Hoof abscesses are common in horses and many horses will develop an abscess at some point in their lives.  Most abscesses occur when the feet are not trimmed correctly or often enough, and a space develops at the junction of the wall and sole called the white line that allows dirt and bacteria to enter the hoof capsule.  Abscesses can also occur when your horse steps on an object that penetrates the sole, like a mesquite thorn, but this is less common.  Generally, these abscesses are easily treated by your veterinarian and competent farriers and they respond to treatment. 

However, if your horse continually develops hoof abscesses or does not respond to treatment, there must be an underlying problem.  I have heard folks say it required 3 months to a year for an abscess to resolve and if this is the case, there is another underlying problem involved.  Laminitis is a common cause of recurrent abscesses as is infection of the coffin bone.  Another cause of recurrent abscesses is a mass called a keratoma that can form around the coffin bone and between the bone and the hoof wall or between the bone and the sole.  These masses can usually be found on an X-ray as a defect in the bone as the mass presses on the bone.  However, Dr. Sammy Pittman indicates in the Remuda Magazine that sometimes a venogram is helpful in identifying these masses.  Surgical removal is the only treatment option for the keratomas and many times a large portion of the hoof wall must be removed to locate and surgically remove the keratoma or a large portion of the sole may need to be removed.  So, if you have a horse with recurrent or non-healing abscesses, there is an underlying problem and X-rays will be required to determine the underlying cause.