Is it permissible to drink or consume dairy products fortified with vitamin D3 in America if it is derived from animal sources such as pigs, fish, or sheep?

You must verify everything you eat or drink, for every body nourished by unlawful means, the Fire is more befitting for it. So, if you are certain that something forbidden has been added to the milk, then it is not permissible to drink it. As for fish liver and the skin of a sheep that has been lawfully slaughtered (dhakat) or tanned (madbugh), they are permissible.