If i was to bet which a horse would go silly on, lupins or barley, i'd bet on barley every time. Simply because it is a grain, and a lot of horses are sensitive to grain. I'm sorry about the comments regarding the pellets. I know not all of them are cheap and nasty, and you can get decent quality at a good price. Just you said fattening pellets, and everything i've seen that's 'cool' and 'fattening' is just pollard, so i'm sorry, i shouldn't assume. If you wanted to try, once your bag of pellets finishes, don't get another one. Just keep him on the lupins, and see what his behaviour does. With feed, and what sets them off, and what they do better on, it's a long and frustrating process of trial and error.