Founder typically affects only the front hooves, but it’s not completely unusual for it to affect only one hoof or all four hooves. In some cases, only the back hooves are affected. There appears to be a correlation between poisonings, vaccinations or major chemical changes to the body and founder in all four feet. When only the back feet are affected, it appears to be more from a true ‘man-made’ issue. Of course, these are never an absolute given, but seem to be what the evidence suggests for this type of founder.
Even though it’s generally the front feet that founder, the back feet can be greatly affected by the horse’s foundered condition. The stress that the back feet will be put through, should the horse be in a foundered state for a reasonably long period of time, can certainly tax them to the point that they appear to be foundered as well. It’s hard to tell often times if the back feet have had laminitis or has simply been stressed to the point to where the lamina has become stretched and the hoof wall starts to take on a dished appearance. Regardless of whether or not the hind feet are stressed or have suffered from laminitis, I treat the hind feet in much the same way as the front feet; I perform ‘founder’ trims on them as well.
A non-metabolic condition that can cause founder is called ‘road-founder’ or ‘concussion founder’. This also has many of the usual characteristics of metabolic founder, but will generally have nothing to do with food; it has to do with the feet taking too hard of a pounding. This situation generally has to do with the lack of conditioning of the feet and body so they can endure the extreme use they have experienced. If your horse is a ‘couch potato’, typically stall-bound, or has a low-exercise daily regiment and / or soft surface to stand on, don’t expect that horse to be able to win an Endurance race without suffering some severe side effects. This type of founder is easy to avoid, though it will require time and patience. The horse will need to be conditioned to the environment and / or extremes he will be exposed to before he will be able to endure what’s being asked of him. Work up to the level he’ll be expected to endure. Think it through logically and take it slowly.