Parboil the brats for 10 minutes, brown in the broiler, and serve the next day in a Nesco floating in beer and onions. PUrists will sneer at pre cooking but it's a necessity in this case. Works for us. Use Johnsonville if you can get them. They have a Stadium brat that is already pre cooked and very tasty.
Foods such as orange juice and milk are definitely enriched with vitamin D, but these foods are not intended to be good sources of Vitamin D, they are merely foods designed to prevent the most obvious vitamin deficiencies, particularly in children.
1 But foods made from milk, like cheese and ice cream, are usually not fortified.  Vitamin D is added to many breakfast cereals and to some brands of orange juice, yogurt, margarine, and soy beverages; check the labels.