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EFFECTS OF DIFFERENT LEVELS OF FORAGE AND CONCENTRATE ON THE METABOLISM OF GLUCOSE AY-HYDROXYBUTYRATE AND NONESTERIFIED FATTY ACID IN LIVERS OF NONLACTATING GOATS.

Byline: S. Zhuang R. Yan W.C. Dong T. Zhang G.J. Chang and X. Z. Shen

ABSTRACT

The aim of this study was to investigate the effects of different levels of forage and concentrates diets on the metabolism of glucose AY-hydroxybutyrate (BOHB) and nonesterified fatty acid (NEFA) in livers of nonlactating goats. Six catheterized GuanZhong goats (402 kg weight) were fed high concentrate diet (HC 40% hay 60% concentrate) or high forage diets (HF 60% hay 40% concentrate). Blood samples were simultaneously taken from the portal hepatic and arterial catheters at 0 h before feeding 2 4 6 and 8 h after feeding. The HC fed goats exhibited higher (Pless than 0.01) plasma glucose concentration and arterial flow accompanied by NEFA BOHB(Pless than 0.01) and hepatic glucagons concentrations (Pless than 0.10) while NEFA portal flow and BOHB hepatic flow decreased (Pless than 0.05). Glucose portal-arterial concentration difference and hepatic-portal concentration differences in BOHB and NEFA tended to decreased (Pless than 0.10) with increasing NEFA portal and hepatic arterial concentration differences (Pless than 0.05) in HC fed goats. There were no differences in net flow of glucose BOHB and NEFA across splanchnic tissues but a decreased net portal absorption in NEFA (Pless than 0.05) accompanied with a tendency for depressing its net PDV plus hepatic uptake (Pless than 0.10). In conclusion the high concentrates diet may increase hepatic gluconeogenesis in nonlactating goats.

Key words: Concentrate Liver Glucose Nonesterified fatty acid AY-Hydroxybutyrate Goat

INTRODUCTION

Glucose is an important intermediary of metabolism in ruminants and nonruminants as a major energy source in the pregnant animal and a primary precursor for lactose synthesis in lactation (Annison and Linzell 1964). As glucose metabolism in ruminants differs from that of nonruminants because circulating glucose is mainly provided by gluconeogenesis in the liver from precursors such as propionic acid or glucogenic amino acids. Glucose is also absorbed in smaller amounts by intestinal. The liver sits at the crossroads of metabolism and plays a key role in coordination of nutrient fluxes and all has the ability to sense the fuel needs all of the other tissues in the body and respond by adjusting its metabolism accordingly. It is well known that glucose metabolism has a close association with hepatic ketogenesis and lipid metabolism in liver where glucose metabolism is integrated with ketone bodies nonesterified fatty acid (NEFA) and volatile fatty acids (VFAs) metabolism (Huntington et al. 1988). In addition the hormones especially insulin and glucagon play the major role of regulating intermediary metabolisms such that normal blood glucose concentration is maintained. A lot of previous researches have evaluated the impact of a dietary regime a dietary composition or some materials relative to glucose production infusion on these metabolisms in pregnant or lactating ruminant animals (Storry and Rook 1965; Huntington et al. 1980; Kraft et al. 2009; Kristensen et al. 2010). But there were a few studies focused on the effect of different concentrate content in a diet on metabolism in nonpregnant or nonlactating ruminants. Our research is aimed to investigate the effect of varying in forage and concentrate on the metabolism of glucose AY-hydroxybutyrate (BOHB) and NEFA in liver of nonpregnant and nonlactating goats.

MATERIALS AND METHODS

Animal and Diets:Six catheterized nonlactating and nopregnant Guan Zhong dairy goats averaging 402 kg body weight (BW) were individually housed in metabolism stalls. These goats were assigned randomly to two groups of three goats each. Two diets were used in the experiment to meet or exceed slightly maintenance nutrients requirement of GuanZhonggoat high concentrate diet (HC 40% hay and 60% concentrate) and high forage diet (HF 60% hay and 40% concentrate; Table 1) providing 0.33 and 0.30 net energy MJ/kg0.75 respectively. Goats were fed one of two diets in a randomized crossover design with two experimental periods. Each experimental period lasted 4 weeks including first 2 weeks for adaptation. The diets were fed in equal portions (0.39 kg DM/goat) twice daily at 08:00 and 20:00. Water was available ad libitum. Catheterization and Blood Collection: Surgical procedures and care of goats were approved by the Nanjing Agricultural University of Animal Care and Use Committee. Chronic indwelling catheters were installed surgically in the mesenteric portal and hepatic veins and a femoral artery to measure blood flow and net flow of across portal-drained viscera (PDV) liver and splanchnic tissues (liver+PDV). Goats were allowed to recover for at least 2 wk after surgery and to return to normal feed consumption before beginning the experiment.From 08:00 to 16:00 six simultaneous blood sample sets were obtained at two hours intervals (0 h before feeding 2 4 6 and 8 hr after feeding) from the portal hepatic and arterial catheters within each experimental period. The blood flow marker para- aminohippuric acid (PAH 1% wt/vol sterile saline solution Alfa Aesar CAS 94-16-6 from Alfa Aesar China (Tianjin) Co. Ltd) infused continuously into the mesenteric vein at the rate of 0.8 ml/min using syring pump (SN-50F6 Sino Medical-Device Technology Co. Ltd. Shenzhen China) following a priming rate (3 ml/min for 5 min) given at 07:00. Samples were kept on ice and transported to the laboratory immediately thenwere centrifuged at 1 469A-g for 20 min at 4 toobtained plasma. The PAH was immediately determined and the remaining plasma was stored at -20 for furtherLaboratory Analyses: Plasma flow rates were determined by using PAH which were measured on plasma deproteinized by 0.5 mol/L trichloroacetic acid according to the procedures described by Katz and Bergman (1969). Plasma glucose and BOHBconcentrations were determined using a commercial kit from KEHUA by auto biochemistry analyzer (HollandWeiTu selectra E). Plasma NEFA concentration was determined by using the test kit supplied JianCheng Bioengineering Institute (Nanjing China). Plasma insulin and glucagon concentrations were determined by using ELISA kits from BluGene Biotech Company Limited (Shanghai China).

Calculations: Portal and hepatic plasma flow rates were calculated from the plasma p-aminohippureate concentrations as described by Katz and Bergman (1969). The net portal release and net hepatic release of blood metabolites were calculated as described by Wieghart et al. (1986). General linear models (GLM) procedure of SPSS 16.0 was used for analysis of variance. This model included fixed effects of diet (D) period (P) sampling time (T) and interaction between diet and sampling time (DT). The animal effect was assumed to be random in this model. Differences were declared significant at Pless than 0.05 and tendencies were declared for 0.05 less than Pless than 0.10 for all statistical tests.

RESULTS

Glucose: Glucose concentrations of hepatic and arterial veins (Pless than 0.01 Table 2) and arterial flux (Table 3) were higher (Pless than 0.05) for goats fed HC diet than that fed HF diet. Goats fed HC diet glucose hepatic flux (P=0.06 Table 3) and the portal-arterial concentration difference (P=0.07 Table 4) tended to higher than that fed HF. Net flux of glucose across splanchnic tissues is presented in Table 5. Negative net portal release values denoted a net utilization of glucose by PDV in both diets. Apparent glucose uptake by PDV was greater in HC vs. HF fed goats with -16.18 vs. -8.99 mmol/h respectively reflecting an 80.02% increase. Positive net hepatic release and net PDV plus hepatic output denoted net production of glucose. Net hepatic release of glucose was more by 16.42% (P=0.39) while PDV plus hepatic output of glucose was less by 10.17% (P=0.68) in HC vs. HF group. There was no interactions between diet type and sampling time for concentration flow and net flux across splanchnic tissues of glucose (Pgreater than 0.05).

Table 1. Chemical composition and nutrient level of diets

###High concentrate###High forage

Ingredient

Chinese wildrye###32.00###48.00

Alfalfa###8.00###12.00

Corn###43.17###28.78

Soybean meal###12.68###8.45

Limestone###1.25###0.77

Calcium phosphate dibasic###1.65###1.10

Salt###0.50###0.40

Premix1###0.75###0.50

Dry mater %###88.60###88.90

Net energy MJ/kg###5.89###5.40

CP2 %###13.45###12.24

NDF3 %###27.69###36.55

ADF4 %###17.54###24.04

AY-Hydroxybutyrate (BOHB): BOHB portal arterial and hepatic concentrations were lower by 17.65% 20.41% (Pless than 0.05) and 25.53% (Pless than 0.01) in goats fed HC diet than that fed HF diet respectively (Table 2). Compared with HF diet HC diet decreased BOHB hepatic flow and hepatic-arterial concentration difference (Table 3 and 4 Pless than 0.05) and tended to decreased hepatic-portal concentration difference (P=0.06 Table 4). There were no difference on net flux of BOHB across splanchnic tissues between two diets but net hepatic release and PDV plus hepatic output were lower by 29.55 % (P=0.16)and 23.59% (P=0.18) in goats fed HC vs. HF (Table 5). Except portal concentration and portal-arterial concentration difference there was no interactions between diet type and sampling time for concentration flow and net flux across splanchnic tissues of BOHB (Pgreater than 0.05).

Nonesterified Fatty Acid (NEFA): The HC diet decreased NEFA concentrations of portal hepatic veins and portal fluxes (Pless than 0.05) significantly for arterial concentration (Pless than 0.01 Table 2 and 3) while increased portal-arterial and hepatic-arterial concentration differences and net portal release (Pless than 0.05 Table 4 and5). NEFA hepatic flux and hepatic-portal concentration difference tended to decrease for goats fed HC diet compared with that fed HF diet (Pless than 0.10 Table 3 and 4). Compared with HF diet NEFA net PDV plus hepatic output tended to increase (P=0.07) while net hepatic release decreased by 28.64% (P=0.13) for goats fed HC diet (Table 5). There was no interaction between diet type and sampling time for concentration flow and net flow across splanchnic tissues of NEFA (Pgreater than 0.05).

Insulin and Glucagon: The plasma insulin and glucagon concentrations and flow of hepatic veins are given in the Table 6. The HC diet tended to enhance glucagon concentration of hepatic vein (Pless than 0.10) as compared with HF diet. Insulin concentration of hepatic vein was greater by 10.04% (P=0.11) in goats fed HC vs. HF. There were no differences in insulin and glucagons flow of hepatic vein between two diets (Pgreater than 0.05). There was no interactions between diet type and sampling time for hepatic concentrations and flow of insulin and glucagon (Pgreater than 0.05).

Table 2. Effects of varying in forage and concentrate content on concentrations of glucose -hydroxybutyrate and

###nonesterified fatty acid in nonlactating goats

###P-Value

###HC###HF###SEM

###Diet###Time###DietTime

Portal concentration mmol/L

Glucose###3.651###3.459###0.083###0.115###0.019###0.829

-Hydroxybutyrate###0.280###0.340###0.017###0.019###0.430###0.005

Nonesterified fatty acid###0.174###0.209###0.012###0.045###0.006###0.061

Hepatic concentration mmol/L

Glucose###4.174###3.845###0.060###0.001###0.002###0.588

-Hydroxybutyrate###0.350###0.470###0.026###0.003###0.591###0.195

Nonesterified fatty acid###0.388###0.487###0.028###0.019###0.225###0.365

Arterial concentration mmol/L

Glucose###3.961###3.610###0.053###0.000###0.000###0.827

-Hydroxybutyrate###0.195###0.245###0.013###0.011###0.007###0.362

Nonesterified fatty acid###0.537###0.690###0.035###0.005###0.385###0.389

Table 3. Effects of varying in forage and concentrate content on flow of glucose -hydroxybutyrate and

###nonesterified fatty acid in nonlactating goats

###P-Value

###HC###HF###SEM

###Diet###Time###DietTime

Plasma flow l/h

Portal###57.619###59.165###2.284###0.379###0.014###0.175

Hepatic###93.875###92.177###2.562###0.945###0.001###0.608

Portal flow mmol/h

Glucose###213.770###205.854###10.998###0.615###0.011###0.288

-Hydroxybutyrate###16.561###19.848###1.483###0.129###0.064###0.536

Nonesterified fatty acid###9.828###12.038###0.732###0.042###0.227###0.211

Hepatic flow mmol/h

Glucose###392.982###355.258###13.756###0.063###0.001###0.229

-Hydroxybutyrate###33.940###42.413###2.845###0.045###0.157###0.712

Nonesterified fatty acid###36.390###44.640###3.057###0.067###0.296###0.711

Arterial flow mmol/h

Glucose###143.718###118.914###6.482###0.012###0.008###0.976

-Hydroxybutyrate###7.390###8.386###0.681###0.311###0.006###0.495

Nonesterified fatty acid###19.848###22.954###1.715###0.212###0.163###0.553

Table 4. Effects of varying in forage and concentrate content on the venous-arterial concentration differences of

###glucose -hydroxybutyrate and nonesterified fatty acid in nonlacating goats

###P-Value

###HC###HF###SEM

###Diet###Time###DietTime

Portal-Arterial concentration mmol/L

Glucose###-0.309###-0.150###0.060###0.071###0.843###0.216

-Hydroxybutyrate###0.085###0.095###0.017###0.683###0.327###0.027

Nonesterified fatty acid###-0.363###-0.482###0.032###0.014###0.794###0.652

Hepatic-Portal concentration mmol/L

Glucose###0.523###0.386###0.063###0.136###0.803###0.515

-Hydroxybutyrate###0.070###0.130###0.022###0.064###0.901###0.306

Nonesterified fatty acid###0.214###0.278###0.024###0.069###0.794###0.708

Hepatic-Arterial concentration mmol/L

Glucose###0.213###0.236###0.037###0.668###0.729###0.095

-Hydroxybutyrate###0.155###0.225###0.024###0.045###0.675###0.309

Nonesterified fatty acid###-0.149###-0.204###0.015###0.016###0.175###0.044

Table 5. Effects of varying in forage and concentrate content on the net flow of glucose -hydroxybutyrate and

###nonesterified fatty acid across splanchnic tissues in nonlactating goats

###P-Value

###HC###HF###SEM

###Diet###Time###DietTime

Net portal release mmol/h

Glucose###-16.177###-8.986###3.142###0.118###0.813###0.148

-Hydroxybutyrate###5.053###5.508###1.183###0.788###0.595###0.190

Nonesterified fatty acid###-21.410###-28.253###2.274###0.043###0.524###0.990

Net hepatic release mmol/h

Glucose###35.495###30.490###4.020###0.387###0.906###0.144

-Hydroxybutyrate###9.990###14.180###2.062###0.163###0.965###0.645

Nonesterified fatty acid###7.221###10.119###1.316###0.132###0.395###0.240

Net PDV plus hepatic output mmol/h

Glucose###19.318###21.504###3.671###0.677###0.928###0.136

-Hydroxybutyrate###15.044###19.688###2.394###0.182###0.943###0.591

Nonesterified fatty acid###-14.696###-18.604###1.460###0.070###0.063###0.107

Table 6. Effects of varying in forage and concentrate content on the hepatic concentrations and flow of insulin

###and glucagon in nonlactating goats

###P-Value

###HC###HF###SEM

###Diet###Time###DietTime

Hepatic concentration ng/L

Insulin###5.271###4.790###0.206###0.110###0.001###0.261

Glucagon###13.176###11.219###0.766###0.082###0.001###0.528

Hepatic flow mg/h

Insulin###0.479###0.449###0.024###0.384###0.000###0.887

Glucagon###1.171###1.043###0.078###0.255###0.005###0.356

DISCUSSION

Glucose is an important intermediary of metabolism in general and is particularly important for foetal growth and lactation. Foetus and uterus utilize glucose as a major energy source in the pregnant animal (Lindsay 1973) and large quantities of glucose are removed by the mammary glands for lactose synthesis in lactation (Annison and Linzell 1964). In ontrast to non- ruminants little carbohydrate in ruminants is absorbed as glucose due to the ruminal fermentation. Thus glucose needs must be hepatic production from precursors. In ruminants the major glucogenic substrates are propionate lactate/pyruvate amino acids and glycerol

with the propionate being the major glucose precursors in fed animal (Lomax and Baird 1983; DanfAr et al. 1995). In present study apparent glucose uptake by PDV was greater in HC vs. HF (i.e net portal release = -16.18 mmol/h vs. -8.99 mmol/h) and the glucose net released from liver were 35.50 mmol/h vs. 30.49 mmol/h while there was no difference in net glucose PDV plus hepatic output between two diets. .The results suggest that the HC diet provide more glucose to utilize. It is presumed that the more propionate yield would be produced and removed to synthesize glucose by liver tissues for HC diet. Huntington and Reynolds (1986) reported that abomasal infusions of glucose and starch could increase arterial plasma concentration and net absorption of glucose. Lemosquet et al. (2009) found that isoenergetic infusions (5.15 Mcal/d of digestible energy) of glucose into the duodenum (7.7 mol/d) propionic acid into the rumen (14.1 mol/d) increased whole body glucose rate of appearance by 48.41% and 19.52% in lactating Holstein cows respectively. In our other experimental (unpublished data) results showed that a positive net portal uptake of propionate was observed in two diets and the HC diet increased net portal uptake of propionate as compared with HF diet (33.72 vs 26.07 mmol/h for HC vs HF diets Pless than 0.05); the net hepatic propionate releases showed a negative value in two diet and more propionate was utilized by liver tissues in HC diet (Net hepatic release =-29.14 vs -24.07 mmol/h for HC vs HF diets Pless than 0.05) which corresponded with the present study and confirmed presumption above. Annison et al. (1974) found that high concentrate diet increased molar proportion of propionic acid in the rumen and increased portal propionate concentration in adult cows. Sutton et al. (2003) reported that the molar proportions of propionic acid in rumen fluid was 18.9 and 37.0 mol/100ml for cows fed normal and low roughage diets respectively and net production of total VFAs was increased in cow fed low roughage diets.In the present study plasma concentration and flow of BOHB decrease (Pless than 0.05) or tend to decrease (Pless than 0.10) in HC diet compared with HR diet associated with the same change in NEFA and though dietary concentrate content had no influence on net flow ofNEFA across splanchnic tissues HC diet decreased netportal absorption (Pless than 0.05) and tended to decreased net gut plus hepatic output of NEFA (Pless than 0.01) which fitted the observations obtained for plasma glucose concentration and net flow across splanchnic tissues. The primary ketone body released into portal blood is BOHB (Katz and Berqman 1969). The anti-ketogenic effect of glucose is mainly to suppression of hepatic ketogenesis by two identified anti-ketogenic mechanisms decreasing the supply of free fatty acids to liver and eliciting metabolic changes within the liver itself that are likely to lead to a decrease in the rate of hepatic ketone formation (Treacher et al. 1976). Thus the decrease in the plasma concentrations and flow of NEFA in the present study was presumably due to increasing supply of glucose by gluconeogenesis from propionic acid in HC diet. This is possibility that fatty acid mobilization in peripheral adipose tissues might be depressed and the rate of triglyceride synthesis might be stimulated in HC diet so that less free fatty acid release into blood to available for hepatic uptake and oxidation. Treacher et al. (1976) reported that glucose infusion via a jugular vein into the normal fed and unfed cows in early lactation for 48 h increased glucose plasma concentration associated with the decreased concentrations of BOHB NEFA and glycerol (Pless than 0.05). Furthermore the changes in concentrations of these blood constituents occurring in the unfed cows were of much more magnitude than those occurring in the well-fed cows. The negative net portal release and net PDV plus hepatic output of NEFA associated with positive that two values in BOHB in the present study indicated NEFA was utilized and BOHB was produced by liver in two diets (Table 5). In addition a decreased net splanchnic flux of NEFA and BOHB in HC diet confirmed the discussion above (Table 5).Two pancreatic hormones insulin and glucagon play important roles in maintaining normal blood glucose concentration by regulating intermediary metabolism in ruminants. The secretion of insulin and glucagon can be influenced by many regulators like as glucose certain amino acids volatile fatty acids adrenal medullary hormones. Our research found that the HC diet enhanced secretion of insulin and glucagons in nonlacting goats compared with HF diet (Table 6). This may be due to more propionic acid and glucose yield produced stimulated insulin and glucagons release. Several researches had found that infusion of propionate or glucose could stimulate insulin and glucagons release (Manns and Boda 1967; Manns et al. 1967; Bassett1971; Aiello et al. 1984). Insulin and glucagon may in turn regulate ruminant metabolism. Insulin acts primarily on extrahepatic tissues as a storage and anabolic hormone specifically adipose tissue and muscle. Its role is to enhance lipogenesis and protein synthesis by promoting glucose acetate free fatty acid and amino acids into peripheral tissues. On the other hand glucagon is primarily involved in regulation at hepatic tissues. Its role is to increase hepatic glucose output and lipolysis by enhancing adipose tissue mobilization and hepatic uptake of certain glucose precursors and gluconeogenesis so that it has a net effect of reducing that glucose precursors like as propionate lactate/pyruvate amino acids and glycerol available for nonhepatic tissues (Brockman 1978). This presumption was proved by the observations of glucose BOHB and NEFA in this present research. In addition it was found that the time affected the majority of values on concentrations and flow but in which no diet time interactions were observed in the present research (Table2 and 3) suggesting diet and sampling time each

contributed to these values but not interactive. Many researchers found that glucose metabolism would change with time after feeding in sheep or dairy cow (Armentano et al. 1984; Reynolds and Huntington 1988; Fujita et al.2006). In view of the present and previous results the response to feeding in glucose metabolism may be influenced by glucogenic precursors especially for propionate availability after feeding due to more rapid fermentation of starch than of fiber. Ross and Kitts (1973) observed that concentrations of propionate acetate and butyrate were higher at 6 hr post feeding than at zero time in Dorset Horn weathers. These results are similar to results indicated by Evans et al. (1975) in Holstein heifers and mixed breed rams fed low-roughage or high-roughage. They found with both cows and sheep concentrations of propionate acetate and butyrate generally in creased after feeding so that the values obtained between 1.5 to 5.5 hr post-feeding were greater than 0.5 hr pre-feeding and 7.5 hr post-feeding values. In our other experimental results (unpublished data) also showed that the concentrations and net PDV plus hepatic outputs of propionate acetate and butyrate increased with time after feeding and reached peak at 2-6 hr post feeding.On the basis of present study on nonlactating goats it was concluded that HC diet would increase plasma glucose concentration and arterial flow accompanied by NEFA and BOHB concentrations and NEFA portal flow and BOHB hepatic flow decreased associated with a tendency for increased glucagons hepatic concentration compared with HF diet. In addition HC diet enhanced NEFA portal-arterial and hepatic- arterial plasma concentrations differences and reduced BOHB hepatic-arterial concentration difference relative to HF diet. Furthermore net portal absorption of NEFA decreased and net PDV plus hepatic absorption of NEFA was tended to decrease when feeding HC die to nonlactating goats. Diet and sampling time had no interaction.

Acknowledgements: This study was supported by a grant from the National Key Basic Research Program Ministry of Science and Technology P. R. China (N0.2011CB100802).

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