In human infants this occurs around the age of one. Breast-feeding is a kind of natural immunization for the infant, providing the mother's antibodies to protect and support the child's immature immune system. Cow's milk was designed to bring a calf to a 2,000 pound cow in one year's time. It was not meant for human infants. No animals, except for humans, consume milk after being weaned.
Many infants drink between one and two quarts of milk on a daily basis.
Although this acts to satisfy their hunger, they are often left with little room for vital iron-containing foods. Cow's milk can produce iron deficiency by providing little dietary iron itself, and at the same time producing iron loss by inducing gastrointestinal bleeding. Iron deficiency anemia makes children act inattentive, apathetic, and irritable. The American Heart Association has strongly urged people to reduce their consumption of milk and dairy products due to milk's relationship to atherosclerosis. Diarrhea, cramps, acne and skin rashes have also been linked to drinking whole cow's milk.