Feeding a mule is no different than feeding a horse. I would never feed them straight corn as there is too much starch and an overload on starch will cause colic and founder. There are great pelleted feeds out there and most are pretty inexpensive, Horse & Mule is a good 10% protein feed that will work great. I would start off with a "coffee can" twice a day. Depending on the size of the mule and their weight gain you may need to adjust this. They also need adequate hay and forage. Corn won't make them "wild" but it will give them excess energy. Read up on horse feeding and you can do the same with your mule.