Glucose response to exogenous insulin and kinetics of insulin metabolism in obese and lean heifers

Invited review: Assessment of body condition score and body fat reserves in relation to insulin sensitivity and metabolic phenotyping in dairy cows

The purpose of this article is to review body condition scoring and the role of body fat reserves in relation to insulin sensitivity and metabolic phenotyping. This article summarizes body condition scoring assessment methods and the differences between subcutaneous and visceral fat depots in dairy cows. The mass of subcutaneous and visceral adipose tissue (AT) changes significantly during the transition period; however, metabolism and intensity of lipolysis differ between subcutaneous and visceral AT depots of dairy cows. The majority of studies on AT have focused on subcutaneous AT, and few have explored visceral AT using noninvasive methods. In this systematic review, we summarize the relationship between body fat reserves and insulin sensitivity and integrate omics research (e.g., metabolomics, proteomics, lipidomics) for metabolic phenotyping of cows, particularly overconditioned cows. Several studies have shown that AT insulin resistance develops during the prepartum period, especially in overconditioned cows. We discuss the role of AT lipolysis, fatty acid oxidation, mitochondrial function, acylcarnitines, and lipid insulin antagonists, including ceramide and glycerophospholipids, in cows with different body condition scoring. Nonoptimal body conditions (under- or overconditioned cows) exhibit marked abnormalities in metabolic and endocrine function. Overall, reducing the number of cows with nonoptimal body conditions in herds seems to be the most practical solution to improve profitability, and dairy farmers should adjust their management practices accordingly.

High body energy reserve influences extracellular vesicles miRNA contents within the ovarian follicle

Aiming to evaluate the effects of increased body energy reserve (BER) in Nellore cows' reproductive efficiency, cows were fed with different nutritional plans to obtain animals with high BER (HBER; Ad libitum diet) and moderate BER (MBER: cows fed 70% of HBER group ingestion). To evaluate the BER, cows were weekly weighted and evaluated for subcutaneous fat thickness and insulin serum concentration along the experimental period. At the end of the experimental period, animals were submitted to estrous synchronization and artificial insemination. Animals were slaughtered approximately 120 h after ovulation induction and the reproductive tracts were collected for embryo recovery and samples collection. Cumulus-oocyte-complexes (COC) and follicular fluid were collected from 3-6 mm in diameter ovarian follicles to perform miRNA analysis of cumulus cells (CC) and extracellular vesicles from follicular fluid (EV FF). As expected, differences were observed among MBER and HBER groups for body weight, fat thickness, and insulin serum concentration. HBER animals showed lower ovulation and embryo recovery rates compared to MBER animals. Different miRNAs were found among CC and EV FF within groups, suggesting that the BER may influence follicular communication. This suggests that small follicles (3-6 mm diameter) are already under BER effects, which may be greater on later stages of follicular development.

Dietary energy level affects adipose depot mass but does not impair in vitro subcutaneous adipose tissue response to short-term insulin and tumor necrosis factor-α challenge in nonlactating, nonpregnant Holstein cows

We assessed effects of overfeeding energy to nonlactating and nonpregnant Holstein cows during a length of time similar to a typical dry period on body lipid storage and the abundance of genes related to insulin signaling, inflammation, and ubiquitination in subcutaneous adipose tissue (SAT) in vitro challenged with insulin and recombinant bovine tumor necrosis factor-α. Fourteen cows were randomly assigned to either a high-energy (OVE; net energy for lactation = 1.60 Mcal/kg of dry matter; n = 7) or control (CON; net energy for lactation = 1.30 Mcal/kg of dry matter; n = 7) diet for 6 wk. Immediately after slaughter, liver, kidneys, and mammary gland were separated and weighed. The adipose tissue mass in the omental, mesenteric, and perirenal depots was dissected and weighed. Subcutaneous adipose tissue was collected from the tail-head region and was used as follows: control, bovine insulin (INS) at 1 µmol/L, tumor necrosis factor-α at 5 ng/mL (TNF), and their combination. Despite a lack of difference in final body condition score, OVE cows had greater energy intake and were heavier than CON cows. Furthermore, overfeeding led to greater mass of mesenteric and perirenal adipose, liver, and mammary gland. Overall, SAT incubated with INS had an upregulation of insulin receptor (INSR), interleukin-10 (IL10), small ubiquitin-like modifier 3 (SUMO3), and ubiquitin conjugating enzyme E2I (UBC9), whereas TNF upregulated peroxisome proliferator-activated receptor gamma (PPARG), diacylglycerol O-acyltransferase 2 (DGAT2), interleukin-6 (IL6), nuclear factor kappa B subunit 1 (NFKB1), small ubiquitin-like modifier 2 (SUMO2), and UBC9. Regardless of in vitro treatment, feeding OVE upregulated PPARG, fatty acid synthase (FASN), and insulin induced gene 1 (INSIG1). Abundance of PPARG was greater in SAT of OVE cows cultured individually with INS and TNF. The interaction between diet and in vitro treatment revealed that sterol regulatory element binding transcription factor 1 (SREBF1) had greater abundance in SAT from the CON group in response to culture with INS, whereas SAT from OVE cows had greater SREBF1 abundance in response to culture with TNF. The mRNA abundance of IL6 and NFKB1 was greater in response to TNF treatment and overall in CON cows. Furthermore, SAT from these cows had greater IL10 abundance when cultured with INS and TNF. Overall, data highlighted that overfeeding energy increases adipose tissue mass in part by stimulating transcription of key genes associated with insulin signaling, adipogenesis, and lipogenesis. Because SAT thickness or mass was not measured, the lack of effect of overfeeding on body condition score limits its use to predict overall body lipid storage. An overt inflammatory response in SAT after a 6-wk period of over-consumption of energy could not be discerned.

Insulin-dependent glucose metabolism in dairy cows with variable fat mobilization around calving

Dairy cows undergo significant metabolic and endocrine changes during the transition from pregnancy to lactation, and impaired insulin action influences nutrient partitioning toward the fetus and the mammary gland. Because impaired insulin action during transition is thought to be related to elevated body condition and body fat mobilization, we hypothesized that over-conditioned cows with excessive body fat mobilization around calving may have impaired insulin metabolism compared with cows with low fat mobilization. Nineteen dairy cows were grouped according to their average concentration of total liver fat (LFC) after calving in low [LLFC; LFC <24% total fat/dry matter (DM); n=9] and high (HLFC; LFC >24.4% total fat/DM; n=10) fat-mobilizing cows. Blood samples were taken from wk 7 antepartum (ap) to wk 5 postpartum (pp) to determine plasma concentrations of glucose, insulin, glucagon, and adiponectin. We applied euglycemic-hyperinsulinemic (EGHIC) and hyperglycemic clamps (HGC) in wk 5 ap and wk 3 pp to measure insulin responsiveness in peripheral tissue and pancreatic insulin secretion during the transition period. Before and during the pp EGHIC, [(13)C6] glucose was infused to determine the rate of glucose appearance (GlucRa) and glucose oxidation (GOx). Body condition, back fat thickness, and energy-corrected milk were greater, but energy balance was lower in HLFC than in LLFC. Plasma concentrations of glucose, insulin, glucagon, and adiponectin decreased at calving, and this was followed by an immediate increase of glucagon and adiponectin after calving. Insulin concentrations ap were higher in HLFC than in LLFC cows, but the EGHIC indicated no differences in peripheral insulin responsiveness among cows ap and pp. However, GlucRa and GOx:GlucRa during the pp EGHIC were greater in HLFC than in LLFC cows. During HGC, pancreatic insulin secretion was lower, but the glucose infusion rate was higher pp than ap in both groups. Plasma concentrations of nonesterified fatty acids decreased during HGC and EGHIC, but in both clamps, pp nonesterified fatty acid concentrations did not reach the ap levels. The study demonstrated a minor influence of different degrees of body fat mobilization on insulin metabolism in cows during the transition period. The distinct decrease in the glucose-dependent release of insulin pp is the most striking finding that explains the impaired insulin action after calving, but does not explain differences in body fat mobilization between HLFC and LLFC cows.

Insulin resistance in dairy cows

Glucose is the molecule that drives milk production, and insulin plays a pivotal role in the glucose metabolism of dairy cows. The effect of insulin on the glucose metabolism is regulated by the secretion of insulin by the pancreas and the insulin sensitivity of the skeletal muscles, the adipose tissue, and the liver. Insulin resistance may develop as part of physiologic (pregnancy and lactation) and pathologic processes, which may manifest as decreased insulin sensitivity or decreased insulin responsiveness. A good knowledge of the normal physiology of insulin is needed to measure the in vivo insulin resistance of dairy cows.

Substrate utilization and dose response to insulin by subcutaneous adipose tissue of Angus steers fed corn- or hay-based diets

We hypothesized that, at a common age endpoint, adipose tissue from corn-fed steers would be less sensitive to insulin than adipose tissue from hay-fed steers. Angus steers were assigned to either a corn-based diet (n = 6) or hay-based diet (n = 6) and fed to common days on feed. Steers fed the corn-based diet had 2.44 cm of fat thickness over the 12th thoracic rib, whereas hay-fed steers had 1.04 cm of fat thickness. At slaughter, subcutaneous adipose samples were collected and portions of subcutaneous adipose tissue were incubated with [U-(14)C]acetate to quantify fatty acid synthesis or with [U-(14)C]glucose to assess glucose utilization in the presence of 0, 100, or 500 ng/mL of insulin. Additional subcutaneous samples were used to evaluate glycolytic intermediate concentrations as indicators of glycolytic flux. Data were analyzed as a split-plot with diet in the main plot and insulin concentration and its interaction with diet in the sub-plot. Within diet, linear and quadratic contrasts of insulin concentration were tested. Diet had no effect (P > or = 0.31) on glucose metabolism or acetate carbon incorporation into total lipids (P = 0.32). Insulin had no effect (P > 0.21) on glucose conversion to CO(2), lactate, or total lipids, nor did it affect (P = 0.28) acetate conversion to total lipids. No diet x insulin interaction (P > 0.36) was observed for any measure of subcutaneous metabolism in vitro. Steers fed the corn-based diet exhibited neither a linear (P > 0.22) nor a quadratic (P > 0.24) effect to increasing insulin concentration. However, when steers were fed the hay-based diet, there was a positive linear (P = 0.06) effect for glucose oxidation. These results suggest that subcutaneous adipose tissue may become resistant to stimulation by insulin in steers fed to a fat thickness above the average feedlot steer, but this is independent of diet.

The role of exogenous insulin in the complex of hepatic lipidosis and ketosis associated with insulin resistance phenomenon in postpartum dairy cattle

As a result of a marked decline in dry matter intake (DMI) prior to parturition and a slow rate of increase in DMI relative to milk production after parturition, dairy cattle experience a negative energy balance. Changes in nutritional and metabolic status during the periparturient period predispose dairy cattle to develop hepatic lipidosis and ketosis. The metabolic profile during early lactation includes low concentrations of serum insulin, plasma glucose, and liver glycogen and high concentrations of serum glucagon, adrenaline, growth hormone, plasma beta-hydroxybutyrate and non-esterified fatty acids, and liver triglyceride. Moreover, during late gestation and early lactation, flow of nutrients to fetus and mammary tissues are accorded a high degree of metabolic priority. This priority coincides with lowered responsiveness and sensitivity of extrahepatic tissues to insulin, which presumably plays a key role in development of hepatic lipidosis and ketosis. Hepatic lipidosis and ketosis compromise production, immune function, and fertility. Cows with hepatic lipidosis and ketosis have low tissue responsiveness to insulin owing to ketoacidosis. Insulin has numerous roles in metabolism of carbohydrates, lipids and proteins. Insulin is an anabolic hormone and acts to preserve nutrients as well as being a potent feed intake regulator. In addition to the major replacement therapy to alleviate severity of negative energy balance, administration of insulin with concomitant delivery of dextrose increases efficiency of treatment for hepatic lipidosis and ketosis. However, data on use of insulin to prevent these lipid-related metabolic disorders are limited and it should be investigated.

Fertility responses and hormonal profiles in repeat breeding cows treated with insulin

The influence of insulin treatment on conception rate and endocrine profile was studied on 21 repeat breeding cows divided randomly into two groups, i.e. insulin treatment (n = 11) and control (n = 10). Cows of the insulin treatment group were injected subcutaneously with a long acting purified form of bovine insulin at 0.2 IU/kg body weight/day on days 8, 9 and 10, and then with 0.75 mg tiaprost (PGF(2)alpha) intramuscularly on day 12 of the oestrous cycle (oestrus = day 0). The cows of the control group only received 0.75 mg tiaprost was injected intramuscularly on day 12. There was no difference (P > 0.05) in the interval to the onset of oestrus and subsequent cycle length between the treatment (84.5 +/- 6.6 h and 21.2 +/- 0.6 days, respectively) and the control (72.3 +/- 5.9 h and 19.7 +/- 0.4 days, respectively) groups. First service conception rate and overall pregnancy rate did not differ (P > 0.05) between the insulin treatment group (45.4 and 63.6%) and the control group (33.3 and 40.0%). Progesterone concentration following administration of insulin increased (P < 0.05) in the insulin treated cows (2.2+/-0.4 ng/ml versus 2.9 +/- 0.4 ng/ml) but the concentration of oestradiol-17beta did not differ. The insulin concentration was higher on day 10 of the oestrous cycle (P < 0.05) in the treatment group (71.0 +/- 12.5 microU/ml versus 38.1 +/- 4.5 microU/ml). The insulin and glucose concentrations were higher (P > 0.05) in animals, which subsequently became pregnant than in non-pregnant animals. The results may indicate that there is beneficial effect of insulin on fertility in repeat breeder cattle.

Physiological responses of pre-ruminant kid goats and lambs to different environmental temperatures

The purpose of this study was to establish the metabolic behaviour of both preruminant kid goats and lambs, when they are kept at different environmental temperatures (12, 24 and 30 degrees C). The animals were fed ad libitum with a milk replacer for the first two months of life. Blood samples were taken from all the animals on days 30, 40, 50 and 60 post partum, to determine serum levels of glucose, insulin, free fatty acids, triiodothyronine (T3) and thyroxine (T4), both when fasting and 4 hours after starting feeding. The high sensitivity of both kinds of animal to the lowest of the environmental temperatures used, particularly for the first periods of life here considered, was established from the glucose/insulin and T3/T4 molar ratios and from the concentrations of free fatty acids. The results obtained by species were also evidence of metabolic behaviour typical of leanner animals in kids.

Ruminant adaptation to negative energy balance. Influences on the etiology of ketosis and fatty liver

Ketosis and fatty liver occur when physiologic mechanisms for the adaptation to negative energy balance fail. Failure of hepatic gluconeogenesis to supply adequate glucose for lactation and body needs may be one cause of ketosis; however, poor feedback control of nonesterified fatty acid release from adipose tissue is another likely cause of ketosis and fatty liver. The types of ketosis resulting from these two metabolic lesions may require different therapeutic and prophylactic approaches.

Effects of exogenous somatotropin on whole-body glycemic response to insulin in young preruminant and ruminant lambs

The purpose of this study was to determine the effects of exogenous recombinant bovine somatotropin (bST) treatment on whole-body glycemic responsiveness and sensitivity to exogenous insulin in preruminant and ruminant lambs. Twelve milk-fed (MF) and 12 ruminating (RUM) wether lambs weighing 20 +/- 0.6 kg were assigned to one of four treatment groups: MF control, MF plus bST, RUM control, and RUM plus bST. Lambs received a daily subcutaneous injection of 160 micrograms of sometribove (recombinant methionyl bST) bST/kg live weight or the equivalent volume of sterile water (control) for 10 d. The MF lambs had higher plasma insulin and nonessential fatty acids and lower acetate concentrations than RUM lambs (all P < 0.05). Plasma insulin-like growth factor concentrations were similar in both. The administration of bST raised plasma insulin-like growth factor-1 (P < 0.001) and insulin (P < 0.05) in MF and RUM lambs, but with greater effect in MF lambs (P < 0.01 and P < 0.1, respectively). Six successive dose-incremented insulin challenges (50, 100, 200, 300, 500, and 700 mU/kg body weight) were performed two per day on Days 8, 9, and 10 of treatment. Dose-response curves for absolute decline in glucose concentration from preinjection baseline to nadir were used to characterize whole-body responsiveness and sensitivity (ED50) to insulin. Somatotropin treatment increased insulin ED50 values 64 and 70% (P < 0.07) in RUM and MF lambs, respectively, suggesting that sensitivity to insulin was reduced. Insulin ED50 values were 40% higher in MF than in RUM lambs (P < 0.05). Insulin clearance rates increased with each dose increment to 300 mU/kg body weight (P = 0.001) and were 50% lower in bST-treated MF lambs than in all other treatment groups (P < 0.05). Results suggest that somatotropin modulates the insulin control of glucose homeostasis similarly in preruminant and ruminant lambs by decreasing sensitivity but not maximum responsiveness.

Effect of prepartum energy intake and postpartum protein source on plasma somatotropin and insulin in lactating cows

Forty-two Holstein cows were fed a high or low energy diet during the last third of lactation, then fed soybean meal or dried brewers grains in the subsequent lactation. Responses of plasma somatotropin and insulin to arginine were measured at 6 and 15 wk postpartum. Basal somatotropin, response area, and peak value were greater at 6 versus 15 wk of lactation. Insulation responses were greater at 15 wk of lactation. At 6 wk, basal somatotropin was higher (6.1 versus 4.1 ng/ml) in cows fed the low energy diet prepartum. Shape of somatotropin response curves at 6 wk differed between prepartum energy intakes, but response areas were similar. Plasma insulin at 6 wk tended to be higher (1.0 versus .7 ng/ml) in cows fed dried brewers grains. At 15 wk, both insulin and somatotropin response areas tended to be smaller for cows fed dried brewers grains, and shape of insulin response curves differed between protein sources. Of the observed hormonal responses to diet, only 6-wk plasma somatotropin was associated with differences in production parameters. Somatotropin secretion during early lactation appears to respond to prepartum changes in the energy status.