Reprinted from horsesidevetguide.com By Doug Thal, DVM DABVP
While there are several more common diagnoses for a horse that is suddenly, inexplicably SEVERELY lame, sole (foot) abscess is the most common cause.
Most horses with sole abscess are very lame at the walk, and some cannot bear weight at all. Early or small sole abscesses may cause less severe lameness. In most cases, horses with sole abscess become increasingly lame until the abscess is either opened and drained by a vet or farrier, or the abscess breaks open on its own. If not treated, many sole abscesses break through an opening in the coronet band.
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. Some horses with sole abscess have low grade fever.
HOW DID THIS HAPPEN?
Sole abscesses usually 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 sole 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 there and try to destroy the bacteria by ingesting them, and they kill bacteria by dumping their toxic enzymes into the area. These enzymes further damage the tissues themselves.
Pus (a toxic stew of dead white blood cells, toxic products from white blood cells liquefied tissue, and dead bacteria) is formed. The pus pocket increases in pressure, causing intense pain from pressure and irritation to 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 band, 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 and severe lameness. They begin by performing a lameness exam.
Digital pulse and heat in a hoof suggest that the lameness originates in the hoof. One important 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. In most cases, the hoof needs to be covered with bandage or boot to protect the defect in the sole until it heals.
Not all cases can be located and drained on the first visit. Abscesses can in some cases be hard to reach. 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 (over several days) at opening the sole to finally find the abscess and get sufficient drainage. It is VERY important to keep trying.
Because they are so lame on the affected limb, horses with sole abscess not resolved within a few days could develop other problems like support-limb laminitis. In addition, if allowed to progress, the bacterial infection can dissect through the tissues of the hoof, spreading infection, and severely and irreparably damage important structure of the hoof.
So…. if your horse is suddenly very lame, you have no idea what might have happened, and you fear the worst, always keep in mind that sole abscess could be the cause. The good news is that sole abscess is very treatable. Remember to contact your vet whenever your horse is severely lame, so that the cause can quickly be determined and appropriate treatment instituted.
Dr. Doug Thal, DVM DABVP. Certified in Equine Vet Practice, Creator of Horse Side Vet Guide, is an equine veterinarian who has been in practice for 24 years. Over that time, he has worked to help horse people better understand their horses physically and mentally, and better understand how to get the most from their equine vet. To do this, he created a Smartphone app for horse people called Horse Side Vet Guide. Every horse person should have it on their phone!