There has been plenty of research that established biotin, a B vitamin, as the best nutrient for hoof quality. My gelding has pretty good feet, but has shoes in front in part because he needs a 2 degree pad. A couple of years ago he got a teeny-tiny horizontal ding on a rear hoof halfway up the wall.
It looked like it would grow out but a very shallow crack developed after a couple of months. I put him on biotin which took care of the crack, but there was also a significant improvement overall. The farrier says the hoof walls and soles are stronger and thicker. The areas around the nail holes don’t crumble. It takes upwards of a year for the hoof to grow out so you have to allow nature to do its thing.
I use Bioflax 20 from HorseTech.com. The base is food grade ground flax. A serving is a small scoop, about 60 cc for 20 mg per day… Among the things I like about HorseTech is that Rod, the owner, is available by phone or email to help you figure out what is best for your horse. I’m also feeding HylaSport CTS for joints and soft tissue support, and natural vitamin E.
Other things I like about HorseTech are the free shipping, free cookies, and amazing customer service. He always has a booth at Equine Affaire. It is a family business. I like to support “local” businesses over the big box sort of places. Iowa is not local to Maine, but my horse was born in Iowa, which is good enough for me.