I have found a lot of good resources about zinc to copper ratios (e.g. Feeding the Hoof) but they all seem to assume that your horses live on pasture that has adequate or even excess iron. Our pastures have very very low iron. So I believe I need to supplement iron, but I don't want to give them more than they need, and certainly not enough to be detrimental to their hoof health. Can anyone direct me to a resource that would show ratios of not just zinc and copper, but also iron?