Identification of promoter response elements that mediate propionate induction of bovine cytosolic phosphoenolpyruvate carboxykinase (PCK1) gene transcription

Cytosolic phosphoenolpyruvate carboxykinase (PCK1) is a key enzyme for gluconeogenesis that is positively regulated by propionate in bovines at the transcription level. The specific elements that determine propionate responsiveness within the bovine PCK1 promoter are unknown. In silico promoter analysis of the bovine PCK1 gene revealed several clusters of transcription factor binding sites. In the present study, we determined the essentiality of the putative cyclic AMP response element (CRE) at -94 through -87 bp and the 2 putative hepatic nuclear factor 4α (HNF4α) binding elements at +68 through +72 and -1,078 through -1,074, respectively, in mediating bovine PCK1 promoter responses to propionate and other regulators, including butyrate, cyclic AMP (cAMP), and glucocorticoids. The wild-type bovine PCK1 promoter [PCK1_(WT)] was ligated to a luciferase reporter gene and transfected into rat hepatoma (H4IIE) cells. Activities of PCK1_(WT) were induced by approximately 2-, 2-, 4-, 8-, 9-, 18-, and 16-fold respectively when exposed to cAMP (as 1.0 mM 8-Br-cAMP), 5.0 μM dexamethasone, cAMP + dexamethasone, 2.5 mM propionate, cAMP + propionate, cAMP + dexamethasone + propionate, and 2.5 mM butyrate. Seven mutants lacking either one single site, 2 of the 3 sites, or all 3 sites, generated by site-directed mutagenesis, were tested. Responses to propionate and all other treatments were completely abolished when CRE at -94 through -87 bp and HNF4α at +68 through +72 bp were both deleted. Our data indicate that these 2 regulatory elements act synergistically to mediate the bovine PCK1 promoter responses to propionate as well as butyrate, cAMP, and dexamethasone. The activation of PCK1 through these regulatory elements serves to activate the metabolic potential of bovine toward gluconeogenesis when the primary substrate for gluconeogenesis, propionate, is also present.

Postruminal protein supply upregulates hepatic lysine oxidation and ornithine transcarbamoylase in lactating dairy cattle

Metabolizable protein supply is a limiting factor for milk production in dairy cows, and the availability of AA is a function of the quantity of the metabolizable protein available and of hepatic AA catabolism. This study aimed to evaluate the effect of postruminal protein infusion on key genes for ureagenesis and AA catabolism. Six multiparous Holstein cows in early lactation were used in a replicated crossover design. Cows were fed a TMR and infused postruminally with either 0 or 600 g/d of milk protein isolate. Periods were 21 d long, consisting of 14 d of adjustment to surroundings, followed by 7 d of protein infusion. On the last day of each infusion, liver samples were collected for mRNA analysis and explant culture, milk samples were collected for mRNA analysis, and blood samples were collected for plasma metabolite analysis. Postruminal infusion of protein increased milk yield by 10.5%, milk fat yield by 12.5%, milk protein yield by 20%, milk lactose yield by 11%, and total solids yield by 15.5%. Postruminal infusion of protein increased milk urea N by 23.5%, blood urea N by 18.6%, and the abundance of hepatic ornithine transcarbamoylase mRNA by 52.8%. Postruminal infusion of protein did not alter the mRNA abundance of hepatic argininosuccinate synthase, α-aminoadipate semialdehyde synthase, cysteine sulfinic acid decarboxylase, or cystathionase. The abundance of RNA for milk proteins was unchanged with postruminal protein infusion. Metabolism of l-[U ¹⁴C] Lys to CO₂ was increased by 127% (0.143 vs. 0.063 ± 0.04 nmol product·mg tissue^-1·h^-1), and the metabolism of l-[U ¹⁴C] Ala to CO₂ increased by 40.5% (0.52 vs. 0.37 ± 0.06 nmol product·mg tissue^-1·h^-1) with postruminal protein infusion. The rate of l-[1-¹⁴C] Met oxidation did not differ. These data indicate increased ureagenesis matched by upregulation of nonessential AA catabolism and a disproportional increase in Lys oxidation in response to increased postruminal protein infusion.

Mammary transcriptome reveals cell maintenance and protein turnover support milk synthesis in early-lactation cows

A more complete understanding of the molecular mechanisms that support milk synthesis is needed to develop strategies to efficiently and sustainably meet the growing global demand for dairy products. With the postulate that coding gene transcript abundance reflects relative importance in supporting milk synthesis, we analyzed the global transcriptome of early lactation cows across magnitudes of normalized RNA-Seq read counts. Total RNA was isolated from milk samples collected from early-lactation cows (n = 6) following two treatment periods of postruminal lysine infusion of 0 or 63 g/day. Twelve libraries were prepared and sequenced on an Illumina NovaSeq6000 platform using paired end reads. Normalized read counts were averaged across both treatments, because EBseq analysis found no significant effect of lysine infusion. Approximately 10% of the total reads corresponded to 12,730 protein coding transcripts with a normalized read count mean ≥5. For functional annotation analysis, the protein coding transcripts were divided into nine categories by magnitude of reads. The 13 most abundant transcripts (≥50K reads) accounted for 67% of the 23M coding reads and included casein and whey proteins, regulators of fat synthesis and secretion, a ubiquitinating protein, and a tRNA transporter. Mammalian target of rapamycin, JAK/STAT, peroxisome proliferator-activated receptor alpha, and ubiquitin proteasome pathways were enriched with normalized reads ≥100 counts. Genes with ≤100 reads regulated tissue homeostasis and immune response. Enrichment in ontologies that reflect maintenance of translation, protein turnover, and amino acid recycling indicated that proteostatic mechanisms are central to supporting mammary function and primary milk component synthesis.

Short communication: Effect of glucose infusion dose and stage of lactation on glucose tolerance test kinetics in lactating dairy cows

The objective for this study was to determine the effect of glucose dose and days following peak milk yield on plasma glucose, serum insulin, and plasma nonesterified fatty acids (NEFA) kinetics during an intravenous glucose tolerance test (IVGTT) in lactating dairy cattle. Six lactating Holstein dairy cows (3 primiparous and 3 multiparous) were assigned to 2 squares and received 0.092, 0.15, or 0.3 g of glucose/kg of body weight (BW) during an IVGTT at 74 and 221 d in milk (DIM), representing early (post-peak) lactation and mid lactation, respectively. Treatments were applied in a replicated Latin square design using contiguous 7-d periods within each stage of lactation. Milk production and dry matter intake were determined daily during the first 6 d of each period. The IVGTT was performed on d 7. For the IVGTT, cows were prepared with indwelling catheters in each jugular vein, and blood samples were collected at -15, -10, 5, 10, 15, 20, 30, 45, 60, 90, and 120 min relative to the glucose infusion. Samples were analyzed for plasma glucose, serum insulin, and plasma NEFA concentrations. Increasing the glucose dose during the IVGTT increased plasma glucose area under the curve (AUC), decreased glucose half-life, and increased maximal plasma glucose concentrations in plasma during the IVGTT. Greater glucose dose during the IVGTT elevated serum insulin AUC and increased nadir NEFA concentrations. Maximal plasma glucose concentration during the IVGTT was lower, whereas maximum NEFA concentration, NEFA AUC, and NEFA clearance rate were greater at 74 than at 221 DIM. Only glucose half-life was responsive to stage of lactation × glucose dose effects during the IVGTT, and the decrease in glucose half-life with increasing glucose dose was greater at 74 than at 221 DIM. Glucose AUC was greater and NEFA AUC lower for cows at 74 than at 221 DIM. For the doses tested, a glucose dose greater than 0.092 g/kg of BW resulted in peak blood glucose concentration that exceeded the previously reported renal glucose excretion threshold of 8.3 mM. There is a need for accompanying data to determine if this is the case for the glucose doses evaluated in this experiment. Based on maximal peak glucose concentrations and effects on glucose half-life, we identify 0.092 g of glucose/kg of BW (0.46 g/kg of metabolic body weight) as the preferred dose for the IVGTT for cows at 74 and 221 DIM in this study.

Heat stress in pigs is accompanied by adipose tissue-specific responses that favor increased triglyceride storage

Heat stress (HS) negatively affects all aspects of performance in pigs. Although certain tissue-specific responses in the liver, skeletal muscle, and intestine are known, there is paucity of information on responses within the adipose tissue. Therefore, the objective of this study was to delineate adipose tissue responses during HS in pigs. Thirty crossbred (Ossabaw × Duroc × Landrace) pigs were assigned to 3 treatments for 7 d. Treatments were 1) control and libitum fed (CON) with room temperature set at 20°C ± 1°C, 2) pair fed (PF) with room temperature as the CON treatment but pair fed to HS pigs, and 3) HS with room temperature 35°C ± 1°C and ad libitum access to feed. Compared with CON pigs, HS pigs had decreased feed intake and elevated skin temperature and respiration rate ( < 0.01). Blood urea nitrogen was higher ( = 0.01) in HS pigs compared with CON pigs only in males. In both subcutaneous and mesenteric adipose tissue, mRNA abundance of phosphoenolpyruvate carboxykinase (PCK1) was more elevated ( < 0.01) in HS groups compared with the CON and PF groups. Heat stress also caused increased heat shock protein 70 (HSP70; = 0.067) and CCAT/enhancer-binding homologous protein (CHOP) content ( < 0.05) in the mesenteric fat compared with the CON treatment. In conclusion, induction of PCK1 expression in adipose tissue by HS suggests elevated glyceroneogenesis might be involved in the increased fat storage in pigs under HS.

Effect of circulating exosomes from transition cows on Madin-Darby bovine kidney cell function

The greatest risk of metabolic and infectious disease in dairy cows is during the transition from pregnancy to lactating (i.e., the transition period). The objective of this experiment was to determine the effects of extracellular vesicles (microvesicles involved in cell-to-cell signaling) isolated from transition cows on target cell function. We previously identified differences in the protein profiles of exosomes isolated from cows divergent in metabolic health status. Therefore, we hypothesized that these exosomes would affect target tissues differently. To investigate this, 2 groups of cows (n = 5/group) were selected based on the concentration of β-hydroxybutyrate and fatty acids in plasma and triacylglycerol concentration in liver at wk 1 and 2 postcalving. Cows with high concentrations of β-hydroxybutyrate, fatty acids, and triacylglycerol were considered at increased risk of clinical disease during the transition period (high-risk group; n = 5) and were compared with cows that had low concentrations of the selected health indicators (low-risk group; n = 5). At 2 time points during the transition period (postcalving at wk 1 and 4), blood was sampled and plasma exosomes were isolated from the high-risk and low-risk cows. The exosomes were applied at concentrations of 10 and 1 µg/mL to 5 × 10³ Madin-Darby bovine kidney cells grown to 50% confluence in 96-well plates. Results indicate a numerical increase in cell proliferation when exosomes from high-risk cows were applied compared with those from low-risk cows. Consistent with an effect on cell proliferation, quantitative reverse transcriptase PCR indicated a trend for upregulation of 3 proinflammatory genes (granulocyte colony-stimulating factor, ciliary neurotrophic factor, and CD27 ligand) with the application of high-risk exosomes, which are involved in cellular growth and survival. Proteomic analysis indicated 2 proteins in the low-risk group that were not identified in the high-risk group (endoplasmin and catalase), which may also be indicative of the metabolic state of origin. It is likely that the metabolic state of the transition cow affects cellular function through exosomal messaging; however, more in-depth research into cross-talk between exosomes and target cells is required to determine whether exosomes influence Madin-Darby bovine kidney cells in this manner.

Short communication: Regulation of hepatic gluconeogenic enzymes by dietary glycerol in transition dairy cows

Nutritional status and glucose precursors are known regulators of gluconeogenic gene expression. Glycerol can replace corn in diets fed to dairy cows and use of glycerol is linked to increased rumen propionate production. The effect of dietary glycerol on the regulation of gluconeogenic enzymes is unknown. The objective of this study was to examine the effect of glycerol on expression of pyruvate carboxylase (PC), cytosolic and mitochondrial phosphoenolpyruvate carboxykinase (PEPCK-C and PEPCK-M), and glucose-6-phosphatase. Twenty-six multiparous Holstein cows were fed either a control diet or a diet where high-moisture corn was replaced by glycerol from -28 through +56 d relative to calving (DRTC). Liver tissue was collected via percutaneous liver biopsy at -28, -14, +1, +14, +28, and +56 DRTC for RNA analysis. Expression of PC mRNA increased 6-fold at +1 and 4-fold at +14 DRTC relative to precalving levels. Dietary glycerol did not alter expression of PC mRNA expression. Expression of PEPCK-C increased 2.5-fold at +14 and 3-fold at +28 DRTC compared with +1 DRTC. Overall, dietary glycerol increased PEPCK-C expression compared with that of cows fed control diets. The ratio of PC to PEPCK-C was increased 6.3-fold at +1 DRTC compared with precalving and tended to be decreased in cows fed glycerol. We detected no effect of diet or DRTC on PEPCK-M or glucose-6-phosphatase mRNA, and there were no interactions of dietary treatment and DRTC for any transcript measured. Substituting corn with glycerol increased the expression of PEPCK-C mRNA during transition to lactation and suggests that dietary energy source alters hepatic expression. The observed increase in PEPCK-C expression with glycerol feeding may indicate regulation of hepatic gene expression by changes in rumen propionate production.

The expression of genes involved in hepatic metabolism is altered by temporary changes to milking frequency

Changes to milking frequency (MF) affect the metabolic and energetic status of dairy cows. However, the duration of altered MF necessary to modify hepatic transcription during early lactation is less clear. Additionally, long-term responses to short-term alterations in MF have not been established. Holstein-Friesian dairy cows (n = 120) were allocated to 3 or 6 wk of either once-daily (1 ×) or thrice-daily (3 ×) milking, immediately postpartum. Following treatment, cows were switched to twice-daily (2 ×) milking. These 4 treatment groups were compared with cows milked 2 × (n = 30) for the whole lactation. Liver tissue was collected by biopsy at 1, 3, 6, and 9 wk postpartum from 12 cows per treatment, RNA was extracted, and transcript abundance of genes involved in hepatic metabolism was quantified. Milking frequency altered the expression of most of the genes measured; however, we observed no effects caused by the length of time on the alternative milking frequency and no interactions between MF and length. During the MF treatment, mRNA expression of some, but not all, genes involved in gluconeogenesis (G6PC, PCK1), fatty acid β-oxidation (CPT1A, CPT2), ketogenesis (HMGCS2), lipid transport (APOA1), and lipolysis (PNPLA2) were lower for cows milked 1 × and plasma glucose and insulin concentrations were greater. Cows milked 3 × had reduced mRNA expression for some of the genes involved in fatty acid synthesis (ACACA) and lipid transport (APOB) and had greater plasma NEFA concentrations at wk 1. At 9 wk postpartum, expression data indicated that cows previously milked 3 × had a greater capacity for gluconeogenesis (PCK1), ketogenesis (HMGCS2), and urea cycling (ASL, CPS1) and lower glucose concentrations than cows previously milked 1 ×, because some of the genes involved in these processes were still altered. Milking cows 1 × relative to 2 ×, however, did not result in significant carryover effects on the expression of the genes measured in this study, indicating that metabolic changes are not sustained beyond the period of reduced MF. Changes to MF altered the hepatic response during early lactation; however, this was not dependent on the duration of MF change. Although we observed only minimal carryover effects on hepatic metabolism from short periods of reduced MF postpartum, there may be long-term effects on urea cycling (ASL, CPS1) and ketogenesis (HMGCS2) when 3 × milking occurs immediately postpartum.

Immune and production responses of dairy cows to postruminal supplementation with phytonutrients

This study investigated the effect of phytonutrients (PN) supplied postruminally on nutrient utilization, gut microbial ecology, immune response, and productivity of lactating dairy cows. Eight ruminally cannulated Holstein cows were used in a replicated 4×4 Latin square. Experimental periods lasted 23 d, including 14-d washout and 9-d treatment periods. Treatments were control (no PN) and daily doses of 2g/cow of either curcuma oleoresin (curcumin), garlic extract (garlic), or capsicum oleoresin (capsicum). Phytonutrients were pulse-dosed into the abomasum of the cows, through the rumen cannula, 2 h after feeding during the last 9 d of each experimental period. Dry matter intake was not affected by PN, although it tended to be lower for the garlic treatment compared with the control. Milk yield was decreased (2.2 kg/d) by capsicum treatment compared with the control. Feed efficiency, milk composition, milk fat and protein yields, milk N efficiency, and 4.0% fat-corrected milk yield were not affected by treatment. Rumen fermentation variables, apparent total-tract digestibility of nutrients, N excretion with feces and urine, and diversity of fecal bacteria were also not affected by treatment. Phytonutrients had no effect on blood chemistry, but the relative proportion of lymphocytes was increased by the capsicum treatment compared with the control. All PN increased the proportion of total CD4(+) cells and total CD4(+) cells that co-expressed the activation status signal and CD25 in blood. The percentage of peripheral blood mononuclear cells (PBMC) that proliferated in response to concanavalin A and viability of PBMC were not affected by treatment. Cytokine production by PBMC was not different between control and PN. Expression of mRNA in liver for key enzymes in gluconeogenesis, fatty acid oxidation, and response to reactive oxygen species were not affected by treatment. No difference was observed due to treatment in the oxygen radical absorbance capacity of blood plasma but, compared with the control, garlic treatment increased 8-isoprostane levels. Overall, the PN used in this study had subtle or no effects on blood cells and blood chemistry, nutrient digestibility, and fecal bacterial diversity, but appeared to have an immune-stimulatory effect by activating and inducing the expansion of CD4 cells in dairy cows. Capsicum treatment decreased milk yield, but this and other effects observed in this study should be interpreted with caution because of the short duration of treatment.

Feeding behaviors of transition dairy cows fed glycerol as a replacement for corn

Feed sorting is a natural behavior of dairy cows that can result in inconsistencies in the nutritive value of a total mixed ration (TMR). The objective of this study was to determine the effects of replacing high-moisture corn with glycerol on feed sorting and the feed intake pattern of transition dairy cows. Multiparous Holstein cows (n=26) were paired by expected calving date, housed in individual tie stalls, and fed diets containing either glycerol or high-moisture corn once daily from d -28 to +56 relative to calving. Glycerol was included at 11.5 and 10.8% of the ration dry matter for the pre- and postpartum diets, respectively. The feed consumption pattern was determined by measuring TMR disappearance during the intervals from 0 to 4 h, 4 to 8 h, 8 to 12 h, and 12 to 24 h relative to feed delivery. Feed sorting was determined on d -16, -9, 9, 16, and 51 relative to calving at 4, 8, 12 and 24 h after feeding. The TMR particle size profile was determined at feed delivery and at 4, 8, 12, and 24 after feed delivery by using the Penn State Particle Separator (Nasco, Fort Atkinson, WI) to yield long (>19 mm), medium (<19 mm, >8 mm), short (<8 mm, >1.18 mm), and fine (<1.18 mm) particles. Overall feed intake did not differ between diets and was 14.7±0.4 and 20.2±0.5 kg/d for the pre- and postpartum intervals, respectively. During the prepartum period, glycerol decreased the amount of feed consumed during the first 4h after feed delivery (7.22 vs. 5.59±0.35 kg; control vs. glycerol, respectively) but increased feed consumed from 12 through 24 h after feed delivery (2.22 vs. 3.82±0.35 kg; control vs. glycerol, respectively). Similar effects on the feed consumption pattern were observed after calving. During the prepartum period, cows fed the control diet sorted against long particles, whereas cows fed glycerol did not sort against long particles (77.2 vs. 101.5±3.50% of expected intake for control vs. glycerol; significant treatment effect). The data indicate that addition of glycerol to the TMR alters the feed consumption pattern to increase feed consumption late in the day at the expense of feed consumed immediately after feeding, and it reduces sorting behavior against long particles. Together, these may reduce diurnal variations in the rumen environment to promote greater rumen health in transition cows.

Regulation of bovine pyruvate carboxylase mRNA and promoter expression by thermal stress

Pyruvate carboxylase (PC) catalyzes the rate-limiting step in gluconeogenesis from lactate and is a determinant of tricarboxylic acid cycle carbon flux. Bovine PC 5' untranslated region (UTR) mRNA variants are the products of a single PC gene containing 3 promoter regions (P3, P2, and P1, 5' to 3') that are responsive to physiological and nutritional stressors. The objective of this study was to determine the direct effects of thermal stress on PC mRNA and gene expression in bovine hepatocyte monolayer cultures, rat hepatoma (H4IIE) cells, and Madin-Darby bovine kidney epithelial (MDBK) cells. Hepatocytes were isolated from 3 Holstein bull calves and used to prepare monolayer cultures. Rat hepatoma cells and MDBK cells were obtained from American Type Culture Collection, Manassas, VA. Beginning 24 h after initial seeding, cells were subjected to either 37°C (control) or 42°C (thermal stress) for 24 h. Treatments were applied in triplicate in a minimum of 3 independent cell preparations. For bovine primary hepatocytes, endogenous expression of bovine PC mRNA increased (P < 0.1) with 24 h of thermal stress (1.31 vs. 2.79 ± 0.49, arbitrary units, control vs. thermal stress, respectively), but there was no change (P ≥ 0.1) in cytosolic phosphoenolpyruvate carboxykinase (PEPCK-C) mRNA expression. Similarly, exposure of MDBK cells to thermal stress increased (P < 0.1) expression of bovine PC mRNA without altering (P ≥ 0.1) PEPCK-C mRNA expression. Conversely, there was no effect (P ≥ 0.1) of thermal stress on endogenous rat PC (0.47 vs. 0.30 ± 0.08, control vs. thermal stress) or PEPCK-C (1.61 vs. 1.20 ± 0.48, arbitrary units, control vs. thermal stress, respectively) mRNA expressions in H4IIE cells. To further investigate the regulation of PC, H4IIE cells were transiently transfected with bovine promoter-luciferase constructs containing either P1, P2, or P3, and exposed to thermal stress for 23 h. Activity of P1 was suppressed (P < 0.1) 5-fold, activity of P2 was unchanged (P ≥ 0.1), and activity of P3 was increased (P < 0.1) by 5.4-fold. These data indicate that response of bovine PC gene to thermal stress is through promoter regulation and suggest that there are unique characteristics of bovine PC promoters that may contribute to the physiological response to thermal stress.

Differential regulation of bovine pyruvate carboxylase promoters by fatty acids and peroxisome proliferator-activated receptor-α agonist

Pyruvate carboxylase (PC) is a critical enzyme in supplying carbon for gluconeogenesis and oxaloacetate for the tricarboxylic acid cycle. The bovine PC (EC 6.4.1.1) gene contains 3 promoter sequences (P3, P2, and P1 from 5' to 3'). Physiological stressors, including the onset of calving and feed restriction, lead to elevated nonesterified fatty acids and glucocorticoid levels that coincide with an increase in PC mRNA expression. The effects of elevated fatty acids on bovine PC mRNA expression and promoter function have not been determined. The objective of this experiment was to determine the direct effects of stearic, oleic, and linoleic acids, dexamethasone, and Wy14643 (a peroxisome proliferator-activated receptor-α agonist) on bovine PC promoter activity. Promoter-luciferase constructs, containing 1,005 bp of P1, 1,079 bp of P2, or 1,010 bp of P3, were transiently transfected into rat hepatoma (H4IIE) cells. Cells were then treated with 1mM stearic, oleic, or linoleic acids, 1 μM dexamethasone, or 10 μM Wy14643 for 23 h. Activity of P1 was suppressed with exposure to stearic acid (1.58 vs. 6.19±0.81 arbitrary units for stearic vs. control, respectively) and enhanced with exposure to Wy14643 (9.26 vs. 6.19±0.81 arbitrary units for Wy14643 vs. control, respectively). Conversely, stearic acid enhanced P3 activity (2.55 vs. 0.40±0.33 arbitrary units for stearic vs. control, respectively). Dexamethasone, linoleic acid, and oleic acid failed to elicit a response from any of the promoters tested. These data demonstrate the direct role of fatty acids in regulating PC expression and indicate that fatty acids provide promoter-specific regulation of PC promoters.

A self referencing platinum nanoparticle decorated enzyme-based microbiosensor for real time measurement of physiological glucose transport

Glucose is the central molecule in many biochemical pathways, and numerous approaches have been developed for fabricating micro biosensors designed to measure glucose concentration in/near cells and/or tissues. An inherent problem for microsensors used in physiological studies is a low signal-to-noise ratio, which is further complicated by concentration drift due to the metabolic activity of cells. A microsensor technique designed to filter extraneous electrical noise and provide direct quantification of active membrane transport is known as self-referencing. Self-referencing involves oscillation of a single microsensor via computer-controlled stepper motors within a stable gradient formed near cells/tissues (i.e., within the concentration boundary layer). The non-invasive technique provides direct measurement of trans-membrane (or trans-tissue) analyte flux. A glucose micro biosensor was fabricated using deposition of nanomaterials (platinum black, multiwalled carbon nanotubes, Nafion) and glucose oxidase on a platinum/iridium microelectrode. The highly sensitive/selective biosensor was used in the self-referencing modality for cell/tissue physiological transport studies. Detailed analysis of signal drift/noise filtering via phase sensitive detection (including a post-measurement analytical technique) are provided. Using this highly sensitive technique, physiological glucose uptake is demonstrated in a wide range of metabolic and pharmacological studies. Use of this technique is demonstrated for cancer cell physiology, bioenergetics, diabetes, and microbial biofilm physiology. This robust and versatile biosensor technique will provide much insight into biological transport in biomedical, environmental, and agricultural research applications.

Feeding value of glycerol as a replacement for corn grain in rations fed to lactating dairy cows

Growth of the corn ethanol industry has created a need for alternatives to corn for lactating dairy cows. Concurrent expansion in soydiesel production is expected to increase availability and promote favorable pricing for glycerol, a primary co-product material. The objective of this study was to determine the feeding value of glycerol as a replacement for corn in diets fed to lactating dairy cattle. Sixty lactating Holstein cows housed in individual tie stalls were fed a base diet consisting of corn silage, legume forages, corn grain, soyhulls, roasted soybeans, and protein supplements. After a 2-wk acclimation period, cows were fed diets containing 0, 5, 10, or 15% refined glycerol for 56 d. Cows were milked twice daily and weekly milk samples were collected. Milk production was 36.3, 37.2, 37.9, and 36.2 +/- 1.6 kg/d and feed intake was 23.8, 24.6, 24.8, and 24.0 +/- 0.7 kg/d for 0, 5, 10, and 15% glycerol treatments, respectively, and did not differ except for a modest reduction in feed intake during the first 7 d of the trial for 15% glycerol (treatment x time effect). Milk composition was not altered by glycerol feeding except that milk urea nitrogen was decreased from 12.5 +/- 0.4 to 10.2 +/- 0.4 mg/dL with glycerol addition. Cows fed diets containing 10 and 15% glycerol gained more weight than those fed rations containing 0 or 5% glycerol but body condition scores did not differ with glycerol feeding. The data indicate that glycerol is a suitable replacement for corn grain in diets for lactating dairy cattle and that it may be included in rations to a level of at least 15% of dry matter without adverse effects on milk production or milk composition.

Intestinal mucin dynamics: response of broiler chicks and White Pekin ducklings to dietary threonine

Mucin dynamics may be particularly sensitive to a Thr deficiency due to the high concentration and structural importance of Thr in the mucin protein backbone. Intestinal mucin secretion, expression of mucin gene (MUC2), and histological characteristics were investigated in male broilers and White Pekin ducklings offered diets containing 3.3, 5.8, or 8.2 g of Thr/kg in 4 studies. Seventy-two birds of each species were fed a standard broiler starter diet from 1 to 14 d of age followed by assignment to 3 dietary treatments in a randomized complete block design for a 7-d feeding trial in experiment 1 (broilers) and experiment 2 (ducklings). The dietary treatments consisted of an isonitrogenous corn-soybean meal-based diet with the addition of crystalline amino acids and graded levels of Thr. Dietary treatments contained 3.3, 5.8, or 8.2 g of Thr/kg. Dietary formulation and experimental design for experiments 3 (broilers) and 4 (ducklings) were similar to experiments 1 and 2 except that birds were fed 3.3 or 8.2 g of Thr/kg for durations of 7 or 14 d. For chicks, increased dietary Thr resulted in higher levels of intestinal crude mucin excretion in experiment 1 (P=0.04) but not in experiment 3, whereas intestinal sialic acid excretion increased in experiment 3 (P=0.02) but not in experiment 1. Furthermore, there was no effect of Thr on intestinal goblet cell density or MUC2 mRNA abundance for broilers. For ducklings, there was an increase in intestinal crude mucin excretion in both experiments (P<0.05) as dietary Thr increased, although there was no effect of Thr on intestinal sialic acid excretion. There was a tendency for an increase in intestinal goblet cell density (cells/microm of villus length; P=0.09) as dietary Thr increased in experiment 2. For experiment 4, intestinal MUC2 mRNA abundance increased (P=0.03) as dietary Thr increased for the 14-d feeding trial but not for the 7-d feeding trial. The data establish a link between dietary Thr and intestinal crude mucin dynamics in chicks for experiment 1 and ducklings for both experiments.

Prepartum Milking of Heifers Influences Future Production and Health

Transition heifers face multiple stressors during the periparturient period, including first exposure to milking, that may adversely impact dry matter intake (DMI), reduce milk production, compromise immune function, and increase susceptibility to disease. It was hypothesized that reducing the combined stressors experienced at calving would improve the periparturient performance, health, and well-being of heifers. The objective of this study was to determine the effect of initiating the milking procedure 3 wk before expected calving on production, DMI, body weight, energy balance, udder health, calving traits, and health status, as indicated by plasma acute phase protein concentrations. Twenty-two primigravid heifers, blocked by expected calving date, were assigned randomly either to a prepartum milking (PM) group or control group. The PM heifers were milked twice daily beginning at 21 d before expected calving, and control heifers were not milked until after calving. All heifers had access to the same precalving and post-calving diets. Results indicated that PM heifers produced more milk during the first 2 wk after calving and had greater DMI as a percentage of body weight during the first month after calving than did control heifers, although energy balance was more negative for PM heifers. The PM heifers had reduced somatic cell counts through the first month after calving and lower average somatic cell scores during lactation despite having more quarters with mastitis infection at calving. The PM heifers had less udder edema at the third milking postcalving, and had reduced concentrations of haptoglobin in blood sooner than did control heifers. These results indicate that prepartum milking is an alternative management practice that has beneficial effects on the production, health, and well-being of first-lactation cows.

Effect of dietary carbohydrate and monensin on expression of gluconeogenic enzymes in liver of transition dairy cows1

Thirty-four multiparous Holstein cows were used in a randomized block design to evaluate the effects of feeding nonforage fiber sources (NFFS), monensin, or their combination on expression of gluconeogenic enzymes in the liver during the transition to lactation. The addition of 0 or 300 mg/d of monensin to a conventional (CONV) or NFFS prepartum diet was evaluated in a 2 x 2 factorial arrangement of treatments. The NFFS diet was formulated by replacing 30% of the forage component of the CONV diet with cottonseed hulls and soyhulls. The CONV and NFFS basal diets were fed at dry-off and continued through parturition. Monensin was fed from -28 d relative to calving (DRTC) through parturition. At calving, all cows were placed on the same diet. Liver biopsy samples obtained at -28, -14, +1, +14, and +28 DRTC were used to determine pyruvate carboxylase (PC) and cytosolic phosphoenolpyruvate carboxykinase (PEPCK-C) mRNA expression. Feeding NFFS resulted in greater (P < 0.05) prepartum DMI compared with the CONV diet. There was no effect of prepartum diets on postpartum DMI or average milk production to 56 d of lactation. Expression of PC mRNA was elevated (P < 0.05) at 1 d postpartum, but there was no effect of NFFS or monensin on PC mRNA abundance. Expression of PEPCK-C mRNA at calving was increased (P < 0.05) with prepartum monensin feeding. The data indicate that feeding monensin to transition cows induces hepatic PEPCK-C mRNA expression before calving. The increased expression of hepatic PEPCK-C mRNA with monensin feeding suggests a feed-forward mechanism of metabolic control in ruminants that links molecular control of gluconeogenesis with the profile of rumen fermentation end products.

Major advances in fundamental dairy cattle nutrition

Fundamental nutrition seeks to describe the complex biochemical reactions involved in assimilation and processing of nutrients by various tissues and organs, and to quantify nutrient movement (flux) through those processes. Over the last 25 yr, considerable progress has been made in increasing our understanding of metabolism in dairy cattle. Major advances have been made at all levels of biological organization, including the whole animal, organ systems, tissues, cells, and molecules. At the whole-animal level, progress has been made in delineating metabolism during late pregnancy and the transition to lactation, as well as in whole-body use of energy-yielding substrates and amino acids for growth in young calves. An explosion of research using multicatheterization techniques has led to better quantitative descriptions of nutrient use by tissues of the portal-drained viscera (digestive tract, pancreas, and associated adipose tissues) and liver. Isolated tissue preparations have provided important information on the interrelationships among glucose, fatty acid, and amino acid metabolism in liver, adipose tissue, and mammary gland, as well as the regulation of these pathways during different physiological states. Finally, the last 25 yr has witnessed the birth of "molecular biology" approaches to understanding fundamental nutrition. Although measurements of mRNA abundance for proteins of interest already have provided new insights into regulation of metabolism, the next 25 yr will likely see remarkable advances as these techniques continue to be applied to problems of dairy cattle biology. Integration of the "omics" technologies (functional genomics, proteomics, and metabolomics) with measurements of tissue metabolism obtained by other methods is a particularly exciting prospect for the future. The result should be improved animal health and well being, more efficient dairy production, and better models to predict nutritional requirements and provide rations to meet those requirements.

Feed restriction induces pyruvate carboxylase but not phosphoenolpyruvate carboxykinase in dairy cows

The ability of dairy cattle to adapt to changes in nutrient intake requires appropriately responsive expression of several key genes in liver. Holstein cows were used in 2 experiments to determine the effect of short-term feed restriction on expression of mRNA for gluconeogenic and ureagenic enzymes in liver. In experiment 1, cows were fed a total mixed diet for ad libitum intake for a 5-d period followed by 5 d of 50% of their previous 5-d ad libitum intake followed by 10 d of ad libitum feeding. Liver biopsies and blood samples were obtained on d 5, 10, and 20 of the experiment, the last day of each feeding period. Pyruvate carboxylase (PC) mRNA increased with feed restriction, but phosphoenolpyruvate carboxykinase (PEPCK) was unchanged. Expression of carbamoyl phosphate synthetase (CPS-I), argininosuccinate synthetase, and ornithine transcarbamylase mRNA were not altered by feed restriction; however, CPS-I mRNA expression tended to increase during realimentation. In experiment 2, cows were fed for ad libitum intake for 5 d and then fed 50% of previous intake for 5 d. Liver biopsy samples collected on d 5 and 10 were used for PC mRNA, PEPCK mRNA, and in vitro measure of gluconeogenesis from radiolabelled propionate and lactate. The data indicate expression of genes for key metabolic processes in liver of lactating cows is responsive to feeding level. Expression of PC mRNA is part of the adaptive response to feed intake restriction and is matched by increased capacity for gluconeogenesis from lactate.

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-(14)C]propionate and 2.0 mM [U-(14)C]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, beta-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 Dexamethasone and Growth Hormone Treatment on Hepatic Gluconeogenic Enzymes in Calves

The hypothesis was tested that dexamethasone (DX) and bovine somatotropin (bST) alter expression or activity of gluconeogenic enzymes in neonatal calves. Holstein dairy calves (n = 24) were randomly divided in 4 groups and were treated with saline (control group), with DX at 30 microg/kg body weight per d (CDX), with 500 mg of sustained-release recombinant bST every 14 d (CbST), and with the combination of DX and bST from d 3 through 42 of life (CbSTDX). Plasma glucose and insulin concentrations were elevated throughout the study in CbSTDX, and insulin concentrations were elevated in CDX from d 7 to 28. Treatment with DX and the combination of DX and bST increased plasma glucagon concentrations from d 14 to 42, but decreased plasma cortisol concentrations on d 7 and 14 when compared with control calves. In liver, phosphoenolpyruvate carboxykinase (PEPCK) mRNA levels were reduced in CDX and CbSTDX when compared with control calves or CbST. The activity of PEPCK on d 14 was higher in CbSTDX compared with control calves. Pyruvate carboxylase mRNA levels were decreased on d 7 in CDX and CbSTDX. Pyruvate carboxylase activities on d 14 and 28 were lower in CDX and CbSTDX than in control calves or CbST. These data indicate an age-dependent response to DX for blood metabolites, expression and activities of hepatic PEPCK and pyruvate carboxylase, and for effects of bST, suggesting that glucocorticoid status is important.

Bovine Somatotropin Increases Hepatic Phosphoenolpyruvate Carboxykinase mRNA in Lactating Dairy Cows,

Somatotropin (ST) increases milk production and through coordinated changes in hepatic glucose synthesis and amino acid metabolism in dairy cows. The objective of this study was to determine the effects of ST on hepatic mRNA expression for phosphoenolpyruvate carboxykinase (PEPCK) and pyruvate carboxylase (PC), enzymes that are critical to the synthesis of glucose in liver and hepatic mRNA expression for carbamylphosphate synthetase I (CPS-I), argininosuccinate synthetase (AS), and ornithine transcarbamylase (OTC), critical enzymes of the urea cycle. Eighteen cows were randomly allocated to 2 treatment groups and received either recombinant bovine ST (Posilac; Monsanto, St. Louis, MO) or saline injections at 14-d intervals during a 42-d period. Expression of mRNA was determined using Northern blot analysis. Nuclei, isolated from liver biopsy samples, were used to determine effects of ST on transcription rate of PEPCK. Milk production was increased with ST (37.3 vs. 35.1+/-0.6 kg/ d). Plasma NEFA was increased with ST (299 vs. 156+/-34 microM). There were no differences in the expression of CPS-I, AS, and OTC mRNA with ST. Expression of PEPCK and IGF-I mRNA were increased with ST but PC mRNA was unchanged. The data indicate increased PEPCK mRNA in cows given ST and indicates a greater capacity for gluconeogenesis from gluconeogenic precursors that form oxaloacetate. The effects of ST to elevate PEPCK mRNA expression require chronic administration and involve increased transcription of the PEPCK gene.

Toll-like receptors 2 and 4, and acute phase cytokine gene expression in dexamethasone and growth hormone treated dairy calves

Cattle are exposed to growth hormone stimulants and to stressors that cause cortisol release. Both of these hormones affect immune responses which may reduce disease resistance. Toll-like receptors are the pattern recognition molecules of pathogens that are on immune cells. They then orchestrate the induction of the appropriate acute phase cytokines of the early innate response. The objective of this study was to determine changes in toll-like receptors and acute phase cytokines following treatment with a synthetic glucocorticoid (dexamethasone) and growth hormone (GH). Twenty-eight calves were given the control (Cnt), dexamethasone (DEX), GH, or dexamethasone and GH (Both) treatments from 3 until 56 days of age. Blood was collected by jugular venipuncture on days 14, 28, 42, and 56. On day 56, a lung lavage was performed and spleen and thymus tissues collected. Total RNA was extracted from blood leukocytes, lung lavage cells, spleen and thymus cells. Real-time reverse transcriptase-polymerase chain reaction (RT-PCR) was used to quantify interleukin-1 (IL-1), IL-1 receptor antagonist (IL-1Ra), tumor necrosis factor (TNF)-alpha, toll-like receptor 2 (TLR2), and toll-like receptor 4 (TLR4). Blood leukocytes had a time effect for IL-1Ra (P < 0.01), with a trend for a treatment effect (P = 0.07) and had a treatment by time interaction (P < 0.05). IL-1, TNF, and TLR2 and TLR4 were greatest (P < 0.05) for Cnt only at day 14. IL-1 expression of lung lavage cells was greatest (P < 0.05) for calves on the Both treatment compared to the other three treatments. However, IL-1Ra was not different among the treatments. Toll-like receptor 2 expression was enhanced with Both compared to either DEX (P < 0.05) or GH (P < 0.05) and tended to be greater than Cnt expression (P = 0.07). Expression of TLR4 tended to be reduced by Both compared to Cnt (P = 0.06). Tumor necrosis factor-alpha was greatly enhanced by Both compared to the other three treatments (P < 0.05). Spleen cell tended to have different IL-1 expression between GH and Both (P < 0.10). Interleukin-1 receptor antagonist and TLR2 and TLR4 were not different among treatments. However, TNF-alpha expression was enhanced by the DEX treatment alone compared to the GH treatment (P < 0.05), and tended (P < 0.10) to be greater than Cnt expression. None of the gene expressions were different among treatments for thymus cells. Lung lavage cell expression appears to be most susceptible to these hormones while blood leukocyte expression was only slightly affected, and thymus cells were not affected at all. These data demonstrate that TLR2 and TLR4 and acute phase cytokine expression can be altered by stress and growth hormones, which may decrease resistance of those animals to disease.

The response of the hepatic insulin-like growth factor system to growth hormone and dexamethasone in calves

Glucocorticoids inhibit postnatal growth and yet can stimulate the somatotropic axis around birth. The aim of the present study was to investigate the effects of dexamethasone on the somatotropic axis and on the responses of the insulin-like growth factor (IGF) system to growth hormone treatment in calves. Calves (n=24) were randomly divided into four groups. Group DX was injected with dexamethasone (30 micro g/kg body weight per day), group GH was injected with 500 mg slow-release bovine growth hormone at 14-day intervals, group GHDX was injected with dexamethasone and bovine growth hormone, and group CNTRL (serving as control) was injected with saline from day 3 to day 42 of life. Blood samples were taken on day 3 and blood and liver samples were obtained on days 7, 14, 28 and 42. Body weight increased in the CNTRL and GH groups up to the end of the study and in the DX and GHDX groups up to the fourth week. Dexamethasone treatment decreased (P<0.05) plasma IGF binding protein (IGFBP)-1 on days 7 and 14, but increased (P<0.05) plasma IGFBP-1, decreased (P<0.05) plasma IGF-I and IGFBP-3, and decreased hepatic mRNA for growth hormone receptor (GHR) and IGF-I on day 42. Growth hormone treatment increased (P<0.05) plasma growth hormone concentrations on days 7 and 14, tended to increase (P<0.1) plasma IGF-I concentrations on day 42, and increased (P<0.05) hepatic mRNA levels of GHR on day 14 and IGF-I mRNA levels on days 7 and 14. The combined dexamethasone and growth hormone treatment increased plasma growth hormone concentrations on day 7 and resulted in the highest plasma concentrations of IGF-I and IGFBP-3 (day 7 to day 28) as well as the greatest abundance of hepatic GHR (day 14) and IGF-I (days 7 and 14) mRNA. Plasma IGFBP-1 concentrations in the GHDX group behaved in a similar manner as in the DX group. In conclusion, the response of the somatotropic axis to growth hormone treatment could be greatly enhanced by dexamethasone treatment during the neonatal and early postnatal period, but body weight gain was not improved. Dexamethasone alone inhibited the somatotropic axis and postnatal growth after the first Month of life.

Effects of feeding silage and grain from glyphosate-tolerant or insect-protected corn hybrids on feed intake, ruminal digestion, and milk production in dairy cattle

Lactating dairy cows were used to determine effects of feeding glyphosate-tolerant or insect-protected corn hybrids on feed intake, milk production, milk composition, and ruminal digestibility. Corn resistant to European corn borer (Ostrinia nubilalis) infestation (Bt-MON810), or its nontransgenic control (Bt-CON), were planted in alternating fields during two successive years. One-half of each strip was harvested for whole plant corn silage and the remainder was allowed to mature and harvested as grain. Effects of feeding diets containing either Bt-MON810 or Bt-CON grain and silage were determined in two experiments (1 and 2) conducted during successive years. In experiment 3, glyphosate-tolerant Roundup Ready corn (RR-GA21) or its nontransgenic control (RR-CON) corn were grown in alternating fields during one cropping season. Diets contained 42 to 60% corn silage and 20 to 34% corn grain from Bt-MON810, RR-GA21, or the appropriate nontransgenic counterpart; treatments were applied using a switchback design. Cows were fed ad libitum and milked twice daily. There were no differences for nutrient composition between silage sources or between grain sources within an experiment. Data for experiments 1 and 2 indicated similar dry matter intake (DMI), 4% fat-corrected milk (FCM) production, and milk composition between Bt-MON810 and Bt-CON diets. There were no differences for DMI, 4% FCM production, and milk composition between RR-GA21 and RR-CON diets. There was no difference in ruminal degradability, determined separately for corn silage and corn grain, for RR-GA21 or Bt-MON810-hybrids compared with their respective controls. These data demonstrate equivalence of nutritional value and production efficiency for corn containing Bt-MON810 compared with its control and for RR-GA21 corn compared with its control.

Rumen undegradable protein, rumen-protected choline and mRNA expression for enzymes in gluconeogenesis and ureagenesis in periparturient dairy cows

The objective of this study was to profile mRNA expression of argininosuccinate synthetase (AS) and ornithine transcarbamylase (OTC), two enzymes that participate in the formation of urea in liver and compare these with changes in mRNA for pyruvate carboxylase (PC) and phosphoenolpyruvate carboxykinase (PEPCK) during the periparturient period in dairy cows. Forty-eight multiparous Holstein cows were fed isoenergetic prepartum diets that contained 10% RDP and either 4.0% RUP or 6.2% RUP and either 0, 6, or 12 g/d of rumen-protected choline (RPC) as CapShure (Balchem Corp., Slate Hill, NY). After calving cows received a common diet and continued RPC as per their prepartum assignments. Liver biopsies were obtained on d -28, -14, 1, 28, and 56 relative to calving, and the abundances of AS, OTC, PC, PEPCK, and 18S mRNA were determined by Northern blot analysis of total RNA. The abundance of OTC mRNA was lowest at calving and was decreased by RPC and 6.2% RUP feeding. Feeding 6.2% RUP did not alter AS, PC, or PEPCK mRNA. The expression of AS mRNA increased and PEPCK mRNA tended to increase from calving to 56 DIM. Pyruvate carboxylase mRNA increased more than twofold at calving. The data indicated adaptation to lactation for gluconeogenic enzymes that is not matched in direction and magnitude by changes in mRNA for urea cycle enzymes. Feeding additional protein, as RUP, failed to induce mRNA for key enzymes in gluconeogenesis or ureagenesis.

Impact of dietary rumen undegradable protein and rumen-protected choline on intake, peripartum liver triacylglyceride, plasma metabolites and milk production in transition dairy cows

The objectives of the present study were to determine the effects of rumen undegradable protein (RUP) level of prepartum diets, the supplementation of a rumen-protected choline product, and their interactions on milk production, feed intake, body weight and condition, blood metabolites, and liver triacylglycerides in dairy cows. Rumen-protected choline (RPC) was fed with two levels of RUP to 48 multiparous Holstein cows in a 3 x 2 factorial arrangement of treatments. Beginning 28 d before expected calving, cows were fed 10% rumen degradable protein, either 0, 6, or 12 g/d of RPC as CapShure (Balchem Corp., Slate Hill, NY) and either 4.0 or 6.2% RUP. After calving and through 120 d of lactation, cows received a common diet and continued RPC as per their prepartum assignment. Prepartum dry matter intake (kg/d) was not affected by RPC or RUP. Postpartum intake decreased when 6.2% RUP was fed prepartum. Milk production to 56 d in milk was decreased when cows were fed 6.2% RUP prepartum. Milk protein (kg/d) decreased when additional RUP was fed prepartum. Cows fed RPC lost more weight during the study period and tended to lose more body condition. Plasma urea nitrogen levels in the prepartum period were reduced for cows fed 4.0% RUP prepartum. Mean liver triacylglyceride determined from samples obtained at -28, -14, +1, +28, and +56 d in milk was not affected by RPC, prepartum RUP, or their combinations. Feeding 12 g of RPC/d in conjunction with 4.0% RUP increased milk production, but feeding RPC with 6.2% RUP prepartum and through 56 d in milk decreased production. The data indicate that 6.2% RUP does not benefit close-up dry cows, and the response to RPC depends the RUP content of the prepartum diet.

Dietary psyllium increases expression of ileal apical sodium-dependent bile acid transporter mRNA coordinately with dose-responsive changes in bile acid metabolism in rats

Psyllium (PSY), a type of dietary fiber containing mainly soluble components, has been shown to decrease serum cholesterol concentrations in several species; however, mechanisms involved are not clearly defined. Four groups of 10 rats were fed semipurified diets containing 10% dietary fiber from cellulose and/or PSY for 21 d. Increasing levels of PSY were fed (0,3.33, 6.67 and 10% PSY) with the remaining 10% made up with cellulose. Liver cholesterol, cholesterol 7alpha-hydroxylase (CYP7A) activity and mRNA, 3-hydroxy-3-methylglutaryl CoA reductase (HMGR) mRNA, ileal apical sodium-dependent bile acid transporter (ASBT) mRNA, fecal bile acids and total steroids, and intestinal bile acid content were measured. All variables responded in a dose-dependent manner to PSY in the diet. Total liver cholesterol content was significantly reduced in all groups fed PSY compared to cellulose-fed controls [138(a), 105(b), 105(b) and 93(c) micromol (SEM = 4.2) for 0, 3.33, 6.67 and 10% PSY, respectively]. Activity of CYP7A was significantly greater in all groups fed PSY compared to the cellulose-fed controls [6.36(c), 16.92(b), 15.28(b) and 20.37(a) pmol x min(-1) x mg protein(-1) (SEM = 3.19) for 0, 3.33, 6.67 and 10% PSY, respectively]. These differences in CYP7A activity were similar to differences in CYP7A, HMGR and ASBT mRNA levels. Fecal bile acid and total steroid excretion as well as total intestinal bile acids were significantly greater in rats fed PSY-containing diets compared to 0% PSY-fed rats. These results suggest that the reduction in liver cholesterol involves modulating the size and composition of the bile acid pool via regulation of ileal ASBT, CYP7A and HMGR mRNA levels.

Changes in mRNA expression for gluconeogenic enzymes in liver of dairy cattle during the transition to lactation

The objective of this study was to profile phosphoenolpyruvate carboxykinase (PEPCK) and pyruvate carboxylase (PC) mRNA expression in the liver of dairy cattle during the peripartum transition and determine changes in abundance of these mRNA in response to protein fed during the prepartum period. Thirty-eight multiparous Holstein cows were fed diets containing either 12% crude protein (CP) and 26% rumen undegradable protein (RUP), 16% CP and 26% RUP, 16% CP and 33% RUP, or 16% CP and 40% RUP on a dry-matter basis beginning 28 d before expected calving. After calving, all cows were fed a common diet through 56 d in milk (DIM). Northern analysis of RNA from liver biopsy samples obtained on days -28, -14, +1, +28, and +56 relative to calving indicated that PC and PEPCK mRNA expression were responsive to onset of lactation but not to prepartum protein or RUP concentration. Abundance of PEPCK mRNA was similar at -28, -14, and +1 DIM but was elevated by +28 and +56 DIM relative to precalving levels. Liver PC mRNA abundance was elevated on +1 DIM, remained elevated through 28 DIM, and declined to precalving levels by 56 DIM. The activity of PC enzyme was correlated (r2 = 0.89) with PC mRNA abundance. The data demonstrate increased abundance of PC mRNA during the early transition period followed by increased abundance of PEPCK mRNA during the postpartum period and suggest increased potential metabolism of lactate, pyruvate, and amino acids that contribute to the liver pyruvate pool.

Impact of dietary protein amount and rumen undegradability on intake, peripartum liver triglyceride, plasma metabolites, and milk production in transition dairy cattle

Feeding strategies of transition dairy cows contribute to the risk factors associated with metabolic disorders that limit production in the ensuing lactation. To investigate the effects of prepartum dietary crude protein (CP) concentration and amount of rumen-undegradable protein (RUP) on postpartum health and production, 44 multiparous Holstein cows were blocked by expected calving date and assigned to one of four isoenergetic prepartum rations beginning 28 d prior to expected calving date. Prepartum rations were: 12% CP and 26% RUP, 16% CP and 26% RUP, 16% CP and 33% RUP, or 16% CP and 40% RUP on a dry matter basis. All cows were fed the same postpartum diet (18% CP, 40% RUP) from 1 to 56 d in milk (DIM). Prepartum dry matter intake (DMI) was not different among dietary treatments. Mean postpartum intakes (kg/d) were higher through 56 DIM (P<0.05) for cows fed the 12% CP:26% RUP diet prepartum compared with any of the 16% CP diets (21.8 vs. 19.8, 18.6 and 18.6; 12% CP:26% RUP vs. 16% CP:26% RUP, 16% CP:33% RUP and 16% CP:40% RUP). There was a DIM x prepartum diet interaction (P<0.05) with the greatest effect of the 12% CP:26% RUP diet evident during the first 35 DIM. Cows fed the 12% CP:26% diet during the transition period tended to produce more milk (kg/d) (P = 0.08) than did cows fed any of the 16% CP diets (40.8 versus 37.8, 38.7, and 37.4; 12% CP:26% RUP vs. 16% CP:26% RUP, 16% CP:33% RUP, and 16% CP:40% RUP). Additional protein (12 vs. 16% CP) in the prepartum diet tended to decrease milk protein (P = 0.10) and milk fat yield (P = 0.08) but did not alter percent milk fat, percent milk protein, or MUN. Liver triglyceride (TG) expressed as milligrams of TG per microgram of DNA or percentage of dry matter (DM) on d -28, -14, +1, +28, and +56 relative to calving were not significantly different among treatments. Maximal (P<0.05) infiltration of TG in liver was observed on +1 d when expressed as a percentage of DM and on +28 d when expressed as milligrams of TG per microgram of DNA. Plasma glucose, calcium, urea nitrogen, beta-hydroxybutyrate, and nonesterified fatty acids were not different (P<0.05) among treatments. The data indicate carryover effects of prepartum dietary protein on postpartum intake and milk production, pointing to beneficial effects of maintaining dietary protein for dairy cows in late gestation at 12% CP.

Select 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors vary in their ability to reduce egg yolk cholesterol levels in laying hens through alteration of hepatic cholesterol biosynthesis and plasma VLDL composition

The inability to markedly attenuate cholesterol levels in chicken eggs has led to speculation that cholesterol is essential for yolk formation and that egg production would cease when yolk cholesterol deposition was inadequate for embryonic survival. However, this critical level hypothesis remains unproven. Here, we determine the relative responsiveness of laying hens to three select inhibitors of 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR), the rate-limiting enzyme of cholesterol biosynthesis. A control diet, either alone or supplemented with one of two dietary levels (0.03 or 0.06%) of atorvastatin, lovastatin, or simvastatin, was fed to White Leghorn hens for 5 wk. Liver cholesterol concentrations (mg/g tissue) were decreased (P </= 0.05) by each HMGR inhibitor; however, total liver cholesterol (mg) did not differ among treatments. Microsomal hepatic HMGR activities were increased one- to twofold in all HMGR inhibitor-treated groups, while HMGR mRNA levels were unaffected. Diameters of plasma VLDL particles, the main cholesterol-carrying yolk precursor macromolecules, were reduced (P </= 0.05) only in hens fed 0.06% atorvastatin, and the particles contained 38% less total cholesterol (P </= 0.05) than controls. Plasma total cholesterol concentrations were lowered (P </= 0.05) by both doses of atorvastatin (-56, -63%) and simvastatin (-36,-45%). Egg cholesterol contents were maximally reduced by 46% (P </= 0.05), 7% (P > 0.05), and 22% (P </= 0.05) in hens fed the 0.06% level of atorvastatin, lovastatin, and simvastatin, respectively, while overall egg production [-19% (P </= 0.05), +4% (P > 0.05), and -3% (P > 0.05)], was much less affected. We concluded that cholesterol per se may not be an obligatory component for yolk formation in chickens and, as such, may be amenable to further pharmacological manipulation

Dietary psyllium increases fecal bile acid excretion, total steroid excretion and bile acid biosynthesis in rats

Psyllium, a source of dietary fiber rich in soluble components results in lower serum cholesterol concentration in several species. Suggested mechanisms for the hypocholesterolemic effect include a greater excretion of fecal bile acids and total steroids, and up-regulation of bile acid biosynthesis. The activity of cholesterol 7alpha-hydroxylase (7alphaOHase), the rate limiting enzyme in bile acid biosynthesis, is higher in rats fed 5% psyllium. Whether this higher activity corresponds to an increase in mRNA levels has not been determined. Four groups of 10 rats were fed a semipurified diet containing 5% cellulose (CEL; control), 5% cellulose plus 1% cholic acid (CCA), 5% cellulose plus 2% cholestyramine (CHY) or 5% psyllium hydrocolloid (PSY) for 3 wk. Liver cholesterol concentration, fecal bile acid and total steroid excretion, 7alphaOHase activity and 7alphaOHase mRNA levels were measured. Liver cholesterol content in rats fed CCA was significantly higher than in all other groups. Rats fed CHY and PSY had significantly lower liver cholesterol content than those fed CEL. Total fecal steroid and bile acid excretions were significantly greater in rats fed CCA, CHY and PSY than in those fed CEL. Activities and mRNA levels of 7alphaOHase in rats fed CHY and PSY were significantly higher than in rats fed CEL or CCA. These data indicate that feeding psyllium to rats increases fecal bile acid and total steroid excretion as well as 7alphaOHase activity and 7alphaOHase mRNA levels.

Chronic and transitional regulation of gluconeogenesis and glyconeogenesis by insulin and glucagon in neonatal calf hepatocytes

Milk-fed calves were used as a source of hepatocytes to establish monlayers to test the effects of chronic (41 h) incubation with no hormone, 100 nM insulin, or 100 nM glucagon on gluconeogenesis (glucose retained as glycogen plus glucose released into the medium) from 2.5 mM [2-(14)C]propionate and 2.0 mM [U-14C]lactate (1.0 mM lactate plus 1.0 mM pyruvate) during a subsequent 3-h (acute) incubation. Media for acute incubations contained no hormone, 0 or 10 nM insulin, or 0, 1, 10, or 100 mM glucagon. Chronic glucagon increased gluconeogenesis from propionate and glyconeogenesis from propionate and lactate compared with chronic exposure to medium with no hormone. A chronic glucagon x acute hormone interaction was manifested as an augmented response to acute glucagon on gluconeogenesis from propionate; a similar potentiation was not evident for gluconeogenesis from lactate. The concentration of glucagon required to acutely stimulate gluconeogenesis was increased by prior incubation with glucagon. Acute glucagon decreased the flux of glucose retained as glycogen regardless of chronic hormone treatment. Chronic incubation with insulin diminished the stimulatory effects of glucagon on gluconeogenesis from lactate. Chronic incubation with insulin did not alter the sensitivity or responsiveness at acute glucagon of gluconeogenesis from propionate. The data demonstrate persisting changes that favor increased basal gluconeogenesis from propionate with chronically elevated glucagon coupled to an increased capacity to respond acutely to glucagon and opposing chronic actions of insulin on lactate metabolism. These data suggest that insulin and glucagon target separate pathways that are unique to metabolism of propionate and lactate.

Effects of fatty acids and hormones on fatty acid metabolism and gluconeogenesis in bovine hepatocytes

Primary cultures of hepatocytes were used to study the effects of extracellular oleate concentration and hormones on fatty acid metabolism and gluconeogenesis. Rates of oleate uptake and oxidation to acid-soluble products varied linearly as oleate concentrations increased (0.1 to 2 mM), but rates of triglyceride accumulation varied quadratically. Insulin increased the proportion of oleate that was esterified by 22% without affecting the formation of acid-soluble products. Cells incubated with 2 mM [1-(14)C]oleate for 24 h eliminated 9.6% of the labeled intracellular lipid as acid-soluble products in the following 24 h when no oleate was present during depletion and eliminated 7.7% when 2 mM oleate was present. Insulin reduced labeled triglyceride depletion by 49%. Gluconeogenesis from [2-(14)C] propionate was depressed by 24%, and formation of acid-soluble products was increased by 46% in cells infiltrated with lipid because of previous exposure to 2 mM oleate for 45 h. Rates of gluconeogenesis from propionate were reduced 23% when 2 mM oleate was present during the 3-h period that gluconeogenesis was measured, and the effect was not modified by lipid infiltration. Lipid infiltration influenced hepatic function, and insulin regulated hepatic triglyceride concentration.

Porcine somatotrophin differentially down-regulates expression of the GLUT4 and fatty acid synthase genes in pig adipose tissue

The present study was conducted to determine whether porcine somatotropin (pST) differentially regulates expression of the GLUT4 and fatty acid synthase (FAS) genes in pig adipose tissue. Three different experiments were conducted in which pigs were treated daily with different doses of pST for different time periods (7 or 14 d and from 60 to 90 kg of body wt). In these experiments, pST significantly and consistently decreased FAS mRNA levels (80%, 66% and 85%, respectively); however, GLUT4 mRNA was not affected by pST in two of the three experiments, and in the one showing an effect (Experiment 2), the decrease was less than observed for FAS (44%). Because of these results, we conducted subsequent experiments to see if the effects of pST on glucose metabolism in cultured pig adipose tissue (48 h) differed when glucose concentrations were changed from 1 to 5 mmol/L. These studies revealed that the antagonistic effect of pST on insulin action was more potent when glucose transport was saturated (5 mmol/L) than when glucose concentration limited glucose entry into the cell (1 mmol/L). In summary, these results suggest that the effects of pST on glucose transport in pig adipocytes are secondary to changes elicited by the hormone on intracellular glucose use for lipogenesis. When considered in the context of the decrease previously observed in glucose transport in pig adipocytes, the findings reported herein suggest that pST acts to decrease GLUT4 protein activity and/or distribution between the plasma membrane and the intracellular pool with little alteration in GLUT4 gene expression or total cell GLUT4 protein.

The growth hormone-dependent decrease in hepatic fatty acid synthase mRNA is the result of a decrease in gene transcription

The present study was conducted to determine the chronic effects of porcine growth hormone administration on fatty acid synthase (FAS) mRNA abundance and gene transcription in growing rats. Growth hormone treatment increased growth rate approximately 27% (P<0.01). Porcine growth hormone decreased FAS mRNA levels by 55%. The reduction in FAS mRNA was due to a marked decrease in transcription of the FAS gene (decreased by 80%). In contrast, porcine growth hormone did not affect mRNA abundance or transcription rate of another insulin-regulated gene, phosphoenolpyruvate carboxykinase. In summary, our results have established that chronic treatment with growth hormone decreases FAS mRNA by decreasing the transcription rate of the gene. Furthermore, they suggest that the effects of growth hormone are specific and are not mediated by general changes in insulin-responsive gene expression in liver.

Insulin and glucagon regulation of gluconeogenesis in preruminating and ruminating bovine

Hepatocyte monolayers were established from young preruminating (7 to 14 d of age) or older ruminating (11 to 12 wk of age) calves and used to evaluate the effects of insulin and glucagon on incorporation of carbon from 2.5 mM [2-14C]propionate and 2.0 mM [U-14C]lactate into glucose and glycogen. Developmental state (young preruminating vs older ruminating) of the donor calf did not affect the rate of gluconeogenesis from propionate in the absence of hormones. Insulin decreased (P < .05) gluconeogenesis and increased (P < .05) glycogenesis from propionate and lactate in hepatocytes from preruminating calves but had no effect on hepatocytes from ruminating calves. Lactate was poorly metabolized to glucose and was not responsive to glucagon in hepatocytes from ruminating calves compared with hepatocytes from preruminating calves. Hepatocytes responded to glucagon by increasing (P < .05) gluconeogenesis from propionate. Maximal responsiveness to glucagon did not differ between ruminating and preruminating calves, but hepatocytes from preruminating calves responded at lower glucagon concentrations (P < .05). These data demonstrate a similar capacity of hepatocytes from preruminating and ruminating calves to metabolize propionate to glucose, but there was a seven- to eightfold decrease in gluconeogenesis from lactate in ruminating calves that was accompanied by a decreased response to acute changes in insulin and glucagon.

Regulation of gluconeogenesis by insulin and glucagon in the neonatal bovine

Hepatocyte monolayers from neonatal calves were used to determine the effects of glucagon and insulin on incorporation of carbon from [2-14C]propionate, [1-14C]lactate, [U-14C]lactate, and [1,3-14C]glycerol into glucose and glycogen. Glucagon increased gluconeogenesis (nmol substrate incorporated into glucose or glycogen.micrograms DNA-1.h-1) from propionate and lactate but not from glycerol. Insulin decreased gluconeogenesis from [2-14C]propionate but was without effect on gluconeogenesis from [U-14C]lactate or [1,3-14C]glycerol. Net de novo glycogenesis (nmol substrate retained in cell glycogen.micrograms DNA-1.h-1) from propionate, lactate, and glycerol was decreased by glucagon and increased by insulin. Glucagon effects on gluconeogenesis, but not glycogenesis, were mimicked by dibutyryl adenosine 3',5'-cyclic monophosphate. Lactate flux through pyruvate carboxylase accounts for > or = 91% of lactate carbon flux to glucose, and this proportion was unchanged by glucagon or insulin. Gluconeogenesis from propionate and lactate is regulated by substrate concentration and glucagon in bovine hepatocyte monolayers. The data indicate that, in neonatal bovine liver, glucagon acts on a process common to lactate and propionate to increase gluconeogenesis, and insulin opposes these effects on gluconeogenesis from propionate but not lactate.

Preparation of extended in vitro cultures of bovine hepatocytes that are hormonally responsive

Hepatocytes isolated from male dairy calves were used in monolayer culture or in suspension culture to determine their suitability for the study of hormonal regulation of hepatic gluconeogenesis. The rate of gluconeogenesis (nanomoles of 2.5 mM [2-14C]propionate incorporated into glucose.microgram of DNA-1.hour-1) was higher for monolayers than for suspension cultures. Gluconeogenesis and ureagenesis (nanomoles of urea N formed.microgram of DNA-1.3 hours-1) were similar in monolayers cultured for 24 and 48 h but declined by 120 h. Ureagenesis was barely detectable in suspension cultures. Glucagon (10 nM) increased gluconeogenesis from propionate in monolayers but was without effect on suspension cultures. Actinomycin D (800 nM) and cycloheximide (200 microM) abolished glucagon stimulation of gluconeogenesis, suggesting that glucagon acts to mediate gene expression. Prolonged exposure (45 h) of monolayers to insulin (1,000 nM) decreased basal gluconeogenic rates but did not affect glucagon-stimulated gluconeogenesis. Prior incubation with glucose or valerate did not affect gluconeogenesis. Cells can be successfully maintained in serum-free media for 41 h at the expense of diminished basal gluconeogenic activity. Culture of bovine hepatocytes as monolayers provides a useful tool for the study of chronic and acute hormonal regulation of specific liver functions in the bovine.

Effects of energy balance on hepatic capacity for oleate and propionate metabolism and triglyceride secretion

The purpose of this study was to identify conditions that could decrease accumulation of triglyceride in liver, preferably by increasing hepatic secretion of triglyceride-rich lipoproteins. Hepatocytes isolated from lactating goats were incubated in vitro, and the fate of [1-14C]oleate was measured to determine hepatic capacity for various routes of long-chain fatty acid metabolism. The effect of in vivo energy balance and modifications of the nutrients present in the culture media were tested. Addition of linoleic acid, isovalerate, niacin, propionate, or propylene glycol did not affect triglyceride accumulation or secretion. Pyruvate decreased intracellular triglyceride accumulation. Changes in oxidation of oleate through manipulation of carnitine acyl transferase activity did not influence oleate esterification rate. Livers and hepatocytes isolated from goats in negative energy balance contained more lipid and triglyceride. Liver cells from goats in negative energy balance had decreased capacity for converting propionate to glucose with no change in ketogenic capacity as judged by acid soluble product formation from oleate. Hepatocytes from goats in negative energy balance retained less oleate as cell triglyceride with no change in triglyceride export, indicating a decreased net rate of esterification. Lactating goats, either in negative or positive energy balance, demonstrated the same low capacity for export of newly synthesized triglyceride as previously reported for fed wethers.

Rumen-protected methionine and lysine: effects on animal performance, milk protein yield, and physiological measures

Eight midlactation Holstein cows were used in a three-period (28 d) switchback design to evaluate addition of a combination of ruminally protected methionine (15 g/d) and lysine (40 g/d) on animal performance, milk protein yield, and physiological measures. Cows were fed for ad libitum intake a total mixed diet consisting of 50% corn silage and 50% concentrate (DM basis) or a similar diet to include the addition of the amino acids. Plasma methionine and lysine were elevated with the addition of amino acids. There were no differences between treatments in DM intake, milk yield, fat yield, milk fat percentage, or 4% FCM yield. Addition of amino acids increased milk protein percent (3.15 vs. 3.25). The quantities of alpha- caseins and beta-casein were increased while the quantity of kappa-caseins was decreased. Analysis of the major whey proteins revealed a decrease in serum albumin. Nutrient digestibility and nitrogen balance did not differ. Addition of methionine and lysine to a corn-based diet increased milk protein percentage and yield, plasma methionine and lysine concentrations, and increased yield of the casein proteins in milk.