My horse wont load in a trailer!! Please help!?

Ok my horse will not load in a trailer no matter what. We've tried puttin other horses in first then put him in. We've tried puttin him in first. Nothin works. We even tried using a different trailer! This really sucks for me because i love to ride him and i love to work cattle on him and i sometimes use him to do rodeo queen competitions. I havent been able to ride him in almost a year because we cant get him to load no matter what we try. I really dont know what to do.