HIGH-FAT DIETS INCREASE PLASMA CHOLECYSTOKININ AND PANCREATIC-POLYPEPTIDE, AND DECREASE PLASMA-INSULIN AND FEED-INTAKE IN LACTATING COWS

High fat diets often decrease feed intake in dairy cows; however, mech anisms underlying fat-induced depression of feed intake are yet to be established. The;postulate that high fat diets decrease feed intake by increasing concentrations of lipid metabolites or satiety hormones in blood was tested by using eight multiparous Holstein cows in a simult aneously replicated 4 x 4 Latin-square design. Treatments were control diet with I) no fat added, 2) 30 g/kg calcium salts of long-chain fat ty acids, 3) 60 g/kg calcium salts of long-chain fatty acids, and 4) 9 0 g/kg calcium salts of long-chain fatty acids. Cows were fed once dai ly a diet of concentrate, corn silage, alfalfa haylage and alfalfa hay (50:25:14:11 on a dry matter basis). Dry matter and energy intakes we re decreased by inclusion of calcium salts of long-chain fatty acids > 30 g/kg of total diet dry matter (P = 0.0001). Plasma nonesterified fa tty acids and triglyceride concentrations were increased linearly by f eeding increasing amounts of fat (P < 0.003 and P = 0.0001, respective ly), whereas plasma beta-hydroxybutyrate and glucose concentrations-we re not influenced by supplemental fat. Fat supplementation increased p ostfeeding plasma cholecystokinin concentrations and linearly increase d plasma pancreatic polypeptide concentrations. Highest concentrations of plasma cholecystokinin (P < 0.001) and pancreatic polypeptide (P < 0.05) were observed in cows fed the 90 g/kg fat supplement. Plasma in sulin was lowered linearly by feeding fat (P = 0.0001). Increased conc entrations of cholecystokinin and pancreatic polypeptide were associat ed with decreased intakes of feed and energy, whereas insulin may not be involved in the control of feed intake in cows fed fat.