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Dose to Bowel Tolerance

Just like in humans, you will know quickly if you are giving too much magnesium: your horse’s stool will get mushy or runny. In that case, cut back on the dosage. Since different forms of magnesium have different absorption rates, dosing to bowel tolerance is the best way to measure how much to give.

Here’s what “dosing to bowel tolerance” looks like in reality: We dosed 3 different horses/different breeds with Magnesium Oxide and I can tell you that the Registered Quarter Horse hits bowel tolerance at just under 2500 mg, as does the Arab/Andalusian cross. The purebred Andalusian does well on 3300 mg, but any more than that and her stool is falling apart on the manure fork, and at 5,000 mg she’s got runny/mushy poop.

So although Dr. Juliet Getty’s recommendation is for 5,000 mg per horse, depending on your horse’s diet and unique body, you would need to adjust for the ideal amount for your horse.

NOTE: If you're feeding the High Point Daily Nutrients for Grass/Hay Fed Horses, it already contains 1700 mg of magnesium oxide per serving. So that may be enough for your horse's daily requirements - depending on need and activity levels.

Keep An Eye on Calcium Levels Too

The only consideration when supplementing with magnesium for horses, is to make sure that calcium levels are higher than magnesium. This is the reverse of the necessary ratio for humans. In humans, magnesium should be at a 2:1 ratio with calcium. But for horses, the ratio is reversed with calcium 2:1 to magnesium. However, Dr. Getty says that if the horse is eating hay or on pasture, then the calcium from hay or grass is likely sufficient to supplement with magnesium at the recommended dosage.