I realize that many parents are often anxious to make the switch from baby formula over to cow's milk for one reason or the other - the cost of formula, to celebrate a new milestone, whatever. However, you won't want to make that step until you've spoken with your pediatrician about your baby's physical development and health needs.
Baby Formula - Milk: The Switch
Having said that, the rule of thumb is that you should not consider making the switch from infant formula to whole cow's milk until your baby is at least 12 months of age. While it generally is no concern to wait longer to make the switch, do not switch before your baby has hit his first birthday.
Why is that? Well, there are few reasons (and lots of medical research) that support that developmental benchmark. For one, babies have greater difficulty digesting cow's milk proteins. Additionally, cow's milk contains larger amounts of sodium, potassium, and chloride than what is inappropriate for a baby's nutrition, and too much of those nutrients can stress your baby's kidneys. And finally, cow's milk isn't as rich in other nutrients and minerals that are rather necessary for your little one, like vitamin E, zinc, and iron. All of those are very good, solid reasons to hold off on cow's milk until at least after age 1.
Toddler Formulas: Necessary or Not?
As far as toddler formulas, again, you'll want to get your pediatrician's insights on whether that is a good option for your baby. You need to know that toddler formulas haven't shown to have any unique health benefits, though they haven't shown to be harmful either.
Breastfeeding and Cow's Milk
Though the American Academy of Pediatrics recommends breastfeeding until at least one year of age, they do recognize that breastfeeding into the toddler year's has several nutritional and health benefits. If your baby continues to nurse 3 to 4 times per day, there may be no nutritional need for you to introduce cow's milk. Once again, be sure to talk to your pediatrician about your plans.
What about generics, DHA, and the like? For more info see: Choosing Baby FormulaAmerican Academy of Pediatrics Committee on Nutrition: The use of whole cow's milk in infancy. Pediatrics. 1992 Jun;89(6 Pt 1):1105-9.