Pup Growth Rate Research Articles

Time Budgets and Foraging Characteristics of Lactating Antarctic Fur Seals

SUMMARY (1) We investigated time allocation to parental care ashore and foraging at sea by lactating Antarctic fur seals at Bird Island, South Georgia, during 1988-89 and 1989-90 and related this to foraging behaviour measured in terms of diving performance at sea and growth of pups. (2) The mean duration of foraging trips was 121 h and 100 h in 1988-89 and 1989-90, respectively, while periods ashore were 55 h and 45 h, respectively in the two years. There was a significant difference between these variables in the two years but there was no significant difference in the percentage of time spent at sea. In both years, there was significant variation between individuals in the foragingattendance time budget. (3) There was a positive correlation between mean time spent ashore and mean time spent at sea for individual seals. The foraging-attendance patterns of seals changed significantly with time through lactation in one year of the study but not in the other. There was no effect of maternal age or size on foraging-attendance time budget. Duration of foraging trips or the period spent ashore had no effect on pup growth rate. (4) During short foraging trips (1-2 d) seals dived for a greater proportion of the time available for foraging than during longer foraging trips (>3 d). Seals fed predominantly on krill during both years. Most foraging occurred at night and this was reflected in diel variation in times of arrival and departure of seals from the pupping colony. Based on estimated swimming speed and travel times to and from Bird Island, it was estimated that seals were normally feeding between 60 and 90 km from Bird Island.

Effect of Lactational Intensity on Extrathyroidal 5’-Deiodinase Activity in Rats

Concentrations of thyroxine and triiodothyronine in serum and 5’-monodeiodination activity in liver and kidney were studied in lactating Sprague-Dawley rats with different litter sizes. Litter sizes were adjusted at birth to 0 (postpartum nonlactating group), 4, 8, 12, and 16 pups per lactating rat. Serum and tissue samples were collected from lactating rats and pups on d 12 of lactation and from 6 nulliparous females. Nulliparous and postpartum nonlactating rats did not differ in serum thyroxine, triiodothyronine concentrations, or in 5’-deiodinase activity in liver and kidney. As litter size increased, maternal serum thyroxine, triiodothyronine concentrations, and 5’-deiodinase activity in liver and kidney decreased. Growth rate of pups was inversely correlated with litter size and positively correlated with concentration of serum thyroxine and liver 5’-deiodinase in mothers. In pups, serum triiodothyronine concentrations decreased as litter size increased, but serum thyroxine concentrations were not affected. Results suggest a relationship between the hypothyroid status of lactating rats and suckling intensity. The thyroid status of the dam may influence thyroid status and the dam may influence thyroid status and growth of offspring.

The Behavioral Ecology of Maternal Effort in Fur Seals and Sea Lions

AbstractOtariid seals form a group of similar species distributed from subpolar to tropical seas. Many species were recently studied under conditions of low and high food abundance during major oceanographic disturbances. Evidence for the phenotypic flexibility of and constraints on the rearing strategy of these species derives from inter- and intra-specific comparisons and experimental measurements. I review how changes in food abundance influence foraging behavior and energetics of mothers, pup growth rates, milk composition, weaning age, and the fertility cost of pup rearing. Eared seal females rear young by alternating between lactation ashore and foraging at sea. Subpolar fur seals always wean pups at four month of age, a trait which seems to be genetically fixed and adaptive in their highly seasonal environment. Temperate and tropical fur seals and sea lions can respond to changes in food abundnace by increasing or decreasing time to weaning. During pup rearing, mothers regulate body mass to different absolute values when abundance of food resources changes. This seems to be a constraint caused by reduced foraging efficiency at low food availability. Most species feed exclusively during the night, but sea lions (Zalophus californianus) and Northern fur seals (Callorhinus ursinus) also forage during the day by diving deeper. Females of some species increase the rate of at-sea energy expenditure at low food abundance while keeping the duration of foraging trips constant. Females of other species stay at sea longer working at the same rate. The latter species may be food specialist with a narrower time window for efficient foraging. Pups grow slower when mothers increase time at sea, and at very low food abundance pups may starve. Pups have little influence on the duration of maternal foraging trips, but may diminish the mothers' time ashore by increasing the rate of milk extraction and prolonged non-nutritive sucking. The impact of long maternal at-sea times is reduced by increasing milk fat content as time at sea increases. This mechanism does not fully compensate pup energy intake rate for longer trip durations. Non-migratory species can partly compensate for reduced pup growth rates by lengthening the lactation period. In the Galapagos fur seal (A. galapagoensis), this entails a considerable cost to the mother by reducing her future fertility. Lactation reduces the probability of a successful simultaneous pregnancy and, if pregnancy succeeds, sibling competition for maternal milk ensues. Competition is usually won by the older sibling leading in many cases to the death of the newborn. The rate of energy transfer to pups is high in food-rich years and low in scarce ones. Because pups are more likely to be weaned as yearlings when juvenile growth rate is high than when it is low, high energy transfer to the pup in year "a" reduces the cost of reproduction incurred in year "a+1". The flexibility of the rearing strategy of temperate and tropical species permits mothers to adjust phenotypically to variance in food availability thus partly masking the theoretically expected trade-offs in the life history of these species.

Lipid metabolism during the initiation of lactation in the rat. The effects of starvation and tumour growth.

1. The effects of starvation post partum (24 h) and tumour growth pre partum on the initiation of lactation in the rat were studied. 2. Tumour growth decreased food intake at 24 h, but not at 2 days post partum. 3. Pup growth rate increased with hyperphagia; starvation and tumour burden decreased pup growth, and starvation decreased maternal body weight. 4. Starvation decreased gastrointestinal-tract mass; tumour growth decreased gastrointestinal-tract and mammary-gland mass. 5. Mammary-gland DNA-synthesis rate was high immediately post partum, but decreased by day 3 of lactation; starvation and tumour burden decreased this rate, and also decreased gastrointestinal-tract DNA-synthesis rate. 6. Arteriovenous differences for glucose and lactate across the mammary gland did not change with time, nor were they affected by the tumour. Starvation decreased arterial glucose and lactate, and the gland extracted less glucose but produced lactate. 7. Mammary-gland lipogenesis was sensitive to starvation and to tumour growth. 8. In contrast with the gradual development of mammary-gland lipogenic enzyme activities, lipoprotein lipase activity was high in the gland by 2 days post partum; starvation or tumour burden decreased the activity. 9. The mammary gland is sensitive post partum to decreased food intake, and to tumour presence. The effects of the latter are apparently independent of hypophagia.

Kin recognition and mate choice in mice: fitness consequences of mating with kin

Breeding pairs of full sibling, half-sibling, first cousin, second cousin and unrelated CFLP laboratory mice were established and allowed to produce litters. The degree of relatedness between parents had a significant effect on both litter size (number of pups) and aggressiveness of male offspring, with litters of less closely related parents being larger at birth and post-weaning, and the male offspring of second cousins, showing the highest frequency of aggressive behaviour. There was no effect of parental relatedness on pup mortality, weight, growth rate or (male) competitive rank but rank among male offspring was significantly correlated with body weight. Previously reported sex differences in kin preference during intersexual interactions are interpreted in the light of these results.

Relationship between Milk Composition and Pup's Growth in Mice

The effect of lactation numbers (first, second, and third) on milk composition and the relationship between milk composition and pup's growth were examined in four strains of mice (SHN, SLN, C3H/He, and GR/A). Although the percentage of milk fat and moisture increased and decreased, respectively, through the first to third lactations in C3H/He mice, no differences in milk composition among lactation numbers were observed in the other mouse strains. In pooled data derived from the four strains of mice, there was no significant correlation between milk composition and body weight or growth rate of pups on Day 12 or 20 of the first lactation. In contrast, the amount of milk fat and moisture was the positively and negatively, respectively, correlated with the pup's growth parameters during the second and third lactations. This was reflected by a lower fat content and a higher moisture content in the milk of GR/A mice, especially evident during the second and third lactations and reduced pup's growth, when compared with the other mouse strains. Milk lactose and ash content was not correlated with pup's growth parameters. The results of our study stress the importance of milk fat for the growth of mouse pups.

Comparative studies on the reproductive biology of three species of laboratory bred Australian conilurine rodents (Muridae: Hydromyinae)

The reproductive biological parameters of laboratory bred and maintained individuals from three species of Australian conilurine rodents, Notomys alexis, Pseudomys australis and P. nanus were determined. Considerable' divergence was found in interbirth intervals (indicative of gestation length) in nonsuckling and suckling mothers, litter size, growth rate of pups, age at weaning, and time of sexual maturity in both males and females. It is concluded that selection has been for rapid production and development of young in P. nanus, whereas in P. australis and, especially N. alexis, litter size has been maximized within the constraints of the mammary formula. These data further emphasize the high degree of plasticity of the reproductive system in this assemblage of old endemic murid rodents of Australasia.

Measurements of Reproductive Traits in a Field Population of Meadow Voles

Neonatal litter size, pup growth, and birth interval were examined within a population of meadow voles ( Microtus pennsylvanicus ) through use of radiotelemetry and live trapping. Litter sizes observed shortly after birth were significantly smaller than predicted from embryo counts obtained during the same period. The observed litter size was correlated negatively with local population density. Examination of the birth interval indicated ≥95% of females conceived during a postpartum estrus. Pup growth rates ( X = 0.44 g/day) did not vary significantly with litter size, maternal weight, or population density. We postulate that selection for an increase in litter frequency limits the range of growth rates possible for individuals in a litter, and that resource reduction at high densities results in a reduction in litter size postpartum, rather than reductions in pup growth rates, litter frequency, or prepartum litter size.

Lactation in mice fed endophyte-infected tall fescue seed

This study was conducted to assess the effects of endophyte-infected Acremonium coenophialum tall fescue (KY-31) seed (80% infected) on lactation in CD-1 dams and suckling performance of pups as measured by pup survival and growth rates. Twenty-four pairs of mature CD-1 mice were randomly allocated to four dietary treatments: 1) 100% mouse chow ad libitum; 2) 40% endophyte-infected tall fescue seed and 60% mouse chow (w/w); 3) reduced intake (100% chow), adjusted daily to the intake level of Treatment 2; and 4) 60% infected tall fescue seed and 40% chow. The mice were preconditioned on their respective diets for 100 d prior to 96 h of cohabitation between pairs of males and females. At parturition the litters were removed, and each dam was given a litter of six pups of equal weight, size and sex ratio to suckle for 15 days. All pups given to all the dams were born to other mice that were not part of the study and had not been exposed to endophyte-containing diets. Dams and litter weights were measured daily for 15 consecutive days. The combined body weight measurements of litters from dams fed the tall fescue containing diets (Treatments 2 and 4) were significantly lower (2.07 ± 0.41 g/d) than that of litters from dams fed the chow containing diets (Treatments 1 and 3) during the suckling trial (P<0.05). Similarly, nine of ten (90%) dams fed the chow containing diets maintained five or more pups (5.5 ± 0.2) throughout the study as compared to five of nine (55.6%) dams fed the tall fescue containing diets that maintained less than five pups (4.5 ± 0.2).

BEHAVIORAL AND PHYSIOLOGICAL MEASUREMENTS OF MATERNAL INVESTMENT IN THE STELLER SEA LION, EUMETOPIAS JUBATUS

AbstractThe onshore and at‐sea cycles of females, suckling behavior of pups and their milk intake were studied in Steller sea lions (Eumetopias jubatus) during 1983 at Año Nuevo Island, California. Females averaged approximately 21 h ashore and 36 h at sea. The trips to sea lengthened as pups aged, resulting in an overall decline in female time ashore to 30% by the sixth week following parturition. Activity budgets of pups showed no significant differences among suckling time, age and sex. Milk intake, estimated using labeled water studies, revealed that heavier pups consumed more milk than lighter ones (milk ingestion in ml/d = 4.26 + 0.0687 [Pup Mass in kg]). Mean milk intake was 1.78 ± 0.33 liters/d. Mean pup growth rate was 0.38 ± 0.1 kg/d. The results suggest that female attendance patterns are shaped by the increasing nutritional demands of growing pups and their increasing efficiency at suckling.

New mutation causing jaundice in mice.

A new mutant causing jaundice in mice is reported. Allelism tests indicate that it is not allelic with known hemolytic anemia mutants in mice [hemolytic anemia (sphha), jaundiced (ja), normoblastic anemia (nb), and spherocytosis (sph and sph2Be)]. The jaundiced condition appears in young mice at about 24 hours postpartum and is due to a major increase in unconjugated bilirubin in serum compared to normal controls. Adult mutant mice are not jaundiced and bilirubin levels do not differ from normal mice. Adult male mutants have reduced testes size and no viable sperm. Female mutants are fertile but overall maternal performance is reduced as indicated by increased mortality and reduced growth rate of pups. Genetic tests indicate that a single autosomal recessive gene is responsible for the condition. We propose that the mutant be designated hyper-unconjugated bilirubinemia, with the gene symbol hub.

Growth rates of Antarctic fur seal Arctocephalus gazella pups at South Georgia

Large numbers of pups of the Antarctic fur seal were weighed at regular intervals through their rearing period in six seasons between 1972 and 1981 at South Georgia. Growth rates and birth and weaning weights were estimated from linear regressions of mean weight on mean age. Female pups had significantly lower growth rates and weaning weights than males, but higher variances for all growth parameters. This may reflect the importance to males of polygynous species of attaining high body weight. Except for an inverse relation between growth rate and birth weight there were no systematic relationships between growth parameters. Seasonal differences in growth rates were substantial and there was no indication that the continuing rapid population increase was affecting pup growth rates. The use of these data in detecting seasonal variations in local food availability is discussed. Preliminary estimates of the energy costs of pup rearing indicate that pup existence metabolism consumes c. 80% and mass gain to weaning only c. 15% of the energy provided by the female.

A maternal defect is responsible for growth failure in vitamin D-deficient rat pups.

Vitamin D deficiency was induced in lactating rats and their pups by placing female rats on a vitamin D-deficient diet immediately after mating. Evidence of vitamin D deficiency included undetectable plasma levels of 25-hydroxyvitamin D3 in the dams, maternal hypocalcemia, the lack of pup growth, and pup hypocalcemia following starvation. This method of producing vitamin D-deficient pups was then used to determine whether the failure of vitamin D-deficient pups to grow properly results from a maternal or neonatal defect. Vitamin D-deficient dams and pups were injected with either vitamin D3 or the ethanol vehicle, and pup growth was monitored over the subsequent 6 days. Providing vitamin D3 to the pups directly had no effect on their growth, but administering vitamin D3 to the dams resulted in a tripling of the pup growth rate. The failure of vitamin D3 to promote pup growth when given directly to the pups was not the result of their inability to metabolize the vitamin because these pups converted [3H]-vitamin D3 to 25(OH)D3, 24,25(OH)2D3, and 1,25(OH)2D3 as determined by comigration with standards on both straight and reverse phase high-performance liquid chromatography systems. These results demonstrate that a maternal defect is responsible for the growth failure observed in vitamin D-deficient rat pups.

Effects of diet and obesity on body weight regulation during pregnancy and lactation in the rat

The effects of obesity level and cafeteria feeding were studied in rats during pregnancy and lactation. The non-fetal weight gain in pregnancy was three times greater with the cafeteria diet than with chow, indicating that fat deposition is not regulated at an optimal level during pregnancy. There was a strong negative correlation between postpartum weight and weight change during lactation. Obese rats were finicky in that their weight changes in lactation were exaggerated when the diet was changed between pregnancy and lactation. Pup growth rate was proportional to maternal energy intake but in this experiment not related to maternal protein, fat or carbohydrate intake. In obese rats switched to chow, intake was inadequate for normal pup growth. Thus, the weight gains in pregnancy are not regulated at a set level, and the weight change in lactation appears to compensate for the weight gain in pregnancy.

Growth rates of Antarctic fur seal Arctocephalus gazella pups at South Georgia : Doidge, D.W., J.P. Croxall and C. Ricketts, 1984. J. Zool., Proc. zool. Soc. Lond., 203(1):87–93. British Antarctic Survey, Natl. Environ. Res. Council, High Cross, Madingley Rd., Cambridge CB3 0ET, UK

Growth rates of Antarctic fur seal Arctocephalus gazella pups at South Georgia : Doidge, D.W., J.P. Croxall and C. Ricketts, 1984. J. Zool., Proc. zool. Soc. Lond., 203(1):87–93. British Antarctic Survey, Natl. Environ. Res. Council, High Cross, Madingley Rd., Cambridge CB3 0ET, UK

Energetic limits on reproduction: Maternal food intake

We examined the factors influencing maternal food intake and pup growth in Norway rats. Mother rats allowed pups in naturally large litters to grow at a slower rate than pups in naturally small litters. Pups reared by dams in a warm ambience (26°C) gained weight more slowly than dams at 22°C, and maternal food intake but not weight gain was depressed in the high ambient temperature. Pup growth at 18°C was unimpaired, with those dams eating no more and gaining no less weight than dams at 22°C. Nest material, however, was found to be essential for the successful rearing of young at cooler ambient temperatures. While restriction of food during gestation resulted in a marginally lower weight gain for the pups during the first 2 weeks postpartum, the dams appeared not to mobilize corporal stores or increase their food intake during lactation. Heavy body weight mothers did not eat any more, nor did they gain any less weight nor rear larger pups than light body weight dams. Rat mothers increased their consumption of a diet diluted with non-nutritive fiber to equal the nutritive intake of their controls, with their pups not differing in their growth rate. Pups reared by dams eating a high quality diet grew faster than pups with dams on the control diet. Food intake by mother rats is required during lactation relative to the amount of milk that is delivered to the pups, rather than to an absolute amount of food. Lactating females with a concurrent pregnancy neither increase their food intake nor appear to mobilize their corporal stores to deal with the added energetic drain of pregnancy. Indeed, their young grew somewhat more quickly than pups nursed by dams that were simply lactating. Taken as a whole, these results suggest that Norway rat dams apparently do not monitor and defend a maximal pup growth rate. Rather, rat dams seem to continue to defend their own homeostasis, and by doing so, allow the young to grow and survive under a wide variety of circumstances.

Effect of Altered Neonatal Nutrition on the Development of Enzymes of Lipid and Carbohydrate Metabolism in the Rat

Rats were overnourished during suckling by litter-size manipulation in order to investigate the possible association of overfeeding in infancy with the development of obesity in later life. Rats were raised in litters of 4, 10 and 16 corresponding to overfeeding, normal feeding and underfeeding during the suckling period. From 6–19 days post partum, growth rates of pups from different litter sizes were significantly different (4 > 10 > 16). Differences in mean body weights between the groups continued to increase after weaning when all groups were allowed access to diet ad libitum and the significant weight difference between overfed and normally fed rats persisted into adult life in both males and females. Overfed animals showed modifications in the development of activities of a number of hepatic enzymes involved in lipid and carbohydrate metabolism. In later life (20 weeks) neonatally overnourished rats exhibited alterations in hepatic enzyme activities that reflected an increased capacity for lipid synthesis by the liver. “Supernourishment” of neonatal rats (by intubation with glucose of animals in small litters), accelerated the appearance of some of these alterations. These studies show that the pattern of early infant nutrition can profoundly influence the activities of liver enzymes in later, adult life.development enzymes lipid metabolism carbohydrate metabolism overnutrition obesity

Tissue distribution of lead in rat pups nourished by lead-poisoned mothers.

Lead accumulation was studied in rats treated with Pb through the dam's milk from birth to weaning. Dams of experimental litters received lead acetate in drinking water, while dams of control litters received a sodium solution. Fluid consumption by dams and pup weight were monitored daily. No differences were seen in the dams' fluid consumption or in mortality or growth rate of pups. Rats were sacrificed after 5, 10, 16, or 21 d of Pb treatment, or 3 and 3.5 mo after weaning. Samples of heart, brain, liver, kidney, intestine, and bone were solubilized in concentration nitric acid and analyzed for Pb by atomic absorption spectrophotometry. Nitric acid digests of blood samples from pups 10 and 21 d old and from animals allowed a Pb-free period of 3-3.5 mo after treatment were also analyzed for Pb concentration. Levels of Pb in all tissues analyzed progressively increased during the first 10 d of treatment. After the Pb-free period only bone Pb concentration remained elevated. The results indicate that treatment of lactating dams is an efficient method of producing chronic Pb exposure of rat pups. The results also provide a means of comparing studies of Pb toxicity in which different treatment paradigms are used.

Pup growth of the New Zealand fur seal Arctocephalus forsteri on the Open Bay Islands, New Zealand

Growth of New Zealand fur seal pups was investigated at Taumaka, Open Bay Islands, New Zealand, from November 1974 to September 1976. Pups were weighed and curvilinear length, axillary girth and foreflipper length measured at about ages 55, 190, 235 and 290 days. Males are significantly heavier and larger than females at each age, wtih the exception of axillary girth at 235 days. Pups born during the austral summer of 1974–5 were smaller overall than were pups born during the following summer. This difference was so great that males aged 140 days in 1976 were larger and heavier than males aged 235 days in 1975. Circumstantial evidence suggests that the difference in growth rates of pups born during the two years may have been a consequence, either directly or indirectly, of environmental temperatures. Pups born during the warmer season (1974–5) had the slower growth.

Relationship between incidence and onset age of mammary tumors and reproductive characteristics in mice

Simple and partial correlation coefficients between incidence or onset age of spontaneous mammary tumors and several reproductive characteristics were examined during the period between the 2nd and the 30th generations of brother × sister mating in SLN female mice as a possible step to evaluate the role of reproductivity in mammary tumorigenesis. Mammary tumor incidence had a simple negative correlation with delivery interval and positive simple correlations with pup's weights at days 12 and 20 or pup's growth rate at day 20 as indices of lactational performance. However, the partial correlation coefficient between mammary tumor incidence and delivery interval was not statistically significant when any index of lactational performance was held constant and vice versa. These results indicate that it is difficult to determine which of these characteristics is more primary for mammary tumor incidence, while both participate in this process. No significant simple correlations were observed between onset age of mammary tumors and any reproductive characteristics, suggesting little dependence of progression of this type of mammary tumors on reproductivity.