What Feed Should I Mix??

I have a Tb ex racer who is abit underweight, my boss suggested feeding him lupins...but I'm not too sure with what to mix with it, I don't want anything that will make him hot headed, please give
Me some suggestions.

Hi,

More hay?? Sorry but without more info, can't really say much. What does he get already? What 'bit underweight' is he? Got pictures? How old, how much work, how living? An ex-racehorse shouldn't have much fat on him, or need it.

Keeping him on a simple, low starch, high roughage diet is the best. Nutrition needs to be balanced, as without supps, most horses will be deficient in a number of important nutrients. I'm no nutritionist, so I use a nutritional service to help me balance nutrition as well as choosing the right ingredients for a healthy diet for my horse's situations. I highly recommend FeedXL.com for this(It's Australian too, as I notice you are). Lupins can be a useful ingredient, among many others.