Maternal and environmental influences on thermoregulation in the neonate

The effect of pre-partum shearing of Corriedale ewes on placental and lamb development and neonatal behaviour

AIMS

To evaluate the effects of early and late pre-partum shearing of Corriedale ewes carrying single fetuses on placental and lamb development and neonatal lamb behaviour.

METHODS

At 70 days of gestation, 37 multiparous Corriedale ewes with known gestation dates were randomly allocated into three groups: S70 (n = 12) and S110 (n = 12), shorn at Day 70 and 110 of gestation, and US (n = 13), that were not shorn pre-partum. Gestation length, lambing duration, placental expulsion time, placental weight, number and weight of cotyledons, and placental efficiency (lamb weight/placental weight) were determined. At birth, body temperature, weight, morphometric measurements, ponderal index (lamb weight/lamb crown-rump length) and behaviour were recorded, with weight remeasured 72 hours later. Four male lambs per group were slaughtered immediately after parturition, and organ weight and perirenal brown fat weight and energy content recorded.

RESULTS

Pre-partum shearing, regardless of timing, increased total dried placental weight per ewe. Pre-partum shearing at Day 70 of gestation increased the number and mean weight of the > 2 to ≤ 3-cm cotyledons, while pre-partum shearing at Day 110 of gestation increased only the weight of these cotyledons. At birth and at 72 hours, lambs from ewes shorn either at 70 days of gestation (birth: 5.5 (95% CI = 4.6-6.4) kg, p = 0.001; 72 hours: 6.4 (95% CI = 6.1-6.8) kg, p = 0.002) or at 110 days of gestation (birth: 5.4 (95% CI = 4.4-6.4) kg, p = 0.001; 72 hours: 6.5 (95% CI = 5.9-7.1) kg, p = 0.001) were heavier than lambs from unshorn ewes (birth: 4.0 (95% CI = 3.3-4.8) kg; 72 hours: 4.8 (95% CI = 3.5-6.1) kg). Lambs born to S70 and S110 ewes suckled sooner (31.5 (95% CI = 14.5-48.5) minutes, p = 0.001; and 39.3 (95% CI = 23.7-55.0) minutes, p = 0.001 respectively), than lambs born to the US group (70.3 (95% CI = 38.6-102.1) minutes). There was no evidence for an effect of pre-partum shearing on gestation length, parturition length, time of placental expulsion, placental efficiency, weight and energy of perirenal brown fat, and lamb temperature at birth.

CONCLUSIONS AND CLINICAL RELEVANCE

Shearing ewes pre-partum may lead to placental changes affecting lamb development and behaviour and associated with higher survival. The findings suggest pre-partum shearing may improve lamb survival, farm profitability and sustainability.

Loss of Uncoupling Protein 1 Expression in the Subcutaneous Adipose Tissue Predicts Childhood Obesity

Stimulation of thermogenesis by inducing uncoupling protein 1 (UCP1) expression in adipocytes is thought to promote weight loss by increasing energy expenditure, and it is postulated that the human newborn has thermogenic subcutaneous fat depots. However, it remains unclear whether a relevant number of UCP1-expressing (UCP1+) adipocytes exist in the early postnatal life. Here we studied the distribution of UCP1 and the expression of thermogenic genes in the subcutaneous adipose tissues of the human fetus, infant and child. We show that the deep layer of human fetal and neonatal subcutaneous fat, particularly the abdominal wall, is rich in UCP1+ adipocytes. These adipocytes develop in the late third trimester and persist throughout childhood, expressing a panel of genes linked to mitochondrial biogenesis and thermogenesis. During the early childhood adiposity rebound-a critical phase that determines obesity risk later in life-the absence of adipose tissue UCP1 expression in children with normal body mass index (BMI) correlates with an obesity-associated gene expression signature. Finally, UCP1 expression is negatively correlated with BMI z-score and adipocyte size in infants and children. Overall, our results show that the absence of UCP1 expression in adipose tissue is an early indicator of adipose tissue expansion in children.

The Role of Brown Adipose Tissue and Energy Metabolism in Mammalian Thermoregulation during the Perinatal Period

Hypothermia is one of the most common causes of mortality in neonates, and it could be developed after birth because the uterus temperature is more elevated than the extrauterine temperature. Neonates use diverse mechanisms to thermoregulate, such as shivering and non-shivering thermogenesis. These strategies can be more efficient in some species, but not in others, i.e., altricials, which have the greatest difficulty with achieving thermoneutrality. In addition, there are anatomical and neurological differences in mammals, which may present different distributions and amounts of brown fat. This article aims to discuss the neuromodulation mechanisms of thermoregulation and the importance of brown fat in the thermogenesis of newborn mammals, emphasizing the analysis of the biochemical, physiological, and genetic factors that determine the distribution, amount, and efficiency of this energy resource in newborns of different species. It has been concluded that is vital to understand and minimize hypothermia causes in newborns, which is one of the main causes of mortality in neonates. This would be beneficial for both animals and producers.

LncDGAT2 is a novel positive regulator of the goat adipocyte thermogenic gene program

Brown and beige adipose thermogenesis are important for newborn mammals to maintain their body temperature. In addition, these thermogenic fats are regulated by multiple molecular interactions. How the long non-coding RNAs (lncRNAs) regulate adipose thermogenesis in newborn mammals upon cold exposure remains unexplored. Here, we identified lncRNAs induced by cold exposure in brown adipose tissue (BAT) of newborn goats and found that lncDGAT2 was enriched in BAT after cold exposure. Functional studies revealed that lncDGAT2 promoted brown and white adipocyte differentiation as well as thermogenic gene expression. Additionally, PRDM4 directly bound the lncDGAT2 promoter to activate the transcription of lncDGAT2 and the PRDM4-lncDGAT2 axis was essential for the brown adipocyte thermogenic gene program. These findings provide evidence for lncRNA and transcription factor regulatory functions in controlling adipose thermogenesis and energy metabolism of newborn goats.

Adipose Tissue Development Relies on Coordinated Extracellular Matrix Remodeling, Angiogenesis, and Adipogenesis

Despite developing prenatally, the adipose tissue is unique in its ability to undergo drastic growth even after reaching its mature size. This development and subsequent maintenance rely on the proper coordination between the vascular niche and the adipose compartment. In this review, the process of adipose tissue development is broken down to explain (1) the ultrastructural matrix remodeling that is undertaken during simultaneous adipogenesis and angiogenesis, (2) the paracrine crosstalk involved during adipose development, (3) the mechanical regulators involved in adipose growth, and (4) the proteolytic and paracrine oversight for matrix remodeling during adipose development. It is crucial to gain a better understanding of the complex relationships that exist between adipose tissue and the vasculature during tissue development to provide insights into the pathological tissue expansion of obesity and to develop improved soft-tissue reconstruction techniques.

The evolutionary significance of human brown adipose tissue: Integrating the timescales of adaptation

While human adaptability is regarded as a classical topic in anthropology, recent work provides new insight into metabolic adaptations to cold climates and the role of phenotypic plasticity in human evolution. A growing body of literature demonstrates that adults retain brown adipose tissue (BAT) which may play a role in non-shivering thermogenesis. In this narrative review, we apply the timescales of adaptation framework in order to explore the adaptive significance of human BAT. Human variation in BAT is shaped by multiple adaptive modes (i.e., allostasis, acclimatization, developmental adaptation, epigenetic inheritance, and genetic adaptation), and together the adaptive modes act as an integrated system. We hypothesize that plasticity in BAT facilitated the successful expansion of human populations into circumpolar regions, allowing for selection of genetic adaptations to cold climates to take place. Future research rooted in human energetics and biocultural perspectives is essential for understanding BAT's adaptive and health significance.

Feasibility of using infrared thermal imaging to examine brown adipose tissue in infants aged 18 to 25 months

BACKGROUND

Recent studies in adults indicate that cold-induced temperature change of supraclavicular skin corresponds with brown adipose tissue (BAT) thermogenesis.

AIM

This study examined the feasibility of using thermography to assess temperature changes in infants aged 18-25 months after mild cooling. Further, this study sought to evaluate whether cold exposure induces a thermal response suggestive of BAT activity underlying the supraclavicular region.

SUBJECTS AND METHODS

Changes in maximum skin temperature at the supraclavicular and interscapular regions were determined using thermal imaging following a mild 5-minute cooling condition (by removal of clothes in a climate-controlled room) in 67 Samoan infants. Temperature changes of the forehead and hand, known BAT-free regions, served as indicators of cooling efficacy.

RESULTS

Infants with increased hand and forehead temperatures after cold exposure were excluded from analysis, reducing the effective sample size to 19 infants. On average, forehead (p < 0.001), hand (p < 0.001) and back (0.029) temperatures dropped significantly while supraclavicular temperatures remained constant. Participants with greater decreases in forehead temperature tended to exhibit greater supraclavicular thermogenesis (p = 0.084), suggesting potential BAT activity in this region.

CONCLUSIONS

While further work is necessary to develop a reliable cooling condition, this study provides proof-of-concept for non-invasive assessment of BAT activity in infants.

Co-Evolution of Breast Milk Lipid Signaling and Thermogenic Adipose Tissue

Breastfeeding is a unique and defining behavior of mammals and has a fundamental role in nourishing offspring by supplying a lipid-rich product that is utilized to generate heat and metabolic fuel. Heat generation from lipids is a feature of newborn mammals and is mediated by the uncoupling of mitochondrial respiration in specific fat depots. Breastfeeding and thermogenic adipose tissue have a shared evolutionary history: both have evolved in the course of homeothermy evolution; breastfeeding mammals are termed "thermolipials", meaning "animals with warm fat". Beyond its heat-producing capacity, thermogenic adipose tissue is also necessary for proper lipid metabolism and determines adiposity in offspring. Recent advances have demonstrated that lipid metabolism in infants is orchestrated by breast milk lipid signals, which establish mother-to-child signaling and control metabolic development in the infant. Breastfeeding rates are declining worldwide, and are paralleled by an alarming increase in childhood obesity, which at least in part may have its roots in the impaired metabolic control by breast milk lipid signals.

Developmental programming of offspring adipose tissue biology and obesity risk

Obesity is reaching epidemic proportions and imposes major negative health crises and an economic burden in both high and low income countries. The multifaceted nature of obesity represents a major health challenge, with obesity affecting a variety of different organs and increases the risk of many other noncommunicable diseases, such as type 2 diabetes, fatty liver disease, dementia, cardiovascular diseases, and even cancer. The defining organ of obesity is the adipose tissue, highlighting the need to more comprehensively understand the development and biology of this tissue to understand the pathogenesis of obesity. Adipose tissue is a miscellaneous and highly plastic endocrine organ. It comes in many different sizes and shades and is distributed throughout many different locations in the body. Though its development begins prenatally, quite uniquely, it has the capacity for unlimited growth throughout adulthood. Adipose tissue is also a highly sexually dimorphic tissue, patterning men and women in different ways, which means the risks associated with obesity are also sexually dimorphic. Recent studies show that environmental factors during prenatal and early stages of postnatal development have the capacity to programme the structure and function of adipose tissue, with implications for the development of obesity. This review summarizes the evidence for a role for early environmental factors, such as maternal malnutrition, hypoxia, and exposure to excess hormones and endocrine disruptors during gestation in the programming of adipose tissue and obesity in the offspring. We will also discuss the complexity of studying adipose tissue biology and the importance of appreciating nuances in adipose tissue, such as sexual dimorphism and divergent responses to metabolic and endocrine stimuli. Given the rising levels of obesity worldwide, understanding how environmental conditions in early life affects adipose tissue phenotype and the subsequent development of obesity is of absolute importance.

Evidence for a sensitive period of plasticity in brown adipose tissue during early childhood among indigenous Siberians

OBJECTIVES

Evolutionary theorists have debated the adaptive significance of developmental plasticity in organisms with long lifespans such as humans. This debate in part stems from uncertainty regarding the timing of sensitive periods. Does sensitivity to environmental signals fluctuate across development or does it steadily decline? We investigated developmental plasticity in brown adipose tissue (BAT) among indigenous Siberians in order to explore the timing of phenotypic sensitivity to cold stress.

METHODS

BAT thermogenesis was quantified using infrared thermal imaging in 78 adults (25 men; 33 women). Cold exposure during gestation, infancy, early childhood, middle childhood, and adolescence was quantified using: (1) the average ambient temperature across each period; (2) the number of times daily temperature dropped below -40°F during each period. We also assessed past cold exposure with a retrospective survey of participation in outdoor activities.

RESULTS

Adult BAT thermogenesis was significantly associated with the average temperature (p = 0.021), the number of times it was below -40°F (p = 0.026), and participation in winter outdoor activities (p = 0.037) during early childhood.

CONCLUSIONS

Our results suggest that early childhood represents an important stage for developmental plasticity, and that culture may play a critical role in shaping the timing of environmental signals. The findings highlight a new pathway through which the local consequences of global climate change may influence human biology, and they suggest that ambient temperature may represent an understudied component of the developmental origins of health and disease.

Supplementing pregnant Merino ewes with caffeine to improve neonatal lamb thermoregulation and viability

Percentages of lamb mortalities prior to weaning are a significant and persistent problem for the Australian sheep industry. Maternal caffeine supplementation reduced stillbirths and improved viability in piglets; however, the efficacy of caffeine in enhancing viability and lamb survival is equivocal. The aim of this study was to determine the optimal concentration and duration of maternal caffeine supplementation to improve lamb viability; time to stand and suck with consumption of colostrum occurring, as well as survival to weaning. Multiparous Merino ewes were supplemented with either 0 (CTL), 10 (C10) or 20 mg/kg (C20) body weight (BW) caffeine in feed after day 120 of gestation (dG), or 20 mg/kg BW (LC20) caffeine from dG 142 until parturition. Ewes were housed indoors in individual lambing pens from dG 130 to 72 -h post-partum (pp). Values for pp ewe and lamb variables were analysed using a generalised linear mixed model in IBM SPSS version 25. While ewes within the CTL, C10 and LC20 groups consumed more caffeine compared to C20 ewes (P =  0.001), lambs of C20 ewes had greater rectal temperatures at 20 -h pp (P =  0.021), greater 4 -h serum IgG concentrations (P =  0.041), a longer latency to first sucking bout (P =  0.030), and a greater number of sucking attempts (P =  0.044) compared to lambs from CTL, C10 and LC20 ewes. These results indicate that caffeine supplementation during late-gestation stimulates neonatal lambs as a result of increased sucking (4 -h serum IgG) and increased temperatures within the first 24 -h.

Energy Supplementation during the Last Third of Gestation Improves Mother-Young Bonding in Goats

Simple Summary

The last third of gestation is a period of high energy demand for the dam, because she needs to support the growth of fetuses and the newborn. Moreover, towards the end of gestation, maternal feed intake is reduced as the mass of the fetoplacental unit increases. The maternal diet often cannot meet nutritional requirements, compromising thermoregulatory capacity, wellbeing, and viability, and the survival of the newborn. We have shown that energy supplementation of the mother during the last third of gestation does not affect progeny birth weight but enhances mother–young bonding.

Abstract

We tested whether maternal energy supplementation during the last third of gestation improves birth weight, neonatal wellbeing, and mother–young bonding. Thirty-six pregnant French Alpine goats were randomly allocated among three nutritional treatments for the last third of pregnancy: (i) Control, fed alfalfa (T-0; n = 12); (ii) alfalfa + 150 g/head daily energy concentrate (T-150; n = 12); (iii) alfalfa + 300 g/head daily energy concentrate (T-300; n = 12). At birth, we collected progeny data on birth weight, birth type, sex, rectal temperature, heart rate, respiratory rate, time to standing, time to udder connection, and time to first feeding. For the dams, we collected data on the duration of labor, time to clean the progeny, and time to allow first suckling. At birth, body weight, rectal temperature, heart rate, and the respiratory rate did not differ among treatments (p > 0.05). In the dams, labor duration was not affected by the treatments (p > 0.05). The T-150 dams were faster to clean the newborn and allow first suckling (p < 0.05). The T-150 progeny were faster to stand and the T-300 progeny were faster to connect to the udder (p < 0.05). We conclude that energy supplementation of the dam during the last third of gestation does not affect the birth weight of the progeny, but enhances the mother–young bonding.

Maternal arginine supplementation enhances thermogenesis in the newborn lamb

Body temperature maintenance is one of the most important physiological processes initiated after birth. Brown adipose tissue (BAT) is an essential mediator of thermogenesis in many species and is responsible for 50% of the heat generated in the newborn lamb. To determine if maternal arginine supplementation could enhance thermogenesis in the neonate, we randomly assigned 31 multiparous Suffolk ewes, gestating singletons or twins, to receive intravenous injections of either l-arginine (27 mg/kg body weight; n = 17) or sterile saline (n = 14) three times daily from day 75 to 125 of gestation (term = 147). Following parturition, lambs were removed from their mothers and subjected to 0 °C cold challenges at 4 and 22 h of age. Rectal temperatures were higher for the duration of the cold challenges in lambs from arginine-treated ewes compared with lambs from saline-treated ewes (P < 0.05). Elevated rectal temperatures were associated with increased (P < 0.05) circulating glycine and serine concentrations in lambs. The mRNA expression of genes related to BAT function changed over time, but not between lambs from arginine-treated vs. saline-treated ewes. Results indicate that maternal arginine treatment increases neonatal thermogenesis after birth. Although the underlying mechanisms remain to be elucidated, these data are a first step in improving neonatal survival in response to cold.

The Effect of Climate Parameters on Sheep Preferences for Outdoors or Indoors at Low Ambient Temperatures

Simple Summary

Sheep may be kept indoors over the winter period, especially in cool climates. There is currently a drive to keep sheep outside, especially on organic sheep farms. This paper examines the preferences that sheep have in cool conditions for outdoor or indoor housing to inform management practices. We found no evidence that mature sheep should be kept confined indoors throughout the winter period, even in normal winter weather conditions in northern Europe, with temperatures as low as −20 °C and where precipitation and relative humidity may be high. In all conditions, during this trial, the majority of ewes preferred to be outside. Access to the outdoor area should be managed to restrict outdoor access for lambs, ewes with unweaned lambs and recently shorn sheep. Conditions in which sheep did choose to move indoors were: low wind chill values (≤10 °C) and/or high air humidity (>90%). In such cases, sheep should have the opportunity to shelter indoors.

Abstract

Threshold temperatures for cold stress in sheep are not well understood, the available literature is somewhat dated and reports relate to winter temperatures that are relatively benign. Sheep’s preferences for outdoor versus indoor environments, when given free access to both, were investigated in the winter period at temperatures as low as −23 °C. Two sheep farms, one with access to a permanent uninsulated barn and one with a polytunnel shelter, both with free access to an outdoor area, were used. Observations were made with a camera positioned to register numbers of sheep outdoors and indoors, with one image taken hourly over twenty-four hours. The sheep clearly preferred to be outdoors; on all occasions the majority of the sheep were outdoors. There was, however, a significant decrease, albeit small, in the numbers of sheep choosing to be outdoors at lower temperatures (p < 0.001), higher relative humidity (p < 0.001) and greater wind chill (p < 0.001). Therefore, even at cooler temperatures than reported previously, sheep are motivated to be outdoors rather than indoors. It is not implicitly good for their welfare, and may not be true for lambs and shorn sheep, but accessing an outdoor area appears to be what they choose to do when given the choice.

Investigation of relationship between vitamin D status and reproductive fitness in Scottish hill sheep

There is a growing interest in the influence of vitamin D on ovine non-skeletal health. The aim of this study was to explore the relationship between pre-mating vitamin D status, as assessed by serum concentrations of 25-Hydroxyvitamin D [25(OH)D; comprising D2 and D3] and subsequent reproductive performance of genetically unimproved Scottish Blackface (UBF), genetically improved Scottish Blackface (IBF) and Lleyn ewes kept under Scottish hill conditions. 25-Hydroxyvitamin D2 (25(OH)D2) and 25-Hydroxyvitamin D3 (25(OH)D3) concentrations were determined in serum samples harvested in November from ewes grazed outdoors. There were no significant differences in 25(OH)D2concentrations amongst the 3 genotypes. Lleyn ewes had significantly higher 25(OH)D3 and 25(OH)D concentrations than both Scottish Blackface ewe genotypes, whereas these vitamin D parameters did not differ significantly between the UBF and IBF ewes. Concentrations of 25(OH)D3 and 25(OH)D were positively associated with subsequent birth weights of singleton and of twin lamb litters. No significant associations between vitamin D status and number of lambs born or weaned per ewe were found. This study demonstrates that concentrations of cutaneously-derived 25(OH)D3, but not of orally consumed 25(OH)D2, differed between breeds. The positive association between ewe vitamin D status and offspring birth weight highlights the need for further investigations.

Cold adaptation in pigs depends on UCP3 in beige adipocytes

Pigs lack functional uncoupling protein 1 (UCP1) making them susceptible to cold. Nevertheless, several pig breeds are known to be cold resistant. The molecular mechanism(s) enabling such adaptation are currently unknown. Here, we show that this resistance is not dependent on shivering, but rather depends on UCP3 and white adipose tissue (WAT) browning. In two cold-resistant breeds (Tibetan and Min), but not a cold-sensitive breed (Bama), WAT browning was induced after cold exposure. Beige adipocytes from Tibetan pigs exhibited greater oxidative capacity than those from Bama pigs. Notably, UCP3 expression was significantly increased only in cold-resistant breeds, and knockdown of UCP3 expression in Tibetan adipocytes phenocopied Bama adipocytes in culture. Moreover, the eight dominant pig breeds found across China can be classified into cold-sensitive and cold-resistant breeds based on the UCP3 cDNA sequence. This study indicates that UCP3 has contributed to the evolution of cold resistance in the pig and overturns the orthodoxy that UCP1 is the only thermogenic uncoupling protein.

Reconstitution of UCP1 using CRISPR/Cas9 in the white adipose tissue of pigs decreases fat deposition and improves thermogenic capacity

Uncoupling protein 1 (UCP1) is localized on the inner mitochondrial membrane and generates heat by uncoupling ATP synthesis from proton transit across the inner membrane. UCP1 is a key element of nonshivering thermogenesis and is most likely important in the regulation of body adiposity. Pigs (Artiodactyl family Suidae) lack a functional UCP1 gene, resulting in poor thermoregulation and susceptibility to cold, which is an economic and pig welfare issue owing to neonatal mortality. Pigs also have a tendency toward fat accumulation, which may be linked to their lack of UCP1, and thus influences the efficiency of pig production. Here, we report application of a CRISPR/Cas9-mediated, homologous recombination (HR)-independent approach to efficiently insert mouse adiponectin-UCP1 into the porcine endogenous UCP1 locus. The resultant UCP1 knock-in (KI) pigs showed an improved ability to maintain body temperature during acute cold exposure, but they did not have alterations in physical activity levels or total daily energy expenditure (DEE). Furthermore, ectopic UCP1 expression in white adipose tissue (WAT) dramatically decreased fat deposition by 4.89% (P < 0.01), consequently increasing carcass lean percentage (CLP; P < 0.05). Mechanism studies indicated that the loss of fat upon UCP1 activation in WAT was linked to elevated lipolysis. UCP1 KI pigs are a potentially valuable resource for agricultural production through their combination of cold adaptation, which improves pig welfare and reduces economic losses, with reduced fat deposition and increased lean meat production.

Impacts of prenatal nutrition on animal production and performance: a focus on growth and metabolic and endocrine function in sheep

The concept of foetal programming (FP) originated from human epidemiological studies, where foetal life nutrition was linked to health and disease status later in life. Since the proposal of this phenomenon, it has been evaluated in various animal models to gain further insights into the mechanisms underlying the foetal origins of health and disease in humans. In FP research, the sheep has been quite extensively used as a model for humans. In this paper we will review findings mainly from our Copenhagen sheep model, on the implications of late gestation malnutrition for growth, development, and metabolic and endocrine functions later in life, and discuss how these implications may depend on the diet fed to the animal in early postnatal life. Our results have indicated that negative implications of foetal malnutrition, both as a result of overnutrition and, particularly, late gestation undernutrition, can impair a wide range of endocrine functions regulating growth and presumably also reproductive traits. These implications are not readily observable early in postnatal life, but are increasingly manifested as the animal approaches adulthood. No intervention or cure is known that can reverse this programming in postnatal life. Our findings suggest that close to normal growth and slaughter results can be obtained at least until puberty in animals which have undergone adverse programming in foetal life, but manifestation of programming effects becomes increasingly evident in adult animals. Due to the risk of transfer of the adverse programming effects to future generations, it is therefore recommended that animals that are suspected to have undergone adverse FP are not used for reproduction. Unfortunately, no reliable biomarkers have as yet been identified that allow accurate identification of adversely programmed offspring at birth, except for very low or high birth weights, and, in pigs, characteristic changes in head shape (dolphin head). Future efforts should be therefore dedicated to identify reliable biomarkers and evaluate their effectiveness for alleviation/reversal of the adverse programming in postnatal life. Our sheep studies have shown that the adverse impacts of an extreme, high-fat diet in early postnatal life, but not prenatal undernutrition, can be largely reversed by dietary correction later in life. Thus, birth (at term) appears to be a critical set point for permanent programming in animals born precocial, such as sheep. Appropriate attention to the nutrition of the late pregnant dam should therefore be a priority in animal production systems.

Invited review: impact of specific nutrient interventions during mid-to-late gestation on physiological traits important for survival of multiple-born lambs

To improve production efficiency, the sheep meat industry has increased flock prolificacy. However, multiple-born lambs have lower birth weights, increased mortality and reduced growth rate compared with single-born lambs. Lamb mortality is a major issue for livestock farming globally and solutions are required to increase survival to realise the value of increased flock fecundity. Nutrition during gestation can influence maternal-foetal placental nutrient transfer and thus foetal growth and organ/tissue development, as well as improve postnatal productivity. This review covers the challenges and opportunities associated with increased prolificacy, highlights gaps in our knowledge and identifies some opportunities for how targeted intervention with specific nutrients during mid-to-late pregnancy may influence lamb survival and productivity with a specific focus on pasture-based systems. This time frame was selected as intervention strategies in short-time windows post-pregnancy scanning and before lambing to improve lamb survival in high-risk groups (e.g. triplets) are likely to be the most practical and economically feasible options for pasture-based extensive farming systems.

Perinatal androgen exposure and adipose tissue programming: is there an impact on body weight fate?

Obesity is a major concern in public health because it is one of the main risk factors for the development of non-transmissible chronic diseases. The fact that there is a clear sex dimorphism in normal body fat distribution points out the role of sex steroids as key factors in the regulation and function of the adipose cell. Androgens affect adipogenesis and fat metabolism in the adipose tissue of males and females. Hormonal disorders during pregnancy may affect the fetal tissues, with long-term implications leading to the development of pathologies during adult life. Obesity and metabolic disease are among these. In this regard, animal models have demonstrated an abnormal fat distribution and modifications in the size and function of adipose cells in the female and male offspring of mothers exposed to androgen excess during pregnancy.

The Ontogeny of Brown Adipose Tissue

There are three different types of adipose tissue (AT)-brown, white, and beige-that differ with stage of development, species, and anatomical location. Of these, brown AT (BAT) is the least abundant but has the greatest potential impact on energy balance. BAT is capable of rapidly producing large amounts of heat through activation of the unique uncoupling protein 1 (UCP1) located within the inner mitochondrial membrane. White AT is an endocrine organ and site of lipid storage, whereas beige AT is primarily white but contains some cells that possess UCP1. BAT first appears in the fetus around mid-gestation and is then gradually lost through childhood, adolescence, and adulthood. We focus on the interrelationships between adipocyte classification, anatomical location, and impact of diet in early life together with the extent to which fat development differs between the major species examined. Ultimately, novel dietary interventions designed to reactivate BAT could be possible.

Fetal programming in meat production

Nutrient fluctuations during the fetal stage affects fetal development, which has long-term impacts on the production efficiency and quality of meat. During the early development, a pool of mesenchymal progenitor cells proliferate and then diverge into either myogenic or adipogenic/fibrogenic lineages. Myogenic progenitor cells further develop into muscle fibers and satellite cells, while adipogenic/fibrogenic lineage cells develop into adipocytes, fibroblasts and resident fibro-adipogenic progenitor cells. Enhancing the proliferation and myogenic commitment of progenitor cells during fetal development enhances muscle growth and lean production in offspring. On the other hand, promoting the adipogenic differentiation of adipogenic/fibrogenic progenitor cells inside the muscle increases intramuscular adipocytes and reduces connective tissue, which improves meat marbling and tenderness. Available studies in mammalian livestock, including cattle, sheep and pigs, clearly show the link between maternal nutrition and the quantity and quality of meat production. Similarly, chicken muscle fibers develop before hatching and, thus, egg and yolk sizes and hatching temperature affect long-term growth performance and meat production of chicken. On the contrary, because fishes are able to generate new muscle fibers lifelong, the impact of early nutrition on fish growth performance is expected to be minor, which requires further studies.

UCP1 is present in porcine adipose tissue and is responsive to postnatal leptin

Intrauterine growth restriction (IUGR) may be accompanied by inadequate thermoregulation, especially in piglets that are not considered to possess any brown adipose tissue (BAT) and are thus entirely dependent on shivering thermogenesis in order to maintain body temperature after birth. Leptin can stimulate heat production by promoting non-shivering thermogenesis in BAT, but whether this response occurs in piglets is unknown. Newborn female piglets that were characterised as showing IUGR (mean birth weight of approximately 0.98 kg) were therefore administered injections of either saline or leptin once a day for the first 5 days of neonatal life. The dose of leptin was 0.5 mg/kg, which is sufficient to increase plasma leptin by approximately tenfold and on the day of birth induced a rapid increase in body temperature to values similar to those of normal-sized 'control' piglets (mean birth weight of ∼1.47 kg). Perirenal adipose tissue was then sampled from all offspring at 21 days of age and the presence of the BAT-specific uncoupling protein 1 (UCP1) was determined by immunohistochemistry and immunoblotting. UCP1 was clearly detectable in all samples analysed and its abundance was significantly reduced in the IUGR piglets that had received saline compared with controls, but was raised to the same amount as in controls in those IUGR females given leptin. There were no differences in gene expression between primary markers of brown and white adipose tissues between groups. In conclusion, piglets possess BAT that when stimulated exogenously by leptin can promote increased body temperature.

The effect of maternal arginine supplementation on the development of the thermogenic program in the ovine fetus

Brown adipose tissue (BAT) is a specialised fat store that is metabolised by the newborn lamb to ensure effective adaptation to the cold challenge of the extra-uterine environment. Increasing BAT reserves therefore has the potential to increase neonatal thermogenesis and survival. It is established that arginine supplementation can increase fetal BAT stores but the biological mechanisms involved are unclear. The objective of this study was to test the hypothesis that increased fetal BAT stores resulting from maternal arginine supplementation is mediated by activation of the thermogenic program. Brown adipose tissue was collected from fetuses of ewes supplemented with arginine from 100 to 140 days of gestation. Increased peri-renal fat stores in fetuses from arginine-supplemented ewes was associated with an increase in uncoupling protein 1 (UCP-1) and PRD1-BF-1-RIZ1 homologous domain containing protein-16 expression, but not proliferator-activated receptor gamma or proliferator-activated receptor gamma-co-activator-1α in BAT. The activity of UCP-1 is regulated by hormones including cortisol and thyroid hormones. Cortisol level in fetuses from supplemented sheep was 68% greater than those from control ewes, indicating that cortisol may control upregulation of UCP-1 expression in the ovine neonate. The DNA and RNA concentration in BAT of both groups suggest that increased peri-renal fat stores is not associated with an increase in cell number or number of ribosomes, but rather an increase in the size of individual fat cells. Collectively, these results indicate that maternal arginine supplementation during mid to late gestation improved the thermoregulatory ability of lambs and this could potentially increase their survival in early life.

Late gestation over- and undernutrition predispose for visceral adiposity in response to a post-natal obesogenic diet, but with differential impacts on glucose-insulin adaptations during fasting in lambs

AIM

To investigate if late gestation under- or overnutrition has similar adverse impacts on visceral adiposity, metabolic and endocrine function in sheep, and if subsequent exposure to a high-fat diet in early post-natal life exaggerates the prenatal programming outcomes later in life.

METHODS

Thirty-six twin-pregnant ewes were fed a NORM (fulfilling 100% of daily requirements for energy and protein), LOW (50% of NORM) or HIGH diet (150% of energy and 110% of protein requirements) during the last 6 weeks of gestation (term = 147 days). Post-natally, the twin lambs were subjected to a high-fat or a moderate diet until 6 months of age (around puberty), where metabolic and endocrine adaptability to fasting was examined, and subgroups of animals were killed.

RESULTS

Animals exposed to either prenatal under- or overnutrition had reduced subcutaneous fat deposition when fed a high-fat diet, resulting in higher ratios of mesenteric and peri-renal fat relative to subcutaneous fat compared to controls. This was not related to prenatal influences on plasma glucose or insulin. Irrespective of the prenatal diet, high-fat-fed lambs underwent changes resembling the metabolic syndrome with higher plasma glucose, cholesterol, non-esterified fatty acids, triglyceride and lactate combined with abdominal obesity. Peri-renal fat appeared to be a particular target of a high-fat diet post-natally.

CONCLUSION

Both prenatal under- and overnutrition predisposed for abdominal adiposity, apparently by reducing the expandability of subcutaneous adipose tissue and induced differential physiological adaptations to fasting. This study does not suggest that exposure to gestational overnutrition will provide a protective effect against development of hyperglycaemia later in life.

Parenteral administration of twin-bearing ewes with L-arginine enhances the birth weight and brown fat stores in sheep

The objective of this study was to evaluate the effects of parenteral administration of L-arginine (Arg) to well-fed twin-bearing ewes from day (d) 100 of pregnancy to birth on fetal growth, body composition and neonatal behavior. Ewes received an i.v. bolus of either 345 μmol Arg-HCl/kg bodyweight or saline solution (control) 3 times a day. At d 140 of pregnancy, Arg-supplemented and control ewes were euthanized and fetal weight and fetal organ weight recorded, and maternal and fetal plasma concentrations of amino acids, hormones and metabolites analyzed. A subset of ewes was allowed to lamb and birth weight, body dimensions and behavior of the lambs in the first 2 hours(h) following birth recorded and blood samples collected. At d 140 of pregnancy, fetal weight internal organ weights were unaffected by treatment with the exception of brown fat stores which were increased by 16% in fetuses from Arg-supplemented ewes relative to controls (P < 0.05). At birth, there was an interaction (P = 0.06) between treatment and sex for birth weight of the lamb. The ewe lambs from Arg-supplemented ewes were 12% (P < 0.05) heavier at birth compared with controls whereas birth weight of male lambs did not differ. These results indicate that maternal Arg supplementation enhanced brown fat stores in the fetus and countered some effect of fetal growth restriction due to litter size in female lambs. Increasing birth weight of female lambs and enhancing brown fat stores of all lambs may have important implications for lamb survival and postnatal growth.

Cold-induced changes in gene expression in brown adipose tissue, white adipose tissue and liver

Cold exposure imposes a metabolic challenge to mammals that is met by a coordinated response in different tissues to prevent hypothermia. This study reports a transcriptomic analysis in brown adipose tissue (BAT), white adipose (WAT) and liver of mice in response to 24 h cold exposure at 8°C. Expression of 1895 genes were significantly (P<0.05) up- or down-regulated more than two fold by cold exposure in all tissues but only 5 of these genes were shared by all three tissues, and only 19, 14 and 134 genes were common between WAT and BAT, WAT and liver, and BAT and liver, respectively. We confirmed using qRT-PCR, the increased expression of a number of characteristic BAT genes during cold exposure. In both BAT and the liver, the most common direction of change in gene expression was suppression (496 genes in BAT and 590 genes in liver). Gene ontology analysis revealed for the first time significant (P<0.05) down regulation in response to cold, of genes involved in oxidoreductase activity, lipid metabolic processes and protease inhibitor activity, in both BAT and liver, but not WAT. The results reveal an unexpected importance of down regulation of cytochrome P450 gene expression and apolipoprotein, in both BAT and liver, but not WAT, in response to cold exposure. Pathway analysis suggests a model in which down regulation of the nuclear transcription factors HNF4α and PPARα in both BAT and liver may orchestrate the down regulation of genes involved in lipoprotein and steroid metabolism as well as Phase I enzymes belonging to the cytochrome P450 group in response to cold stress in mice. We propose that the response to cold stress involves decreased gene expression in a range of cellular processes in order to maximise pathways involved in heat production.

Brown adipose tissue growth and development

Brown adipose tissue is uniquely able to rapidly produce large amounts of heat through activation of uncoupling protein (UCP) 1. Maximally stimulated brown fat can produce 300 watts/kg of heat compared to 1 watt/kg in all other tissues. UCP1 is only present in small amounts in the fetus and in precocious mammals, such as sheep and humans; it is rapidly activated around the time of birth following the substantial rise in endocrine stimulatory factors. Brown adipose tissue is then lost and/or replaced with white adipose tissue with age but may still contain small depots of beige adipocytes that have the potential to be reactivated. In humans brown adipose tissue is retained into adulthood, retains the capacity to have a significant role in energy balance, and is currently a primary target organ in obesity prevention strategies. Thermogenesis in brown fat humans is environmentally regulated and can be stimulated by cold exposure and diet, responses that may be further modulated by photoperiod. Increased understanding of the primary factors that regulate both the appearance and the disappearance of UCP1 in early life may therefore enable sustainable strategies in order to prevent excess white adipose tissue deposition through the life cycle.

A comparative approach to understanding tissue-specific expression of uncoupling protein 1 expression in adipose tissue

The thermoregulatory function of brown adipose tissue (BAT) is due to the tissue-specific expression of uncoupling protein 1 (UCP1) which is thought to have evolved in early mammals. We report that a CpG island close to the UCP1 transcription start site is highly conserved in all 29 vertebrates examined apart from the mouse and xenopus. Using methylation sensitive restriction digest and bisulfite mapping we show that the CpG island in both the bovine and human is largely un-methylated and is not related to differences in UCP1 expression between white and BAT. Tissue-specific expression of UCP1 has been proposed to be regulated by a conserved 5′ distal enhancer which has been reported to be absent in marsupials. We demonstrate that the enhancer, is also absent in five eutherians as well as marsupials, monotremes, amphibians, and fish, is present in pigs despite UCP1 having become a pseudogene, and that absence of the enhancer element does not relate to BAT-specific UCP1 expression. We identify an additional putative 5′ regulatory unit which is conserved in 14 eutherian species but absent in other eutherians and vertebrates, but again unrelated to UCP1 expression. We conclude that despite clear evidence of conservation of regulatory elements in the UCP1 5′ untranslated region, this does not appear to be related to species or tissues-specific expression of UCP1.

Nutritional regulation of fetal growth and implications for productive life in ruminants

The maternal nutritional and metabolic environment is critical in determining not only the reproductive success but also the long-term health and viability of the offspring. Changes in maternal diet at defined stages of gestation coincident with different stages of development can have pronounced effects on organ and tissue function in later life. This includes adipose tissue for which differential effects are observed between brown and white adipose tissues. One early, critical window of organ development in the ruminant relates to the period covering uterine attachment, or implantation, and rapid placental growth. During this period, there is pronounced cell division within developing organelles in many fetal tissues, leading to their structural development. In sheep, a 50% global reduction in caloric intake over this specific period profoundly affects placental growth and morphology, resulting in reduced placentome weight. This occurs in conjunction with a lower capacity to inactivate maternal cortisol through the enzyme 11β-hydroxysteroid dehydrogenase type 2 in response to a decrease in maternal plasma cortisol in early gestation. The birth weight of the offspring is, however, unaffected by this dietary manipulation and, although they possess more fat, this adaptation does not persist into adulthood when they become equally obese as those born to control fed mothers. Subsequently, after birth, further changes in fat development occur which impact on both glucocorticoid action and inflammatory responses. These adaptations can include changes in the relative populations of both brown and white adipocytes for which prolactin acting through its receptor appears to have a prominent role. Earlier when in utero nutrient restricted (i.e. between early-to-mid gestation) offspring are exposed to an obesogenic postnatal environment; they exhibit an exaggerated insulin response, which is accompanied by a range of amplified and thus, adverse, physiological or metabolic responses to obesity. These types of adaptations are in marked contrast to the effect of late gestational nutrient restriction, which results in reduced fat mass at birth. As young adults, however, fat mass is increased and, although basal insulin is unaffected, these offspring are insulin resistant. In conclusion, changes in nutrient supply to either the mother and/or her fetus can have profound effects on a range of metabolically important tissues. These have the potential to either exacerbate, or protect from, the adverse effects of later obesity and accompanying complications in the resulting offspring.

Adipose tissue and fetal programming

Adipose tissue function changes with development. In the newborn, brown adipose tissue (BAT) is essential for ensuring effective adaptation to the extrauterine environment, and its growth during gestation is largely dependent on glucose supply from the mother to the fetus. The amount, location and type of adipose tissue deposited can also determine fetal glucose homeostasis. Adipose tissue first appears at around mid-gestation. Total adipose mass then increases through late gestation, when it comprises a mixture of white and brown adipocytes. BAT possesses a unique uncoupling protein, UCP1, which is responsible for the rapid generation of large amounts of heat at birth. Then, during postnatal life some, but not all, depots are replaced by white fat. This process can be utilised to investigate the physiological conversion of brown to white fat, and how it is re-programmed by nutritional changes in pre- and postnatal environments. A reduction in early BAT deposition may perpetuate through the life cycle, thereby suppressing energy expenditure and ultimately promoting obesity. Normal fat development profiles in the offspring are modified by changes in maternal diet at defined stages of pregnancy, ultimately leading to adverse long-term outcomes. For example, excess macrophage accumulation and the onset of insulin resistance occur in an adipose tissue depot-specific manner in offspring born to mothers fed a suboptimal diet from early to mid-gestation. In conclusion, the growth of the different fetal adipose tissue depots varies according to maternal diet and, if challenged in later life, this can contribute to insulin resistance and impaired glucose homeostasis.

Arginine nutrition and fetal brown adipose tissue development in nutrient-restricted sheep

Intrauterine growth restriction is a significant problem worldwide, resulting in increased rates of neonatal morbidity and mortality, as well as increased risks for metabolic and cardiovascular disease. The present study investigated the role of maternal undernutrition and L-arginine administration on fetal growth and development. Embryo transfer was utilized to generate genetically similar singleton pregnancies. On Day 35 of gestation, ewes were assigned to receive either 50 or 100% of their nutritional requirements. Ewes received i.v. injections of either saline or L-arginine three times daily from Day 100 to Day 125. Fetal growth was assessed at necropsy on Day 125. Maternal dietary manipulation altered circulating concentrations of leptin, progesterone, and amino acids in maternal plasma. Fetal weight was reduced in nutrient-restricted ewes on Day 125 compared with 100% fed ewes. Compared with saline-treated underfed ewes, maternal L-arginine administration did not affect fetal weight but increased weight of the fetal pancreas by 32% and fetal peri-renal brown adipose tissue mass by 48%. These results indicate that L-arginine administration enhanced fetal pancreatic and brown adipose tissue development. The postnatal effects of increased pancreatic and brown adipose tissue growth warrant further study.

Thermogenesis, blood metabolites and hormones, and growth of lambs born to ewes supplemented with algae-derived docosahexaenoic acid

Neonatal lamb mortality is a major factor affecting profitability in the sheep industry, and lamb thermogenesis is a key element in neonatal lamb survival. Increased lamb vigor has been reported when ewes were supplemented during late gestation with algae-derived docosahexaenoic acid (DHA); however, the effects of DHA on lamb thermogenesis and immunocompetence have not been investigated. Eighty twin-bearing Targhee ewes (ages 2 to 5 yr; 68.5 ± 3 kg) were assigned randomly to 1 of 2 supplement treatments to determine the effects of feeding DHA to ewes during late gestation and early lactation on lamb thermogenesis, serum metabolites and hormones, and lamb growth. Supplement treatments were 12 g·ewe(-1)·d(-1) of algae-derived DHA (DHA Gold Advanced Bionutrition Corp., Columbia, MD; algae-derived DHA); and no algae-derived DHA (control). Supplements were individually fed daily during the last 30 d (±7 d) of gestation and pen fed (6 pens/treatment with 6 or 7 ewes/pen) during the first 38 d (±7 d) of lactation. One hour after lambing and before nursing, twin-born lambs were weighed, blood sampled via jugular puncture, and placed in a dry cold chamber for 30 min (0°C), and rectal temperatures were recorded every minute for 30 min. Lambs were removed from the cold chamber, blood sampled, warmed for 15 min, and returned to their dam. Ewes were blood sampled, and colostrum samples were collected 1 h postpartum. Ewe and lamb sera were assayed for glucose, NEFA, cortisol, and leptin. Lamb rectal temperature, glucose, NEFA, cortisol, leptin, and birth weights did not differ between treatments. The BW at 38 d was greater (P = 0.03) for lambs born to control ewes than for lambs born to algae-derived DHA-supplemented ewes; however, the colostrum of algae-derived DHA-supplemented ewes had a greater specific gravity (P = 0.05) than for control ewes. Overall, despite a potentially positive effect on ewe colostral IgG concentrations, supplementation of algae-derived DHA during late gestation and early lactation had a negative effect on lamb BW and did not affect indices of lamb thermogenesis.

Maternal undernutrition and endocrine development

Maternal undernutrition, whether it occurs before conception, throughout gestation or during lactation, may lead to physiological adaptations in the fetus that will affect the health of the offspring in adult life. The timing, severity, duration and nature of the maternal nutritional insult may affect the offspring differently. Other factors determining outcome following maternal undernutrition are fetal number and gender. Importantly, effects of maternal undernutrition may be carried over into subsequent generations. This review examines the endocrine pathways disrupted by maternal undernutrition that affect the long-term postnatal health of the offspring. Maternal and childhood undernutrition are highly prevalent in low- and middle-income countries, and, in developed countries, unintentional undernutrition may arise from maternal dieting. It is, therefore, important that we better understand the mechanisms driving the long-term effects of maternal undernutrition, as well as identifying treatments to ameliorate the associated mortality and morbidity.

Session on ‘Obesity’ Adipose tissue development, nutrition in early life and its impact on later obesity

It is now apparent that one key factor determining the current obesity epidemic within the developed world is the extent to which adipose tissue growth and function can be reset in early life. Adipose tissue can be either brown or white, with brown fat being characterised as possessing a unique uncoupling protein (uncoupling protein 1) that enables the rapid generation of heat by non-shivering thermogenesis. In large mammals this function is recruited at approximately the time of birth, after which brown fat is lost, not normally reappearing again throughout the life cycle. The origin and developmental regulation of brown fat in large mammals is therefore very different from that of small mammals in which brown fat is retained throughout the life cycle and may have the same origin as muscle cells. In contrast, white adipose tissue increases in mass after birth, paralleled by a rise in glucocorticoid action and macrophage accumulation. This process can be reset by changes in the maternal nutritional environment, with the magnitude of response being further determined by the timing at which such a challenge is imposed. Importantly, the long-term response within white adipocytes can occur in the absence of any change in total fat mass. The present review therefore emphasises the need to further understand the developmental regulation of the function of fat through the life cycle in order to optimise appropriate and sustainable intervention strategies necessary not only to prevent obesity in the first place but also to reverse excess fat mass in obese individuals.

Disruption of the novel gene fad104 causes rapid postnatal death and attenuation of cell proliferation, adhesion, spreading and migration

The molecular mechanisms at the beginning of adipogenesis remain unknown. Previously, we identified a novel gene, fad104 (factor for adipocyte differentiation 104), transiently expressed at the early stage of adipocyte differentiation. Since the knockdown of the expression of fad104 dramatically repressed adipogenesis, it is clear that fad104 plays important roles in adipocyte differentiation. However, the physiological roles of fad104 are still unknown. In this study, we generated fad104-deficient mice by gene targeting. Although the mice were born in the expected Mendelian ratios, all died within 1 day of birth, suggesting fad104 to be crucial for survival after birth. Furthermore, analyses of mouse embryonic fibroblasts (MEFs) prepared from fad104-deficient mice provided new insights into the functions of fad104. Disruption of fad104 inhibited adipocyte differentiation and cell proliferation. In addition, cell adhesion and wound healing assays using fad104-deficient MEFs revealed that loss of fad104 expression caused a reduction in stress fiber formation, and notably delayed cell adhesion, spreading and migration. These results indicate that fad104 is essential for the survival of newborns just after birth and important for cell proliferation, adhesion, spreading and migration.

Nutrition and its contribution to obesity and diabetes: a life-course approach to disease prevention?

Whilst previously type 2 diabetes occurred in older adults, its incidence, together with obesity, has increased rapidly in children. An improved understanding of this disease pathway from a developmental view point is critical. It is likely that subtle changes in dietary patterns over an extended period of time contribute to diabetes, although this type of rationale is largely ignored in animal studies aimed at determining the mechanisms involved. Small-animal studies in which large, and often extreme, changes in the diet are imposed at different stages of the life cycle can have substantial effects on fat mass and/or pancreatic functions. These responses are not representative of the much more gradual changes seen in the human population. An increasing number of studies indicate that it is growth rate per se, rather than the type of dietary intervention that determines pancreatic function during development. Epigenetic mechanisms that regulate insulin secretion by the pancreas can be re-set by more extreme changes in dietary supply in early life. The extent to which these changes may contribute to more subtle modulations in glucose homeostasis that can accompany excess fat growth in childhood remains to be established. For human subjects there is much less information as to whether specific dietary components determine disease onset. Indeed, it is highly likely that genotype has a major influence, although recent data relating early diet to physical activity and the FTO gene indicate the difficulty of establishing the relative contribution of diet and changes in body mass to diabetes.

Effects of maternal cold exposure and nutrient restriction on the ghrelin receptor, the GH-IGF axis, and metabolic regulation in the postnatal ovine liver

Maternal cold exposure of pregnant sheep promotes fetal growth, whereas nutrient restriction (NR) can reverse this effect. The present study was designed to establish whether cold exposure induced by winter shearing of the mother at 70 days gestation (term=147 days), with or without NR (induced by a 50% reduction in maternal food intake from 110 days gestation), has specific effects on mRNA abundance of hepatic genes related to growth and liver energy metabolism that could regulate postnatal body and liver growth. Measurements of hepatic gene expression for the GH secretagog receptor-1a (GHSR-1A), peroxisome proliferator-activated receptor (PPAR)alpha, phosphoenolpyruvate carboxykinase (PEPCK), and glucose-6-phosphatase activity together with glycogen content were made in the livers of offspring at 1 and 30 days of age. Maternal NR reduced liver mass at day 1, whereas offspring of cold-exposed mothers had larger livers at day 30 irrespective of maternal diet. Cold exposure resulted in the up-regulation of GHSR-1A mRNA abundance and reduced glucose-6-phosphatase activity at 1, but not 30 days of age, whereas IGF-II mRNA was decreased at 1 and 30 days. PPARalpha mRNA abundance was enhanced, while PEPCK was reduced in 30-day old offspring of cold-exposed mothers. NR caused reductions in IGF-I mRNA and, at 1-day postnatal age, down-regulated GHR, while, at 30 days, reduced GHSR-1A gene expression and hepatic glycogen content. In conclusion, we have shown that maternal cold exposure and NR have different effects on the hepatic GH-IGF and metabolic axis that may contribute to changes in liver growth over the first month of life.

Timing of nutrient restriction and programming of fetal adipose tissue development

It is apparent from epidemiological studies that the timing of maternal nutrient restriction has a major influence on outcome in terms of predisposing the resulting offspring to adult obesity. The present review will consider the extent to which maternal age, parity and nutritional restriction at defined stages of gestation can have important effects on fat deposition and endocrine sensitivity of adipose tissue in the offspring. For example, in 1-year-old sheep the offspring of juvenile mothers have substantially reduced fat deposition compared with those born to adult mothers. Offspring of primiparous adult mothers, however, show increased adiposity compared with those born to multiparous mothers. These offspring of multiparous ewes show retained abundance of the brown adipose tissue-specific uncoupling protein 1 at 1 month of age. A stimulated rate of metabolism in brown fat of these offspring may act to reduce adipose tissue deposition in later life. In terms of defined windows of development that can programme adipose tissue growth, maternal nutrient restriction targetted over the period of maximal placental growth results in increased adiposity at term in conjunction with enhanced abundance of mRNA for the insulin-like growth factor-I and -II receptors. In contrast, nutrient restriction in late gestation, coincident with the period of maximal fetal growth, has no major effect on adiposity but results in greater abundance of specific mitochondrial proteins, i.e. voltage-dependent anion channel and/or uncoupling protein 2. These adaptations may increase the predisposal of these offspring to adult obesity. Increasing maternal nutrition in late gestation, however, can result in proportionately less fetal adipose tissue deposition in conjunction with enhanced abundance of uncoupling protein 1.

Anabolic effects of insulin and IGF-I in the ovine fetus are reduced by prolonged maternal fasting

Fetal nutritional stress may result in intrauterine growth restriction and postnatal insulin resistance. To determine whether insulin resistance can begin in utero, we subjected late-gestation (130-135 days) ewes to 120 h of complete fasting and compared the results with our previous work in fed ewes (38). We determined the effect of insulin and/or recombinant human (rh)IGF-I infusion on ovine fetal phenylalanine kinetics, protein synthesis, and phenylalanine accretion. Experimental infusates were 1) saline, 2) rhIGF-I plus a replacement dose of insulin (40 nmol IGF-I/h + 16 mIU insulin/h), 3) insulin (890 mIU/h), and 4) IGF-I plus insulin (40 nmol IGF-I/h + 890 mIU insulin/h). During hormone infusion, both glucose and amino acid concentrations were clamped at basal concentrations. Amino acid infusion was required during infusion of either hormone to maintain plasma concentrations constant. However, the amount required during insulin infusion was less than during IGF-I infusion and 40% less than the amount required during identical studies in nonfasted animals. Phenylalanine used for protein synthesis and accretion was increased compared with control animals but again less so than in the nonfasted animals. In contrast to nonfasted animals, neither hormone increased the fractional synthetic rate of skeletal muscle protein nor that of plasma albumin. These results indicate that a short but severe nutritional stress can significantly alter the fetal anabolic response to insulin even when both glucose and amino acid substrate supplies are restored. Therefore, adaptive responses characterized by insulin resistance begin in utero when the fetus is subjected to sufficient nutritional stress.

Adipose tissue in human infancy and childhood: an evolutionary perspective

Humans diverge from most mammals, including nonhuman primates, by depositing significant quantities of body fat in utero and are consequently one of the fattest species on record at birth. While explanations for the fat layer of human neonates have commonly assumed that it serves as insulation to compensate for hairlessness, empirical support for this hypothesis is presently weak. Whether the tissue's abundance at birth and growth changes in adiposity during infancy and childhood might be explained in light of its role as energy buffer has not been assessed, and this possibility is explored through development of a model of fat function and growth centered on two related hypotheses. The first is that the greater adiposity of human neonates is at least partially explainable as an accompaniment of the enlarged human brain, which demands a larger energy reserve to ensure that its obligatory needs are met when the flow of resources from mother or other caretakers is disrupted. The second is that age-related changes in the likelihood of experiencing such disruption have influenced the pattern of investment in the tissue, reflected today in peak adiposity during infancy and a decline to a leaner childhood period. Nutritional disruption is common at birth and until lactation is established, during which time human newborns survive from fats deposited prenatally, suggesting one possible explanation for the early onset of fat deposition. At weaning, the transition from breast milk to supplemental foods and the parallel transition from maternal to endogenous immune protection interact to increase the frequency and impact of nutritional disruption, and this may help explain why newborns devote roughly 70% of growth expenditure to fat deposition during the early postnatal months. Evidence is presented that fat stores are mobilized during infections, hinting at one possible mechanism underlying the association between nutritional status and infectious morbidity and mortality among infants in nutritionally stressed human populations. Consistent with the proposed hypothesis, well-fed infants acquire peak fat reserves by an age of peak prevalence of malnutrition, infectious disease, and fat reserve depletion in less-buffered contexts, and childhood--characterized by minimal investment in the tissue--is a stage of reduced risk of energy stress. The model presented here foregrounds energy storage in adipose tissue as an important life-history strategy and a means to modify mortality risk during the nutritionally turbulent period of infancy.