It may also be a problem of your horse being bullied by other horses. We were at a really bad barn a while ago and my horse River didn’t want to go out to pasture. I spend a lot of time at the barn and observed what was going on. When I would go out to get him he would not come to me when I called him. This had never been a problem. He also would stand at the very back of the pasture away from the majority of horses. He would come in all beat up. I observed the horses and saw that they were beating the snot out of him. He was afraid to walk past these horses even when being led in. I also observed that when being led in or out of the barn that the barn worker was bringing in 8-9 horses at a time. This just doesn’t work. We were at that barn for about 4 months and left. We are now at a barn with enough trained workers and both my horses are very happy.