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 (SEM 0.42); the restricted control cows received 7 kg/d. Postpartum triacylglycerol concentrations in liver biopsies were one- to twofold higher in the test than in the control cows. The higher plasma nonesterified fatty acid (NEFA) concentrations 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 mitochondrial 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 beta-oxidation to protect the hepatocytes against further accumulation of triacylglycerols. The activities of hepatic phosphatidate phosphohydrolase, diacylglycerol 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 triacylglycerol accumulation that is mainly determined by a raised hepatic uptake of plasma NEFA.

We studied development of fatty liver in high producing dairy cows with free access to feed during the dry period and thus showed the combined effects of parturition and prepartum overfeeding. Postpartum liver triacylglycerol concentrations at 1 wk postpartum, as measured in liver biopsies, had increased more than 6-fold, which was preceded or accompanied by an increase in plasma NEFA concentrations. Concentrations of hepatic phospholipid changed only slightly. The amounts of total lipids in serum, very low density lipoproteins, and high density lipoproteins significantly decreased by .5 wk after parturition, and concentrations of high density lipoproteins rose steadily. The pattern was similar for concentrations of total cholesterol and phospholipid in serum. Total lipid concentrations in low density lipoproteins were not altered after parturition. The activity of microsomal phosphatidate phosphohydrolase in the liver showed a transient increase at .5 wk after calving, but activity of microsomal glycerolphosphate acyltransferase remained relatively constant. The activities of diacylglycerol acyltransferase had increased about twice at 1 wk after calving and remained at this high level until at least 4 wk after parturition. The rise in activity of diacyglycerol acyltransferase was probably a response to the extra influx of fatty acids to channel them into triacylglycerol. Activities of microsomal cholinephosphate cytidylyltransferase initially increased after calving and then decreased slightly. Activities of hepatic choline kinase had increased after calving. This study indicates that hepatic triacylglycerol accumulates because of the increased hepatic uptake of NEFA and the simultaneous increase in activity of diacylglycerol acyltransferase.

Cholesterol and phospholipid concentrations in serum lipoproteins, plasma activities of lecithin:cholesterol acyltransferase (LCAT) and phospholipid transfer protein (PLTP) and lipoprotein lipase (LPL) activity in adipose tissue biopsies were measured ante and post partum in dairy cows given either free or restricted access to feed during the dry period. After parturition, all cows were fed ad libitum. The purpose of this study was to try to understand the earlier observed marked drop post partum in plasma triacylglycerol (TAG) in terms of lipoprotein metabolism in cows developing fatty liver post partum. As would be expected, free access to feed during the dry period induced a rise of hepatic TAG concentrations post partum associated with a decrease in plasma TAG levels. Total and free cholesterol concentrations in the VLDL, IDL, LDL and HDL2 fractions fell immediately after parturition. VLDL and IDL cholesterol concentrations remained at a constant, low level during the entire sampling period post partum, whereas the drop in LDL and HDL2 cholesterol post partum was followed by a rebound rise. Plasma LCAT and PLTP activities decreased by on average 19% and 33%, respectively, after parturition and then rose to values seen before parturition, but there was no effect of feeding regimen during the dry period. Activities of LCAT and PLTP were significantly correlated with cholesterol and phospholipid concentrations in LDL and HDL2. Plasma LCAT activity, as measured with exogenous substrate, and PLTP activity were both positively correlated with HDL3 phospholipid levels. LPL activity in adipose tissue dropped after parturition, the drop being smaller after feeding ad libitum during the dry period. It is concluded that the drop in adipose tissue LPL activity post partum is at variance with the simultaneous fall in plasma TAG. Possibly, the decrease in adipose tissue LPL activity helps to channel fatty acids away from adipose tissue into the udder. The post-partum changes in lipid transfer proteins in the blood are in line with the changes observed in the levels of the lipoproteins.

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The hypothesis was tested that goats allowed ad libitum access to feed during the dry period develop higher post partum hepatic triacylglycerol concentrations than do goats given a restricted amount of feed during the dry period. Goats in their second or more pregnancies were either given a restricted amount of hay, maize silage and concentrate (n = 5) or had free access to this feed mixture while the composition was kept constant (n = 11). After parturition both groups were allowed ad libitum access to feed. Post partum liver triacylglycerol concentrations, as measured in liver biopsies, were significantly raised in goats allowed ad libitum access to feed during the dry period. The increase in liver triacylglycerols was associated with slightly higher plasma concentrations of non-esterified fatty acids but lower serum 3-hydroxybutyrate concentrations. The feeding regimen during the dry period did not significantly influence post partum liver glycogen concentrations and serum levels of glucose, cholesterol, and insulin. The increase in post partum liver triacylglycerol concentrations in the goats allowed ad libitum access to feed instead of a restricted ration during the dry period, was associated with a significant rise in serum alkaline phosphatase activities, whereas other liver function and cell damage indicators in serum, i.e. aspartate aminotransferase, lactate dehydrogenase, gamma glutamyl transpeptidase, and bilirubin, were unchanged. Feed intake after parturition tended to be higher in the goats allowed ad libitum access to feed during the dry period but milk production was significantly raised.(ABSTRACT TRUNCATED AT 250 WORDS)