My OTTB used to load just fine in either a step up or ramp trailer with no problem! The other day we took him out for the day he loaded fine in the AM, unloaded fine at the park. When we went to leave... He refused to go in?! Took us 4 hours to get him loaded!! Ever since he wont go in the trailer, I have tried food, everything! Please help as I have never trained a horse to load a trailer!