INFUSION OF LONG-CHAIN FATTY-ACIDS VARYING IN SATURATION AND CHAIN-LENGTH INTO THE ABOMASUM OF LACTATING DAIRY-COWS

Free long-chain fatty acids were infused into the abomasum of lactating dairy cows to determine postruminal effects on feed intake, production and composition of milk nutrient digestibilities, and metabolites in blood. Four Holstein cows averaging 120 DIM and fitted with ruminal cannulas were used in a 4 x 4 Latin square design with 14-d periods. Treatments were abomasal infusions of 1) control, 168 g/d of meat solubles (carrier for fatty acids), 2) control plus 450 g/d of mostly saturated fatty acids (C-16:C18 = .75), 3) control plus 450 g/d of a mixture of saturated and unsaturated fatty acids (C-16:C18 = .40), and 4) control plus 450 g/d of mostly unsaturated fatty acids (C-16:C18 = .11). Production of milk and milk components, DMI, and intake of digestible energy decreased linearly as unsaturation and chain length of infused fatty acids increased. Percentages of fat, CP, and SNF in milk and total tract apparent digestibilities of DM, OM, ADF, NDF, energy, and fatty acids were not affected significantly by treatments. Infusing fatty acids decreased proportions and yields of short- and medium-chain fatty acids and increased proportions and yields of unsaturated C18 fatty acids in milk fat. Increasing unsaturation and chain length of infused fatty acids linearly decreased proportion and yield of palmitic acid but increased proportions and yields of polyunsaturated C18 fatty acids in milk fat. Infusing fatty acids increased concentrations of NEFA and cholesterol in blood plasma. The profile of fatty acids reaching the intestine may be an important determinant of responses to supplemental fats fed to lactating dairy cows.