"Hopefully not too OT, but my horse has been on a mineral-balanced diet for several months with improvement in his health -- I tested his pasture and hay for nutrients and balanced against those values. There are a couple Yahoo groups about insulin resistance in horses, etc. I will be adding borax to his diet and see if that helps his arthritis"
Good idea about Borax; one heaped teaspoon or two (depends of the weight) should help; easy to give in water. Make sure he has salt, real salt, too. Iodine is a must for these big animals!
You may also check out DE (Diatomaceous earth), silica supplement; you never have to give worm/ parasites remedy after this, and it helps the calcium utilization.
I used to work with horses earlier, so it is of special interest for me!