Originally Posted by AshleyJade
He's on Nature's Variety Prairie, the Lamb flavor.
Prairie is generally considered to be a "quality" food, so vitamins or other supplements are unnecessary. You have to be careful not to overdose certain vitamins, so it's not wise to supplement except on a vet's advice.
You could perhaps feed another quality canned food in addition, if you're worried about imbalances, and your cat tolerates it. Something along the lines of Merrick, Felidae, Natural Balance, California Natural, etc.. The problem with feeding just one food is that cats can become fixated on that particular brand, and eat nothing else, so giving prescription diets, when necessary, can be nearly impossible.