I've done a bit of research on the health of the human body, and I recall stories of people who had lyme disease and got rid of it.
Now I know that a horse and human are not one and the same.........
Google; lyme disease + colloidal silver
It's simple to make. My family got sick when swine flu was the big scare. I just drank my home made colloidal silver and never did I get sick.
I don't know if it would work for a horse, but it may be worth researching.?
Also I guess I should mention that diet plays a huge role in human health. So I'm sure that it also plays a big role in the health of any other animal. Are you feeding your horse anything that it shouldn't be eating? Grains? Molasses/sweet feed? Etc....?
Truth passes through three stages. First it is ridiculed. Second it is violently opposed. Third it is accepted as self evident.