I've been reading a very interesting book - Feet First: Barefoot Performance and Hoof Rehabilitation, by Nic Barker & Sarah Braithwaite, who also do the Rockley Farm blog. This book isn't just about barefoot horses, and barefoot performance horses (including hunting, eventing and show jumping). It's about what they've learned in the rehabilitation of horses whose hoof structure has been compromised: the book is about the whole horse, and makes the extremely important point that the horse's hoof health is a direct expression of the horse's overall health, and that simply changing how you trim a horse, or taking a horse barefoot, will not necessarily improve things if the overall health and management of the horse are not also changed. It is also clear that a lot of lameness attributed to legs or body is really the result of unhealthy hooves, and that setting the horse on the road to healthy hooves can substantially improve soundness.
The book is chock-full of excellent drawings, photos and explanations of what makes for a healthy hoof and an unhealthy hoof from a biomechanical point of view. There are before and after photos and case histories for a number of horses. And their standards are high - they define a horse with healthy hooves as one "who is sound, without shoes, over challenging surfaces, at any speed" (p. 14), and are critical of barefoot practitioners who aggressively trim horses in a way that produces lameness or horses that can only work on softer surfaces. The trimmer should look for feedback from the horse - "As a general principle, any trim which leaves a horse less sound after the trim than it was before, is a mistake. There may be occasional exceptions, but it should be an extremely rare occurrence for a horse to be less capable after a trim. It is never productive, let alone fair, to make a horse sore, and certainly no horse should be routinely uncomfortable after being trimmed (or shod)." (p. 130)
The real contribution of this book is the importance it places on diet and feeding, and exercise and the environment the horse lives in - these are what produce a healthy hoof and the trimming is subsidiary, although important. As they say bluntly: "The truth is that you can't improve a hoof that much by trimming it ." (p. 126) Positive changes in hoof structure, shape and quality come about through changes in diet, as well as changes in how the horse is worked and maintained on a variety of surfaces.
There are excellent sections on diet and how to deal with and prevent various common foot ailments. They point out that recurrent abscesses are not normal, and often relate to dietary issues as well as the surfaces the horse is maintained on.
Whether your horse is shod or barefoot, I highly recommend the book (available through Amazon), although it is expensive. Their blog is also well worth following and frequently is very educational.