Once baby hits age one, his digestive system is able to handle the proteins in cow's milk, says Janelle Aby, MD, medical director of the Well Baby Nursery at Lucile Packard Children’s Hospital Stanford. Before that, they could cause an allergic reaction causing gastrointestinal bleeding.
Baby should have whole milk until age two, since the fat it contains is important for development. Talk over cow's milk vs. soy and other milks with baby's doctor, if you're interested in giving them to baby. Some parents are set on organic milk, but it's not a necessity. "There haven't been any studies looking at clinical benefits for infants drinking organic milk as compared with regular milk," says Aby, "so although many people are willing to spend extra for organic milk, we don't know if it's really better."
To be honest, the switch is probably less exciting for your baby than it is for you...no more measuring out scoops of formula or subjecting your breasts to the pump. Since it isn't as sweet, many babies initially balk at cow's milk. Start out by mixing one part cow's milk with three parts formula or breast milk, and then increasing the proportion of cow's milk each day over the course of a week or more. Chances are, he won't even notice the transition.