Apples contain a multitude of important vitamins and nutrients. In particular, Red Delicious, Northern Spy and Ida Red apples contain powerful antioxidants. As with most vegetables, organic apples are best for dogs; they contain one-third more antioxidants than regular apples [source: Donamor].
Apples are an excellent source of vitamin C for dogs; in fact, one apple contains about 1,500 mg of vitamin C [source: Donamor]. The skin of an apple contains high levels of vitamin A and pectin, a fiber that can improve digestion by strengthening intestinal muscles. Pectin also works to get rid of toxins in the intestinal tract and creates short-chain fatty acids that keep away dangerous bacteria.
If your dog doesn't like eating apple slices, put apples in a food processor to make applesauce that you can use as a base for dog biscuits.