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, mechanisms 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 simultaneously replicated 4 x 4 Latin-square design. Treatments were control diet with 1) no fat added, 2) 30 g/kg calcium salts of long-chain fatty acids, 3) 60 g/kg calcium salts of long-chain fatty acids, and 4) 90 g/kg calcium salts of long-chain fatty acids. Cows were fed once daily 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 were decreased by inclusion of calcium salts of long-chain fatty acids >30 g/kg of total diet dry matter (P = 0.0001). Plasma nonesterified fatty acids and triglyceride concentrations were increased linearly by feeding increasing amounts of fat (P < 0.003 and P = 0.0001, respectively), whereas plasma beta-hydroxybutyrate and glucose concentrations were not influenced by supplemental fat. Fat supplementation increased postfeeding plasma cholecystokinin concentrations and linearly increased 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 insulin was lowered linearly by feeding fat (P = 0.0001). Increased concentrations of cholecystokinin and pancreatic polypeptide were associated with decreased intakes of feed and energy, whereas insulin may not be involved in the control of feed intake in cows fed fat.