What are you feeding it for? It's more of a"natural thing" that is widely believed to not work for fly and internal parasites, so most horsemen don't bother with it in favor for proven things. If you don't like heavily deworming your horses, then have your vet do routine fecals and deworm only when needed.
That said, if you're dead set on feeding it to minis for some reason, try 1/4 cup daily.