Vitamins for Pets - How Essential Are They?A vitamin supplement for pets is essential to your pet's wellbeing unless you're already feeding your pet its natural raw diet in precisely the proportions it would eat in the wild. If not, your pet is, to a greater or lesser extent, deficient in vitamins which it needs for optimal health. Certainly, your pet may get by without them, but if you want to ensure a long and healthy life for your pet, your pet needs a vitamin supplement. Vitamins can also be.