PRODUCTION, DIGESTION, AND HEPATIC LIPID-METABOLISM OF DAIRY-COWS FEDINCREASED ENERGY FROM FAT OR CONCENTRATE

Eight Holstein cows ((X) over bar = 52 DIM) were used in a replicated Latin square design (28-d periods) to determine the effects of source and amount of dietary energy on hepatic lipid metabolism. Diets were 1 ) low concentrate without supplemental fat (1.6 Mcal of NE(I)/kg), 2) low concentrate with supplemental fat (1.7 Mcal/kg), 3) high concentra te without supplemental fat (1.7 Mcal/kg), and 4) high concentrate wit h supplemental fat (1.8 Mcal/kg). Intakes of DM and digestible energy were greatest for diets 2 and 3. Milk production, efficiency, and milk CP production were not different among diets. Milk fat percentage and production were increased by supplemental fat and decreased by high c oncentrate. Contents of CP, true protein, and casein in milk were decr eased by supplemental fat and increased by high concentrate, Digestibi lity of fatty acids was decreased by either supplemental fat or high c oncentrate. Concentrations of NEFA and somatotropin in plasma were inc reased, and concentration of IGF-I was decreased, by supplemental fat; NEFA, BHBA, and IGF-I were decreased by high concentrate. In vitro ra tes of peroxisomal beta-oxidation and esterification of palmitate and concentrations of total lipid and triglycerides in liver were not diff erent among diets, but glycogen content was increased by high concentr ate, The rate of total beta-oxidation of palmitate in liver slices ten ded to be increased by supplemental fat; total metabolism of palmitate was increased by supplemental fat and tended to be increased by high concentrate. Supplemental fat may affect hepatic lipid metabolism in d airy cows; effects of dietary fat during the periparturient period des erve investigation.