In the fall of 1998, I moved three of my horses from the OH/PA border to the low desert area of Southern California for five years.
The two Walkers hooves went thru the strangest metamorphosis I have ever seen. Their soles and frogs looked almost mutant
The Arab's hooves never missed a beat and always stayed the same (imagine that --- his gene pool realized it was back in the desert evidently).
Along with the very arid climate we moved to, their diet made a huge difference too. That was when I took everyone off sweet feed and never looked back. I had them on Nutrina but I can't remember which one as I've been gone from SoCal for five years and the less I remember the happier I am
The only external treatment that worked with any success the five years I was out there was Mollimentum.
It is a hoof grease and easiest put on with a cheap two inch paint brush.
If it was hotter than 95 degrees the Mollimentum came out. I would slather the Mollimentum on their hooves (top and underside) every day during those hot days. Thru the cooler months I would use Fiebing's hoof oil once or twice a week unless it was in the rainy season, then I left their hooves alone in that regard.
For my part, it seems their hooves needed a lot more attention in that environment than they did when I lived on the OH/PA border and from what they need now that we are in Middle Tennessee.
When I brought my horses back east of the Mississippi, their soles and frogs (mainly soles) made the transition back to what I call normal in just a few months, but I sure could see the "change rings" on everyone's hooves until they all grew a completely new hooves.
I know how frustrating this issue is for you. Hope this helps you some.
I forgot to say that each of these horses has only one white hoof and those hooves are as tough as the dark ones. It was the environment they were introduced to.
If I were going to recommend anything to put in their feed, it would be Omega-3 Horseshine first and BOSS second. I won't use BOSS because it's really high in Omega-6 --- not a good thing for my metabolic horse.
The Omega-3 Horseshine does wonders for everyone's hooves and coats. Even their winter coats are "slick and shiny, their hooves are the pliable-hard they should be no matter how much rain we get. I wish I'd known about in when I lived in SoCal---