I have a thoroughbred with thin soles.  I have had him only since February.  The first thing I did was add copper, zinc, methionine, biotin, and lysine to his supplements, as all are important to building healthy hooves.   Then I searched for the right hoof trimmer, which in my case meant finding a barefoot trimmer.  After trying a local barefoot trimmer and a farrier I have finally settled on a barefoot trimmer who, IMO, knows what she is doing.  I have to pay an extra trip charge for her on top of the trim charge because of the distance, but I just do what I have to do.    You might have to search for an experienced barefoot trimmer who knows what they are doing.  Ask for their training and education credentials, and for references.

I have also put a hoof dressing on to try to keep moisture in, but haven't used it consistently.  There are different thoughts on the usefulness of hoof dressings but I thought it couldn't hurt - might help.  Hoof dressings by themselves will do nothing if you do not have the diet, supplements, and trim in place.

After the trim, I would recommend putting hoof boots on your horse for turnout.  I did not do that and my horse ended up with an abscess. 

If you are riding him/her now, use hoof boots.

Barbara Rosensteel (and Ranger)
Tennessee