Once again, infants should remain on cow's milk prior to one year of age. First, cow's milk is for baby cows. It is not designed to be the main source of human infant nutrition. It has too much salt, few vitamins, and no iron. Up until a year, an infant is still drinking large quantities of milk.
Milk has a lot of calories.
If one adds up the infant's total caloric intake, a large percentage is still coming from his formula or milk. It is not nutritionally good for cow's milk to be the main source of calories for an infant. It's OK to have some cow's milk, but not the majority of the diet. In addition, studies have shown that infants less that one year of age are far more likely to be iron deficient and anemic if cow's milk is introduced too early. Furthermore, in those infants that drink more than one quart of cow's milk daily run a greatly increased risk of small amounts of blood being lost in their bowels.