Question: I have a black horse that bleached almost to buckskin in the summer, and rust in the winter. Our water source is very high in both iron and sulphur, so I am wondering if copper supplementation would be good. If so, should I also buy the zinc pellets and would that give me a balanced copper:zinc ratio? Thank you! Dr. Kellon: To do this correctly you should work from water and hay ananlysis results but to get started use 15 g of Poly Cu pellets and 22.5 g (1.5 scoop) of Poly Zn. Just be aware if you are using any form of selenium than selenium yeast it may interfere with absorption.
Also consider the option of filtering. A paper was just published describing how chronic intake of high iron water can cause potentially fatal liver damage. You can check your horse's total body iron status by sending blood for serum iron, ferritin, iron binding capacity to: 
This Kansas State lab is the only one in the world that can do the ferritin testing. Samples should be sent to them directly because sample handling is critical to accurate results.