Hoof abscesses can be caused by a lack of blood flow to the corium, or the introduction of bacteria and moisture to the hoof. A lack of blood flow, due to pressures on the corium, will cause tissue in the hoof to die. When blood flow returns to this area an abscess will appear. The pus from the abscess will then expel the dead tissue from the hoof.
While the cause of your horse’s abscess may never be pinpointed, the most common cause is the introduction of a foreign object. Sand, a tiny rock, or even soil will embed itself in to the soft white line area of the horses hoof and then bacteria will make its way to the lamina under the hoof wall causing the abscess. This bacterium finds its way into the hoof by way of cracks, hoof defects, hoof separation, and introduction of foreign objects to name a few.
Some horses will experience an abscess shortly after a shoeing. This is usually because a nail was driven in too close to the white line where the bacteria will attach itself and cause an abscess.