We're boarding 2 horses, quarter-mix somethings, a gelding and a mare. We don't know too much about horses, and the owners hardly EVER come by. Here's what's happening: the gelding is 7yo and spunky and a bully. He follows the mare, won't let her eat grain or hay unless we separate them, etc. He just bosses her all day long. They're in a huge pasture, so it's not like he doesn't have enough grass to be happy. Tonight I saw him biting her. She's standing there eating grass and he bites her for no reason. She hollers at him pathetically but he keeps at it. She's had low weight issues, so when we do supplement their feed, we have to feed them separately or she won't get her share. Is there anything I can do about this behavior of his? If I get another water trough, I could put each in a separate pasture, but don't horses like companions, even if they're mean?