I feed Nutrena Life Design Complete and use Daily Omega Plus, and I've gotten amazing results with it. It isn't just for a shiny coat... it has a LOT of great vitamins and minerals and is in a flaxseed base.
And there's another bonus... it actually makes your horse water-resistant. Whenever I hose my horse off, the water runs right off her and she dries in minutes. I don't even need to sweat scrape her. It's great for getting rid of sweat, too.
Daily Omegas Plus - Multi-Purpose Supplements from SmartPak Equine
Oh, and she's pastured about 75% of the day.