High quality pet food manufacturers work hand in hand with veterinarians and nutritionists to assure that their product not only  tastes good but contains all of the nutrients that your pet requires throughout his life.  The vitamins are already in there. Steven Cohn, who is a Veterinarian with Nestle Purina Pet Care Company says that if your pet is normal and healthy and you’re feeding him quality food from a reputable company, you don’t have to provide any vitamin supplements to the pet’s diet.  Dr. Cohn says that extra vitamins can do more harm than good.  He says that the only time vitamin supplements may be called for is if your pet is suffering from a disease or disorder.  In this situation, your veterinarian will determine which extra vitamin supplements are needed. So keep feeding high quality food and provide plenty of treats and forget about extra vitamin supplement unless recommended by your vet.