R.K.
I'm going to guess you are a vegan? I don't know much about this type of stuff but I'm sure your children's doctor would be able to help you make the best choice for your son. I think the way I did it with my kid's from formula to cow's milk was a few bottles a day, add a couple ounces of milk to the bottle. Every week add 2 more ounces until they are completely transitioned. That's how I did it. But make sure to ask the doctor first!