The most commonly known antioxidants are Vitamin C and Vitamin E. Bioflavenoids are the antioxidants found in fruits and vegetables that have Vitamin C like activity. Carotenoids are the antioxidants found in orange and green vegetables that also can be converted into Vitamin A by the body. Fresh foods also contain other antioxidant enzymes like superoxide dismutase and catalase. While abundant in fresh foods, antioxidants are destroyed during the high temperature processing of dog foods. So dry kibble typically has Vitamins C and E added back in after the cooking process. However, feeding fresh fruits and vegetables or a whole food derived supplement containing this variety, is the best way to provide a more complete blend of antioxidants.
All dogs should have additional antioxidants supplied during times of stress. This includes if your dog is ill, suffers from allergies, has cancer, or show signs of cognitive decline. Even if your dog is healthy, a good way to help your dog stay that way is to provide fresh fruits and vegetables as treats , especially if your dog is eating a commercial dog food.