Vitamin Supplement for Yearling?

I will be getting my filly next month. She is an 18 month old quarter horse.

Currently, she is being fed Purina Strategy and hay. She also gets Dynamite added to her feed each day.

I plan on keeping her on the Strategy, but I'm not sure about the vitamin? I've never been a huge proponent of giving extra supplements if they aren't neccessary, but she will be my first young'un, and also my first horse in Colorado. Maybe she needs it because she's a growing girl? I don't know. Does she really need one?

If I do put her on a vitamin supplement, I was thinking of trying Farnams Vita Plus. It's a lot easier to get than the Dynamite and I've heard good things about it.

Any thoughts?

We have fed stratagey and good grass hay or pasture since our babys were weaned. They are healthy and happy. I did give the Vita/Min supplement right after weaning but stopped after a few months. I'm a great believer in keeping the diet as natural as possible and that is hay or grass.