Ruling on Vitamin D3 derived from animal sources
Question

                Can we drink milk and other dairy products fortified with Vitamin D3 in the USA? They say Vitamin D3 is derived from animal sources like pig skin, pig brain, fish liver and sheep skin. They add it after processing.
Praise be to Allah.
    You have to make sure about any food or drink that enters 
    your body, for every body that is nourished on haraam things, the Fire has 
    more right to it. So you have to be sure. If anything that Allaah has 
    forbidden has been added to milk or anything else, then in that case it is not permissible for you to drink it. Fish liver, however, is halaal even if it was “dead meat”, and sheep skin is permissible if the animal was slaughtered properly according to sharee’ah or if it was tanned properly.