I am no foot expert but we have a horse with the same issue.
I have found that a hoof supplement has helped tremendously! I have used both Horseshoers Secret and the one by SmartPak(I can't remember the name). My husband(who used to be a farrier by trade, and shoes our horses) couldn't believe the difference it had made. And he has owned that horse for 7 years.
Same as you, the moisture from the pasture, we lived in east TX in the humidity and the pasture ran down into a lake, so her hooves would turn into mush and break off and wouldn't hold a shoe.
And then we moved back to NV, we have no pasture and it is very dry here, then the opposite problem- too dry and brittle.
In both situations having the right nutrition has made a world of difference.
I am also not a horse nutrition expert but the supplement helped. Also since our horses are dry lotted, despite having excellent hay I do feed a loose vitamin/mineral mix formulated for this area and for horses that do not get fresh green grass.
But in the mean time of waiting for the new supplemented healthy hoof to grow out enough to tack a shoe to I love the Keratex Hoof Hardener. I am not a fan of painting stuff onto feet to magically make them better, but I do think it helps some.
So take it for what it's worth, like I said I am no expert in either category feet or nutrition but there are folks on here that are.
I DON'T LEAD 'EM AND FEED 'EM, I RIDE 'EM AND SLIDE 'EM.