(Med-Vet Pharmaceuticals) Adequate levels of magnesium are vital for normal muscle function, and can help your horse properly utilize glucose to maintain a healthy blood sugar level. Horses with symptoms of pre-Cushings, laminitis or founder may be aided by adding magnesium to their diet. Each daily 2 oz. serving provides 5000 mg magnesium. For working or performance horses, double dosage. Pellets.