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Proper horse care also means selecting a qualified farrier to perform skilled and regular trimmings. This isn't necessarily as easy as it sounds, for just about anyone can slap on a farrier's apron and carve away at a hoof while pronouncing himself a qualified blacksmith. Whereas a bad haircut from an unqualified barber will do you no long-term harm, a poor trim or shoeing from an unqualified farrier can do significant harm to your horse… up to the point of making him lame.
I don't want the above statement to be viewed as a scare tactic, but in my time I've had more than a few blacksmiths work on my horses and trust me when I say the difference between an average and a great blacksmith is amazing.
Equally important is that your farrier be familiar with any special requirements for your horse's breed, such as gaited horses that often require angles different from a Quarter Horse.
There is a debate among the horse world: barefoot versus shod. Personally I'm an advocate for barefoot. Scientific studies have shown that blood circulation is decreased significantly along the hoof and leg of a shod horse. In addition the shoe can cause the hoof's to compress, causing damage along the corium area and potentially leading to future abscesses (especially when/if the shoes are removed).
Many argue that if a horse has to travel rocky trails then bare hooves won't be able to withstand the rigors of the ride. This is partially true, depending on your horse's circumstances. Some hooves are more durable than others, so it's possible that a horse with particularly sensitive feet should be shod before attempting rough terrain. You also don't want to take your horse on rough trails or pavement regularly if your horse was previously shod for a long period of time and is now barefoot; the hooves need time to heal and strengthen.
A hoof is much like our own foot. If we were to take off our shoes and run through the woods, chances are it would be a rather painful experience. But if we stopped wearing shoes permanently, with time our feet would toughen until we could traverse rugged terrain comfortably.
The same is true of your horse – although his hoof is always "hard" to us (just as our skin would always be soft to him), unless the hoof is toughened through direct and regular use, you can do damage by riding him hard on tough terrain. So once he's been shod for an extended period, you're pretty much forced to either keep him that way indefinitely (which isn't ideal for a horse's hoof) or to allow his hooves many months to toughen and heal before taking him on rough terrain.
In the end there is no black and white answer. I would sum it up as: shoes can benefit a horse during specific requirements or periods, but overall a reliance on shoes could do serious damage to your horse's long-term hoof health.