Abstract Supplement containing animal tallow protected with formaldehyde-treated soybean meal was introduced into concentrates at 0, 21, and 32% and fed ad libitum to Holstein cows in a changeover design during early lactation. Primary objective was to determine whether feeding protected tallow in concentrates would increase voluntary energy intake, milk yield, and fat test without adversely affecting other milk components or flavor. Intakes of total dry matter and from concentrates were decreased, dry matter from forage increased, and energy intake was unchanged by feeding protected tallow at each percent. Treatments did not affect milk yield significantly but did increase output of 4% fat-corrected milk. Solids-corrected milk yield and gross energetic efficiency were not improved consistently by feeding protected tallow. Supplement increased fat tests by .43 and .76 percentage units over control when fed at 21 and 32% but lowered protein and lactose content of milk. Cholesterol, formaldehyde, and flavor of milk were unaffected by treatment whereas cholesterol and triglycerides in blood plasma rose dramatically during short-term feeding of protected tallow. Blood glucose remained unchanged.