Written by Dr. Mike Stanford, DVM, Rappahannock Equine Clinic
From our Nov/Dec 2013 issue
If you have had horses for any length of time, there is one thing you may have learned: Horses and wounds seem to go together. Our tack trunks seem to be filled with a variety of creams, gels, and ointments in the colors of the rainbow. What is the best way to treat wounds though? From little scratches to serious lacerations, wounds all follow the same healing pattern. In this article we will look at how wounds heal and what we can do to get the best result possible.
Phases of wound healing
The inflammatory phase: Within moments of a wound occurring, the little blood vessels in the affected area constrict to limit the amount of bleeding into the area. This effect is short-lived though, and within 5 to 10 minutes the vessels open up to allow blood and plasma to leak into the wound as well as white blood cells that have begun to accumulate. A clot generally forms at this time to minimize the bleeding, to create a protected environment for healing to occur in, and to provide a framework or scaffold for future repair. When this clot dehydrates, it forms a scab that will protect the wound from the outside environment.
The debridement phase: In this phase, the white blood cells that have been accumulating in the area of the wound begin the process of cleaning up. Some of the white blood cells kill bacteria, break down debris, and enhance the inflammatory response. Others surround and engulf foreign material and damaged tissue. These white blood cells remain active as long as there is contamination or damage in the wound area, and though it is essential in the early stages of healing, excessive white cell activity and inflammation will slow overall healing of the wound. For this reason, adequate cleansing of the wound is critical.
The repair phase: Epithelialization, or the growth of new epithelial or surface cells, begins to occur very rapidly after injury. In a sutured wound, epithelial cells may cover the wound in as fast as 12–24 hours. In an open, full-thickness wound, a bed of granulation tissue must form first to provide a surface for the new epithelial cells to grow across. This granulation tissue is made up of cells that provide the new connective tissue to fill in the defect as well as new blood vessels and begins to appear 3–6 days after the injury occurs. In addition to providing the new surface for the epithelial cells, granulation tissue is also very resistant to infection. Wound contraction occurs during the repair phase. Through the action of specialized cells, the edges of the open wound are moved toward the center of the wound. This effect is most pronounced in areas where the skin is quite loose.
The maturation phase: During this phase of healing, the wound increases in its tensile strength as collagen fibers are aligned along areas of stress. It is important to remember that a scar will never be as strong as the tissue that it replaced. Most estimates claim that the scar is 15–20 percent weaker than the surrounding tissues.
So, what can we do to promote the good repair and healing of an injury in our horses?
Initial care of the injury: It goes without saying that many wounds are easily taken care of at home with no professional involvement. Careful cleansing and the application of an appropriate topical product can be all that is needed. Be cautious though, as sometimes the smallest wound can create the largest problems. Puncture wounds and even small wounds over joints are veterinary emergencies and require immediate professional evaluation and care. Antiseptic products containing povidone-iodine and chlorhexidine are very common and effective. Be careful, as some horses may have skin sensitivity to the povidone-iodine products. Therefore, all cleansing solutions should be thoroughly rinsed off after use. Also, be sure to keep chlorhexidine-containing products away from the eyes.
“To suture or not to suture?” That is the question: I’m often told by clients that they would have called me to suture a wound but it had been more than 6 hours. They knew I would not be able suture it and so they have just been cleaning it as best they can. This so-called “Golden Period” is from early research on laboratory animals. It was felt at that time that it took more than 6 hours for a wound to develop significant enough numbers of bacteria to become clinically infected if the wound was sutured. More recent studies have shown that there are many more factors involved, and the most important criteria for a decision of how to treat the wound comes from examination of the wound and the overall health of the patient. From the discussion of the healing phase above, we see that the epithelium can cover a sutured wound in as fast as 12–24 hours, whereas an open wound could take days to weeks to months. It never hurts to look and consider. Many wounds can be closed or at least minimized to promote healing.