Production, digestion, and hepatic lipid metabolism of dairy cows fed increased energy from fat or concentrate.

Eight Holstein cows (mean = 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 NEI/kg), 2) low concentrate with supplemental fat (1.7 Mcal/kg), 3) high concentrate without supplemental fat (1.7 Mcal/kg), and 4) high concentrate with 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 concentrate. Contents of CP, true protein, and casein in milk were decreased by supplemental fat and increased by high concentrate. Digestibility of fatty acids was decreased by either supplemental fat or high concentrate. Concentrations of NEFA and somatotropin in plasma were increased, and concentration of IGF-I was decreased, by supplemental fat; NEFA, BHBA, and IGF-I were decreased by high concentrate. In vitro rates of peroxisomal beta-oxidation and esterification of palmitate and concentrations of total lipid and triglycerides in liver were not different among diets, but glycogen content was increased by high concentrate. The rate of total beta-oxidation of palmitate in liver slices tended 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 dairy cows; effects of dietary fat during the periparturient period deserve investigation.