Clinically, Magnesium (Mg) has been used to help maintain peripheral circulation in humans with diabetes and other conditions.
It is also used to treat cases of spontaneous smooth muscle contraction in humans. This includes conditions such as asthma, preeclampsia and eclampsia, seizures and other problems with muscle spasms and arrhythmias. Horses with true Cushing's disease (a tumor of the anterior pituitary) have elevated cortisol levels. This high steroid level over time leads to the development of a secondary insulin resistance. Some horses, particularly those with the "easy keeper" gene are prone to developing a primary insulin resistance if they are fed high carbohydrate diets.
Along with the development of the other physical symptoms, such as a cresty neck and abnormal pockets of fat over the shoulders and around the tail head, there is an increased tendency to founder, which can be devastating for both horse and owner. Changing the diet to a low carbohydrate diet (also known as the low-glycemic diet) and increasing the intake of magnesium and chromium can help with the symptoms of cresty neck and the concurrent tendency to founder.
Exactly how magnesium and chromium bring this about is not yet known. It has yet to be proven scientifically, but there have been many instances where feeding the extra magnesium and chromium, along with a low glycemic (sugar) diet has reduced the potential to founder and allowed the horse to return to a more normal life. It may be partially due to the importance of magnesium as a co-factor in enzymes that control the metabolism of carbohydrates, most specifically the enzymes that are involved in insulin response. Cells deficient in Mg show impaired carbohydrate metabolism and a reduced insulin response. The magnesium can be supplied in many different forms.
The best results come from the chelated (bound to an amino-acid) forms of the mineral. The chelated form is easier to absorb and thus allows the mineral to get into the system more easily. Chromium is at present supplied in the form of chromium piccolinate, whose main function is to metabolize sugar in the body. Chromium enriched yeast products are beginning to appear also, since chromium grows on yeast. Chromium piccolinate can be obtained from your drug store, or from certain select nutritional supplement companies. The best results appear to come from the supplementation of 10g of Mg and 200 ppm of chromium per day.