i assume we're talking about black bears. . .which are basically harmless. . .generally. . .however, they are opportunists and will eat pretty much anything that isn't nailed down.
mothers with cubs should always be given plenty of room.
encounters with humans where an attack occurs are rare, but not unheard of.
a bear will eat deer fawns when they are first dropped in the spring and unable to run. . .i've seen this with my own eyes. . .like i said, they're oppotunists. . .but horses?? i can't even imagine a bear (or bears) bothering with a horse.
the only other thought that comes to mind is that these are potentially "problem bears" that for one reason or another have lost (or never developed) their fear/shyness of humans. they may even be problem bears that were relocated from some other, more populated, area. if they keep hanging around and become a nuisance, call your local game authorities and get them to trap them and move them. . .where they will most likely become a problem for someone else.
where i live, problem bears usually wind up getting "euthanized" by the offended property owner.
when i first moved here, i was a little freaked by it. the bears, the giant spiders, the coyote noises during the night. now i love it. well maybe not bears, but i like them.
I know a horse will fight back. If there is more then one bear the chances are slim to none for the horse. However, one kick from a horse will most likely make the bear run off it does not kill it