It is red, rubbery, disgusting to look at and bleeds easily, but it's a darn good thing horses can produce it. In fact, horses tend to produce exuberant granulation tissue or "proud flesh" faster than almost any other animal. Proud flesh helps heal wounds associated with a significant loss of tissue.
Horses evolved in a hostile environment. Survival dictated a means of filling in wounds. Large wounds needed to heal rapidly, since an injured horse that could not run or keep up with the herd quickly became another animal's meal. The early horse developed a type of tissue that starts to grow as early as three days after a wound occurs.
Since many equine wounds affect the lower body and legs--areas that don't contain much muscle or underlying tissue--proud flesh develops from capillaries or small blood vessels located in these areas.
These vessels grow into loops, and other types of cells, such as fibroblasts, invade the developing granulation tissue. The
fibroblast cells form collagen, the material that effectively fills in the damaged area.
Granulation tissue provides a surface over which epithelial or skin cells may migrate. These cells are responsible for repairing skin defects, but they grow only in one direction. They cannot grow down into a wound, and they cannot grow up over a lump. Granulation tissue fills in a large wound so that epithelial cells can grow across the surface of the wound and allow the skin to recover the area.
Granulation tissue is resistant to infection, so it protects dangerous wounds from bacterial damage. It carries fibroblasts that are crucial to the development of collagen, which gives skin its elasticity. And it provides a framework for wound contraction.
While this type of tissue helps the horse heal itself, it is called "exuberant" because the process can get out of hand. The very tissue that aids in wound healing can become a problem when the amount produced is greater than what is needed.
Horses can rapidly produce tissue that grows up over the level of the skin, and a large, red, unsightly mass results. This proud flesh tends to bleed excessively when it is bumped, rubbed or otherwise traumatized, and its presence keeps the skin cells from growing across the defect and healing the wound. In these situations, the excessive tissue must be removed.
Don't waste time. Aggressive treatment will lead to a better outcome.
Caustic agents and substances called astringents effectively remove proud flesh chemically by cauterizing it or "burning" the cells. These compounds, which include strong iodine, lye and sulfur, are not selective in their destruction, however, and often destroy surrounding skin cells. That means slower healing time and larger scar formation.
The very tissue that aids in healing can become a problem when the amount produced is greater than needed
Surgical removal of the excessive tissue and the application of a bandage tend to result in a far better cosmetic outcome. Studies have shown that a bandage reduces formation of granulation tissue and increases the amount of carbon dioxide near the wound's surface. This keeps the wound more acidic, which inhibits bacterial growth.
All of these small factors contribute to quicker healing and less scar formation.
A better plan is to get a head start on granulation tissue formation, using an antibiotic cream mixed with a steroid solution. The antibiotic helps to keep the wound from becoming infected, and the steroid greatly reduces the body's production of proud flesh.
Applying the antibiotic cream to the outer edges of the wound and working in toward the center as the wound heals in with granulation tissue can help result in a healing that fills in flat with the surrounding tissue surface.
The epithelial cells can then grow on top of the granulation tissue framework and easily and cosmetically close the wound.
This approach results in the best overall healing, but it requires conscientious and dedicated care. The granulation process must be recognized early and treatment started quickly, otherwise the tissue will rapidly grow above the level of the skin and the ointment will not be as effective.
Proud flesh can very rapidly overgrow, so daily treatment is important.
Other topical treatments are available. N-butyl-cyanoacrylate is slowly becoming more popular. It is a surgical compound similar to the substance that makes up Super Glue, and is used to cover the surface of large wounds. It is easy to use and reduces contamination, as well as slowing the formation of granulation tissue.
Some veterinarians cover large wounds with strips of equine placental tissue that has been collected after a foaling, cleaned, cut into pieces and stored until needed.
This tissue also provides a barrier to infection and reduces proud flesh formation.
Surgical lasers may change the way excessive granulation cases are handled. Lasers can remove excessive tissue, but they also cauterize small blood vessels, especially important since proud flesh is made up of capillaries.
The laser is so accurate that it can remove granulation tissue while leaving the healing skin cells. Laser use may someday result in the best healing of all.