Cellulitis

By: Katie Jones, CVT

Many riders have had the experience of walking out to the barn only to find one or more of their horse’s legs are swollen.   There are a few different possibilities to why the localized swelling in the legs has started. The most common reason is seen with horses on prolonged stall rest; they commonly can develop “stocked up” legs when they are unable to leave their stall. “Stocking up” usually doesn’t cause lameness and the swelling typically diminishes once the horse moves. Another cause, and the one we’ll be discussing today, is the development of cellulites. Compared to “stocking up”, cellulitis is slightly more complicated and many times requires treatment for it to resolve.

Cellulitus 1The initial cause of cellulitis can’t always be identified. It is commonly caused by a wound which allows bacteria to get beneath the skin and spread to deeper tissue. The wound can range widely in size and depth depending on the cut, scrape, bruise, or insect bite. When wounds are exposed to deep mud, sand, or any moist environment, bacteria can enter under the compromised skin. The most common species of bacteria which cause cellulitis are: Staphylococcus aureus, Streptococcus species, E. Coli, and Pseudomonas.

Cellulitis is characterized by warm, painful tissue which can swell within a couple hours. Cellulitis most commonly occurs in the hind legs with potential swelling reaching 2-3 times the legs’ normal size.   (The horse may also develop a fever and increased heart rate.) When blood work is done by the veterinarian, it will often reveal an increased white blood cell count and fibrinogen.  All of these factors will confirm a cellulitis diagnosis. With the swelling and pain associated with cellulitis, secondary complications may develop over the treatment time. Some complications associated with cellulitis are: thrombosis (or hardening) of the blood vessels in the affected limb, extensive tissue necrosis due to the swelling which can also cause the loss of skin and/or hair, or potentially the development of laminitis in the opposite limb.

Treatment for cellulitis is focused on using broad-spectrum antimicrobials as well as non-steroidal anti-inflammatory agents (Bute or Banamine®); hydrotherapy, compression wraps, and hand-walking can also aid the reduction of swelling. If feathers (long hair) are present on the affected leg, the hair should be clipped to help kept it clean and dry while it heals.

In horses who do recover, scar tissue can form in the affected leg; this decreases the body’s ability to drain fluid from the area which then prevents the leg from regaining its original contour. In addition, if the skin was damaged, its natural defenses are weakened allowing cellulitis to redevelop or become chronic.   Some pointers to prevent cellulitis from developing are:

  1. Maintain an exercise program for your horse. Movement improves fluid drainage from the leg through the lymphatic system.
  2. Keep your horse’s legs clean and dry as much as possible. Don’t leave horses out in deep standing water or mud.
  3. Monitor their legs for heat or swelling if environmental conditions are not ideal.
  4. Call your veterinarian with any concerns in order to start treatment early.

Cellulitis can be managed with proper care and monitoring.   Once the cellulitis has been cleared, it is critical to continue monitoring the leg and environment the horse is kept in to reduce the chance of reoccurrence. If there are any signs that cause concern, early communication with a veterinarian will diminish the risk of permanent damage to the leg.

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