My neighbor has an old horse and he comes with a problem. He eats too much. He has to be kept off grass and closely monitored when he is in a field. I've watched for nine months as he gorges, without lifting his head, until he's stowed away at night, in a bare yard, with some hay.
This morning, with permission, I put a fly halter on him (he seemed a bit agitated yesterday ?). He ate for about an hour (maybe less) and then went into the shade and fell asleep. He's been there since - content; no foodie panic; not bothered by flies - in fact, a very different horse. Here he is as I've never seen him and much to the surprise of his owner.