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TABLE 1 Composition of

TABLE 1 Composition of the ration as fed Ingredient, g/kg Grass silage Corn silage Solvent extracted rapeseed meal Sugar beet pulp pellets Concentrate Chemical analysis, g/kg Dry matter Crude protein Crude fiber Crude fat Ash GLYCEROLIPID SYNTHESIS IN BOVINE FATTY LIVER 77 140 630 23 47 160 524.5 71.0 96.3 26.3 38.0 1 The concentrate consisted of (g/kg): corn meal, 100; wheat meal, 20; dehydrated sugarbeet pulp, 125; dehydrated citruspulp, 100; solvent extracted soybean meal, 70; tapioca, 25; palmnuts, 3; palmnut expeller, 50; coconut expeller, 30; corn gluten feed, 350; linseed, 10; linseed expeller, 25; sugar cane molasses, 30; premix, 62. The premix consisted of two proprietary preparations (g):Rundvee Geel*, 22; Vevomix«,40 (Brokking, Lopik, The Netherlands). unknown. Hepatic triacylglycerol synthesis is regu lated by the activities of glycerolphosphate acyltransferase (GPAT, EC, phosphatidate phosphohydrolase (PAP, EC and diacylglycerol acyltransferase (DGAT, EC among others. In sheep with fatty liver induced by administration of phloridzin plus epinephrine, the activity of PAP was raised and to a lesser extent that of GPAT also (Herdt et al. 1988). In drug-treated sheep there were raised plasma NEFA concentrations and raised hepatic DGAT activities (Herdt et al. 1988). Hepatic DGAT is under positive feed-forward control by fatty acids (Haagsman and Van Golde 1981). Thus, we hypoth esized that the postpartum activity of DGAT is higher in overconditioned cows developing fatty liver than in cows that had been fed restricted amounts of feed during the dry period. Hepatic cholesterol levels may be unaltered, but hepatic phospholipid levels may be lowered in cows developing fatty liver after calving (Fronk et al. 1980). One of the major phospholipids in liver is phosphatidylcholine. Therefore, the activity of cholinephosphate cytidylyltransferase (CPCT, EC, which regulates the synthesis of phospha tidylcholine, may be lower in cows with fatty liver. Fatty liver in sheep induced by administration of phloridzin plus epinephrine was associated with de pressed hepatic CPCT activities (Herdt et al. 1988). The development of fatty liver may have conse quences for serum lipid concentrations. Serum con centrations of triacylglycerols, phospholipids and total cholesterol have been shown to be low in cows with fatty liver (Fronk et al. 1980, Holtenius 1989), but the postpartum time course of these lipids in affected and control cows has not yet been investigated in detail. Contrary to the findings of Fronk et al. (1980) and Holtenius (1989), Uhlig et al. (1988) showed raised serum cholesterol concentrations in cows with fatty liver when compared with normal cows. In this experiment we used two groups of dairy cows, one of which was given free access to feed during the dry period, and the other fed according to the energy requirements as set by the National Research Council (1989). After parturition, the animals of both groups were given free access to feed. The objective of this study was to obtain information about the activities of hepatic glycerolipid synthesizing enzymes and serum lipid con centrations in periparturient dairy cows developing fatty liver after overfeeding during the dry period when com pared with control cows. Accumulation of triacylgly cerols in the bovine liver is associated with increased plasma activities of láclatedehydrogenase and aspartate aminotransferase (Uhlig et al. 1988). To further char acterize the cows used we not only determined these two serum liver-damage-indicator enzymes, but also measured serum alkaline phosphatase activity and total bilirubin concentrations. MATERIALS AND METHODS Animals and diets. We used 18 pregnant, multiparous Holstein Friesian X Dutch Friesian cows. Eight of the cows were allocated to the control group (mean age 4.9 ±0.32 y [mean ±SEM];mean milk production 9154 ±716 kg in the previous 305 d) and 10 to the test group (mean age 4.8 ±0.21 y; average milk production 8702 ±250 kg in the previous 305 d). Average body weights at the start of the experiment, i.e., 2-3 mo before parturition, were 650 ±19.3 kg and 643 ±17.2 kg for the control and the test group, respectively. All cows were housed in a stanchion barn with wheat straw as bedding material. They were fed individually and had free access to tap water. All cows were fed grass silage and a mixed ration of corn silage and concentrates throughout (Table 1). After parturition each cow also received 1 kg of solvent extracted rapeseed per day for each 10 kg of dry matter feed intake. The rapeseed meal was composed of (g/kg): dry matter, 925; crude protein, 339; crude fiber, 123; crude fat, 33; ash, 71. During the 2 to 3-mo dry period the control cows were fed at the energy level indicated by the National Research Council (1989), and the cows in the test group were given free access to feed. At regular intervals throughout the ex periment, feed samples and orts were collected to cal culate dry matter intake. One week before the expected calving date, the control cows were also given free access to feed. Thus, after parturition all cows had free access to feed. Animals were weighed at regular intervals before and after parturition, and milk yields were recorded daily. The experimental design was approved by the an imal experiments committee of the Faculty of Veterinary Medicine. Sampling procedures and sample preparation. Blood and liver samples were collected at 0.5 wk an- Downloaded from by guest on December 18, 2012

78 VAN DEN TOP ET AL. tepartum and at 0.5, 1, 1.5, 2, 3, 5, 8 and 12 wk postpartum. Blood was also sampled at 4 wk antepartum. Blood was collected from the tail vein in evacuated tubes, and liver biopsies were obtained as described (Van den Top et al. 1995). For plasma NEFA and serum insulin determination, the samples were stored at -20°C. Liver tissue samples were homogenized with five strokes of a glass-Teflon Potter-Elvehjem tissue homogenizer in 9 volumes of a buffer containing 0.25 mol/L sucrose, 20 mmol/L Tris-HCl (pH 7.4) and 1 mmol/L Na EDTA. The homogenate was centrifuged at 600 X g for 5 min. The supernatant was recentrifuged at 10,000 X g for 15 min. The pellet was termed mitochondrial fraction. From the supernatant a microsomal pellet was obtained by centrifugation at 105,000 X g for 65 min. The final supernatant was termed cytosol. Assay procedures. Samples of the feed compo nents were subjected to the Weende analysis (Joslyn 1970). For protein determination, nitrogen was mea sured with the Kjeldahl method (Nederlands Normalisatie Instituut 1966) and multiplied by 6.25. For crude fat determination the Folch et al. method (1957) was used. Feed samples were incinerated at 550°C for 12 h in a furnace to determine ash content. Plasma glucose, serum total cholesterol, total bilirubin, alkaline phosphatase (EC, aspartate aminotransferase (EC, lactate dehydrogenase (EC; Beckman Instruments B.V., Mijdrecht, The Netherlands), free cholesterol, 3-hydroxybutyrate (Boehringer Mannheim GmbH, Almere, The Neth erlands), phospholipids (bioMérieux, Marcy-FEtoile, France) and plasma NEFA (NEFA C, Instruchemie B.V., Hilversum, The Netherlands) were determined enzymatically with commercially available kits (glu cose kit no. 442640; total cholesterol kit no. 467825; total bilirubin kit no. 442745; alkaline phosphatase kit no. 443799; asparate aminotransferase kit no. 442665; lactate dehydrogenase kit no. 442660; free cholesterol kit no. 310328; 3-hydroxybutyrate kit no. 127841, phospholipids kit no. 61491). Serum insulin concentrations were determined using an RIA kit (Coat-a-Count® Insulin, Diagnostic Products Corpo ration, Los Angeles, CA). The accuracy of each assay was monitored with the use of a commercial reference serum sample (Beckman Multilevel Decision Com prehensive Control Serum, Beckman Instruments B.V. Mydrecht, The Netherlands) and the outcome deviated

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