Thirty-two cows, averaging 112 DIM, were assigned to four dietary treatments: 1) control, 2) Ca salts of fatty acids, 3) nicotinamide, and 4) Ca salts of fatty acids blended with nicotinamide during manufacture. Preliminary studies showed that nicotinamide survives blending with Ca salts of fatty acids during manufacture and that a blended mixture of nicotinamide and Ca salts of fatty acids gave results similar to those from nicotinamide plus Ca salts of fatty acids supplemented separately. Calcium salts of fatty acids increased milk fat percentage, decreased milk protein percentage, but had no effect on production of milk, FCM, fat, or protein. Nicotinamide increased production of milk and protein, decreased fat percentage, but had no effect on either production of FCM and protein or percentage of protein. Calcium salts of fatty acids increased NEFA in blood, and dietary nicotinamide increased concentrations of nicotinamide in blood, but glucose and BHBA in blood were unaffected by either dietary ingredient. Therefore, in these midlactation cows, the decreased milk protein percentage caused by supplemental dietary fat was prevented by nicotinamide. Supplementation with only nicotinamide increased total production of milk protein.