Cracks can vary in severity from shallow (does not completely penetrate the hoof wall) to deep (penetrates through the hoof wall). Shallow cracks can occur from changes in hydration and/or from mechanical failure. Deep cracks are from severe mechanical failure and can be painful. These usually occur when load placed on the wall is greater that what the wall can support. These cracks can be supported nutritionally to support stronger hoof tubules. Hooves that become over grown have extra "leverage" that is being applied to the hoof wall. Much like trying to pry your own fingernail backwards, it is only a matter of time before it gives way and cracks. This is why application of a good mustang roll or bevel is extremely helpful in alleviating pressure so that cracks can grow out.
There are farriers that stitch, patch, or wire close a deep and painful crack. This will provide relief as it doesn't allow the crack to flex and induce pain. However, I feel the body can heal amazingly well on its own. I do feel that we must relieve pain and reduce the pressure that caused the crack in the first place. I feel if you make a horse bear 100 percent of it's weight on the hoof wall, the wall will fail and you will get quarter cracks or crushed heels. I rarely see quarter cracks in barefoot horses. Restoring proper biomechanics is a must to rehabilitating deep cracks and nutrition must be addressed to ensure that the body is able to proliferate the epidermal cells of the hoof.
On occasion wall cracks become stubborn to get rid of. They can have an underlying fungal component. I suggest soaking affected hooves in Apple Cider Vinegar for 20 minutes 2-3 times weekly. This will promote a healthy environment and the fungus won't be able to survive.
