Ask the Vet, Sallie S. Hyman VMD, DACVIM: Equine Hoof Abscesses

Ouch!  My Foot Hurts ...!


During your routine morning check on your horse, you find him three legged lame.  You can't see anything wrong with him, other than that one foot is warmer than the others and he really doesn't want to put any weight on it.  Don't panic! Do, however, call your veterinarian immediately and arrange for an evaluation.   In most cases, your horse probably has a hoof abscess.  

The weather on the East Coast this winter has been warmer and wetter than normal, leading to muddy, wet pastures.  These conditions have resulted in an increased number of hoof abscesses.  Just what is a hoof abscess and how can you help to prevent them, and treat them so your horse will sound and ready to go as quickly as possible?

First, let's examine the structure of the hoof.


The external hoof consists of the coronary band, the periople, the hoof wall, the white line, the sole, and the frog.

  • The coronary band (sometimes called the coronet) is a tough vascular structure that is considered the upper most portion of the hoof.  It sits between the skin and the hard hoof wall.  It helps to dissipate the concussion on the soft tissue structures within the hoof wall during each stride.  It also products the tubules of the outer hoof wall.
  • The periople is a protective layer that covers newly formed hoof wall just below the coronary band.  This structure often has a whitish appearance when wet.  The hoof wall consists of an inner and outer layer.  The inner hoof wall layer is usually white in color and is easily identified in a freshly trimmed hoof.  This layer is more pliable and has a higher moisture content than the outer layer.
  • The outer hoof wall is usually pigmented.  It provides protection to the structures beneath it and regulates the moisture content of the hoof.   The outer wall is designed to store and release energy during the phases of the stride to help propel the horse.
  • The white line actually appears more yellow than white and is where the sole and hoof wall join.
  • The sole is the bottom of the foot.  The frog is a thick, rubbery, triangular structure on the solar surface of the foot.  It is designed to absorb shock, provide traction, and assists circulation in the digital cushion of the foot.   

The most important internal structures of the hoof are the coriums and the digital cushion. 

  • The coriums produce the elements of the hoof capsule.  For example, the solar corium produces the sole, the frog corium produces the frog, the coronary corium produces the hoof wall, etc.  These structures are very vascular and sensitive to any condition that can compromise their blood supply.
  • The digital cushion sits between the coffin bone and the frog.  it is a spongy structure that acts as a shock absorber though a complex transfer of blood through venous plexi.

So what is a hoof abscess?


An abscess is a localized accumulation of pus and debris located within the layers of the hoof capsule, most commonly subsolar or submural.  Abscesses usually occur one of three ways: a penetrating wound to the hoof; bacterial migration through cracks, nail holes, or a damaged white line; or by damage to the coriums due to decreased blood flow.

Migration of bacteria is the most common cause of abscesses.  The white line gets damaged by moisture, dirt, or other debris and makes a tract for bacteria to get into the hoof capsule.  The soft tissues become inflamed, white blood cells migrate to the area, and the bacteria fight back at the white blood cells by releasing enzymes that cause tissue liquefaction.  This liquefaction leads to the grey/black "pus" that often explodes out of an abscess.  The inflamed area becomes walled off and becomes an abscess.

The inflammation and encapsulated area puts pressure on surrounding tissues causing the pain associated with abscesses.  This area of pus will try to find the easiest place to drain.  Sometimes it can find a way out through the bottom of the sole, but often times, it will find an easier way through the soft tissues of the coronary band.  This is often referred to as a "gravel" when an abscess breaks out at the coronary band.

How do I know my horse has an abscess?


Most hoof abscesses present as acute lameness.  One day your horse is perfectly sound; the next he is three legged. Some abscesses will start out as a more subtle lameness and progress, but most are seemingly overnight.

The signs, aside from the lameness, include heat in the foot and an increased digital pulse.  You can feel for this pulse by palpating the artery that runs on the inside and outside of the fetlock.  Normally a faint pulse can be felt. With an abscess, the intensity of the pulse increases greatly.

Testing the hoof with hoof testers is the next step.  Most abscesses will be localized to a very specific area, although occasionally, a large subsolar abscess will cover the entire sole.  Radiographs are not normally taken, but your vet may take one to rule out a fractured coffin bone.  Swelling in the pastern and fetlock area may occur in abscesses that migrate toward the coronet.

How do I treat an abscess?


Treatment consists of providing a means of drainage for the abscess.  Your farrier or veterinarian can use a hoof knife to try to establish drainage of the white line where your horse was sensitive to hoof testers.  It is not recommended to dig a hole in the main portion of the sole.  This rarely provide relief, makes a defect in the sole that prove slow or difficult to hear and can open up an area of bacteria to invade and cause a bone infection on the coffin bone.

If the abscess has started to  migrate dorsally to the coronet, a veterinary podiatrist (a vet who specializes in feet) or a farrier working with a vet can establish drainage through the dorsal hoof wall.  A very small hole is created in the hoof wall to relive the pressure and allow drainage.  It is thought that making the hole in the hoof wall is more humane than the pain that your experiences waiting for the abscess to make its way up to the coronary band.  The defect that results in the coronary band from the rupture of  an abscess can also affect the quality of the hoof permanently. 

To encourage drainage of an abscess, horse owners can soak the affected foot in warm water with Epson salt, and wrap the foot with a drawing solve such as ichthamol, or animalintex.  Mild discomfort may not require anti-inflammatory medications such as Equioxx, but severe cases should receive some medication for pain relief.  Antibiotics are usually not necessary unless a secondary cellulitis develops or there is a penetrating wound.

 
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