Ugh that is a bad idea. And bareback? 10x worse.
I've been planning and preparing for a cross country ride for 5 years. I've always wanted to do it, and I will do it someday. When I say cross country, I literally mean from Wisconsin to Florida and back. Crazy? Yes.
In my research and study, I've learned that to do this, I'll ride 15-20 miles a day. This means, it could take well over 6 months to ride one way. Am I still going to do it? Hell yes. I've done my research, and I'm confident about it.
BUT, I've read the horror stories, the bad luck, the stories of when the rider had to shoot their horse because it spooked at something random and got hit by a car, etc. If your horse spooked and the two of you got hit by a car, and you were bareback, you would have very little chance of living, let alone your horse. It would be tragically terrible. If your horse isn't conditioned for this ride, and isn't conditioned for trails, please, please, please no. Show your friend this thread, I really hope she doesn't attempt it.
Also--- a horse can fluctuate 50 lbs on any given day. What if it gets dehydrated? How will she feed him/her? What if he colics? Does the horse have shoes/boots so his feet don't grind off to the coffin bone? How fit is her horse? Her horse could lost a lot of weight, especially if it is a particularly hot day.
Your other question... to get the horse used to the trails, the best thing you can do is practice. Start by walking around the farm. Go a little farther each session. Let him take it all in, teach him to walk through water, brush, mud, fields, tall grass, etc. Take it slowly.
Desensitize him at home first, to plastic bags, etc. You can find a lot of random things on the trail. Teach him to spook in place. There is no harm in going for walks in hand through the neighborhood, my horse and I do it a lot.
Owner and head trainer of SE-Wisconsin Horse Care
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