Sole (foot) abscesses are the most common cause of sudden and severe, unexplained lameness in horses. Most horses with sole abscess are very lame at the walk, and some cannot bear weight at all. Occasionally, early or small sole abscesses cause less severe lameness.

Horses with sole abscess often have swelling of the lower limb, which can be confused with other injuries. Most horses with sole abscess have strong digital pulse present, and usually the affected hoof is warmer than the unaffected one.

Sole abscesses develop as a consequence of some separation in the sole of the foot that allows bacteria to colonize the deeper tissues of the foot. Abscesses can develop from any penetration of the sole by a foreign body, such as a nail. A bruise can turn into an abscess- a blood clot and damaged tissue under the sole becomes very prone to colonization by even a few bacteria.

Whatever the cause: Somehow bacteria get into the deeper tissues of the hoof. They start to multiply. Inflammatory infection-fighting cells (white blood cells) migrate to the area. They accumulate and try to destroy the bacteria by ingesting bacteria, and dumping their toxins into the area. The enzymes damage the tissues themselves, and pus (a toxic stew of dead white cells, toxic products from white blood cells liquified tissue, dead bacteria) is formed. The pus pocket increases in pressure, causing intense pain from nerve endings in the sensitive tissues of the hoof. This leads to severe lameness. The abscess worsens (the pus pocket enlarges and spreads under the sole or hoof wall) until it breaks open at the coronet, or it is opened by vet or farrier and drained through the sole.

DIAGNOSIS: Vets are on the lookout for this condition in any horse with sudden unexplained lameness. Digital pulse and heat in a hoof suggest that the lameness originates there. The key to diagnosis is the use of a hoof tester to localize the pus pocket.

TREATMENT: Pain rapidly decreases when the abscess is opened and the pus is drained. But it can take days for the damaged tissues to heal completely and lameness to fully resolve.

Not all cases are located and drained on the first visit. Abscesses can in some cases be difficult to locate. The severity of the lameness may influence how aggressive vets are in trying to find and open the abscess. In some cases, treatment might require several attempts (on subsequent days) at opening the sole to finally find the abscess and get sufficient drainage. It is important to keep trying. Horses with closed infection of the hoof suffer in severe pain. They may also develop other problems like support-limb laminitis.