Acute metabolic responses of postpartal dairy cows to subcutaneous glucagon injections, oral glycerol, or both

This study examined the effects of multiple subcutaneous glucagon injections with or without co-administration of oral glycerol on energy status-related blood metabolites and hormones of Holstein dairy cows in the first 2 wk postpartum. Twenty multiparous cows were fed a dry cow ration supplemented with 6 kg of cracked corn during the dry period to increase the likelihood of developing postpartal fatty liver syndrome. Cows with a body condition score of ≥3.5 points (1- to 5-point scale) were assigned randomly to 1 of 4 treatment groups: saline, glucagon, glycerol, or glucagon plus glycerol. Following treatment, serial blood samples were collected over an 8-h period to determine the effects of glucagon and glycerol on blood metabolites and hormones. Treatment effects were determined by comparing the concentrations of metabolites and hormones during the first 4-h period and the entire 8-h period after treatment administration (time 0) with the concentration of the same compounds at time 0 on d 1, 7, and 13 postpartum. Administration of glucagon alone increased concentrations of plasma glucagon and insulin on d 1, 7, and 13 and increased plasma glucose and decreased plasma nonesterified fatty acids (NEFA) on d 7 and 13 postpartum relative to the saline group. Administration of glycerol alone increased plasma glucose on d 7 and plasma triacylglycerols on d 1 postpartum. Glycerol administration also decreased plasma glucagon and NEFA on d 1, 7, and 13 and plasma β-hydroxybutyrate (BHBA) on d 1 postpartum relative to the saline group. Administration of glucagon plus glycerol increased and sustained concentrations of plasma glucagon, glucose, and insulin on d 1, 7, and 13 and decreased plasma NEFA on d 1, 7, and 13 and BHBA on d 1 and 7. Early postpartal treatment of dairy cows with glucagon plus glycerol increased plasma glucose and insulin, decreased plasma NEFA and BHBA, and increased secretion of liver NEFA as plasma triacylglycerols. This suggests that glucagon and glycerol, when co-administered, act to decrease the likelihood of metabolism-related syndrome development in dairy cows.     

Prevention of fatty liver in transition dairy cows by subcutaneous injections of glucagon

The main objective of this study was to test the extent to which injecting glucagon subcutaneously for 14 d beginning at d 2 postpartum would prevent fatty liver development in transition dairy cows. Twenty-four multiparous Holstein cows were fed 6 kg of cracked corn in addition to their standard diet during the last 30 d of a dry period to induce postpartum development of fatty liver. Glucagon at either 7.5 or 15 mg/d or saline (control) was injected subcutaneously 3 times daily for 14 d beginning at d 2 postpartum. Glucagon at 15 mg/d prevented liver triacylglycerol accumulation in postpartum dairy cows. Glucagon at 7.5 mg/d showed potential for fatty liver prevention. Glucagon increased concentration of plasma glucose and insulin and decreased plasma nonesterified fatty acid concentrations. No effects of glucagon were detected on plasma β-hydroxybutyrate concentrations. Glucagon affected neither feed intake nor milk production. Moreover, milk composition was not altered by glucagon. Milk urea N concentrations decreased, and plasma urea N concentrations tended to decrease during glucagon administration, indicating that glucagon may improve protein use. Liver glycogen concentrations were not affected by glucagon. No significant differences in body condition scores were detected among treatments throughout the study. These results indicate that subcutaneous glucagon injections can prevent fatty liver in transition dairy cows without causing major production and metabolite disturbances.     

Replacing corn with glycerol in diets for transition dairy cows

Expansion of the biofuels industry has increased the availability of glycerol as an alternative feed for dairy cows. The objective of this study was to determine the effects of glycerol on feed intake, milk production, rumen volatile fatty acids, and metabolic parameters in transition dairy cows. Multiparous Holstein cows were fed diets containing either high-moisture corn (n = 11) or glycerol (n = 12) from −28 to +56 d relative to calving. Glycerol was included at 11.5 and 10.8% of the ration dry matter for the pre- and postpartum diets, respectively. Prepartum feed intake was not changed by glycerol feeding (14.9 vs. 14.6 kg/d, control vs. glycerol) nor did postpartum feed intake differ (19.8 vs. 20.7 kg/d, control vs. glycerol). Overall milk yield did not differ (35.8 vs. 37 kg/d, control vs. glycerol) and milk composition, milk urea nitrogen, somatic cells, and energy balance were not different with glycerol feeding. Blood glucose content was decreased in cows fed glycerol during the prepartum period (59.1 vs. 53.4 mg/dL), and β-hydroxybutyrate concentration was increased (0.58 vs. 0.82 mmol/L, control vs. glycerol). Concentrations of blood nonesterified fatty acids did not differ between the treatment groups, and no response to glycerol for blood metabolites during the postpartum period was observed. Total rumen volatile fatty acid concentrations (mmol/L) did not differ between treatments, but proportions of rumen propionate and butyrate were greater for cows fed glycerol (22.7 vs. 28.6% of propionate, control vs. glycerol; and 11.5 vs. 15.3% of butyrate, control vs. glycerol) at the expense of acetate (61.4 vs. 51.5%, control vs. glycerol). These data indicate that glycerol is a suitable replacement for corn grain in diets for transition dairy cows.     

Effects of chromium propionate supplementation during the periparturient period and early lactation on metabolism,performance, and cytological endometritis in dairy cows

Multiparous Holstein cows (n = 61) were used to determine the effects of chromium propionate (Cr-Pro) supplementation during the periparturient period and early lactation on metabolism, performance, and the incidence of cytological endometritis (CE). After a 1-wk preliminary period, cows were assigned randomly to 1 of 2 treatments from 21 d before expected calving through 63 d postpartum: (1) control (n = 31) and (2) Cr-Pro (n = 30) administered by daily topdress at a rate of 8 mg/d of Cr. A tendency was detected for increased dry matter intake (DMI) during the prepartum period for cows fed Cr-Pro. Moreover, cows fed Cr-Pro tended to have lower plasma concentrations of nonesterified fatty acids during the prepartum period. However, effects of Cr-Pro supplementation on postpartum DMI and milk yield were not significant. Cows fed Cr-Pro tended to have higher urea N concentrations in milk. An interaction of treatment and day existed during the postpartum period, such that cows fed Cr-Pro had lower plasma glucose concentrations within the first day postpartum compared with controls. Plasma haptoglobin concentration was not affected by treatment during the postpartum period. Blood neutrophil glycogen concentrations were not affected by treatment when sampled at either 7 d postpartum or on one day between 40 and 60 d (48 d ± 0.44 standard error) postpartum. Evaluation of endometrial cytology by low volume lavage at 7 d postpartum (first lavage) and on one day between 40 and 60 d (second lavage) postpartum revealed that cows fed Cr-Pro tended to have a higher percentage of neutrophils at first lavage and decreased incidence of CE as assessed at second lavage. In conclusion, supplementation with Cr-Pro resulted in trends for increased DMI and lower plasma nonesterified fatty acids prepartum. Postpartum production and energy metabolism were not affected by treatment; however, Cr-Pro supplementation tended to affect the postpartum influx of neutrophils into the uterus and decreased the incidence of CE, suggesting positive effects of Cr-Pro supplementation on uterine health.     

Potential treatment of fatty liver with 14-day subcutaneous injections of glucagon

Fatty liver is a major metabolic disease of dairy cows in early lactation that can be treated with 14-d continuous, intravenous infusions of 10 mg/d of glucagon. The objective was to test whether similar effects can be obtained with 14-d subcutaneous 7.5- or 15-mg daily dosages of glucagon beginning at d 8 postpartum. Multiparous Holstein cows (n = 32) were grouped on the basis of their liver triacylglycerol concentration at d 8 postpartum into "normal" (n = 8; triacylglycerol < 1% liver wet wt) and "susceptible" (n = 24; triacylglycerol > 1% liver wet wt) cows. Susceptible cows were assigned randomly to three groups and beginning at d 8 postpartum received 0, 2.5, or 5 mg of glucagon in 60 ml of saline by subcutaneous injections every 8 h for 14 d. Beginning at d 8 postpartum, normal cows received 60 ml of saline by subcutaneous injections every 8 h for 14 d. Both dosages of glucagon increased concentrations of plasma glucose and insulin and decreased concentrations of plasma nonesterfied fatty acids. Glucagon injections of 15 mg/d decreased concentrations of liver triacylglycerol in cows older than 3.5 yr, but not in younger multiparous cows. Our results document that subcutaneous injections of glucagon have the potential to decrease the degree of fatty liver in older dairy cows in early lactation.     

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 1,000 g 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.     

Prepartum 2,4-thiazolidinedione alters metabolic dynamics and dry matter intake of dairy cows

Thiazolidinediones (TZD) are potent, synthetic ligands for peroxisome proliferator activated receptor-gamma (PPAR-γ) that reduce plasma nonesterified fatty acids (NEFA) and potentiate the action of insulin in peripheral tissues of several species. Holstein cows (n = 9) entering their second or greater lactation were used to determine whether late prepartum administration of TZD would affect periparturient metabolism and milk production. Cows were limit-fed a total mixed ration (TMR) during the prepartum period to provide no more than 130% of predicted energy requirements. During the postpartum period cows were fed a common TMR for ad libitum intake. Cows were administered either 2,4-TZD (4.0 mg/kg of body weight) or saline (control) by intrajugular infusion once daily from 25 d before expected parturition until parturition. Plasma samples were collected daily from 26 d before expected parturition through 7 d postpartum. Plasma NEFA concentrations decreased during the prepartum period (d −21 to −1; 70 vs. 83 ± 4 μEq/L) and tended to be decreased during the peripartum period (d −7 to d +7; 113 vs. 205 ± 32 μEq/L) due to prepartum TZD administration. Plasma concentrations of glucose were not affected by treatment; however, plasma β-hydroxybutyrate concentrations decreased in TZD-treated cows (8.6 vs. 10.7 ± 1.7 mg/dL) as parturition approached, and plasma insulin concentrations increased during the peripartum period (0.65 vs. 0.38 ± 0.07 ng/mL). Postpartum liver triglyceride and glycogen content was not affected by treatment. Prepartum TZD administration tended to increase dry matter intake during the peripartum and postpartum periods (16.6 vs. 14.6 ± 0.8 kg/d and 20.0 vs. 17.2 ± 1.2 kg/d, respectively). Milk yield for the first 30 d postpartum and milk composition measured on d 8 postpartum were not affected by treatment. There was no effect of prepartum TZD administration on insulin-dependent glucose utilization assessed using insulin challenge during either the prepartum or postpartum periods. These results suggest that administration of TZD during the late prepartum period has the potential to improve metabolic health and DMI of periparturient dairy cows and warrants further investigation.     

Short communication: insulin alters hepatic progesterone catabolic enzymes cytochrome P450 2C and 3A in dairy cows

High proportions of embryonic and early fetal losses in dairy cattle are associated with low peripheral concentrations of progesterone, which could result from increased catabolism, decreased production, or both. Progesterone catabolism occurs primarily in the liver via the cytochrome P450 2C (CYP2C) and cytochrome P450 3A (CYP3A) subfamilies (EC 1.14.14.1; unspecific monooxygenases). Recent observations from our laboratory have shown that the fractional rate constant of progesterone decay can be dramatically reduced by insulin because of a decrease in hepatic CYP2C and CYP3A activity. Little information exists on the regulation of progesterone catabolic enzymes in dairy cows. We hypothesized that elevated insulin concentrations would down-regulate hepatic CYP2C and CYP3A mRNA; therefore, our objectives were to determine the relative abundance of hepatic CYP2C and CYP3A mRNA in dairy cows in response to elevated concentrations of insulin. In the first experiment, 17 mature Holstein cows were drenched daily with 500 mL of water (n = 10) or propylene glycol (a gluconeogenic substrate; n = 7) from 10 d before their expected calving date until d 25 postpartum. Cows drenched with propylene glycol had a 30% increase in peripheral concentrations of insulin. Liver biopsies were collected on d 25 postpartum to determine the relative abundance of CYP2C and CYP3A mRNA. In the second experiment, 19 mature, lactating Holstein cows were randomly assigned to a hyperinsulinemic-euglycemic clamp (0.3 or 1.0 μg of insulin/kg of BW per h; n = 6 each) or remained as controls (saline infused; n = 7) for 96 h beginning on d 10 postpartum. Insulin infusion resulted in a 2.6- or 8- fold increase in peripheral concentrations of insulin, respectively. On d 14 postpartum, a liver biopsy was collected to determine CYP2C and CYP3A mRNA abundance. In experiment 1, the relative abundance of CYP2C mRNA in cows treated with propylene glycol did not differ from controls; however, the relative abundance of CYP3A mRNA in the propylene glycol group was 63% that of controls. For experiment 2, there was a dose-dependent decrease in the relative abundance of both CYP2C and CYP3A mRNA with increasing dosage of insulin. In conclusion, this study demonstrated that, in the cow, either providing a gluconeogenic feed-stuff or treatment with insulin decreased the abundance of mRNA for enzymes responsible for hepatic progesterone catabolism.     

Relationships between endometritis and metabolic state during the transition period in pasture-grazed dairy cows

The primary objective of this study was to identify relationships between endometritis and metabolic state during the calving transition and early lactation periods. A subset of mixed age and breed dairy cows (n = 78) from a seasonal, pasture-grazed herd of 389 cows was examined. The selected cows were grouped as having endometritis at d 42 postpartum or being unaffected by endometritis. Endometritis was defined as >6% (upper quartile) of uterine nucleated cells being polymorphonuclear cells (H-PMN; n = 38); unaffected by endometritis was defined as ≤1% of nucleated cells being polymorphonuclear (L-PMN; n = 40). Milk yield was determined at each milking, and milk composition (fat and protein) was determined at 2-wk intervals. Blood samples collected on d −14, 0 (d of calving), 4, 7, 14, 28, and 42 were analyzed for indicators of energy status (nonesterified fatty acids, glucose, and urea), liver function (albumin, globulin, glutamate dehydrogenase, and aspartate aminotransferase), inflammation (haptoglobin), and mineral status (Ca and Mg). Samples collected weekly from d 21 to 63 or 70 were analyzed for progesterone content. The postpartum anovulatory interval was defined to end on the first day postpartum that plasma progesterone concentration was ≥1 ng/mL. A greater percentage of H-PMN cows failed to ovulate before d 63 or 70 (34%) compared with L-PMN cows (10%), although the proportions of cows ovulating within either polymorphonuclear group was similar through d 56 postpartum. Plasma concentrations of albumin and the albumin:globulin ratio were consistently lower in H-PMN cows. Plasma Mg was lower, whereas glutamate dehydrogenase and aspartate aminotransferase were higher, in H-PMN cows during early lactation compared with L-PMN cows. Circulating metabolites indicative of energy status (nonesterified fatty acids, glucose, and urea) were not different between polymorphonuclear groups. Among 3- to 5-yr-old cows, daily milk yield for the first 42 d after calving was lower for H-PMN cows than for L-PMN cows. Among cows >5 yr old, protein percentage was lower in H-PMN cows compared with L-PMN cows. In summary, endometritis at 42 d postpartum in the herd studied was associated with an increased likelihood of remaining anovulatory. These cows had lower albumin concentrations throughout the calving transition period, perhaps indicating impaired liver function, with lower plasma Mg and evidence of hepatocellular damage in early lactation. Similar profiles of nonesterified fatty acids and glucose indicated that energy status was not a risk factor for endometritis.     

Subclinical hypocalcemia,plasma biochemical parameters,lipid metabolism,postpartum disease,and fertility in postparturient dairy cows

A study was conducted to evaluate the potential association between Ca status at calving and postpartum energy balance, liver lipid infiltration, disease occurrence, milk yield and quality parameters, and fertility in Holstein cows. One hundred cows were assigned to 1 of 2 groups based on whole-blood ionized Ca concentration ([iCa]) on the day of calving [d 0; hypocalcemic [iCa] <1.0 mmol/L (n = 51); normocalcemic [iCa] ≥1.0 mmol/L (n = 49)]. Cows were blocked based on calving date and parity. Blood samples were collected approximately 14 d from expected calving date (d −14), the day of calving (d 0), and on d 3, 7, 14, 21, and 35 postpartum for measurement of plasma nonesterified fatty acid, iCa, total Ca, glucose, and total and direct bilirubin concentrations, and plasma aspartate aminotransferase and gamma glutamyl transferase activities. Liver biopsies were obtained from a subset of cows on d 0, 7, and 35 for quantification of lipid content. Milk samples were collected on d 3, 7, 14, 21, and 35 postpartum for measurement of somatic cell count and percentages of protein, fat, and solids-not-fat. Data for peak test-day milk yield, services per conception, and days open were obtained from Dairy Herd Improvement Association herd records. Disease occurrence was determined based on herd treatment records. Hypocalcemic cows had significantly higher nonesterified fatty acids on d 0. Hypocalcemic cows also had significantly more lipid in hepatocytes on d 7 and 35 postpartum. However, no statistically significant differences were observed between groups for plasma aspartate aminotransferase and gamma glutamyl transferase activities or total and direct bilirubin concentrations. Milk protein percentage was lower in hypocalcemic cows on d 21 and 35. However other milk quality variables (somatic cell count, milk fat percentage, and solids-not-fat) and milk yield variables (peak test-day milk yield and 305-d mature-equivalent 4% fat-corrected milk yield) did not differ between groups. No differences were observed between groups in the occurrence of clinical mastitis, ketosis, displaced abomasum, dystocia, retained placenta, metritis, or fertility measures (percentage cycling at 50–60 d postpartum, services per conception, or days open). These data suggest that early lactation fatty acid metabolism differs between cows with subclinical hypocalcemia and their normocalcemic counterparts.     

Energy balance, metabolic status, and the first postpartum ovarian follicle wave in cows administered propylene glycol

Mature Holstein cows were drenched daily with either 500 mL of water (control; n = 28) or propylene glycol (PPG; n = 28) from d 10 before parturition until d 25 postpartum. Follicular development was monitored thrice weekly by transrectal ultrasound. Blood samples were collected every 30 min from a subset of 10 cows per treatment on d −10, 2, and 25 to assess glucose and insulin response to treatments, and on d 10 postpartum, blood was collected every 10 min for 12 h to determine LH pulse profiles. Both insulin and glucose were elevated on d 2 and 25 following PPG administration, but only insulin was elevated on d −10. On d 10 postpartum, the number of LH pulses, mean LH, and pulse amplitude were not different between control and PPG cows. The proportion of first postpartum dominant follicles that became ovulatory, atretic, or cystic was not different between control and PPG cows. Despite evidence of improved metabolic status, PPG failed to increase LH pulse frequency, and failed to increase the proportion of first postpartum follicle waves resulting in ovulation. The dominant follicle of each cow was retrospectively categorized as being ovulatory (n = 17), nonovulatory high estradiol (n = 6), nonovulatory low estradiol (n = 24), or cystic (n = 8). Differences in dry matter intake and energy balance among cows in the different follicle categories were apparent as early as 3 wk before parturition. The nonovulatory low estradiol cows had lower pre- and postpartum dry matter intake and energy balance compared with ovulatory cows. The nonovulatory low estradiol cows also had postpartum metabolic hormone and metabolite profiles indicative of more severe negative energy balance.     

Metabolism of dairy cows as affected by prepartum dietary carbohydrate source and supplementation with chromium throughout the periparturient period

Holstein cows (n = 72) entering second or later lactation were used to determine whether metabolic indices and hepatic capacities for oxidation and gluconeogenesis from propionate are affected by source of carbohydrate in the prepartum diet and chromium-l-methionine (Cr-Met) supplementation throughout the periparturient period. Cows were fed prepartum diets as total mixed rations with the concentrate portion based either on starch-based cereals [high nonfiber carbohydrate (NFC); 1.59 Mcal/kg of net energy for lactation (NE_L), 14.4% crude protein (CP), 40.3% NFC] or nonforage fiber sources (low NFC; 1.54 Mcal/kg of NE_L, 14.5% CP, 33.6% NFC) from 21 d before expected parturition until parturition. After parturition all cows were fed a common lactation total mixed ration (1.74 Mcal/kg of NE_L, 16.5% CP, 40.0% NFC). The Cr-Met was supplemented once daily via gelatin capsule at dosages of 0, 0.03, or 0.06 mg of Cr/kg of BW^0.75. Thus, treatments were in a 2 (carbohydrate source) × 3 (Cr-Met) factorial arrangement. There was no effect of prepartum carbohydrate source on pre- and postpartum plasma concentrations of glucose, nonesterified fatty acids (NEFA), β-hydroxybutyrate (BHBA), insulin, glucagon, or insulin to glucagon ratio. However, cows fed the low NFC diet during the prepartum period tended to have greater plasma NEFA and lower BHBA concentrations postpartum. Liver glycogen concentrations tended to be greater on d 1 postpartum for cows fed low NFC prepartum. Supplementing 0.03 mg/kg of BW^0.75 of Cr as Cr-Met increased prepartum plasma glucose and glucagon concentrations and tended to decrease prepartum plasma NEFA concentrations compared with either 0 or 0.06 mg of Cr/kg of BW^0.75. Postpartum plasma glucose concentrations decreased linearly and glucagon concentrations were increased quadratically by administering increasing amounts of Cr-Met. Supplementing Cr-Met did not affect prepartum plasma concentrations of insulin or BHBA, postpartum NEFA or BHBA, or liver composition. There was an interaction of prepartum carbohydrate source and Cr-Met supplementation such that in vitro hepatic conversion of [1-¹⁴C]propionate to both CO₂ and glucose was similar or increased when Cr-Met was supplemented to cows fed the low NFC diet but decreased when Cr-Met was supplemented to cows fed the high NFC diet. Insulin addition in vitro did not affect hepatic metabolism of propionate on d 1 postpartum. Overall, both the NFC content of the prepartum diet and Cr-Met had only modest effects on metabolic indices in this experiment.     

Effects of short-term glucagon administration on gluconeogenic enzymes in the liver of midlactation dairy cows

During lactation, the dairy cow experiences an increased demand for glucose to support milk production. Increased glucose demand can be met through increased capacity for gluconeogenesis, increased supply of glucose precursors, or a combination of both processes. Glucagon, a key hormone in glucose homeostasis, acts to promote gluconeogenesis and increase glucose output from liver. The objective of this study was to determine the effect of short-term administration of glucagon on expression of gluconeogenic enzymes in lactating dairy cattle. Sixteen multiparous Holstein cows were selected from the Purdue University Animal Sciences Dairy Research Center herd. Cows were stratified on the basis of milk production and days in milk and randomly assigned to either a saline or glucagon injection group (n = 8 per group). Cows were injected subcutaneously at −21, −14, −7, and 0 h relative to final glucagon and saline injections with either 3.75 mg of lyophilized bovine glucagon (15 mg/d) dissolved in 60 mL of 0.15 M NaCl (pH 10.25) or 60 mL of 0.15 M NaCl. Liver biopsy samples were obtained 1 wk before injection to establish baseline values and at 3 h after cows received final glucagon and saline injections. Biopsy samples were analyzed for mRNA abundance, enzyme activity, protein abundance, and in vitro measures of gluconeogenesis. Glucagon did not alter pyruvate carboxylase or cytosolic phosphoenolpyruvate carboxykinase (PEPCK) mRNA abundance, enzyme activity, or protein abundance, although there was a tendency for greater mRNA expression with the glucagon treatment (4.69 vs. 6.78, arbitrary units). Glucagon injections did not change mitochondrial PEPCK mRNA expression. Gluconeogenesis from 2.5 mM [2-¹⁴C]propionate and 2.0 mM [U-¹⁴C]lactate was similar in liver biopsy samples from glucagon-treated and control cows. There was no effect of glucagon on dry matter intake and milk production. Glucose, nonesterified fatty acids, β-hydroxybutyrate acid, and insulin were not altered by glucagon. Blood glucagon was elevated, 76.09 vs. 96.14 pg/mL, for cows receiving glucagon injections. The data indicate that 24-h administration of glucagon does not alter cytosolic PEPCK mRNA expression or result in immediate alterations in total PEPCK enzyme activity and gluconeogenic capacity.     

Effects of dietary alpha-amylase on metabolism and performance of transition dairy cows

Twenty-four multiparous Holstein cows [body weight, 759 kg (SD = 30 kg); body condition score, 3.2 (SD = 0.13)] were used in a randomized complete block design to determine the effect of feeding α-amylase during the transition period on rumen fermentation, key metabolic indicators, and lactation performance. Cows were assigned to either a control diet or the control diet supplemented with α-amylase (662 fungal amylase units per gram, AMA) at 0.1% of diet dry matter (DM). Experimental diets were fed from 21 d before expected calving through 21 d in milk. From 22 to 70 d in milk, all cows were fed a similar lactation cow diet. Average pre- and postpartum DM intakes were 12.4 and 17.8 kg/d, respectively, and did not differ between treatments; however, DM intakes during the last week prepartum decreased to a greater degree in AMA than control cows compared with wk −2. Supplementing diets with α-amylase tended to increase proportions of ruminal butyrate prepartum but not postpartum. Treatment differences were not detected for concentrations of insulin in plasma and lipid and glycogen in liver tissue. Prepartum, concentrations of β-hydroxybutyrate and nonesterified fatty acids were increased in cows fed AMA compared with the control diet. Postpartum, concentrations of glucose in plasma tended to be increased by feeding AMA. Increased plasma β-hydroxybutyrate and nonesterified fatty acids pre- but not postpartum and a tendency for increased plasma glucose postpartum demonstrate shifting reliance from lipid- to carbohydrate-based metabolism postpartum in cows fed α-amylase.     

Effects of prepartum 2,4-thiazolidinedione on insulin sensitivity, plasma concentrations of tumor necrosis factor-α and leptin, and adipose tissue gene expression

Administration of peroxisome proliferator-activated receptor gamma (PPARγ) ligands, thiazolidinediones (TZD), to prepartum dairy cattle has been shown to improve dry matter intake and decrease circulating nonesterified fatty acids (NEFA) around the time of calving. The objective of this work was to elucidate mechanisms of TZD action in transition dairy cattle by investigating changes in plasma leptin, tumor necrosis factor-α (TNFα), the revised quantitative insulin sensitivity check index (RQUICKI), and adipose tissue gene expression of leptin, PPARγ, lipoprotein lipase (LPL), and fatty acid synthase (FAS). Multiparous Holstein cows (n = 40) were administered 0, 2.0, or 4.0 mg of TZD/kg of body weight (BW) by intrajugular infusion once daily from 21 d before expected parturition until parturition. Plasma samples collected daily from 22 d before expected parturition through 21 d postpartum were analyzed for glucose, NEFA, and insulin. Plasma samples collected on d −14, −3, −1, 1, 3, 7, 14, and 49 relative to parturition were also analyzed for leptin and TNFα. Adipose tissue was collected on d 7 before expected parturition from a subset of cows, and gene expression was examined via quantitative real-time PCR. A tendency for a treatment by time effect on plasma leptin prepartum was observed such that values were similar on d −14 but cows receiving 2.0 mg/kg of BW of TZD tended to have lower circulating leptin as calving approached. Postpartum leptin tended to be increased linearly (2.3, 2.4, and 2.5 ± 0.1 ng/mL for 0, 2.0, and 4.0 mg/kg treatments, respectively) in cows that received TZD prepartum. Plasma TNFα increased linearly (2.6, 3.7, and 4.0 ± 0.1 pg/mL) in response to TZD treatment and decreased through the first week postpartum. Calculation of RQUICKI 1/[log(glucose) + log(insulin) + log(NEFA)] suggested altered insulin sensitivity in cows administered TZD that may depend on day relative to calving. Administration of TZD increased adipose tissue expression of PPARγ mRNA (11.0, 13.3, and 12.8 ± 1.9). Administration of TZD had a quadratic effect on gene expression of leptin (16.2, 10.7, and 17.4 ± 1.6) and no effect on LPL expression, and expression of FAS was lower for TZD-treated cows than for controls (8.2, 4.2, and 6.1 ± 1.8, respectively). Results imply altered expression and plasma concentrations of leptin, increased plasma TNFα concentrations, and increased expression of PPARγ in adipose tissue as potential mechanisms for the effects of TZD administration on transition dairy cattle.     

Effects of exogenous glucagon on lipids in lipoproteins and liver of lactating dairy cows

Decreased concentrations of phospholipids, free cholesterol, and cholesteryl ester in plasma and liver are associated with fatty liver, a major metabolic disease of dairy cows in early lactation. The objective was to test whether daily subcutaneous injections of 7.5 and 15 mg of glucagon, which can decrease concentrations of liver triacylglycerol, affect concentrations of plasma lipoprotein components and liver lipids other than triacylglycerol. Multiparous Holstein cows (n = 32) were grouped on the basis of liver triacylglycerol concentrations at d 8 postpartum into "normal" (n = 8; triacylglycerol <1% liver wet wt) and "susceptible to fatty liver" (n = 24; triacylglycerol >1% liver wet wt) cows. Susceptible cows were assigned randomly to three groups and beginning at d 8 postpartum received 0 (same for Normal cows), 2.5, or 5 mg of glucagon by subcutaneous injections every 8 h for 14 d. In comparison to saline injections, subcutaneous injections of glucagon either increased or tended to increase concentrations of phospholipids and free cholesterol in liver, with greater increases of the latter during ambient temperatures below 35 degrees C. Glucagon injections decreased or tended to decrease concentrations of very low-density lipoprotein-triacylglycerol, high-density lipoprotein1-phospholipids, and high-density lipoprotein2-free cholesterol in plasma, with no changes of the latter two during ambient temperatures below 35 degrees C. The results indicate that subcutaneously administered glucagon has only minor effects on the lipid transport in plasma of dairy cows in early lactation with more beneficial effects occurring during ambient temperatures below 35 degrees C and, most importantly, no indications that glucagon has negative effects.     

Hyperketonemia during lipopolysaccharide-induced mastitis affects systemic and local intramammary metabolism in dairy cows

Hyperketonemia interferes with the metabolic regulation in dairy cows. It is assumed that metabolic and endocrine changes during hyperketonemia also affect metabolic adaptations during inflammatory processes. We therefore studied systemic and local intramammary effects of elevated plasma β-hydroxybutyrate (BHBA) before and during the response to an intramammary lipopolysaccharide (LPS) challenge. Thirteen dairy cows received intravenously either a Na-dl-β-OH-butyrate infusion (n = 5) to achieve a constant plasma BHBA concentration (1.7 ± 0.1 mmol/L), with adjustments of the infusion rates made based on immediate measurements of plasma BHBA every 15 min, or an infusion with a 0.9% NaCl solution (control; n = 8) for 56 h. Infusions started at 0900 h on d 1 and continued until 1700 h 2 d later. Two udder quarters were challenged with 200 μg of Escherichia coli LPS and 2 udder quarters were treated with 0.9% saline solution as control quarters at 48 h after the start of infusion. Blood samples were taken at 1 wk and 2 h before the start of infusions as reference samples and hourly during the infusion. Mammary gland biopsies were taken 1 wk before, and 48 and 56 h (8 h after LPS challenge) after the start of infusions. The mRNA abundance of key factors related to BHBA and fatty acid metabolism, and glucose transporters was determined in mammary tissue biopsies. Blood samples were analyzed for plasma glucose, BHBA, nonesterified fatty acid, urea, insulin, glucagon, and cortisol concentrations. Differences were not different for effects of BHBA infusion on the mRNA abundance of any of the measured target genes in the mammary gland before LPS challenge. Intramammary LPS challenge increased plasma glucose, cortisol, glucagon, and insulin concentrations in both groups but increases in plasma glucose and glucagon concentration were less pronounced in the Na-dl-β-OH-butyrate infusion group than in controls. In response to LPS challenge, plasma BHBA concentration decreased in controls and decreased also slightly in the BHBA-infused animals because the BHBA concentration could not be fully maintained despite a rapid increase in BHBA infusion rate. The change in mRNA abundance of citrate synthase in LPS quarters was significant between the 2 treatment groups. The results indicate that elevated circulating BHBA concentration inhibits gluconeogenesis before and during immune response to LPS challenge, likely because BHBA can replace glucose as an energy source.     

Glucagon increases hepatic mRNA concentrations of ureagenic and gluconeogenic enzymes in early-lactation dairy cows

Exogenous glucagon increases hepatic glucose synthesis in part by increasing hepatic extraction of amino acids from blood for conversion to glucose. To examine the role of glucagon in orchestrating gene expression of gluconeogenic and ureagenic enzymes, we determined the mRNA concentrations of key hepatic ureagenic and gluconeogenic enzymes at d 11, 15, and 22 postpartum in multiparous Holstein cows that received 0 or 5 mg of glucagon in 60 mL of saline by subcutaneous injection every 8 h for 14 d starting on d 8 postpartum. On d 11 postpartum, glucagon increased the hepatic mRNA concentrations for all measured ureagenic enzymes (carbamoylphosphate synthetase I, ornithine transcarbamylase, and argininosuccinate synthetase) and gluconeogenic enzymes (pyruvate carboxylase and cytosolic and mitochondrial forms of phosphoenolpyruvate carboxykinase) and increased or tended to increase mRNA concentrations of gluconeogenic enzymes on d 15 postpartum but not on d 22. The effect of glucagon to increase mRNA concentrations of ureagenic and gluconeogenic enzymes was limited to times when concentrations of plasma insulin were not increased. Our results suggest that hepatic gene expression of key ureagenic and gluconeogenic enzymes in early-lactation dairy cows is responsive to hormonal regulation by glucagon.     

Performance and metabolic and endocrine changes with emphasis on glucose metabolism in high-yielding dairy cows with high and low fat content in liver after calving

Elevated liver fat content occurs in high-yielding dairy cows during the transition from pregnancy to lactation after fat mobilization and may affect hepatic glucose metabolism, but the degree of liver fat storage is highly variable. Therefore, we studied metabolic and endocrine changes and hepatic glucose metabolism in cows that markedly differ in liver fat content. Multiparous cows from the same herd with high (HFL; n = 10) and low (LFL; n = 10) liver fat contents (mean of d 1, 10, and 21 after calving for each cow, respectively) were studied from 60 d before expected calving to 56 d in milk. Cows were fed ad libitum and all cows received the same diets. Liver samples were taken on d 1, 10, and 21 after calving; mean fat content (±SEM) in liver of HFL cows was 174 ± 9.6 mg/g, whereas mean liver fat content in LFL cows was 77 ± 3.3 mg/g. Blood samples were taken 20 and 7 d before expected calving and 0, 7, 14, 28, and 56 d after calving to measure plasma concentrations of nonesterified fatty acids, β-hydroxybutyrate, glucose, insulin, glucagon, insulin-like growth factor-I, and leptin. In liver, glycogen content as well as mRNA levels of phosphoenolpyruvate carboxykinase, pyruvate carboxylase, glucose-6-phosphatase, and glucose transporter were measured by quantitative real-time PCR. Back fat thickness decreased and dry matter intake increased with onset of lactation, and back fat thickness was higher but dry matter intake was lower in HFL than in LFL. Energy-corrected milk yield did not differ between groups, but milk fat content was higher and lactose content was lower in HFL than LFL at the beginning of lactation. Energy balance was more negative in HFL than in LFL. Plasma nonesterified fatty acids and β-hydroxybutyrate concentrations increased and plasma glucose concentration tended to decrease more in HFL than LFL with onset of lactation. Glucagon to insulin ratios increased more in HFL than LFL with onset of lactation. Hepatic glycogen content was higher in LFL than HFL, whereas mRNA levels of glucose-6-phosphatase and pyruvate carboxylase were higher in HFL than in LFL, and cytosolic phosphoenolpyruvate carboxykinase mRNA level increased similarly after parturition in both groups. In conclusion, an elevated liver fat content was related to greater fat mobilization and reduced feed intake and was associated with effects on hepatic glucose metabolism. As environment and feeding management were the same, individual cow factors were responsible for differences in energy metabolism during the transition period.