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Biochemical and Molecular Roles of Nutrients Higher Postpartum Hepatic Triacylglycerol Concentrations in Dairy Cows with Free rather than Restricted Access to Feed During the Dry Period Are Associated with Lower Activities of Hepatic Glycerolphosphate Acyltransferase1'2 A. MARC VAN DEN TOP,3 MATH J. H. GEELEN,* THEO WENSING, G. HENK WENTINK, ARIE TH. VAN 'T KLOOSTER, AND ANTOH C. BEYNEN Department of Large Animal Medicine and Nutrition and "Laboratory of Veterinary Biochemistry, Faculty of Veterinary Medicine, Utrecht Uniuersity, 3508 TD Utrecht, The Netherlands ABSTRACT We investigated the activities of hepatic glycerolipid synthesizing enzymes during postpartum fatty liver development in 10 high-producing dairy cows that had free access to feed during the dry period; a parallel group of 8 control cows was fed according to recommended energy requirements. After calving, both test and control cows had free access to feed. In the period of 10-14 wk before calving, voluntary dry matter intake of the test cows was 20.6 kg/d (SEM0.42); the restricted control cows received 7 kg/d. Postpartum triacy Iglycerol concentrations in liver biopsies were oneto twofold higher in the test than in the control cows. The higher plasma nonesterifled fatty acid (NEFA) con centrations after parturition in the test vs. the control group were probably caused by a more negative energy balance in the test cows, which was associated with a slightly lower postpartum dry matter intake. After calving, hepatic mitochondria! glycerolphosphate acyltransferase (GPAT) activities were significantly lower in the test than in the restricted control cows. A low GPAT activity may divert fatty acids from esterification to /^-oxidation to protect the hepatocytes against further accumulation of triacylglycerols. The activities of he patic phosphatidate phosphohydrolase, diacyIglycerol acyltransferase, and cholinephosphate cytidylyltransferase were not different in the two groups. This study indicates that in cows given free instead of restricted access to feed during the dry period have a postpartum hepatic triacy Iglycerol accumulation that is mainly de termined by a raised hepatic uptake of plasma NEFA. J. Nutr. 126: 76-85, 1996. INDEXING KEY WORDS: •dairy cows •dry period •fatty liver •glycerolipid-synthesizing enzymes Fatty liver development in periparturient dairy cows (Reid 1980) is associated with impaired health, fertility and production (Morrow et al. 1979, Reid and Roberts 1983). Fatty liver, i.e., accumulation of triacylglycer ols, may develop after liberal feeding during the final phase of the lactation and the dry period (Fronk et al. 1980, Johannsen et al. 1988, Reid et al. 1986). Overconditioned cows, when compared with normal cows, have less appetite at calving (Bines and Morant 1983,Garnsworthy and Topps 1982), which, in com bination with the high energy need for the onset of milk production, results in a greater negative energy balance. As a result, the overconditioned cows mobi lize more fat from their adipose tissue stores, which is mirrored in higher plasma nonesterified fatty acid (NEFA)4levels (Fronk et al. 1980, Reid et al. 1986). The fatty acids can be oxidized or esterified by the liver, and, if esterified, are secreted from the liver with VLDL particles. Because the ruminant liver cannot rapidly upgrade VLDL production, possibly because of a nonflexible synthesis of apoprotein B (Marcos et al. 1990), accumulation of triacylglycerols in the liver can occur when NEFA concentrations fise suddenly. Fatty liver development in dairy cows may be ini tiated by a rise in plasma NEFA concentrations, but the response of glycerolipid-synthesizing enzymes is ' Research in the Laboratory of Veterinary Biochemistry was supported by the Nehterlands Foundation for Chemical Research (SON) with financial aid from the Netherlands Organisation for Sci entific Research (NWO). 2 The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact. 3To whom correspondence should be addressed. 4 Abbreviations used: CPCT = cholinephosphate cytidylyltransferase; DGAT = diacylglycerol acyltransferase; GPAT = glycerol phosphate acyltransferase; NEFA = nonesterified fatty acids; PAP = phosphatidate phosphohydrolase. 0022-3166/96 $3.00 ©1996 American Institute of Nutrition. Manuscript received 20 March 1995. Initial review completed 15 June 1995. Revision accepted 25 September 1995. 76 Downloaded from jn.nutrition.org by guest on December 18, 2012

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