This is copied from Natural Balance Hoof Care on Television
Q) Many farriers say that the frog should not be on the ground because the foot has to flex outward at the bottom and to do that the sole has to flatten when he bears weight. They say this is necessary for circulation and shock absorption. So why would I want to leave all that frog there? Wouldn’t having the frog on the ground prevent this?
A) Well, think about this. If the frog was not supposed to be on the ground, why does it always do so in bare feet, and why is the foot designed to fill up with dirt when it gets long? Doesn’t the packed dirt support the frog even when the hoof wall has grown longer than the sole? The old theory about the foot flattening and flexing outward at the bottom is based on incomplete information about what the foot needs and how it functions when left to its own maintenance. Although horses have managed to survive the practice of removing frog for years we need to remember that horses manage to replace the frog support rapidly. The frog always rapidly grows back when pared away and in shod horses the foot fills with packed dirt almost immediately when it is on the ground. That self-replacement of the support is possibly why we thought the practice of paring frog was working OK, because the horses manage it themselves despite our efforts to remove it. Unfortunately some shod horses have to live or work on hard surfaces where the frog cannot contact the ground. They suffer faster consequences and are more likely to develop side bone, ringbone, contracted heels and other lameness.
Q) Then you are saying the dirt is supposed to be left in the foot?
A) That is correct. There are newer studies that shoe how the dirt that fills alongside the frog area actually acts along with the frog and bars in supporting and helping the foot expand more at the top, in the heel bulbs and coronary band. This action absorbs shock and circulates blood more efficiently. Keep in mind, that urine and manure soaked shavings doesn’t necessary provide the best environment, so it is best for the compaction of material be good “clean” dirt. If you get a good compaction of dirt in and around the frog, it will also help keep unwanted bacteria from getting in there. Maintaining a “healthy” frog through consistent use will also help battle unwanted bacteria.