I have to agree with Kevin.
Horses ( including mustangs) can walk across almost any terrain barefoot. But when you start asking them to "Do it my way" They do get sore.
My gelding is 6 and never had shoes until this fall. I rode him across all kinds of terrain. He would go where I pointed him, but he was always watching his feet, He would brush me on trees and rocks, in order for him to get to the softer material on the side of a trail. He would walk and trot, but didn't like to canter or run down trails. Since I've put shoes on him, he has become much more confident and powerful in going down the trail. He stays in the trail vs trying to walk the edge. I'm not getting brushed off as much. Maybe because he is carrying my extra 200lbs, maybe because we ride really rough country. Maybe because as my wife says, A short ride to me is a an all day adventure of 20-30 miles, a good ride to me is a 50 mile endurance ride or a 100 miles over 3 days.
I don't ride in arenas or man made trails. We go out and ride in the real world. My horses don't get the luxury of taking a differnt way home if they don't like the trail. They have to go the way I choose to take. Regardless of the footing.
My 6 year old gelding with boots on during a summer ride.
One of the trails we ride. It's easy for a boot to get caught between rocks. And when they get pulled off they tear.
Al the horses in these pictures are barefoot. And very capable to walking down some very rough trails for a day maybe two of work.
I have have found that I either have to put boots on or put shoes on to make them comfortable. And I'm fed up with boots. I've tried the Std Easyboot,, the EPICs, The BARES, and now the Gloves. They are great for walks and trots. But they don't hold up to cantering, They don't stay on when the horse is cutting has to change direction radicaly, such as in a spook or chasing a cow. Boots don't do well when a horse is having to pick his way through blow down timbers or big rocks where the boot gets wedged between rocks or catches on branches of a log. My boots have been fit by an authorized Easycare professional. So I'm sure they fit properly
If you are only going out and walking down a trail. Maybe trotting or cantering in places of good footing, if your horse is carrying a lighter load, Bare foot will work fine. Especiall if the horses have a day or two off beetween rides. But if you ride 3-4-5 days in a row over difficult terrain, carries a heavier load, is asked to move out with burst of speed, regardless of the footing ( such as chasing a cow on the open range, or mustangs running scared from a helocopter), thye needs some kind of protection or they will get sore.
My horses will stay barefoot 10 months of the year. I do believe it's healthier for their feet. I will use boots on the rougher rides. But come fall when I go hunting and my horses will spend at least 15 days of October Maybe 20 having to work hard in the mountains, riding across rocks, ice, snow and mud. Packing full sized men, layered in heavy clothing and carrying rifles and extra equipment. I think for now on, I will shoe them.
Kevin, lets trade some rides, I'll come ride up Logan canyon with you, and you come join me in Ogden Valley or on Antelope Island this winter.