So I am not having this problem I am just very very curious about it. There are some horses in a pasture along the road that I drive to get to work. They seem to be in fairly good conditon and have a large pasture with a shed and trees. But sometimes when I drive by I see them eating the bark off of the trees? What exactly does that mean and why are they doing it? If you look when you drive by there are patches missing from the tree bark that is from them nibbling on it.