Response of Plasma Leptin Concentration to Jugular Infusion of Glucose or Lipid Is Dependent on the Stage of Lactation of Holstein Cows

Effect of intravenous lipid infusion on biomarkers of insulin resistance and immune functions of dry and nonpregnant dairy cows

During the transition period, dairy cows often experience negative energy balance, which can induce metabolic and immunological disturbances. Previous work has shown that there is a relationship between the dysfunction of immune cells and the increase in blood nonesterified fatty acid (NEFA) concentration. Nevertheless, it is difficult to determine the exact effect of NEFA on the immune system, as other metabolic and hormonal perturbations occur simultaneously during the transition period. In the present study, we have determined the effect of NEFA on immune functions using an experimental model designed to assess the effects independently of energy balance, as well as hormonal and metabolic changes due to parturition. Six dry and nonpregnant cows were infused with either sterile water (control treatment) or a lipid emulsion (Intralipid 20%, Frenesius Kabi, lipid treatment) at a rate of 1 mL/kg per hour for 6 h according to a crossover design. Blood concentrations of NEFA, β-hydroxybutyrate (BHB), and glucose were measured every hour throughout the infusion period, and 1 and 18 h after the end of infusion. Proliferation and interferon-γ secretion of lymphocytes, phagocytosis, and oxidative burst of neutrophils and blood insulin concentration were evaluated before, during, and at the end of the infusion. For NEFA, BHB, and glucose, treatment × time interactions were present. When compared with the control condition, NEFA and BHB levels were greater in the plasma of cows infused with lipids from 1 h after the start of infusion until 1 h after the end of infusion. Glucose level also increased in response to lipid infusion from 2 h of infusion until 1 h after the end of treatment. For sterile water and lipid infusions, respectively, maximal concentrations were 0.06 ± 0.10 mM and 1.39 ± 0.10 mM for NEFA, 0.70 ± 0.05 mM and 1.06 ± 0.05 mM for BHB, and 4.56 ± 0.27 mM and 6.90 ± 0.27 mM for glucose. For all blood metabolites, there were no differences between treatments 18 h postinfusion. Lipid infusion significantly increased blood insulin concentration at 3 and 6 h of infusion. However, it returned to its basal concentration 18 h after the end of the infusion. Lymphoproliferation declined as early as 3 h after the start of the lipid infusion. At 3 and 6 h of infusion, lipid treatment significantly reduced INF-γ concentration in the culture cell supernatant. The lipid infusion did not affect neutrophil phagocytosis. Nevertheless, the efficacy of the response was affected by a reduction of neutrophils' oxidative burst. These results confirm that NEFA inhibits immune functions independently of energy balance and other changes that occur during the transition period. They also indicate that high blood lipid concentration causes insulin resistance.

Invited review: The influence of immune activation on transition cow health and performance-A critical evaluation of traditional dogmas

The progression from gestation into lactation represents the transition period, and it is accompanied by marked physiological, metabolic, and inflammatory adjustments. The entire lactation and a cow's opportunity to have an additional lactation are heavily dependent on how successfully she adapts during the periparturient period. Additionally, a disproportionate amount of health care and culling occurs early following parturition. Thus, lactation maladaptation has been a heavily researched area of dairy science for more than 50 yr. It was traditionally thought that excessive adipose tissue mobilization in large part dictated transition period success. Further, the magnitude of hypocalcemia has also been assumed to partly control whether a cow effectively navigates the first few months of lactation. The canon became that adipose tissue released nonesterified fatty acids (NEFA) and the resulting hepatic-derived ketones coupled with hypocalcemia lead to immune suppression, which is responsible for transition disorders (e.g., mastitis, metritis, retained placenta, poor fertility). In other words, the dogma evolved that these metabolites and hypocalcemia were causal to transition cow problems and that large efforts should be enlisted to prevent increased NEFA, hyperketonemia, and subclinical hypocalcemia. However, despite intensive academic and industry focus, the periparturient period remains a large hurdle to animal welfare, farm profitability, and dairy sustainability. Thus, it stands to reason that there are alternative explanations to periparturient failures. Recently, it has become firmly established that immune activation and the ipso facto inflammatory response are a normal component of transition cow biology. The origin of immune activation likely stems from the mammary gland, tissue trauma during parturition, and the gastrointestinal tract. If inflammation becomes pathological, it reduces feed intake and causes hypocalcemia. Our tenet is that immune system utilization of glucose and its induction of hypophagia are responsible for the extensive increase in NEFA and ketones, and this explains why they (and the severity of hypocalcemia) are correlated with poor health, production, and reproduction outcomes. In this review, we argue that changes in circulating NEFA, ketones, and calcium are simply reflective of either (1) normal homeorhetic adjustments that healthy, high-producing cows use to prioritize milk synthesis or (2) the consequence of immune activation and its sequelae.

Evaluating acute inflammation's effects on hepatic triglyceride content in experimentally induced hyperlipidemic dairy cows in late lactation

Inflammation appears to be a predisposing factor and key component of hepatic steatosis in a variety of species. Objectives were to evaluate effects of inflammation [induced via intravenous lipopolysaccharide (LPS) infusion] on metabolism and liver lipid content in experimentally induced hyperlipidemic lactating cows. Cows (765 ± 32 kg of body weight; 273 ± 35 d in milk) were enrolled in 2 experimental periods (P); during P1 (5 d), baseline data were obtained. At the start of P2 (2 d), cows were assigned to 1 of 2 treatments: (1) intralipid plus control (IL-CON; 3 mL of saline; n = 5) or (2) intralipid plus LPS (IL-LPS; 0.375 μg of LPS/kg of body weight; n = 5). Directly following intravenous bolus (saline or LPS) administration, intralipid (20% fat emulsion) was intravenously infused continuously (200 mL/h) for 16 h to induce hyperlipidemia during which feed was removed. Blood samples were collected at -0.5, 0, 4, 8, 12, 16, 24, and 48 h relative to bolus administration, and liver biopsies were obtained on d 1 of P1 and at 16 and 48 h after the bolus. By experimental design (feed was removed during the first 16 h of d 1), dry matter intake decreased in both treatments on d 1 of P2, but the magnitude of reduction was greater in LPS cows. Dry matter intake of IL-LPS remained decreased on d 2 of P2, whereas IL-CON cows returned to baseline. Milk yield decreased in both treatments during P2, but the extent and duration was longer in LPS-infused cows. Administering LPS increased circulating LPS-binding protein (2-fold) at 8 h after bolus, after which it markedly decreased (84%) below baseline for the remainder of P2. Serum amyloid A concentrations progressively increased throughout P2 in IL-LPS cows (3-fold, relative to controls). Lipid infusion gradually increased nonesterified fatty acids and triglycerides in both treatments relative to baseline (3- and 2.5-fold, respectively). Interestingly, LPS infusion blunted the peak in nonesterified fatty acids, such that concentrations peaked (43%) higher in IL-CON compared with IL-LPS cows and heightened the increase in serum triglycerides (1.5-fold greater relative to controls). Liver fat content remained similar in IL-LPS relative to P1 at 16 h; however, hyperlipidemia alone (IL-CON) increased liver fat (36% relative to P1). No treatment differences in liver fat were observed at 48 h. In IL-LPS cows, circulating insulin increased markedly at 4 h after bolus (2-fold relative to IL-CON), and then gradually decreased during the 16 h of lipid infusion. Inducing inflammation with simultaneous hyperlipidemia altered the characteristic patterns of insulin and LPS-binding protein but did not cause fatty liver.

Review: Lipid biology in the periparturient dairy cow: contemporary perspectives

Coordinated changes in energy metabolism develop to support gestation and lactation in the periparturient dairy cow. Maternal physiology involves the partitioning of nutrients (i.e. glucose, amino acids and fatty acids (FA)) for fetal growth and milk synthesis. However, the inability of the dairy cow to successfully adapt to a productive lactation may trigger metabolic stress characterized by uncontrolled adipose tissue lipolysis and reduced insulin sensitivity. A consequence is lipotoxicity and hepatic triglyceride deposition that favors the development of fatty liver disease (FLD) and ketosis. This review describes contemporary perspectives pertaining to FA surfeit and complex lipid metabolism in the transition dairy cow. The role of saturated and unsaturated FA as bioactive signaling molecules capable of modulating insulin secretion and sensitivity is explored. Moreover, the metabolic fate of FA as influenced by mitochondrial function is considered. This includes the influence of inadequate mitochondrial oxidation on acylcarnitine status and the use of FA for lipid mediator synthesis. Lipid mediators, including the sphingolipid ceramide and diacylglycerol, are evaluated considering their established ability to inhibit insulin signaling and glucose transport in non-ruminant diabetics. The mechanisms of FLD in the transition cow are revisited with attention centered on glycerophospholipid phosphatidylcholine and triglyceride secretion. The relationship between oxidative stress and oxylipids within the context of insulin antagonism, hepatic steatosis and inflammation is also reviewed. Lastly, peripartal hormonal involvement or lack thereof of adipokines (i.e. leptin, adiponectin) and hepatokines (i.e. fibroblast growth factor-21) is described. Similarities and differences in ruminant and non-ruminant physiology are routinely showcased. Unraveling the lipidome of the dairy cow has generated breakthroughs in our understanding of periparturient lipid biology. Therapeutic approaches that target FA and complex lipid metabolism holds promise to enhance cow health, well-being and productive lifespan.

The relationship of body condition indicators with the level of plasma cocaine and amphetamine regulated transcript and energy metabolism indicators in dairy cows

The factors affecting the course of lactation and intensity of milk secretion include the condition and body weight, as well as chewing time. A little researched factor is also the cocaine and amphetamine regulated transcript (CART) which has been suggested to have an anorexigenic function. This study sought to examine the dependent indicators of condition and chewing time on daily milk yield assessment in the context of the concentration of CART, glucose and ß-hydroxybutyrate (BHB) in blood. Higher CART levels contributed to shorter chewing time (min/day), lower body condition and lower body weight. Blood glucose concentration showed a stronger correlation with body weight and condition than with blood BHB concentration. An important practical aspect of the results is the relationship shown between CART and chewing time and the potential relation between daily milk production and chewing time. Importantly, the animals with lower daily milk production had relatively the highest concentration CART. This may suggest that this neuropeptide is indirectly involved in milk production, especially by shortening the chewing time. The obtained results help to better explain the mechanisms involved in milk secretion and the process of rumination and digestion. More research is required, but they also show important functions of other examined neuropeptides.

Comparison of surrogate indices for insulin sensitivity with parameters of the intravenous glucose tolerance test in early lactation dairy cattle

The aim of this study was to investigate the correlation between different surrogate indices and parameters of the intravenous glucose tolerance test (IVGTT) in dairy cows at the start of their lactation. Ten dairy cows underwent IVGTT on Days 3 to 7 after calving. Areas under the curve during the 90 min after infusion, peak and nadir concentrations, elimination rates, and times to reach half-maximal and basal concentrations for glucose, insulin, nonesterified fatty acids, and β-hydroxybutyrate were calculated. Surrogate indices were computed using the average of the IVGTT basal samples, and their correlation with the IVGTT parameters studied through the Spearman's rank test. No statistically significant or strong correlation coefficients (P > 0.05; |ρ| < 0.50) were observed between the insulin sensitivity measures derived from the IVGTT and any of the surrogate indices. Therefore, these results support that the assessment of insulin sensitivity in early lactation cattle cannot rely on the calculation of surrogate indices in just a blood sample, and the more laborious tests (ie, hyperinsulinemic euglycemic clamp test or IVGTT) should be employed to predict the sensitivity of the peripheral tissues to insulin accurately.

Effect of circulating glucagon and free fatty acids on hepatic FGF21 production in dairy cows

Modern dairy cows meet the energy demand of early lactation by calling on hormonally driven mechanisms to increase the use of lipid reserves. In this context, we recently reported that fibroblast growth factor-21 (FGF21), a hormone required for efficient use of lipid reserves in rodents, is upregulated in periparturient dairy cows. Increased plasma FGF21 in early lactation coincides with elevated circulating concentrations of glucagon (GCG) and nonesterified fatty acids (NEFA). To assess the relative contribution of these factors in regulating FGF21, two experiments were performed in energy-sufficient, nonpregnant, nonlactating dairy cows. In the first study, cows were injected with saline or GCG every 8 h over a 72-h period. GCG increased hepatic FGF21 mRNA by an average of fivefold over matched controls but had no effect on plasma FGF21. In the second study, cows were infused and injected with saline, infused with Intralipid and injected with saline, or infused with Intralipid and injected with GCG. Infusions and injections were administered intravenously over 16 h and subcutaneously every 8 h, respectively. Intralipid infusion increased plasma NEFA from 92 to 550 µM within 3 h and increased plasma FGF21 from 1.3 to >11 ng/ml 6 h later; FGF21 mRNA increased by 34-fold in liver but remained invariant in adipose tissue. GCG injections during the Intralipid infusion had no additional effects on plasma NEFA, liver FGF21 mRNA, or plasma FGF21. These data implicate plasma NEFA as a key factor triggering hepatic production and increased circulating concentrations of FGF21 in early lactation.

Endogenous and dietary lipids influencing feed intake and energy metabolism of periparturient dairy cows

The high metabolic priority of the mammary gland for milk production, accompanied by limited feed intake around parturition results in a high propensity to mobilize body fat reserves. Under these conditions, fuel selection of many peripheral organs is switched, for example, from carbohydrate to fat utilization to spare glucose for milk production and to ensure partitioning of tissue- and dietary-derived nutrients toward the mammary gland. For example, muscle tissue uses nonesterified fatty acids (NEFA) but releases lactate and amino acids in a coordinated order, thereby providing precursors for milk synthesis or hepatic gluconeogenesis. Tissue metabolism and in concert, nutrient partitioning are controlled by the endocrine system involving a reduction in insulin secretion and systemic insulin sensitivity and orchestrated changes in plasma hormones such as insulin, adiponectin, insulin growth factor-I, growth hormone, glucagon, leptin, glucocorticoids, and catecholamines. However, the endocrine system is highly sensitive and responsive to an overload of fatty acids no matter if excessive NEFA supply originates from exogenous or endogenous sources. Feeding a diet containing rumen-protected fat from late lactation to calving and beyond exerts similar negative effects on energy intake, glucose and insulin concentrations as does a high extent of body fat mobilization around parturition in regard to the risk for ketosis and fatty liver development. High plasma NEFA concentrations are thought not to act directly at the brain level, but they increase the energy charge of the liver which is, signaled to the brain to diminish feed intake. Cows differing in fat mobilization during the transition phase differ in their hepatic energy charge, whole body fat oxidation, glucose metabolism, plasma ghrelin, and leptin concentrations and in feed intake several week before parturition. Hence, a high lipid load, no matter if stored, mobilized or fed, affects the endocrine system, metabolism, and feed intake, and increases the risk for metabolic disorders. Future research should focus on a timely parallel increase in feed intake and milk yield during early lactation to reduce the impact of body fat on feed intake, metabolic health, and negative energy balance.

Experimental hyperlipidemia induces insulin resistance in sheep

This study aimed to evaluate the effects of intravenous infusion of a soybean-based lipid emulsion on some blood energy-related metabolites and insulin sensitivity indexes in sheep. Four clinically healthy ewes were assigned into a 2-treatment, 2-period cross-over design. Either normal saline (NS) or lipid emulsion (LE) was intravenously introduced at a rate of 0.025 mL·kg(-1) min(-1) for 6 h. The concentrations of blood nonesterified fatty acid (NEFA), beta-hydroxybutyrate, triglyceride, cholesterol, urea, creatinine, cortisol, glucose, and insulin were measured at different time points. After 6 h, intravenous glucose tolerance test was performed. Lipid infusion elicited an increase (P < 0.05) in the NEFA, beta-hydroxybutyrate, and triglyceride concentrations compared with the baseline value and NS infusion. Infusion of NS did not influence blood glucose concentration; however, LE infusion increased plasma glucose concentration (P < 0.05). At time point 12 h, serum insulin concentrations were increased (P < 0.05) in NS treatment; however, such an increase was not observed in the LE treatment. Insulin sensitivity index for the LE infusion was lower (P < 0.05) than that for the NS treatment. The glucose effectiveness was not (P > 0.05) different among treatments. In the LE treatment, acute-phase insulin responses increased (P < 0.05) and disposition index decreased (P < 0.001) compared with NS treatment. The results showed that experimentally induced NEFA in blood could cause insulin resistance in sheep. The current model could be used to evaluate the pathogenesis of conditions associated with increased lipid mobilization and insulin resistance.

Effects of lipid and propionic acid infusions on feed intake of lactating dairy cows

Propionic acid is more hypophagic for cows with elevated hepatic acetyl coenzyme A (CoA) concentration in the postpartum period. The objective of this experiment was to evaluate the interaction of hepatic acetyl CoA concentration, which is elevated by intravenous lipid infusion, and intraruminal propionic acid infusion on feed intake and feeding behavior responses of lactating cows. Eight multiparous, ruminally cannulated, Holstein dairy cows past peak lactation were used in a replicated 4×4 Latin square experiment with a 2×2 factorial arrangement of treatments. Treatments were propionic acid (PI) infused intraruminally at 0.5mol/h for 18h starting 6h before feeding and behavior monitoring or sham control (CO), and intravenous jugular infusion of lipid (LI, Intralipid 20%; Baxter US, Deerfield, IL) or saline (SI, 0.9% NaCl; Baxter US) infused at 250mL/h for 12h before feeding and behavior monitoring, and then 500mL/h for 12h after feeding. Changes in plasma concentrations of metabolites and hormones and hepatic acetyl CoA from before infusion until the end of infusion were evaluated. We observed a tendency for an interaction between PI and LI for the change in plasma nonesterified fatty acid (NEFA) concentration from the preliminary day to the end of the infusion period. Infusion of propionic acid decreased dry matter intake (DMI) 15% compared with CO, but lipid infusion did not affect DMI over the 12h following feeding. Infusion of propionic acid tended to decrease hepatic acetyl CoA concentration from the preliminary day to the end of the infusion compared with CO, consistent with PI decreasing DMI by stimulating oxidation of acetyl CoA. Contrary to our expectations, LI did not increase concentration of NEFA or β-hydroxybutyrate in plasma, concentration of acetyl CoA in the liver, or milk fat yield, suggesting that the infused lipid was stored or oxidized by extra-hepatic tissues. As a result, we detected no interaction between PI and LI for DMI. Although the effect of PI on DMI was consistent with our previous results, this lipid infusion model using cows past peak lactation was not useful to simulate the lipolytic state of cows in the postpartum period in this experiment.

Short communication: Glucose infusion into early postpartum cows defines an upper physiological set point for blood glucose and causes rapid and reversible changes in blood hormones and metabolites

Low blood glucose concentrations after calving are associated with infertility in postpartum dairy cows perhaps because glucose is a master regulator of hormones and metabolites that control reproductive processes. The hypothesis was that low blood glucose postpartum is caused by inadequate glucose entry rate relative to whole-body demand as opposed to the alternative possibility that postpartum cows have a lower regulatory set point for blood glucose. Eight early postpartum (10 to 25 d) dairy cows (5 Holstein and 3 Guernsey) were jugular catheterized. During the first 24 h, cows were infused with physiological saline at 83.3 mL/h. After 24 h, the infusion solution was switched to 50% dextrose that was infused at a rate of 41.7 mL/h (total daily glucose dose=500 g). On d 3 and d 4, the rate of glucose infusion was increased to 83.3 mL/h (daily dose=1,000 g) and 125 mL/h (daily dose=1,500 g), respectively. On d 5, physiological saline was infused at 83.3 mL/h. Blood was sampled hourly through a second jugular catheter (contralateral side) and analyzed for glucose, nonesterified fatty acids, β-hydroxybutyrate, insulin-like growth factor 1, and insulin. Blood glucose concentrations on d 1 (saline infusion) averaged 53.4±1.7 mg/dL. Blood glucose concentrations increased on d 2 when cows were infused with 500 g/d and increased further on d 3 when cows were infused with 1,000g of glucose/d. Increasing the infusion rate to 1,500 g/d on d 4 did not cause a further increase in blood glucose concentrations. Based on a segmented regression analysis, the upper physiological set point for blood glucose was 72.1 mg/dL. Both insulin and insulin-like growth factor 1 concentrations increased in response to glucose infusion and decreased when cows were infused with saline on d 5. Serum nonesterified fatty acids and β-hydroxybutyrate concentrations decreased in response to glucose infusion and rebounded upward on d 5 (saline infusion). In conclusion, early postpartum cows had circulating blood glucose concentrations that were well below the upper set point defined in this study (72.1 mg/dL). Infusing approximately 1,000 g of glucose daily increased blood glucose to the physiological set point and rapidly changed the hormonal and metabolic profile that typifies postpartum cows. The inability of the early postpartum cow to achieve an adequate entry rate for glucose relative to whole-body demand is a possible mechanism that links postpartum physiology and nutrition to reproduction in dairy cows.

Triennial Growth Symposium: neural regulation of feed intake: modification by hormones, fasting, and disease

Appetite is a complex process that results from the integration of multiple signals at the hypothalamus. The hypothalamus receives neural signals; hormonal signals such as leptin, cholecystokinin, and ghrelin; and nutrient signals such as glucose, FFA, AA, and VFA. This effect is processed by a specific sequence of neurotransmitters beginning with the arcuate nucleus and orexigenic cells containing neuropeptide Y or agouti-related protein and anorexigenic cells containing proopiomelanocortin (yielding the neurotransmitter α-melanocyte-stimulating hormone) or cells expressing cocaine amphetamine-related transcript. These so-called first-order neurons act on second-order orexigenic neurons (containing either melanin-concentrating hormone or orexin) or act on anorexigenic neurons (e.g., expressing corticotropin-releasing hormone) to alter feed intake. In addition, satiety signals from the liver and gastrointestinal tract signal through the vagus nerve to the nucleus tractus solitarius to cause meal termination, and in combination with the hypothalamus, integrate the various signals to determine the feeding response. The activities of these neuronal pathways are also influenced by numerous factors such as nutrients, fasting, and disease to modify appetite and hence affect growth and reproduction. This review will begin with the central nervous system pathways and then discuss the ways in which hormones and metabolites may alter the process to affect feed intake with emphasis on farm animals.

Sunflower-seed oil, rapidly-degradable starch, and adiposity up-regulate leptin gene expression in lactating goats

We conducted experiments to evaluate the effects of lipid supplementation and the nature of starchy concentrate on the regulation of leptin synthesis in lactating goats. Multiparous goats in mid- to late lactation received diets based on different forages and containing plant oil or seeds rich in either 18:1c9, 18:2n-6 or 18:3n-3 corresponding to 3%-7% dry matter (DM) as lipid supplements, or diets based on concentrate as either rapidly or slowly degradable starch. The isoenergetic replacement of a part of the concentrate by either oleic sunflower-seed oil, formaldehyde-treated linseeds, or linseed oil did not modify leptinemia and the leptin mRNA concentration in adipose tissues, suggesting a lack of effect of 18:1c9, 18:3n-3, or their biohydrogenation products. Conversely, leptinemia and the leptin mRNA abundance were increased (by 20% and 140%, respectively, P<0.05) in goats fed sunflower-seed oil under a grassland hay-based diet but not a maize silage-based diet, at similar energy intakes and adiposity. Thus, 18:2n-6 per se may up-regulate leptin gene expression, but the effect could be blunted by other fatty acids formed during the ruminal digestion of sunflower-seed oil when combined with maize silage. Consumption of rapidly but not slowly degradable starch increased (by 17%, P<0.05) leptinemia. Moreover, during lactation, plasma leptin was positively correlated (P<0.05) to adiposity parameters and negatively correlated to fiber intake. The results suggest that leptinemia responds poorly to nutritional factors in lactating goats, thus highlighting the physiological need to sustain hypoleptinemia during lactation.

Hormonal regulation of glucose clearance in lactating northern elephant seals (Mirounga angustirostris)

Northern elephant seals exhibit the rare strategy of fasting and lactating concomitantly. We investigated hormonal regulation of glucose clearance in northern elephant seals using glucose tolerance tests (GTT) performed early in lactation and again just prior to weaning. For comparison, identical measurements were made on separate females late in the molt fast. Serial blood samples were used to assess glucose clearance and hormone responses for 3 h post glucose injection. Plasma glucose remained elevated at the end of the sampling period in all groups. Glucose clearance rates were not significantly different among test groups. A significant insulin response was observed in early lactation, no significant response was observed late in lactation and an intermediate response was observed late in the molt fast. The insulin response to a glucose load decreased with adipose tissue proportions. Plasma glucagon decreased significantly following GTT in early and late lactation, although the magnitude of the depression was small in comparison to other species. Hypoinsulemia may be critical to facilitate net lipolysis late in lactation. Consistently low glucose clearance among test groups suggests insulin insensitivity within peripheral tissues. Glucagon suppression independent of insulin release suggests modification of the typical insulin-glucagon counter-regulation. These findings suggest that metabolic features of diabetic-like conditions may be adaptive in the context of long-term fasting.

Inverse regulation of leptin mRNA expression by short- and long-chain fatty acids in cultured bovine adipocytes

Leptin is an adipose tissue-derived cytokine plays key roles in the regulation of food intake and energy expenditure. However, regulatory mechanisms of leptin gene expression are not fully elucidated in ruminants that utilize short-chain fatty acids (SCFA), known as volatile fatty acids, as principal energy sources. In this study, we determined effects of SCFA and long-chain fatty acids (LCFA) on leptin expression in bovine adipocytes. Bovine stromal vascular cells isolated from subcutaneous adipose tissue of Holstein cows were cultured to confluence and treated sequentially with dexamethasone and isobutylmethylxanthine for 2 days and insulin and troglitazone for 12 days to achieve full differentiation to adipocytes. The cells started to accumulate lipids 4 days after the onset of treatment, with increased mRNA expression of leptin, as well as aP2, adiponectin, and PPAR-gamma. Removal of fetal calf serum and reduction of glucose in the culture medium of differentiated adipocytes decreased leptin mRNA expression. Subsequent addition of acetate, butyrate, or propionate dose-dependently restored and rather increased leptin expression, while addition of LCFA suppressed it. The stimulatory effect of acetate was abolished by prior treatment of the cells with pertussis toxin and by addition of LCFA. Furthermore, cows fasted for 48h and fed thereafter, elaborate reduced and increased plasma leptin levels, respectively. Thus, these results suggest that plasma leptin levels in cows are inversely controlled at the transcription level by VFA and LCFA, and that the effects of SCFA possibly act through a G protein-coupled receptor for SCFA.

Differences between primiparous and multiparous dairy cows in the inter-relationships between metabolic traits, milk yield and body condition score in the periparturient period

During the early postpartum period dairy cows mobilize fat and muscle to support lactation. This is associated with alterations in blood metabolite and hormone profiles which in turn influence milk yield and fertility. This study developed models to determine how metabolic traits, milk yield and body condition score were inter-related at different times in the periparturient period and to compare these relationships in primiparous (PP, n=188) and multiparous (MP, n=312) cows. Data from four previous studies which included information on blood metabolic parameters, parity, milk yield, body condition score and diet were collated into a single dataset. Coefficients of polynomial equations were calculated for each trait between -1 week pre-calving and week +7 postpartum using residual maximum likelihood modelling. The completed dataset was used in a multiple correlation model to determine how the best fit curves were related to each other over time. PP cows had higher concentrations of insulin-like growth factor-I and lower beta-hydroxybutyrate concentrations throughout, higher leptin concentrations pre-partum and both the peak in non-esterified fatty acids and the nadir in urea concentration occurred earlier after calving. These differences were associated with significantly lower milk production. Leptin concentrations fell at calving and were related to body condition score. Insulin was negatively correlated with yield in MP cows only. In MP cows the relationship between insulin-like growth factor-I and yield switched from negative to positive between weeks +4 and +7. Both beta-hydroxybutyrate and urea were positively related to yield in PP cows. In contrast, in MP cows beta-hydroxybutyrate was negatively correlated with yield and urea was strongly related to body condition score but not yield. These results suggest that there are differences in the control of tissue mobilization between PP and MP cows which may promote nutrient partitioning into growth as well as milk during the first lactation.

Induction of Hyperlipidemia by Intravenous Infusion of Tallow Emulsion Causes Insulin Resistance in Holstein Cows

The objective was to test whether the induction of elevated blood nonesterified fatty acids (NEFA) by i.v. infusion of a tallow emulsion altered glucose tolerance and responsiveness to insulin in Holstein cows. Six non-lactating, nongestating Holstein cows were assigned to a crossover design. One cow was excluded before initiation of the experiment because of complications from mastitis. Treatments consisted of 11-h i.v. infusions of saline (control) or a 20% (wt/vol) triacylglycerol (TG) emulsion derived from tallow (tallow) to elevate plasma NEFA. Each period consisted of two 11-h infusions (INF1 and INF2), separated by 1 d in which cows were not infused. Intravenous glucose tolerance tests (IVGTT) and insulin challenges (IC) were performed 8 h after initiation of INF1 and INF2, respectively. The infusion of treatments continued during the 3 h of sampling for IVGTT and IC. Cows were fed every 4 h at a rate to meet energy requirements for 5 d prior to each period, and every 2 h during the first 8 h of infusions. Infusion of tallow induced hyperlipidemia by increasing plasma NEFA (295 +/- 9 vs. 79 +/- 7 microEq/L), serum TG (41.0 +/- 6 vs. 11.4 +/- 4.4 mg/dL), and glycerol (0.81 +/- 0.09 vs. 0.23 +/- 0.1 mg/dL) concentrations during INF1. During INF2, tallow treatment increased plasma NEFA (347 vs. 139 +/- 18 microEq/L), serum TG (20.8 +/- 4.6 vs. 13.1 +/- 2.3 mg/dL), and glycerol (0.88 +/- 0.04 vs. 0.31 +/- 0.02 mg/dL) concentrations. Induction of hyperlipidemia impaired glucose clearance during IVGTT, despite the greater endogenous insulin response to the glucose infusion, leading to a lower insulin sensitivity index [0.29 vs. 1.88 +/- 0.31 x 10(-4) min(-1)/(microIU/mL)]. Accordingly, hyperlipidemia impaired glucose clearance during IC (1.58 vs. 2.72 %/min), reflecting lower responsiveness to insulin. These data show that induction of hyperlipidemia causes insulin resistance in Holstein cows by impairing both sensitivity and maximum responsiveness to insulin. The induction of insulin resistance by TG, NEFA, or both may increase the availability of glucogenic nutrients to the periparturient dairy cow. Yet excessive elevation of NEFA may potentially lead adipocytes to become more insulin resistant, further increasing plasma NEFA concentration and the risk of metabolic disorders.

Effects of supplementation of whole corn germ on reproductive performance, calf performance, and leptin concentration in primiparous and mature beef cows

A 2-yr study using primiparous and multiparous, spring-calving, crossbred beef cows was conducted to evaluate the effects of supplemental whole corn germ on reproductive performance, calf performance, and serum leptin concentrations. Each year, cows were blocked by age and BCS and assigned randomly to one of three treatments: PRE (n = 115) cows received 1.14 kg/d (DM basis) of whole corn germ for approximately 45 d before calving; POST (n = 109) cows were fed 1.14 kg/d of whole corn germ for approximately 45 d after calving; and control cows (n = 118) were fed similar energy and protein from dry-rolled corn (1.82 kg of DM/d) for 45 d before and after calving. Additionally, PRE cows were grouped with controls after calving, and POST cows were grouped with control cows before calving, so that corn germ-supplemented cows received the control supplement in the alternate feeding period. Cow BW (538 +/- 13 kg) and BCS (5.4 +/- 0.13) did not differ among treatments at any time during the experiment. Calf birth weight (39 +/- 2 kg), weaning weight (225 +/- 7 kg), and age-adjusted weaning weight (234 +/- 8 kg) did not differ because of dam supplementation regimen. Treatment did not affect the proportion of cows exhibiting ovarian luteal activity before the start of the breeding season (67%) or pregnancy rate (91%). The interval from exposure to bulls until subsequent calving did not differ (P = 0.16) among PRE (298 +/- 2.3 d), POST (303 +/- 2.6 d), and control (304 +/- 2.3 d) cows. Leptin concentrations did not differ among treatments and were 2.15 +/- 0.75, 1.88 +/- 0.76, and 1.91 +/- 0.75 ng/mL for control, POST, and PRE cows, respectively. Age and week relative to calving influenced leptin concentration. Primiparous cows had similar leptin concentrations to 3-yr-old and mature cows for wk -7 and -6 relative to calving, but lower (P < 0.10) concentrations than mature cows for wk -5, and lower (P < 0.05) concentrations than either 3-yr-old or mature cows for wk -4 to +7 relative to calving. Serum leptin was correlated with BCS (P < 0.0001; r = 0.35) at initiation of the feeding period and was correlated with BCS (P = 0.02; r = 0.12) and weight (P < 0.01; r = 0.14) at the completion of the supplement period, but it was not correlated with initial BW or interim BCS. Calving interval was not correlated (P > 0.12) with weekly measures of serum leptin concentration. Supplementing beef cows with whole corn germ had no effect on cow performance, calf performance, or serum leptin concentrations of cows.

Leptin expression in ruminants: nutritional and physiological regulations in relation with energy metabolism

Leptin, mainly produced in adipose tissue (AT), is a protein involved in the central and/or peripheral regulation of body homeostasis, energy intake, storage and expenditure, fertility and immune functions. Its role is well documented in rodent and human species, but less in ruminants. This review is focused on some intrinsic and extrinsic factors which regulate adipose tissue leptin gene expression and leptinemia in cattle, sheep, goat and camel: age, physiological status (particularly pregnancy and lactation) in interaction with long-term (adiposity) and short-term effects of feeding level, energy intake and balance, diet composition, specific nutrients and hormones (insulin, glucose and fatty acids), and seasonal non-dietary factors such as photoperiod. Body fatness strongly regulates leptin and its responses to other factors. For example, leptinemia is higher after underfeeding or during lactation in fat than in lean animals. Physiological status per se also modulates leptin expression, with lactation down-regulating leptinemia, even when energy balance (EB) is positive. These results suggest that leptin could be a link between nutritional history and physiological regulations, which integrates the animal's requirements (e.g., for a pregnancy-lactation cycle), predictable food availability (e.g., due to seasonal variations) and potential for survival (e.g., body fatness level). Reaching permissive leptin thresholds should be necessary for pubertal or postpartum reproductive activity. In addition to the understanding of leptin yield regulation, these data are helpful to understand the physiological significance of changes in leptin secretion and leptin effects, and how husbandry strategies could integrate the adaptative capacities of ruminant species to their environment.

Pregnancy increases plasma leptin in nulliparous but not primiparous goats while lactation depresses it

Most dairy ruminants are still lactating during early pregnancy, which could induce hormonal adaptations different from those observed during pregnancy alone. The incidence of concomitant lactation and pregnancy on plasma leptin has not been studied, and physiological factors involved in its regulation have not been addressed in goats. We assayed leptinemia throughout the pregnancy-lactation cycle in nulliparous and primiparous goats, starting 165 days prior to parturition and finishing 59 days after. During the first half of pregnancy, primiparous goats were lactating. Lactating non-pregnant primiparous goats were studied in parallel. Plasma leptin increased (+49%) up to mid-pregnancy in nulliparous, but not in primiparous goats. Furthermore, leptinemia was similar between pregnant and non-pregnant lactating primiparous goats, suggesting a strong leptinemia down-regulation by late lactation. Plasma leptin decreased from mid-pregnancy to parturition, more markedly in nulliparous goats, and remained depressed during early lactation at a similar level in both female types. It was lower, at 130 days of pregnancy, in goats carrying two fetuses. The leptinemia down-regulation by late pregnancy was highlighted by the lack of plasma leptin increase after drying-off late-pregnant primiparous goats, while it strongly increased in non-pregnant goats. The observation of leptinemia increase only in nulliparous goats suggests that it is not an essential endocrine adaptation during early pregnancy. By contrast, in both female types, the low leptinemia during transition from late pregnancy to lactation, and during late lactation, may be important for the adaptations that occur during lactation such as the partitioning of energy and nutrients towards essential functions and/or hyperphagia.