I agree with Spirithorse's advice; my Appy was protective over food when I got him...he would try to charge anyone that came near (not horses, but people!), and I implimented that kind of strategy; I brought his feed out, lead him up to it, asked him to wait, then allowed him to get in. I would randomly walk away, and walk back up, and when he pinned his ears and tried to chase me away, I turned his 'game' around and chased him off instead, and didn't let him near me or the food until he had a 'friendly' expression. I made sure to touch him before allowing him into the bucket too, so he knew I was truly 'in charge'...then I would invite him to eat again, and we would repeat the exercise. It didn't take him long at all to realize that being crabby over his food only got him NO food!
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."