Yes, region creates these issues. Think short grass & pulling roots up...hay fed on ground, etc. It has them consuming sand. Horses LOVE short grass.
In my horse breeding days, forums had discussions about this & many were from FL, the land of sand! It is often a condition that presents with poor condition, diarrhea, weight loss. Something many will automatically think "worms". Sand Clear works. Another thing which seemed to be helping, wet beet pulp with flaxseed added a couple days. The flax became gelatinous and helped carry sand out. Off course, feeding off ground had to be controlled as much as poss.
The first horse I ever trained when I was a teenager was a totally unhandled 6 year old mare off of a large ranch. She had never been haltered, didn't lead, load or trust humans in the least. She was a solid colored registered Appaloosa that went on to present me with several beautiful colored app foals.
As I said - she was unhandled when I got her. We put her in a shed (much like your hawg shed) with a small corral around it where she stayed for several months until she learned to love me. The first farrier that worked on her was awesome and taught me a tip that I ended up using on this mare and almost every other horse I ever owned. He took a branch with a bit of a "Y" at the end so that there was a small protrusion. He would tap her leg (not hard - just enough to be annoying to her and she'd pick the leg up). As soon as her foot came off the ground he'd take hold of it and reward her with a bite of grain. Of course his one session with her didn't "train" her so I worked with her every day. In a week or so that mare would pick up her feet on command. By then I would only use my fingers to tap her below the knee - tell her "UP" and she'd pick up her foot and hold it up until I took hold.
Every farrier I ever used for the next 20 years thanked me (and her) for that! Except the stupid one that thought when she picked up a back foot that she was threatening him. I set him right very quickly and all was good.