Effect of Dietary Fat and Postruminal Casein Administration on Milk Composition of Lactating Dairy Cows

Perturbation of the amino acid status of lactating dairy cows was undertaken to characterize the mechanism of dietary fatinduced milk protein depression. Four first lactation heifers fitted with rumen cannulas were assigned to a'factorial arrangement of treatments: two diets and two casein infusion sites within a 4 x 4 Latin square design. Diets were formulated with yellow grease at 0 or 4% of DM. An 8% sodium casehate solution was infused continuously at 5.04 kg/d (SE = .05) into the rumen or abomasum during the last 5 d of each 21d period.