"What about this one for horses? It seems a little more basic:"
A step in the right direction, but I'm still a bit sceptical because I'm not sure where magnesium sulfate,potassium sulfate, and calcium lactate pentahydrate fit in.
Personally, I prefer to keep it simple with compounds I'm familiar with, e.g sodium chloride, potassium chloride, magnesium oxide, and calcium carbonate. I'm also comfortable with citrate salts of the above, especially calcium citrate. This is not to say the Farnam product is bad, just that I'd be a bit reluctant to try it, especially since they don't specify the proportions of the different salts in the product. If you do decide to give it a try, would you post back on your results? I, for one, would be interested to hear how it turns out.