Prepared commercial formulas are commonly made from cow's milk. They come in three forms: ready to use liquid, concentrated liquid, and powdered. In order to make them somewhat more like human milk in effect, the percentages of protein and salt have been reduced, the sugar has been increased with the addition of lactose, and the cows butterfat has been replaced with vegetable oils. Vitamins a,c, and D have been added. Prepared formulas are available with or without iron, according to the doctor's advice.