You may want to try lowering his Oaten Chaff and perhaps even his Copra if he isn't a hard keeper. As for herbal remedies, I occasionally use Quietex tubed formula for trailering and it seems to work, it also comes in powder form for daily use. Other people in my barn have used Easy Boy and they said it seemed to work. The active ingredient in many common calming supplements is Valerian root.
However, in the end, some horses are just hotter than others. My first horse was like yours- he would seem calm and then something would come out and he'd bolt. The important part is what you do after the spook. You have to be calm and pretty much pretend it didn't happen, take him right back to work and don't let him freak himself out. If you see something coming that you think might spook him, occupy his mind, for example ask for a trot circle and don't allow him to get distracted. Be aware of yourself and ask yourself if you are tense or nervous. It often helps to turn your own fear into determined 'anger', as in thinking "I am going to trot right by that trailer and nothing in this world can stop me!" If you don't want him to spook, don't give him a chance to. Even when you're walking warming up or taking a break, don't just go in a circle around and around, do serpentines and diagonals. Keep him focused on you and not what's going on outside.
Hope this helped!
"The trouble with the world is that the stupid are certain and the intelligent are full of doubt"
Last edited by roro; 05-13-2010 at 02:26 AM.