Milk production and concentrations of blood metabolites as influenced by the level of wet distiller’s solubles in dairy cows receiving grass silage-based diet Pekka Huhtanen and Harri Miettinen Huhtanen, P. & Miettinen, H. 1992. Milk production and concentrations ofblood metabolites as influenced by the level of wet distiller's solubles in dairy cows receiving grass silage-based diet. Agric. Sci. Finl. 1:279-290. (Univ. Helsinki, Dept. Anim. Sei., SF-00710 Helsinki, Finland, Valio, Finnish Co-op. Dairies' Association, R & D Centre, P.O. Box 176, SF-00181 Helsinki, Finland.) Twelve Finnish Ayrshire cows were used in a 4 x 4 Latin square design with 4-week experimental periods to study the effects of replacing increasing amount ofbarley with wet distiller’s solubles (WDS) on feed intake, milk production, digestibility and blood constituents. The four dietary treatmentsconsisted of grass silage ad libitum and 7.8 kg dry matter (DM)/d of barley, of which 0 (WDSO), 1 (WDSI), 2 (WDS2) and 3kg DM/d (WDS3) was replaced with WDS. Mainly because of a greater intake of concen- trate with WDS containing diets silage DM intake varied quadratically (P<0.05) with increasing level of WDS with a minimum being observed with diet WDS 1. The total DM intake (Pc0.05), milk yield (P<0.05) and lactose yield (P<0.01) increased linearly with the level of WDS. Milk protein yield varied both linearly (P<0.05) and quadrati- cally (P<0.05) with the level of WDS reaching a maximum with diet WDS2. WDS had no significant effect on milk fat or protein content but lactose content increased (P<0.001) with the level of WDS. The effects of the treatments on digestibility of diet- ary constituents were generally small, although in certain cases significant. Replacing barley with WDS increased linearly the plasma concentrations of butyrate (P<0.10), glucose (P<0.10), non-esterified fatty acids (NEFA) (P<0.05), and urea (P<0.001). Inclusion of WDS in the diet increased the postprandial peaks of plasma propionate, butyrate, insulin and urea, and decreased that ofketones (acetoacetate and betahydroxy- butyrate). Based on the effects of WDS on the mean plasma concentrations and post- prandial pattern of changes in the blood and plasma metabolites, it is concluded that feeding WDS as a replacement of barley most likely increased hepatic gluconeogen- esis and urea synthesis. This conclusion is supported by the changes in the milk com- position and in the relative yields of milk constituents with increasing rate of WDS inclusion. Key words; silage, distiller’s solubles, milk production,blood metabolites Introduction Distiller’s solubles, a by-product from the integrated starch-ethanol process (NÄSI 1988) are mainly used as a protein source for dairy cattle. Increasing di- etary crude protein (CP) concentration by including dried distiller’s solubles (DDS) in a grass silage- based diet had no effect on milk yield or milk com- position (Ala-Seppälä et al. 1988). In contrast, increasing protein content in the supplement by 279 Agric. Sei. Finl. 1 (1992) https://www.c-info.fi/en/info/?token=DZmqy_LuoTw15C2L.iGS50FRkihyCdS1X25tyRw.HcJL8_Bi6Nf-s1hSAUoQtvTMAQYikDsUiYveQWiAqFZLB1mR7lkgEFry6aQZOyYKlby8IHJKWVrvruw4rvEV_SpXMdxaBjQlWlvDdHarsqXjGddL32eE_50SFF2DkKECFE7_Tv5qh8oQhuQ05rYBXbDOU6d32JgJ0ujkJGDlqiVwMJcTf-ywjIlM2fwTC-WKJ4_lE734S_xIWDT7ybsEA5vTAoIIyaQj6Gq5sG6b3awzC9dFQE2-TFhTpVpvFYTdF3Tk46NPyQnds_m-hYffaPHAxJ9FNSGAUg including soybean meal or fish meal has consistently increased milk yield in cows given grass silage ad libitum (Thomas and Rae 1988; Chamberlain et al. 1989). Therefore, the absence of production res- ponse to DDS suggests that the diets were limited in the supply of protein, probably because of a high proportion ofrumen degradable N in the DDS. This is supported by the fact that replacing barley or bar- ley fibre with untreated wet distiller's solubles (WDS) had no effect on duodenal non-ammonia N flow in cattle (Huhtanen 1992). In the following study, a treatment of DDS with a formaldehyde rea- gent tended to increase milk and milk protein yield as compared with untreated DDS (Huhtanen et al. 1991),and the performance of the cows given treat- ed DDS was similar to that observed with isonitro- genous rapeseed meal supplementation. In commercial farming, distiller's solubles are used mainly in wet form to avoid expensive drying procedures. In addition to high CP content (appro- ximately 300 g/kg DM), WDS also contain about 150 and 50 g/kg DM of lactic acid and glycerol. Feeding WDS diets to cattle increased molar pro- portions of propionate mainly at the expense of acetate in the rumen fluid (Huhtanen 1992). The changes in the rumen volatile fatty acids (VFA) are most probably due to fermentation of lactate to pro- pionate (Chamberlain et al. 1983; Newbold et al. 1986; Jaakkola and Huhtanen 1989; 1992). Substituting barley with treated WDS can thus increase the supply of substrates, propionate from the rumen and amino acids from the small intestine, available for hepatic gluconeogenesis. Increased hepatic glucose production increases plasma glu- cose concentration (Annison et al. 1974) which in turn can increase lactose and milk production. Increased plasma propionate and glucose levels can stimulate insulin release (Bines and Hart 1984; Jenny and Polan 1975), and according to the glu- cogenic theory of McClymont and Vallance (1962), this can lead to a decline in milk fat content. In previous studies (Huhtanen et al. 1992), chang- ing the ratio of glucogenic (propionate) to non- glucogenic (acetate and butyrate) VFA has been shown to affect both the composition of blood and milk. The purpose of this study was to evaluate the effects of WDS in the silage-based diet on feed intake, milk production and digestibility in dairy cows. Blood metabolites were determined to assess the possible effects of WDS on nutrient supply in more detail. Material and methods Animal production study Twelve (6 primiparous and 6 multiparous) Finnish Ayrshire autumn calving cows were used in a balanced 4x4 Latin square experiment. Each ex- perimental period was of 4 weeks duration. The cows were divided into three blocks of four cows so that each group was as similar as possible in milk yield during the week before the start of the experi- ment and parity. Within each block, the cows were allocated at random to treatment sequences. The four treatments consisted of grass silage ad libitum and barley (7.8 kg DM/d) of which 0,1, 2 or 3 kg DM/d was replaced with WDS. The treatments are shown in Table 1. At the start of the experiment, the mean number ofdays after calving was 44 (SE 5.0) and milk yield 27.9 kg/d (SE 1.58).The animals were housed and milked in individual stalls throughout the experi- ment. Grass silage was offered twice daily in suffi- cient quantities to allow proportional refusal of 0.05-0.10. The supplements were given in two equal meals at 6.00 and 14.00 hours on a flat-rate basis throughout the experimental period. The cows were changed to a new dietary treatment within four days. Food Direct-cut silage was made from a primary growth timothy-meadow fescue sward. The herbage was harvested with a precision-chop forage harvester and ensiled in a clamp silo. Formic acid (800 g/kg, AIV II) was applied during ensiling with the rate being 4-5 Et. 280 Agric. Sei. Finl. 1 (1992) Table I. Dietary treatments. Treatment WDSO WDSI WDS2 WDS3 Silage ad lib ad lib ad lib ad lib Barley (kg DM/d) 7.80 6.80 5.80 4.80 WDS (kg DM/d) - 1.00 2.00 3.001.00 2.00 3.00 Mineral A 1 (kg/d) 0.25 0.17 0.08 Mineral B 1 (kg/d) - 0.08 0.170.08 0.17 0,25 1 Ca:P 2.1 2 Ca:P 6.7 WDS obtained from the integrated starch-ethanol process (NÄSI 1988) was treated with a formalde- hyde reagent (European Patent Office, 1982) to reduce ruminal degradability of crude protein. To ensure the preservation of WDS over a 2-week sto- rage period, benzoic acid was applied at the rate of 1 kg/t. To balance different the calcium and phos- phorus content of barley and WDS, the mineral mixture given with barley (Ca:P 2.1) was gradually replaced with a mixture in which the Ca:P ratio was 6.7. Before feeding, WDS was mixed with rolled barley. Measurements and recordings The final two weeks of each period was used for recording purposes. Silage samples were taken twice a week for pH and oven DM determination and samples dried at 60 °C were bulked over one period. Fresh silage samples were frozen for ammo- nia, lactic acid and volatile fatty acid (VFA) ana- lyses. Samples ofbarley and WDS were taken daily and bulked over one period to provide a sample for each period. WDS samples were stored as frozen. Milk yields of individual animals were recorded daily and samples for fat, protein and lactose ana- lyses, in proportion to yield, were taken on days 20, 21, 26 and 27 of each period.. Live weights were recorded at biweekly intervals before the afternoon feeding on two consecutive days. Live weight change was calculated as a linear regression of live weight and time. Ration digestibility and energy utilization Apparent digestibility of the diets was determined using acid insoluble ash (AIA) as an internal mar- ker (Van ICeulen and Young 1977). The four high producing cows in the first block were used in digestibility study. Faecal grab samples were taken during the last week of each experimental period on 5 consecutive days at 7.00 and 16.00h. ME intake was calculated according to MAFF (1984) and as 0.82 x DE intake (ARC 1980). Milk energy content was calculated from the equations of Tyrrel and Reid (1965). The energy require- ments for maintenance and live weight change were calculated according to MAFF (1984). The utilization of ME for milk production was calcu- lated both ignoring (k,) or including (k10) the effect oflive weight change. Blood sampling The two blocks of the cows which had the highest milk yield before the experiment were used for blood sampling. Ten blood samples at hourly inter- vals were taken via an indwelling jugular vein catheter (Cava-Fix, B. Braun Melsungen AG, 1.2- 2.1/Gl4, 70 cm) on the last day ofeach experimen- tal period starting before the afternoon feeding. The cows were catheterised on the day before sampling. Chemical analyses Chemical analyses and calculation of feeding values were made as described by Huhtanen et al. (1988). Fresh samples of WDS were used for ana- lyses. Gross energy (GE) content of the feed and faecal samples was determined by an adiabatic bomb calorimeter (Parr 1108). The chemical com- position and calculated feeding values of the ex- perimental feeds are presented in Table 2. Milk fat, protein and lactose contents were analyzed by an infra-red milk analyzer. Milk urea concentration was analysed according to Rajamäki and Raura- maa (1984) and acetone according to Rajamäki and Rauramaa (1985). 6-hydroxybutyrate (BHB) 281 Agric. Sei. Fint. 1 (1992) and acetoacetate were analysed from the whole blood and glucose, non-esterified fatty acids (NEFA), insulin, urea and VFA were analyzed from the plasma. NEFA were analysed from the samples taken before feeding and 2,4, 6 and 8 hours after feeding. The methods of the blood ana- lyses are described in detail by Miettinen and Huhtanen (1989). Different from the previous experiment, plasma glucose was analysed enzyma- tically using commercial reagents (BioMeriux, France). The plasma VFA were measured by head space gas chromatography. Statistical analyses The model used to analyze feed intake and animal production data was: Y,jklm =S, + Cfft +Pk+ T, + (SP) |k + (ST)„ + e,jklm, where S, C, P and T are square, cow, period and treatment effects. The data from the digestibility study was analysed by the analyses of variance for Table 2. Chemical composition and feeding values of the experimental feeds. Silage Barley WDS Dry matter (g/kg) 207 871 366 In dry matter (g/kg) Ash 75 22 136 Crude protein 154 132 293 Ether extract 54 35 65 Crude fibre 269 49 9 NFE 1 448 765 495 NDF 525 192 10 ADF 287 53 6 ADL 18 9 7 GE (MJ/kg DM) 19.3 18.8 19.5 Feed values FIP/kgDM 0.75 1.18 1.02 ME (MJ/kg DM) 10.6 13.8 12.6 DCP 3 g/kg DM 111 99 243 'NFE =nitrogen free extractives, 2FU =fattening feed unit, 'DCP = digestible crude protein. In silage: pH 3.73; in DM (g/kg): water soluble carbohydrates 32, lactic acid 48, ace- tic acid 16, butyric acid 0.5; in total nitrogen (g/kg): ammonia N 27, soluble N 580. Latin square experiments. The data from blood analyses was analysed by slit-plot analyses of vari- ance (Snedecor and Cochran 1967) using the fol- lowing model: Y =C+ P + T +e .. + H + (HC) + (HP). + ijklmn i j k ijkl m v 'im v 7jm (HT) km + eijk|mn, where C, P, T and H are the effects of cow, period, treatment and sampling time. The sums of squares of treatment effects were further partitioned using polynomial contrasts into linear, quadratic and cubic effects of the level of WDS in the diet. The sums of squares of the H x T interac- tion were divided into the following contrasts: WDS linear x H (9 df), WDS quadratic x H (9 df) and WDS cubic x H (9 df). Results Feed intake and nutrient supply Including WDS in the diet increased the concen- trate DM intake (Table 3). Mainly because of the differences in concentrate intake, silage DM intake varied quadratically (P<0.05) with a minimum in cows given diet WDSI. Total DM intake (P<0.05) and calculated intake of ME (P<0.10) and DCP (PO.OOl) increased linearly with the level of WDS. A quadratic (P<0.05) response to WDS was noted for calculated FU intake. With increasing level of WDS, dietary CP concentration increased from 146 (diet WDSO) to 172 g/kg DM (diet WDS3) with a respective ofNDF from 392 to 348 g/kg DM. Digestibility The differences between the treatments in the digestibility of dietary constituents were small, al- though in some cases statistically significant (Table 4). Milk yield and milk composition The yield and composition ofmilk and the yield of milk constituents for cows receiving the experi- mental diets are shown in Table 5. A linear increase 282 Agric. Sei. Finl. 1 (1992) Table 3. Feed intake and estimated nutrient consumption for cows given the experimental diets. Treatment Significance of effect SEM WDSO WDSI WDS2 WDS3 Linear Quadr. Cubic Feed intake (kg DM/d) Silage 9.90 9.14 9.53 9.70 0.168 NS * NS Concentrate 6.51 7.74 7.54 7.45 Total 16.41 16.88 17.11 17.15 0.190 * NS NS FU/d 15.14 15.85 15.81 15.63 0.177 NS * NS ME (MJ/d) 194.9 202.6 203.4 202.3 2.32 o NS NS DCP (g/d) 1748 1924 2060 2233 24.4 *** NS NS SEM =standard error ofmeans Significance: o (P<0.10); * (P<0.05); ** (P<0.01); *** (P0.001) Table 4. Digestibility of dietary constituents by the cows given the experimental diets. Treatment Significance of effect SEM WDSO WDSI WDS2 WDS3 Linear Quadr. Cubic Organic matter 0.779 0.771 0.787 0.785 0.0036 NS NS NS Crude protein 0.716 0.700 0.719 0.720 0.0049 NS NS NS Ether extract 0.660 0.658 0.685 0.691 0.0066 ** NS NS Crude fibre 0.713 0.713 0.720 0.722 0.0030 * NS NS NFE' 0.827 0,818 0.837 0.834 0,0039 NS NS * NDF 2 0.731 0.734 0.743 0.739 0.0038 NS NS NS Cellulose 0.781 0.783 0.796 0.795 0.0026 ** NS NS Hemicellulose 0.719 0.723 0.731 0.718 0.0049 NS NS NS Gross energy 0.752 0.752 0.764 0.764 0.0059 NS NS NS 1 Nitrogen free extractives 2 Neutral detergent fibre For significance: see Table 3 (P<0.05) in response to WDS was observed for milk yield, but the effect tended to level out with the lowest level of WDS. Milk fat content de- creased slightly (P>0.10) with the level of WDS, and as a result, yields of fat and fat corrected milk (FCM) were not changed. Both the linear and quad- ratic response to WDS in milk protein yield were significant (P<0.05) with a maximum obtained with diet WDS2. As the increase in milk yield was associated with a linear increase (PO.OOl) in lactose content, there was a linear (P<0.01) in- crease in lactose yield with the level of WDS. Milk urea concentration increased linearly (P<0.001) and quadratically (P<0.01) while milk acetone con- tent tended to decrease with the level of WDS. No significant square x treatment interactions were observed, but the response to WDS tended to be slightly greater in high yielding cows. Mean live weight or live weight change were not significantly affected by the treatments. Utilization of ME The efficiency of the utilization ofME for milk pro- duction decreased with the level of WDS in the diet (Table 6). The difference was greater when the 283 Agric. Sei. Fin!. 1 (1992) Agric. Sei. Finl. 1(1992) Table 5. Yields ofmilk and milk constituents, milk composition, live weight and feed conversion for cows given the experi mental diets. Treatment Significance of effect SEM WDSO WDSI WDS2 WDS3 Linear Quadr. Cubic Milk yield (kg/d) 23.6 24.5 24.4 24.4 0.25 * NS NS FCM yield (kg/d) 25.4 25.8 25.8 25.8 0.27 NS NS NS Milk composition (g/kg) Fat 45.4 44.7 44.4 44.2 0.66 NS NS NS Protein 32.6 32,6 32.9 32.2 0.30 NS NS NS Lactose 46.8 47.3 47.5 47.8 0.12 *** NS NS Yield (g/d) Fat 1060 1070 1067 1068 15.0 NS NS NS Protein 769 785 797 784 6.1 * * NS Lactose 1104 1151 1154 1168 12.8 ** NS NS Milk urea (mmol/1) 3.15 3,10 3.46 3.86 0.045 *** ** NS Milk acetone (mmol/1) 0.066 0.059 0.059 0.057 0.0066 NS NS NS Live weight Mean (kg) 529 530 526 527 1.7 NS NS NS Change (kg/d) 0.05 0.07 -0.09 -0.16 0.101 NS NS NS Feed conversion (FU/kg FCM) 0.430 0.448 0.461 0.462 0.0120 o NS NS For significance: see Table 3 Table 6. Calculated efficiency of the utilization ofME for milk production in the cows given the experimental diets. Treatment Significance of effect SEM WDSO WDSI WDS2 WDS3 Linear Quadr. Cubic ME intake (MJ/d)' 194.9 202.6 203.4 202.2 2.52 o NS NS ME intake (MJ/d)2 189.2 196.8 204.1 202.2 2.40 **• NS NS ME requirement (MJ/d) Maintenance 50.1 50.2 49.9 50.0 0.12 NS NS NS Live weight change3 2.8 2.9 -2.0 -4.1 3.15 o NS NS Milk energy yield (MJ/d) 77.2 78.9 79.1 79.1 0.94 NS NS NS Efficiency Including LW change' 0.545 0.528 0.510 0.509 0.0124 * NS NS Ignoring LW change' 0.533 0.517 0.517 0.520 0.0092 NS NS NS 1 Calculated according to MAFF (1984) 2 Calculated as 0.82 x DE intake 3 Allowing 28 MJ for each kg lost and subtracting 34 MJ for each kg gained For significance: see Table 3. 284 effect of LW change was taken into account (k|0) than when the effect ofLW change was ignored (k,). Blood metabolites The effects of WDS on blood metabolites are shown in Table 7. There was a linear increase in the plasma concentrations of butyrate (P<0.10), glu- cose (P<0.10), NEFA (P<0.05) and urea (PO.OOl) with increasing rate of WDS inclusion. The plasma insulin concentration of the first block of the four high producing cows was lower than the mean value for all other cows (26.0 vs. 30.3 mU/1). Diet- ary effects on blood metabolites were similar in both blocks. The postprandial increases in plasma concentrations of propionate (P<0.05), butyrate (PO.OOl), insulin (P0.05) and urea (P0.05) increased linearly with the level of WDS (Fig 1.). In other metabolites, the diet x sampling inter- action did not reach statistical significance. Discussion Feed intake in response to WDS supplementation increased, in contrast to our earlier studies with DDS (Ala-Seppälä et al. 1988; Huhtanen et ai. 1991). This was mainly because the intake of bar- ley on WDSO diet was less than offered. However, among the WDS diets, the increase in silage and total DM intake suggests that the substitution rate of WDS is smaller than that of barley. The differ- ences in the digestibility, though statistically signi- ficant, were trivial and too small to affect feed intake. As the amount of WDS in the diet increased, there was a linear decrease from 6.44 to 5.99 kg/d (PO.01) in NDF intake, suggesting that factors other than rumen fill were controlling the feed intake of WDS containing diets. The response to WDS in milk yield was slightly greater than in the previous study with treated DDS (Huhtanen et al. 1991), probably because of a greater increase in feed intake. The response in milk yield can be accounted for by increased sup- ply of ME with the WDS diets, even though most of the extra energy had been partitioned towards body tissues. The mean response of 0.11 kg milk per 1 MJ increase in ME is similar to that reported by Gordon (1984) for cows receiving increasing amounts ofconcentrate. None the less, the possible effects of treatment of WDS with the formalde- hyde reagent can not be ruled out. Treatment of DDS with the same reagent tended to increase (Huhtanen et al. 1991) and treatment of barley or oats increased milk yield (Kassem et al. 1987; Table 7. The concentrations of some blood and plasma metabolites in cows given the experimental diets. Treatment Significance of effect SEM WDSO WDSI WDS2 WDS3 Linear Quadr. Cubic Acetoacetate (mmol/1) 0.155 0.138 0.119 0.121 0.0021 NS NS NS B-hydroxybutyrate (mmol/1) 1.37 1.18 1.13 1.09 0.0157 NS NS NS VFA (pmol/1) Acetate 1079 985 1105 984 105.2 NS NS NS Propionate 22.2 28.0 30.9 27.4 3.51 NS NS NS Isobutyrate 6.6 7.7 8.1 7.2 0,89 NS NS NS Butyrate 42.9 52.3 53.4 54.4 4.03 o NS NS Isovalerate 4.6 5.0 5.0 5.0 0.59 NS NS NS Glucose (mmol/1) 3.35 3.46 3.56 3.55 0.080 o NS NS Insulin (mU/1) 1 27,9 30.9 32.7 29.7 1.79 NS NS NS NEFA (pmol/1) 92 93 99 103 3.87 * NS NS Urea (mmol/1) 3.58 3.86 4.72 5.08 0.214 *** NS NS ■The biological activity of the bovine insulin standards used was approximately 27 IU/mg 285 Agric. Sei. Finl. 1 (1992) Martin and Thomas 1988). However, it should be noted that in the latter studies the rate ofapplication of the reagent on a crude protein basis was 4-5 times greater than in the present study. There were differences in the response to WDS in the yield of milk constituents indicating corres- ponding changes in the precursor ratio (Oldham and Emmans 1988). Fat yield was unaffected, pro- tein yield was moderately increased and the great- est increase occurred in lactose yield. Enhanced lactose yield with increasing rate of WDS inclusion was due to increases both in milk yield and lactose content. Assuming 47 g/kg lactose in milk, the 64 g of lactose/d increase with dietWDS3 corresponded to about 1.4 kg milk, which is greater than the observed 0.8-0.9 kg/d improvements in actual milk yield with the WDS diets. Thus it appears that WDS provides the cows with a mixture of nutrients which favours especially lactose synthesis. In cattle fed a grass silage-based diet,replacing either barley or barley fibre with untreated WDS increased the molar proportion of propionate in rumen VFA mainly at the expense of acetate (Huhtanen 1992), probably as a result of lactate fermentation (Cham- berlain et al. 1983; Jaakkola and Huhtanen 1992). Enhanced ruminal propionate production increases the supply of glucose precursors to the liver and hepatic gluconeogenesis. Since glucose is Fig. 1. The postprandial changes in plasma propionate, butyrate, urea and insulin concentration (� WDSO, • WDSI, ■ WDS2 and � WDS3). 286 Agric. Sei. Finl. 1 (1992) the main substrate for lactose synthesis (Kuhn 1983), and milk yield is largely determined by lac- tose secretion (Sutton 1989), greater milk yield with WDS diets may be explained by enhanced supply of lactose precursors. The lower milk lac- tose content with diets favouring low propionate to butyrate ration in rumen VFA (WDSO) is consistent with our rumen VFA infusion studies, which de- monstrated a decrease in lactose content with decreasing propionate to butyrate ratio. The response to WDS in milk protein yield may be explained by an increased supply of amino acids. However, a replacement of barley or barley fibre with untreated WDS did not affect duodenal NAN flow suggesting that all extra N from WDS was absorbed as ammonia from the rumen (Huhta- nen 1992). Neither any effects on ammonia pro- duction in vitro were detected with the level ofform- aldehyde used in the present study, and the rate of application had to be three times greater to reduce the rate of ammonia production (Kukkonen and Huhtanen, unpublished). These observations sug- gest that the response to WDS in protein yield may, at least partially, be due to increased ruminal pro- pionate production which reduces the use of amino acids in gluconeogenesis (Armstrong 1982). Although including WDS in the diet might be expected to reduce milk fat content as a result of changes in the rumen fermentationpattern (Huhta- nen 1992), the changes observed were small and statistically not significant. Typically characteristic of grass silage-barley diets (Thomas and Cham- berlain 1982), the proportion ofbutyrate remained high when barley was partially replaced with WDS (Huhtanen 1992). This suggests that milk fat con- tent may not be reduced by moderate changes in the ratio of acetate to propionate when the proportion of butyrate is high. Live weight change tended to decrease with increasing level of WDS, in agreement with Ala- Seppälä et al. (1988) and Huhtanen et al. (1991). Differences in the concentrations of most of the blood metabolites and milk acetone do not, how- ever, indicate increased mobilization of body tis- sues with the level of WDS, rather the reverse. There may be considerable errors in estimating live weight change, especially in change-over experi- ments, and the differences may be related to the changes in gut fill rather than in actual energy balance. Smaller live weight gain in cows receiving diets containing distiller’s solubles are probably related to a smaller rumen volume (Huhtanen 1992). Similar effects of distiller’s solubles on calcu- lated utilization of ME were observed in our previ- ous studies (Ala-Seppälä et al. 1988;Huhtanen et ai. 1991). Decreasing efficiency of ME utilization for lactation with increasing level of WDS could be related to the above mentioned difficulties in esti- mating energy balance from live weight change. The energy cost of synthesizing and excreting the surplus nitrogen as urea can also account for part of the difference (see Oldham 1984). Although replacing barley with WDS in the con- centrate has been found to decrease the concentra- tion and proportion of acetate and increase those of propionate in the rumen fluid of cattle (Huhtanen 1992), in the present study the rate of WDS in- clusion did not significantly affect the average plasma concentrations of acetate or propionate (Table 7). However, a large increase in the post- prandial peak of propionate with WDS diets (Fig. 1) may indicate an increased ruminal propionate production from enhanced lactate intake (Cham- berlain et al. 1983; Jaakkola and Huhtanen 1992).Lactate intake increased from 475 g/d to 884 g/d as the rate of WDS inclusion increased from 0 to 3 kg DM/d. The increase in the mean concentration ofplasma glucose with WDS diets is most likely caused by the increased supply of glucogenic precursors, pro- pionate and amino acids, from the digestive tract to the liver (Brockman, 1986).The increase in gluco- neogenesis with WDS diets is further supported by higher lactose content and yield as compared with the barley diet. The decrease in plasma glucose concentration by intravenous infusion of insulin has also been shown to reduce milk lactose content and yield (Thomas et al. 1987). According to the glucogenic theory (McCly- 287 Agric. Sei. Fin!. 1 (1992) mond and Wallace 1962), the increased absorp- tion of propionate increases the hepatic glucose production and insulin secretion. In agreement with this, the postprandial peak in plasma propionate was increased with the WDS diets, and the change in the mean plasma insulin concentrations was par- allel with the changes in the mean concentrations of plasma propionate and glucose. The glucogenic theory is further supported by the slightly lower milk fat content with WDS diets compared to the control diet. However, the possible effect of buty- rate on plasma insulin (Manns et al. 1967) can not be ruled out. Of plasma VFA, butyrate had the highest positive correlation with insulin during the postprandial period (eg. 3 h after feeding r=0.536; P<0.0l). The increase in plasma NEFA concentrationmay indicate a greater tissue mobilization in cows given increasing amounts of WDS or may be a conse- quence of the enhanced supply of dietary fat (770 g/d for diet WDSO and 870 g/d for diet WDS3) (Giesecke 1983). The changes, although non- significant, in the concentrations of blood ketones and plasma insulin supports the latter. In the present study, the concentration of plasma butyrate was higher than that reported by Sutton et al. (1986) and Huhtanen et al. (1992). This maybe related to the basal diet of restrictively fermented silage and barley, which is known to produce a butyrate type rumen fermentation (Huhtanen 1988; 1992). The increase in the plasma butyrate concentration with increasing amount of WDS in the diet indicates either an increased postprandial absorption of butyrate from the rumen (Stern et al. 1970; de Jong 1982; Huhtanen et al. 1992) or dif- ferences in the conversion of butyrate to BHB both in the rumen epithelium and liver. The ratio of plasma butyrate to blood BHB increased with the level of WDS in the diet from 0.031 to 0.050, indi- cating a decreased conversion of butyrate to BHB in the rumen epithelium or in the liver. The blood concentration of ketones decreased slightly with increasing amount of WDS in the diet. This sug- gests that either BHB was cleared more rapidly or that ketogenesis decreased when glucose availabil- ity increased in relation to energy requirements (Amaral et al. 1990). Similarly, Orskov and MacLeod(1990) reported that an increase in blood glucose concentration with decreased blood BHB concentration. The increased intake of protein was the obvious reason for the increased plasma urea concentration with increasing rate of WDS inclusion in the diet (Oltner and Wiktorsson 1983; Ropstad et al. 1989; Clement et al. 1991), which indicates ineffi- cient use of extra protein supplied by WDS. The concentration of urea in milk also increased with the level of WDS in the diet, although the relative increase of urea was much smaller in milk than in plasma. It is concluded that the substitution ofbarley with WDS increased yields ofmilk, protein and lactose. This may be due to greater absorption of gluco- genic precursors from the digestive tract and increased hepatic gluconeogenesis. Acknowledgements. 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Manuscript received March 1992 Pekka Huhtanen University ofHelsinki Department of Animal Science SF-00710 Helsinki, Finland Harri Miettinen Valio, Research and Development Centre Box 176 SF-00181 Helsinki, Finland SELOSTUS Tärkkelysrankin vaikutus maidontuotantoon ja veren metaboliitteihin lypsylehmillä säilörehuun perustuvalla ruokinnalla Pekka Huhtanen ja Harri Miettinen Helsingin yliopisto ja Valion tutkimus- ja tuotekehityskeskus Tuoreen tärkkelysrankin vaikutuksia rehun syöntiin ja sula- vuuteen, maidontuotantoon ja verimetaboliitteihin tutkittiin 12 ay-rotuisella lehmällä tasapainotetun latinalaisen neliön mukaan tehdyssä kokeessa. Lehmät saivat säilörehua vapaasti ja litistettyä ohraa 9 kg/pv, jonka kuiva-aineesta 0 (TRO), 1 (TRI), 2 (TR2) ja 3 kg (TR3) korvattiin tuoreen tärkkelysrankin kuiva-aineella. Tärkkelysrankki paransi väkirehun maittavuutta, minkä tuloksena säilörehun syönti vaihteli käyräviivaisesti (P<0.05) rankkitason mukaan ollen pienin TRI-ruokinnalla. Kuiva-aineen syönti (P<0.05), mai- totuotos (P<0.05) ja laktoosituotos (P<0,01) lisääntyivät lineaarisesti rankkimäärän lisääntyessä. Rankkimäärän kas- vaessa valkuaistuotos lisääntyi sekä lineaarisesti (P<0.05) että käyräviivaisesti (P<0.05) saavuttaen maksiminsa TR2- ruokinnalla. Rankilla ei ollut merkitsevää vaikutusta maidon rasva- tai valkuaispitoisuuteen, mutta laktoosipitoisuus nousi (P<0.01) rankkimäärän lisääntyessä. Ohran asteittai- nen korvaaminen rankilla lisäsi plasman glukoosi- (PO. 10), voihappo- (PO. 10), urea- (P0.001) ja vapaiden rasvahap- pojen (P0.05) pitoisuutta. Ruokinnan jälkeiset maksimit plasman propionihappo-, voihappo-, insuliini- ja ureapitoi- suudessa lisääntyivät rankkitason lisääntyessä. Vastaavasti veren ketoaineiden pitoisuudet ruokinnan jälkeen vähenivät. Veriplasman metaboliiittien keskimääräisten pitoisuuksien ja ruokinnan jälkeisten muutosten perusteella arvioituna rankki näyttäisi lisäävän maksan glukoneogeneesiä ja urea- synteesiä. Lisääntynyt glukoosin tuotanto on todenäköisesti peräisin pötsin lisääntyneestä propionihapon tuotannosta rankin sisältämän maitohapon käydessä pääasiassa propioni- hapoksi. Muutokset maidon koostumuksessa ja maidon komponenttien suhteellisissa tuotoksissa tukevat näitä johto- päätöksiä. 290 Agric. Sei. Finl. 1 (1992)