Left Hand: From the alberta agriculture web site:
In general, "white" salt is plain sodium chloride. "Red" salt is sodium chloride with added iodine (also known as iodized salt, which is similar to our own table salt). "Brown" salt usually contains trace minerals, such as copper, zinc, manganese, iodine and cobalt, and may or may not contain sodium chloride. "Blue" salt contains sodium chloride, iodine and cobalt. While the colours help us identify these products, variations in colour and content do exist—best to read the label.
When buying a salt block, the motto seems to be "red is for horses, blue is for cows." Is blue salt harmful to horses? NO. In fact, the only nutritional difference between red salt and blue salt is the added cobalt in the blue salt. Both contain sodium chloride and both contain iodine. The blue cobalt-added salt was designed for cattle and other ruminants. The bacteria in the rumen use cobalt to synthesize vitamin B12. Similarly, the bacteria in the hindgut of the horse also use cobalt to synthesize vitamin B12. However, horses do not appear to require lots of extra cobalt in their diet to benefit from adequate B12 synthesis. Although the level of cobalt in blue salt is higher than what they need, it is not harmful to horses.
I have just started with Hoffmans and am not going to change at this point. Time needs to pass for effects to be properly recognized. I am not having any health issues whatsoever with my horses, so am not concerned. The manufacturer recommends either top-dressing or free choice. So I'm not "force-feeding" a free choice only mineral. Regardless, if the horse didn't want it, they wouldn't eat their pellets with the mineral on it. At least, my horses wouldn't. They have lots of hay and their pellets are a training / routine tool more than a dietary benefit.
Since yesterday, I have communicated with Hoffmans. Their email response is terrific. I am very impressed. BTW, I had the 250 gr top-dressing wrong -- should have been 150 to 200 gram. Anyway, their spokesperson told me it will take two weeks for the horses to get their systems in balance. If after that time, the horses are still "pigging out" on it, I should cut the minerals with salt 1:4 salt:mineral ratio. I'm just trying to determine the proper salt to use now -- pickling or iodized. I'm leaning to the pickling, but I need to find out again what iodine is for. That will help me to decide.
For tonight, I refilled their feeder with enough mineral for 3 days supposedly and put chunks of blue salt block in it.
Oh, and Hoffmans told me that eating a lot to begin with is common and it won't hurt them.