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Fatty Acid Metabolism in Liver of Dairy Cows Fed Supplemental Fat and Nicotinic Acid During an Entire Lactation¹

Department of Animal Sciences, University of Illinois, Urbana 61801

Corresponding author:
J. K. Drackley; e-mail:
drackley{at}uiuc.edu.

Liver biopsies from 38 multiparous Holstein cows were used to determine rates of peroxisomal ß-oxidation and total ß-oxidation of palmitate in liver homogenates and contents of total lipid, triglyceride, and glycogen during the lactation cycle. Cows were assigned to one of four diets from wk 4 through wk 42 of lactation: control, control plus nicotinic acid (12 g/d), supplemental fat, or supplemental fat plus nicotinic acid. Liver biopsies were obtained at wk 3 (covariate), 6, 12, 24, and 42 of lactation. Neither supplemental fat nor nicotinic acid affected palmitate oxidation in liver homogenates or liver composition. Peroxisomal ß-oxidation capacity and the ratio of peroxisomal to total ß-oxidation decreased from wk 3 to 12 and then increased at wk 42. Contents of total lipid and triglyceride decreased, and content of glycogen increased, from wk 3 to 12. Total oxidation capacity in liver homogenates was correlated negatively with total lipid and triglyceride in liver, yields of milk and solids-corrected milk (SCM), and plasma nonesterified fatty acids (NEFA), and was correlated positively with liver glycogen, dry matter intake (DMI), energy balance, and plasma glucose. Peroxisomal ß-oxidation was correlated negatively with yields of milk and SCM. The ratio of peroxisomal to total ß-oxidation was correlated positively with liver total lipid, liver TG, and plasma NEFA and negatively with DMI and energy balance. When only data from wk 3 postpartum were considered, both total and peroxisomal ß-oxidation were correlated negatively with hepatic concentrations of total lipid and TG. Peroxisomal ß-oxidation in liver of dairy cows is not affected by feeding supplemental fat or nicotinic acid during wk 4 to 42 of lactation but may be a part of the hepatic adaptations to negative energy balance.

Key Words: peroxisomes • fatty acid metabolism • fat • liver

Abbreviation key: LCFA = long-chain fatty acids, NA = nicotinic acid, PPAR = peroxisome proliferator-activated receptor-, TG = triglyceride.

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