water (30:1:69, w/w), and drinking water, restored lung and body growth and the appearance of ACA to control values. Early weaning of pups to dry semi-ground Purina chow food and drinking water also induced a transient rise in ACA on day 19. This early rise in ACA was completely absent in pups weaned on day 16 to milk, whereas it persisted in pups weaned similarly to a gel diet. Interestingly, lung glycogen decreased on day 19 in pups weaned early to dry semi-ground Purina chow food without (group 2) or with triiodothyronin administration (group 3), and on day 25 after normal weaning on day 22 (Nijjar, M.S. Biochim. Biophys. Acta 586: 464–472,1979). These data indicate 1) that reduced food intake (starvation) in pups weaned on day 16 to dry semi-ground Purina chow food was responsible for the delayed growth of body and lung, and the delayed appearance of ACA in lung after day 22, and 2) that a change in diet from milk to Purina chow food and associated alterations in hormones, possibly cortisol and insulin, were responsible for the appearance of ACA in rat lung. It would appear that reduced intake of food (starvation) and associated changes in hormones in rat pups at weaning induce ACA in lungs, stimulating adenylate cyclase to produce more cyclic AMP. A rise in cyclic AMP may initiate a cascade of enzymic reactions resulting in enhanced metabolism of glycogen to intermediates which are utilized for the production of energy during the time that the exogenous source of energy i.e. food, is restricted.  相似文献   

16.
The objective of this work was to study the effect of early weaning on circadian rhythm and the behavioral satiety sequence in adult rats. Male Wistar rat pups were weaned for separation from the mother at 15 (D15), 21 (D21) and 30 (D30) days old. Body weight and food intake was measured every 30 days until pups were 150 days old. At 90 days of age, the circadian rhythm of food intake was evaluated every 4 h for three days. Behavioral satiety was evaluated at 35 and 100 days of age. This work demonstrated that body weight and food intake were not altered, but the behavioral satiety sequence demonstrated that the D15 group delayed satiety compared with the D30 group at 100 days of age. In the circadian rhythm of the food intake study, early weaning (D15) changed food intake in the intermediary period of the light phase and in the intermediary period of the dark phase. In conclusion, our study showed that early weaning may alter the feeding behavior mainly in relation to satiety and the circadian rhythm of feeding. It is possible that the presence of other environmental stimuli during early weaning can cause hyperphagia and deregulate the mechanisms of homeostasis and body weight control. This study supports theories that depict insults during early life as determinants of chronic diseases.  相似文献   

17.
Early weaning may be used in beef cattle production to improve reproduction rates in range conditions. However, weaning causes a stress response in cows, which may be especially strong in early weaning management, as the bond between the cow and the calf is still strong. We hypothesized that weaning calves in two steps, with the aid of anti-sucking devices (nose flaps) would reduce the behavioural stress response in the cows separated from their calves 2 months after parturition. We compared the behaviour frequency and weight change in cows that were weaned abruptly, by separation of the calf on day 0 of the study, or in two steps, consisting of the use of anti-sucking nose flaps for 5 days before permanent separation; a third group was not weaned to serve as control. Thirty-six crossbred multiparous Aberdeen Angus×Hereford cows and their calves (n=12/treatment) were managed in three paddocks with similar pasture availability, with four dyads from each treatment per paddock. Cows’ behaviour was observed by direct visual instantaneous sampling, at 10 min intervals from days −3 to 11. Weaning the calves in two steps clearly attenuated the behavioural stress response observed in abruptly weaned cows, which included reductions in grazing and lying, and increases in pacing, walking and vocalizing. Our results corroborate those previously shown for cows nursing older calves, and indicate that step weaning can reduce the behavioural stress response of cows at weaning, even when the calf is weaned shortly after birth, when the bond between the cow and calf is still very strong.  相似文献   

18.
Studies using both Fisher 344 and Sprague-Dawley (SD) rat lines have shown that gestational and/or lactational maternal lead (Pb) exposure causes delayed reproductive maturation in their respective female offspring. Because these studies utilized different experimental regimens for dosing and for monitoring Pb levels, it has not been possible to determine which rat line provides the best model for low level Pb toxicity studies. This study was designed to address this issue. Adult Fisher and SD female rats were dosed with either a solution of PbAc containing 12 mg of Pb/ml or sodium acetate (NaAc) for controls. Dosing began 30 days prior to breeding and continued until their pups were weaned at 21 days of age. At the time of breeding and through weaning the blood lead (BPb) levels in the Fisher dams averaged 37.3 microg/dl and the SD dams averaged 29.9 microg/dl. Pb delayed the timing of puberty (p < 0.01) in Fisher offspring, and suppressed serum levels of luteinizing hormone (LH, p < 0.001) and estradiol (E2, p < 0.01). These effects did not occur in the SD offspring. Doubling the dose given to the SD rats increased their BPb levels to 62.6 microg/dl, yet there were still no effects noted. These results indicate that Fisher offspring are more sensitive to maternal Pb exposure with regard to puberty related insults than are SD rats, suggesting that the Fisher line may be a more reliable rodent model to study the effects of low level Pb toxicity.  相似文献   

19.
The purpose of this study was to evaluate the most appropriate rat age for the start of administration, and the effect of weaning, in the immature rat uterotrophic assay using ethynylestradiol (EE). Animals weaned on postnatal day (PND) 20 were administered subcutaneously EE at doses of 0.06-6 micrograms/kg/day for 3 days beginning on PND 21, 23 or 25. EE at the same doses was also administered to rats weaned on PND 17 or 20 from PND 21 for 3 days. Although uterine weight was significantly increased in the rats given 0.6-6 micrograms/kg EE in both of the studies, the percentage increase relative to the control in each group given EE from PND 21 and weaned on PND 20 was higher than in those groups given EE from PND 23 or 25, and the group weaned on PND 17.  相似文献   

20.
Sexual behaviour of adult male rats weaned prematurely--on day 15 after birth--and of males weaned at the optimal age--on day 28--was compared at two life periods: at the age of 90 days and when the males were one year old. Sexual behaviour was evaluated by means of three characteristics: a) sniffing behaviour, b) copulatory readiness, c) copulatory performance. The differences in sniffing behaviour between prematurely and normally weaned males were assessed in terms of their responsiveness to sccents of unrelated adult males or oestrous females and from the point of view of both housing conditions after weaning and the animals' sexual experience. No differences were found in copulatory readiness as well as in copulatory performance between the two groups of males tested in their interaction with a female exhibiting complete precopulatory pattern. The morphological examination revealed no differences in the weight of reproductive organs and in spermatozoa development. We conclude that the sexual behaviour as well as reproductive organs of male rats are very resistant to early separation of pups from the mother which contrasts with some earlier findings.  相似文献   

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