Get iodine out of hair?

My horse cut its self a few days ago and i put iodine on the wound to clean it up... and being stupid me didnt think about it and now i cant get it off the rest of his hair and we have a show this sunday... i have tried regular shampoo, regular house soap, glo-white shampoo (he's a white horse) and the white stain remove stuff... and no luck it hasnt even lightened... i would appriciate any ideas... thanks