I've looked on the internet and in my books, and haven't come across anything similar.
I will give you this extra information, hopefully it will be of some help:
His front feet have always been good and healthy, but his backs have lacked concavity until but a week ago, now his backs look much better
His white-line is pulled out, and has been for a few months; I'm working with my farrier to get it better.
It has been extremely wet for the last 6 months, which is unusual because I live in Texas.
I recently started him on cinnamon, as horse herbalist recommend for easy keepers who are on lush grass to keep them from foundering.
I've also recently start him on one clove of garlic a day, as a immune booster.
About 2 months ago I changed his trim to a 'wild horse' trim; he had been barefoot before, and he did not have any problems with this new trim.
So, anybody know what this is? My game-plan is to soak his feet in ACV for a week, and get my farrier out to look at him; but any other help would be much appreciated.
P.S. I'll have pictures up latter today, most likely.