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Hepatic lipid metabolism and peroxisomal beta-oxidation in dairy cows
Five experiments were conducted to measure peroxisomal $beta$-oxidation in the liver of cows and to determine the effects of physiological state and source of dietary energy (carbohydrate or lipid) on liver metabolism, blood metabolites, and production variables. The in vitro capacity for peroxisomal $beta$-oxidation of palmitate in liver homogenates represented approximately 50% of the total $beta$-oxidative capacity in cows but only 30% in rats. Fasting increased peroxisomal $beta$-oxidation in rats but not cows. The rate of peroxisomal $beta$-oxidation was not altered by diet during midlactation, but increased in late lactation. Feeding supplemental fat throughout the dry period increased the rate of peroxisomal $beta$-oxidation. Dietary fat can increase the rate of peroxisomal $beta$-oxidation, but this appears to be limited to the periparturient period. When supplemental dietary energy was fed as carbohydrate or lipid, the rate of palmitate esterification in liver slices from cows in midlactation was not altered, but esterification decreased when fat was fed throughout the dry period. Feeding supplemental fat throughout the dry period decreased hepatic concentrations of total lipid and triglyceride after parturition; the decrease was related to increased peroxisomal $beta$-oxidation, decreased esterification, and decreased concentration of NEFA in plasma. Source of dietary energy did not alter the accumulation of total lipid or triglyceride in the liver of cows in mid-or late lactation. Hepatic glycogen content was increased by feeding additional concentrate throughout the dry period or during midlactation. Nicotinic acid increased hepatic concentration of total lipid when it was added to a control diet but decreased hepatic lipid when added to a fat-supplemented diet during early lactation. Milk production was not altered by source of dietary energy but was increased by nicotinic acid. Yield and percentage of milk fat decreased when cows in midlactation were fed diets supplemented with additional concentrate, but increased when diets were supplemented with fat. Feeding supplemental fat during the dry period decreased milk fat percentage and yield during early lactation, but did not affect milk production. Yields and percentages of milk CP and N fractions generally were not changed by source of dietary energy. Feeding additional concentrate decreased the digestibility of fatty acids of cows in midlactation.
- "Five experiments were conducted to measure peroxisomal $beta$-oxidation in the liver of cows and to determine the effects of physiological state and source of dietary energy (carbohydrate or lipid) on liver metabolism, blood metabolites, and production variables. The in vitro capacity for peroxisomal $beta$-oxidation of palmitate in liver homogenates represented approximately 50% of the total $beta$-oxidative capacity in cows but only 30% in rats. Fasting increased peroxisomal $beta$-oxidation in rats but not cows. The rate of peroxisomal $beta$-oxidation was not altered by diet during midlactation, but increased in late lactation. Feeding supplemental fat throughout the dry period increased the rate of peroxisomal $beta$-oxidation. Dietary fat can increase the rate of peroxisomal $beta$-oxidation, but this appears to be limited to the periparturient period. When supplemental dietary energy was fed as carbohydrate or lipid, the rate of palmitate esterification in liver slices from cows in midlactation was not altered, but esterification decreased when fat was fed throughout the dry period. Feeding supplemental fat throughout the dry period decreased hepatic concentrations of total lipid and triglyceride after parturition; the decrease was related to increased peroxisomal $beta$-oxidation, decreased esterification, and decreased concentration of NEFA in plasma. Source of dietary energy did not alter the accumulation of total lipid or triglyceride in the liver of cows in mid-or late lactation. Hepatic glycogen content was increased by feeding additional concentrate throughout the dry period or during midlactation. Nicotinic acid increased hepatic concentration of total lipid when it was added to a control diet but decreased hepatic lipid when added to a fat-supplemented diet during early lactation. Milk production was not altered by source of dietary energy but was increased by nicotinic acid. Yield and percentage of milk fat decreased when cows in midlactation were fed diets supplemented with additional concentrate, but increased when diets were supplemented with fat. Feeding supplemental fat during the dry period decreased milk fat percentage and yield during early lactation, but did not affect milk production. Yields and percentages of milk CP and N fractions generally were not changed by source of dietary energy. Feeding additional concentrate decreased the digestibility of fatty acids of cows in midlactation."@en
- "Hepatic lipid metabolism and peroxisomal beta-oxidation in dairy cows"@en