High-oil, high-protein diets and milk secretion by cows.

Intakes of grass silage and yield and composition of milk were examined in cows given high-protein diets to which two quantities of soybean oil had been added either as intracellular or extracellular inclusions. Adding extra protein to the diet did not prevent reduction of dry matter intakes of forage when soybean oil was added to the diet of cows. There is a fundamental difference in the mechanism by which high-starch diets reduce intake of forage dry matter from that of high-oil diets. In diets containing extracellular unsaturated oils, concentration of oil in the total ration, not the amount of oil per se, is the primary determinant reducing milk fat percentage.