Calming supplement

what you are looking for is vitamin B-1 and magnesium. B-1 is a natural "calmer" and some horses are deficient in magnesium, which makes them reactive to things. it wont give you a drugged effect, it just makes the jumpy touchy ones less stupid. if Rugby misses a dose or two, i can see a difference --he starts spooking at his food and everything that moves
the vit E and selenium isnt a bad idea anyway-- vit E is good for a hard working horses muscles and selenium is deficient in most east coast areas. endurance horse often need more selenium.
i feed a B-1 crumble i bought at the tack store and  the brand of joint supplement ive been using contains magnesium and calcium (Pureform)

check out susan garlinghouse, she is a vet and endurance rider who loves the nutrition stuff--
www.allcreaturesanimalhealth.com/site/view/212994_EquineNutritionArticles.pml