Multivitamins can help support your pet’s immune system and their overall well-being. Vitamin A, C, D, E, K and B vitamins are essential for your pet’s diet, according to AKC. Some multivitamins for dogs include these nutrients, which could keep your pet’s coat shiny and soft, and keep them active as they age. Glucosamine is a natural compound found in cartilage that provides cushion for the joints.