I totally want my horse to be involved in my wedding!
Whether it just be my engagement pictures, or the wedding itself, my horses mean a lot to me, and are a big part of my life. Therefore, why wouldn't I want to involve them?
I've thought about it quite a bit (more than I should, probably, as I'm not engaged!), and it would be easiest to have your horse trained to drive, so that they could wisk you and your guy away in a carriage (you'd have to rent/borrow one). Otherwise, having the horse be the ring bearer has been something I've been thinking of. Either way, you should probably hire someone unrelated to watch over your horse during the ceremony. If you have a friend that is horsey, you might ask them to lead your horse down the aisle with the ring.
I would definitely have a second plan of action just in case your horse is goosey that day. Big crowds + goosey horse = Big Problems! You'd need to be entirely honest with yourself and make sure that your horse is prepared for such a thing. You don't want to start off your new life together by having your horse trample the flower girl...
So, if the horse isn't proving to be cooperative when pulling a carriage, have a decorated car waiting around the block. If the horse is being too much of a turd to allow him down the aisle, you could have the flower girl second as a ring bearer. Just have backups.
Just remember- if you would happen to ride your horse into the reception, something could happen. You could get dumped, your horse could act like an ars, or, at the very least, you could mess up that wonderful hair that your hairdresser JUST did for you, lol!
You'd have to imagine what it'd be like to get on your horse with a wedding dress, too. How does the dress fall? Since no one really rides sidesaddle anymore, you'd be showing some leg, most likely. Are you riding in heels? Are you going to get on in front of a large crowd? (Personally, that last one would make me rethink the whole, "riding off into the sunset" thing! I really, really don't want embarassing pictures of me attempting to mount a horse in my wedding dress floating around the internet, lol!) You can pull it off, but there's a lot to think of! I think that this woman pulled it off quite well: