I was taught that the it should be loose enough so the horse has to carry the bit on it's own, but not so loose it falls out of it's mouth or dangles around and accessive ammount. But not overly tight where it's crammed up in the horse's mouth, or the horse shows discomfort.
My horse's aren't the best with the bit, but one because one is the horse equivilant of someone with ADD or ADHD, always needing something to do, and uptight. The other horse I did not train, but she must've been pestered so much, because she will not take the bit at all. But this rule has made it a bit more comfortable for the both of them. I don't like it when people cram a bit in horse's mouths. It should be more of a back-up, not completely relied on.
If a horse isn't carrying the bit well, and it's at the proper length or tightness, then I'd suggest leaving the horse out to pasture or even in it's stall with the bit. Have it eat with it on for a few days, just put on a headstall that isn't for show, if you have one. I have numerous crappy headstalls that aren't very appealing, and I've thrown them on my horse with his bit, and it made a difference come lesson day. He wasn't so focused on that, and I made him do groundwork and stuff, jumping over barrels and sidepassing, etc to give him something to think about. Just what I was taught, and it has worked.
Last edited by ButtInTheDirt; 02-16-2011 at 10:07 AM.