I completely understand the frustration of trying to diagnose and treat lameness in a horse, I have a mare that has frustrated both my vet and my farrier in her lameness and 'quirks'...she has the ability to move soundly one day and not so much the next. She has been retired to be a broodmare at the age of 8 as they believe her problems arise from a demineralized coffin bone and the sensitivity that brings...(and yes we had xrays done to confirm).
However, in trying to figure out what was wrong with her I did a LOT of research on navicular as I thought that was her problem. I had the pleasure of having a barefoot trimmer come out to assess Katie and her lameness (she never presented ANY heel pain or soreness, but an irregular gait and uneven action in her front). In order to keep her comfortable, I do HAVE to keep her heels kept low, and her toes squared off to maintain a good breakover.
I have a good link for anyone interested in the reading ...http://www.equinextion.com/id36.htm
I truly believe that general "unsoundness" has alot to do with the farrier and the understanding of proper hoof health, angles and breakover...as well as the other joys that horse owners are dealt as far as injuries go. But as far as the actual hoof goes, alot of farriers that do the "pasture trim" simply knock off the toe and leave the heels to grow too long which leads to heel pain and at times, the horse being lame. There is more to trimming hooves than just cutting and rasping, some horses need a more detailed approach to maintain their hoof
I'm a true believer in natural hoof care, allowing the hoof to be balanced and maintained to alleviate stress and pain whenever possible. My horses who routinely do some serious trails do not need shoes, boots or anything else to keep them sound...but I DO have a farrier that comes out every 6-7 weeks (rain, snow or shine) to keep my horses trimmed and in balance.
I think regular trimming, even every 2-4 weeks for certain horses by a GOOD farrier would be much more beneficial than some of the supplements that are marketed....but again, that is just me and my limited opinion. I will ADMIT to buying supplements for my mare to help her but I have found the trimming did far more for her than anything else - but perhaps that is just my experience. I do know that my mare is FAR better with regular, balanced trims which makes me feel like I am doing what I can for her :).