The science is clear - magnesium deficiency is very rare. But there are two circumstances when we may add TINY amounts of magnesium.
The First is if there is a flush of usually Spring grass on rich, well fertilised pasture. This grass is often VERY high in potassium. Though there will be plenty of magnesium in the grass the horse has to pee a lot to get rid of the potassium. Because it struggles to control magnesium it can lose too much. This is an affect that rarely lasts more than a few days and we would normally add just 0.1 - 0.4 grams of magnesium a day.
The Second is when the horse tells us it needs it. If the customer is disappointed with behaviour after loading chelated calcium one of our fine tuning options is magnesium. We designate it FineTUNE 2. Again we normally work within the range of 0.1 - 0.4 grams a day. That compares to 3 grams for most modern balancers and 12-20 grams for many formulated feeds.