Relationship between triacylglycerol concentration in the liver and first ovulation in postpartum dairy cows

The relationship between accumulation of triacylglycerols in the liver and first ovulation post partum was studied in an experiment with 32 dairy cows. During the dry period, 16 treated cows were fed a high energy diet to induce overconditioning, while 16 control cows were fed a recommended diet. After parturition, the treated cows entered deeper negative energy balance state, required more days to reach the nadir of negative energy balance, required more days to regain positive value of energy balance, and lost more body weight than the control cows. The treated cows also accumulated greater amounts of triacylglycerols in the liver and had higher concentrations of nonesterified fatty acids and 3-hydroxybutyrate post partum than the control cows. Although the number of days to first ovulation did not differ significantly between the 2 groups, the results of pooled data demonstrated that the liver triacylglycerol concentration was positively correlated with the number of days to first ovulation. In conclusion, negative energy balance caused the body fat of cows to mobilize. As a consequence, the cows accumulated greater amounts of triacylglycerols in the liver, and this accumulation was associated with an increase in the interval from parturition to first ovulation.     

Energy allocation and reproductive development in wild and domestic house mice

The growing mammal has many competing demands for energy, including some that are associated specifically with reproductive development. The concern of the present experiment was with the effect of domestication on energy allocation in relation to puberty. Food consumption, rate of growth, fertility onset, fat deposition and spontaneous locomotor activity were compared during peripubertal development in both sexes of two stocks of house mice, one wild and one domestic. The onset of fertility occurred much earlier in CF-1 females than it did in wild females; in sharp contrast the males of these two stocks achieved fertility at the same time. Food consumption, growth rate and final body weight were greater and locomotor activity was depressed in both sexes of the domestic stock. Proportionately less fat was deposited throughout development in CF-1 females when compared to wild females; fat deposition increased during development in CF-1 males while decreasing in wild males. Most of the energy-related differences noted here are compatible with a hypothesis that selection during domestication has focused on the need for a larger mass of the female mouse which, in turn, has been required to support a larger litter size. With specific regard to the reproductive development of the female, the data presented here are not compatible with the hypothesis that the first ovulation is regulated directly by critical amounts of body fat.     

Strategies to improve fertility of high yielding dairy farms: Management of the dry period

Reproductive performance of dairy cattle has been related to a wide variety of indicators of energy status, e.g., extent of negative energy balance, time of energy balance nadir, body weight loss, body condition score, and body condition score loss. Energy balance begins to decrease during the last few weeks prior to calving primarily due to a 30-35% reduction in feed intake. Cows typically remain in negative energy balance for five to seven weeks postpartum. Nutritional strategies to improve energy balance during the transition period include fat supplementation and feeding additional nonfiber carbohydrate. Unfortunately, neither approach is likely to markedly enhance energy status, although fat supplementation may increase reproductive efficiency independent of any effect on energy balance. Alternative management strategies may be required to improve fertility of dairy cows. Shortening or eliminating the dry period may improve energy status of dairy cows and increase reproductive efficiency. Shortening or eliminating the dry period may enhance dry matter intake during the transition period, decrease milk energy output, or both. A preliminary study using small animal numbers indicated that reducing dry period length to 28 or 0 days may decreases days to first ovulation, increase first service conception rate, and decrease days open. A follow-up study employing large animal numbers confirmed that reducing dry period length from 55 to 34 days can decrease days to first ovulation and decrease the percentage of anovular cows. The reduction in days open was greater for older cows than second parity cows. The reduction in days open was not related to effects of treatment on milk yield. Shortening or eliminating the dry period may be a more successful approach to improving reproductive efficiency than diet manipulation.     

The role of exercise in thermogenesis and energy balance

The role of exercise training in energy balance has been reviewed. Recent well-conducted studies showed that exercise may increase energy expenditure not only during the period of exercise itself but during the postexercise period as well. This notion of excess postexercise oxygen consumption (EPOC), which has been a controversial issue for many years, is now becoming a generally well-accepted concept, the consensus being that EPOC takes place following prolonged and strenuous exercise bouts. Besides, the role of EPOC in long-term energy balance remains to be determined. Long-term energy balance studies carried out in rats show that exercise affects energy balance by altering food intake and promoting energy expenditure. In male rats exercise causes a marked decrease in energy intake which contributes, in association with the expenditure of exercise itself, to retard lean and fat tissue growth. From the suppressed deposition of lean body mass, decreases in basal metabolic rate can be predicted in males. In female rats, exercise does not affect food intake; the lower energy gain of exercise-trained females results from the elevated expenditure rate associated with exercise itself. In both male and female rats, there is no evidence that exercise training affects energy expenditure other than during exercise itself unless the habitual feeding pattern of the rats is radically modified. The interactive effects of diet and exercise, which have to be further investigated in long-term energy balance, emerge as a promising area of research.     

Reproductive and physiological costs of repeated immune challenges in female Wellington tree weta (Orthoptera: Anostostomatidae)

Fitness‐related traits, such as immunity and reproduction, are typically condition dependent, and are predicted to trade off against each other because they share a pool of energy and resources. It is generally assumed that the resources and energy required for immune processes and reproduction is contained in the body fat; however, few studies quantify the effect of an immune insult on fat load. I tested the hypothesis that if mounting an immune response is physiologically costly in terms of consuming limited resources from body fat, and reproduction also relies on these resources, then an immune challenge should cause a reduction in fat load and an associated decline in reproduction. I tested this hypothesis by assaying the fat content of female Wellington tree weta (Hemideina crassidens) after repeated challenges with lipopolysaccharide (LPS), and counting the number of oviposited eggs in addition to assaying the egg protein content, a possible measure of egg quality. In line with my prediction, immune‐challenged females had significantly smaller fat loads and laid significantly fewer eggs than saline‐injected controls. Moreover, the protein content of the eggs laid by immune‐challenged females was significantly lower than that of controls. My experimental results show that an immune challenge with a non‐pathogenic stimulant increases fat consumption, which in turn limits the resources available for reproduction. These findings support the hypothesis that reproduction and immunity are condition dependent, and are traded off against each other. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104 , 38–46.     

长期强迫运动对大绒鼠体重、能量代谢和血清瘦素的影响

动物稳定体重的维持需要能量摄入和消耗之间的平衡。运动是影响动物能量平衡的重要因素之一。为了解运动对大绒鼠(Eothenomys miletus)的生理学效应,在室内条件下,测定了强迫运动训练(运用小鼠封闭跑台)8周后大绒鼠的体重、代谢率、摄入能、血清瘦素和身体组成的变化。结果显示,强迫运动训练8周对大绒鼠的体重无显著影响;大绒鼠的代谢率和摄入能均显著增加,训练8周后静止代谢率较对照组增加了29.9%,运动最大代谢率较对照组增加了10.7%;强迫运动训练8周组的身体脂肪重量比对照组降低了28.9%,血清瘦素水平比对照组下降了27.4%,对照组的瘦素与体脂含量具有明显的相关性,但运动组则不具有相关性;运动组的肝重量和消化道重量较对照组均显著增加;而体水重量则显著降低。这些结果表明,在强迫运动训练期间大绒鼠主要通过动员储存的脂肪、增加代谢率和食物摄入的方式来维持自身的体重及能量平衡。瘦素在长期强迫运动过程中对身体脂肪含量的变化具有调节作用。     

The contribution of animal models to the study of obesity

Obesity results from prolonged imbalance of energy intake and energy expenditure. Animal models have provided a fundamental contribution to the historical development of understanding the basic parameters that regulate the components of our energy balance. Five different types of animal model have been employed in the study of the physiological and genetic basis of obesity. The first models reflect single gene mutations that have arisen spontaneously in rodent colonies and have subsequently been characterized. The second approach is to speed up the random mutation rate artificially by treating rodents with mutagens or exposing them to radiation. The third type of models are mice and rats where a specific gene has been disrupted or over-expressed as a deliberate act. Such genetically-engineered disruptions may be generated through the entire body for the entire life (global transgenic manipulations) or restricted in both time and to certain tissue or cell types. In all these genetically-engineered scenarios, there are two types of situation that lead to insights: where a specific gene hypothesized to play a role in the regulation of energy balance is targeted, and where a gene is disrupted for a different purpose, but the consequence is an unexpected obese or lean phenotype. A fourth group of animal models concern experiments where selective breeding has been utilized to derive strains of rodents that differ in their degree of fatness. Finally, studies have been made of other species including non-human primates and dogs. In addition to studies of the physiological and genetic basis of obesity, studies of animal models have also informed us about the environmental aspects of the condition. Studies in this context include exploring the responses of animals to high fat or high fat/high sugar (Cafeteria) diets, investigations of the effects of dietary restriction on body mass and fat loss, and studies of the impact of candidate pharmaceuticals on components of energy balance. Despite all this work, there are many gaps in our understanding of how body composition and energy storage are regulated, and a continuing need for the development of pharmaceuticals to treat obesity. Accordingly, reductions in the use of animal models, while ethically desirable, will not be feasible in the short to medium term, and indeed an expansion in activity using animal models is anticipated as the epidemic continues and spreads geographically.     

Mouse models for the central melanocortin system

Obesity is characterized by an excess storage of body fat and promotes the risk for complex disease traits such as diabetes mellitus and cardiovascular diseases. The obesity prevalence in Europe is rising and meanwhile ranges from 10 to 20% in men and 15–25% in women. Body fat accumulation occurs in states of positive energy balance and is favored by interactions among environmental, psychosocial and genetic factors. Energy balance is regulated by a complex neuronal network of anorexigenic and orexigenic neurons which integrates peripheral and central hormonal and neuronal signals relaying information on the metabolic status of organs and tissues in the body. A key component of this network is the central melanocortin pathway in the hypothalamus that elicits metabolic and behavioral adaptations for the maintenance of energy homeostasis. Genetic defects in this system cause obesity in mice and humans. In this review we emphasize mouse models with spontaneous natural mutations as well as targeted mutations that contributed to our understanding of the central melanocortin system function in the control of energy balance.     

Energetic consequences of seasonal breeding in female Japanese macaques (Macaca fuscata)

Japanese macaques inhabit a relatively cold environment and females of this species could have developed strategies of energy economy to face the sometimes-harsh seasonal conditions of temperate climates, as well as reproductive costs, and thus regulate their energy balance. Here, we explore the relationship between nutritional status, body composition, seasonality, and reproductive status using isotope-labeled water, anthropometric measurements, and leptin assays from 14 captive female Japanese macaques. Our results indicated that body mass provided the best predictor of fat-free mass and fat mass. These females varied in estimated percent body fat between 8 and 25% (18% on average at the beginning of the mating season and 13% during the birth season). Higher body mass and body fat content were observed at the beginning of the mating season, which supports the hypothesis that individual females need to attain a sufficient physical condition to cover energy costs associated with mating activity, and to survive under severe ecological conditions in winter with high thermoregulatory costs. We found a relationship between conception rates and energetic condition or body fat, with females that conceived during one mating season being fatter after the end of their previous mating season. Together, these results suggest that, even in captive settings with constant food availability, seasonal breeding entails relatively high energy costs, and that females with higher energy status could invest more in reproductive activities and could afford to reproduce more rapidly.     

Antiobesity effects of green tea catechins: a mechanistic review

Green tea catechins (GTC) are polyphenolic compounds present in the unfermented dried leaves of the plant, Camellia sinensis. Results from a number of randomized, controlled intervention trials have shown that consumption of GTC (270 mg to 1200 mg/day) may reduce body weight and fat. There are several proposed mechanisms whereby GTC may influence body weight and composition. The predominating hypothesis is that GTC influences sympathetic nervous system (SNS) activity, increasing energy expenditure and promoting the oxidation of fat. Caffeine, naturally present in green tea, also influences SNS activity, and may act synergistically with GTC to increase energy expenditure and fat oxidation. Other potential mechanisms include modifications in appetite, up-regulation of enzymes involved in hepatic fat oxidation, and decreased nutrient absorption. This article reviews the evidence for each of these purported mechanisms, with particular reference to studies in humans.     

Effects of dietary energy source on energy balance, metabolites and reproduction variables in dairy cows in early lactation

This paper summarizes three recent studies by the same authors with the objective to study the effect of dietary energy source on the energy balance (EB) and risk for metabolic and reproductive disorders in dairy cows in early lactation. The first study, a literature survey, illustrated that feeding extra glucogenic nutrients relative to lipogenic nutrients, decreased milk fat and seems to decrease plasma non-esterified fatty acid (NEFA) and beta-hydroxybutyrate (BHBA) concentration. However studies are scarce and mostly confound the effect of energy source with level of energy intake, compromising eventual effects on EB and fertility. Therefore, in the second study, 16 dairy cows were either fed a glucogenic or a lipogenic diet (isocaloric) and EB was determined in climate-controlled respiration chambers from week 2 until 9 of lactation. Glucogenic diet decreased milk fat yield and milk energy and tended to decrease body fat mobilization compared with lipogenic diet. The objective of the third study was to study the effect of dietary energy source on EB, metabolites and reproduction variables. Dairy cows (n=111) were fed glucogenic, lipogenic or mixed diet from week 3 until week 9 relative to calving. Multiparous cows fed glucogenic diet had lower milk fat yield, higher calculated EB, and lower plasma NEFA, BHBA and liver triacylglyceride concentration and tended to have fewer days to first postpartum ovulation. In conclusion, increasing the glucogenic nutrient availability improved the EB and had potential to reduce the risk for metabolic disorders and to improve reproductive performance in dairy cows.     

Role of set-point theory in regulation of body weight

In adult individuals body weight is maintained at a relatively stable level for long periods. The set-point theory suggests that body weight is regulated at a predetermined, or preferred, level by a feedback control mechanism. Information from the periphery is carried by an affector to a central controller located in the hypothalamus. The controller integrates and transduces the information into an effector signal that modulates food intake or energy expenditure to correct any deviations in body weight from set-point. Evidence for involvement of various factors and physiological systems in the control of food intake and regulation of body weight and fat are reviewed within the context of a control model. Current working hypotheses include roles for nutrients, dietary composition and organoleptic properties, hormones, neural pathways, various brain nuclei, and many neurotransmitters in the regulation of food intake. It is concluded that regulation of body weight in relation to one specific parameter related to energy balance is unrealistic. It seems appropriate to assume that the level at which body weight and body fat content are maintained represents the equilibria achieved by regulation of many parameters.     

Urinary C-peptide is not an accurate bioindicator of energy balance in humans

The apprehension of the factors that affect long term regulation of energy balance is indispensable to understand the rise in obesity prevalence as well as to delineate levers to prevent it. Accurate measurements of energy balance are however challenging during free‐living conditions. Recent studies proposed urinary C‐peptide, a metabolic byproduct of insulin synthesis, as reliable noninvasive assessment of energy balance. These studies were in fact essentially based on correlations between urinary C‐peptide and energy intake and only focused on nonhuman primates. During a bed‐rest study conducted in 16 healthy women in a controlled environment, we tested the existence of a relationship between 24 h‐urinary C‐peptide and energy balance in humans. Daily energy intake and body mass, body composition (dual‐energy X‐ray absorptiometry (DXA)) and total energy expenditure (doubly labeled water (DLW) method) was measured and energy balance was calculated as the difference between energy intake and expenditure. Urinary C‐peptide was positively correlated with bed‐rest‐induced changes in fat mass (r² = 0.285; P = 0.03) and energy balance assessed at the end of the bed‐rest (r² = 0.302; P = 0.027). However, in this tightly controlled environment, urinary C‐peptide only accounted for 30% of variations in energy balance. No relationship was noted between urinary C‐peptide and body or fat mass both at baseline and at the end of the bed‐rest. These results indicate that urinary C‐peptide cannot be used as an accurate biomarker of energy balance in the general human population in free‐living conditions.     

Abnormalities of Fuel Utilization as Predisposing to the Development of Obesity in Humans

A number of recent investigations in man have demonstrated that a low ratio of fat to carbohydrate oxidation (i.e., a high respiratory quotient or RQ) was associated with actual and/or subsequent body weight gain in obese non-diabetic Pima Indians, in American men of various ages and in post-obese European women investigated shortly after the cessation of a hypocaloric diet. It is well known that numerous exogenous and endogenous factors influence the RQ at rest such as: the level of feeding (positive vs. negative energy balance), the composition of food eaten (high vs. low carbohydrate), the size of the glycogen stores, the amount of adipose tissue as well as genetic factors. It should be stressed that some nutritional situations can coexist during which a low ratio of fat to carbohydrate is observed (i.e., a high RQ) despite weight loss. Furthermore, in most studies mentioned above, the low fat to carbohydrate oxidation ratio explains less then 10% of the variance in weight gain, suggesting that numerous additional factors also play a substantial role in the onset of weight gain. It is concluded that: 1) A low fat to carbohydrate oxidation ratio or an abnormal fat oxidation is difficult to define quantitatively since it is largely influenced by the energy level and the composition of the diet. 2) Following a dynamic adaptation phase to positive energy balance, a low fat oxidation is progressively compensated: increased body fat is the price to pay for normalizing fat oxidation since, at least in resting conditions, there is an increase in fat oxidation of approximately 20 g/day for each 10 kg additional fat gain. The subject with a low fat to carbohydrate oxidation ratio will equilibrate at a body fat level allowing to reach a new fat balance.     

House sparrows (Passer domesticus) increase protein catabolism in response to water restriction

Birds primarily rely on fat for energy during fasting and to fuel energetically demanding activities. Proteins are catabolized supplemental to fat, the function of which in birds remains poorly understood. It has been proposed that birds may increase the catabolism of body protein under dehydrating conditions as a means to maintain water balance, because catabolism of wet protein yields more total metabolic and bound water (0.155·H(2)O(-1)·kJ(-1)) than wet lipids (0.029 g·H(2)O(-1)·kJ(-1)). On the other hand, protein sparing should be important to maintain function of muscles and organs. We used quantitative magnetic resonance body composition analysis and hygrometry to investigate the effect of water restriction on fat and lean mass catabolism during short-term fasting at rest and in response to a metabolic challenge (4-h shivering) in house sparrows (Passer domesticus). Water loss at rest and during shivering was compared with water gains from the catabolism of tissue. At rest, water-restricted birds had significantly greater lean mass loss, higher plasma uric acid concentration, and plasma osmolality than control birds. Endogenous water gains from lean mass catabolism offset losses over the resting period. Water restriction had no effect on lean mass catabolism during shivering, as water gains from fat oxidation appeared sufficient to maintain water balance. These data provide direct evidence supporting the hypothesis that water stress can increase protein catabolism at rest, possibly as a metabolic strategy to offset high rates of evaporative water loss.     

The influence of energy intake and percentage of body fat on the reproductive performance of nonpregnant mares

Sixty mares in transition from winter anestrus to normal cyclicity were assigned to a 3 x 2 factorial experiment to determine the effect of energy intake and percentage of body fat on the interval to first ovulation. The factors were 1) percentage of body fat--thin (<11.5), good (11.5 to 15), or fat (>15); and 2) energy intake--maintenance (100% of National Research Council (NRC) digestible energy requirement for maintenance) or high energy (150% of NRC digestible energy requirement for maintenance). Percentage of body fat was estimated by ultrasonographic scanning of rump fat thickness. Energy treatments began on April 2 and ended on June 4. Mares were teased daily with a stallion and their ovaries were palpated per rectum daily or every third day. A high energy intake was effective in hastening ovulation for mares in the thin group (P < 0.05) but not for mares in the moderate or fat groups. Mares in the fat group had a shorter (P < 0.05) interval from April 2 to ovulation (26.4 +/- 4.2 d) than those in the good or high energy-thin groups (48.7 +/- 2.8 and 49.1 +/- 4.2 d, respectively). Duration of the initial estrus was shorter (P < 0.05) for mares in the fat group (16.2 +/- 5.7 d) compared with mares in the good group (34.7 +/- 3.9 d) and tended (P<0.12) to be shorter than mares in the high energy-thin group (29.0 +/- 5.7 d).     

Photoperiod Regulates Lean Mass Accretion,but Not Adiposity,in Growing F344 Rats Fed a High Fat Diet

In this study the effects of photoperiod and diet, and their interaction, were examined for their effects on growth and body composition in juvenile F344 rats over a 4-week period. On long (16L:8D), relative to short (8L:16D), photoperiod food intake and growth rate were increased, but percentage adiposity remained constant (ca 3-4%). On a high fat diet (HFD), containing 22.8% fat (45% energy as fat), food intake was reduced, but energy intake increased on both photoperiods. This led to a small increase in adiposity (up to 10%) without overt change in body weight. These changes were also reflected in plasma leptin and lipid levels. Importantly while both lean and adipose tissue were strongly regulated by photoperiod on a chow diet, this regulation was lost for adipose, but not lean tissue, on HFD. This implies that a primary effect of photoperiod is the regulation of growth and lean mass accretion. Consistent with this both hypothalamic GHRH gene expression and serum IGF-1 levels were photoperiod dependent. As for other animals and humans, there was evidence of central hyposomatotropism in response to obesity, as GHRH gene expression was suppressed by the HFD. Gene expression of hypothalamic AgRP and CRH, but not NPY nor POMC, accorded with the energy balance status on long and short photoperiod. However, there was a general dissociation between plasma leptin levels and expression of these hypothalamic energy balance genes. Similarly there was no interaction between the HFD and photoperiod at the level of the genes involved in thyroid hormone metabolism (Dio2, Dio3, TSHβ or NMU), which are important mediators of the photoperiodic response. These data suggest that photoperiod and HFD influence body weight and body composition through independent mechanisms but in each case the role of the hypothalamic energy balance genes is not predictable based on their known function.     

A role for leptin in sexual maturation and puberty?

Leptin, the ob gene product, is involved in the regulation of body weight in rodents, primates and humans. It provides a molecular basis for the lipostatic theory of the regulation of energy balance. White adipose tissue and placenta are the main sites of leptin synthesis. There is also evidence of ob gene expression in brown fat. Leptin seems to play a key role in the control of body fat stores by coordinated regulation of feeding behaviour, metabolic rate, autonomic nervous system regulation and body energy balance. Apart from the function of leptin in the central nervous system on the regulation of energy balance, it may well be one of the hormonal factors that signal to the brain the body's readiness for sexual maturation and reproduction. During late pregnancy and at birth when maternal fat stores have been developed, leptin levels are high. During these developmental stages leptin could be a messenger molecule signalling the adequacy of the fat stores for reproduction and maintenance of pregnancy. At later stages of gestation leptin could signal the expansion of fat stores in order to prepare the expectant mother for the energy requirements of full-term gestation, labour and lactation. Leptin serum concentrations change during pubertal development in rodents, primates and humans. In girls, leptin serum concentrations increase dramatically as pubertal development proceeds. The pubertal rise in leptin levels parallels the increase in body fat mass. In contrast, leptin levels increase shortly before and during the early stages of puberty in boys and decline thereafter. Testosterone has been found to suppress leptin synthesis by adipocytes both in vivo and in vitro. The decline of leptin levels in late puberty in boys accompanies increased androgen production during that time and most likely reflects suppression of leptin by testosterone and a decrease in fat mass and relative increase in muscle mass during late puberty in males. This overview focuses on those topics of leptin research which are of particular interest in reproductive and adolescent medicine.     

Effects of leptin infusion during peak lactation on food intake, body composition, litter growth, and maternal neuroendocrine status in female Brandt's voles (Lasiopodomys brandtii)

During lactation, female small mammals frequently reduce their fat reserves to very low levels. The function of this reduction is unclear, as calculations suggest that the contribution of the withdrawn energy from fat to the total energy balance of lactation is trivial. An alternative hypothesis is that reducing fat leads to a reduction in circulating adipokines, such as leptin, that play a role in stimulating the hyperphagia of lactation. We investigated the role of circulating leptin in lactation by repleting leptin levels using miniosmotic pumps during the last 7 days of lactation in Brandt's voles (Lasiopodomys brandtii), a model small wild mammal we have extensively studied in the context of lactation energy demands. Repletion of leptin resulted in a dose-dependent reduction of body mass and food intake in lactating voles. Comparisons to nonreproducing individuals suggests that the reduced leptin in lactation, due to reduced fat stores, may account for ～16% of the lactational hyperphagia. Reduced leptin in lactation may, in part, cause lactational hyperphagia via stimulatory effects on hypothalamic orexigenic neuropeptides (neuropeptide Y and agouti-related peptide) and inhibition of the anorexigenic neuropeptide (proopiomelanocortin). These effects were reversed by the experimental repletion of leptin. There was no significant effect of leptin treatment on daily energy expenditure, milk production or pup growth, but leptin repletion did result in a reversal of the suppression of uncoupling protein-1 levels in brown adipose tissue, indicating an additional role for reducing body fat and leptin during peak lacation.