Sorry, I know I'm kinda randomly popping in, and I apologize if I say something that's already been discussed....
In Montana, a BI is proof that you own your horse, as much as or more so than a bill of sale. I'm not sure why that is, but that's what people are all about. Every time I've bought a horse, that has been a major point. And you can get permanent ones, where the inspector gives them to you and they are all laminated and nice and they say the owners name... And it's for as long as you keep your horse. Some you have to get... like every time you leave your county, but it gets expensive.
Just throwing that out there. =)
To rein a horse is not only to guide him,
but also to control his every movement.