This probably can't/won't be done but it's worth a shot...
Script AI to the Horse, and add similar animals like deer, moose, bears, and maybe even birds. Now since I don't know much about scripting, I was thnking maybe the AI horse would be a seperate bot or that if it is mounted it reverts back to a normal horse.
Birds would just fly around in a (relatively) small arc to prevent them from, say, going off the edge of Slate. Bears would do bear stuff but when shot, would be likie a Witch in Left4Dead: Low health if it's not aggressive (i.e. headshot kills it) but if hit with a non-lethal projectile, it would get pissed off, go on a rampage, and boost it's health up to say 300 or so. It could follow you around like the horse used to when you shot it (unless that was from an add-on but I don't think so).
I got the idea for the horses when I was playing Gmod the other day shooting birds, and then yesterday my friend built a ranch but he complained of the horses not moving which gave me the horse idea. The bears? I just like bears. They're terrifying.
If nobody wants to script all of them then I would suggest you just make the bear.
Another option: the bear can be mounted and ridden into battle and it damages enemies on contact with its claws. >:D
