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- Wound size and duration are powerful influences on the amount of scarring that occurs.
All horses wear a history of their mishaps and calamities on their hides, though most repair work is hardly visible after a few months while a few injury sites remain glaringly obvious for life. Whether healing results in unblemished skin or an unsightly and disabling scar depends upon the wound type, its location on the body, any complicating factors during healing and the wounded individual's repair capabilities.
Only a never-injured horse is an unscarred horse, for the inalterable reality of mammalian life is that repaired tissue is inferior to the original, even when there's hardly a ripple in the hair overlying the healed spot.
"Scarring is an inevitable consequence of injury," says Derek Knottenbelt, MRCVS, head of equine studies at England's University of Liverpool and author of Handbook of Equine Wound Management. "It's a mechanism for limiting the amount of damage. Some reptiles and insects can 'remake' themselves [when injured], but as we've evolved, we've lost the ability to regenerate tissue. Even when you nick yourself and it eventually looks normal, there will always be a scar." Despite the inevitability of scarring, good nursing and appropriate veterinary care can encourage the least disfiguring outcome for wounds of all types.
Wounds under Repair
All wounds, whether inflicted by a protruding nail, battering horseshoe or surgical scalpel, go through the same stages of repair to return the tissues to wholeness. When the healing process is compromised and wound closure is hindered during one or more of these phases, scar tissue tends to proliferate. Thus, the best scar-minimizing strategy for horses is early and appropriate intervention that encourages rather than impedes the healing process.
Phase 1: Immediately after a horse is wounded, the blood vessels at the site constrict to taper blood flow and prevent hemorrhaging. Fibrin, a fibrous protein activated in the blood, forms a clot in and over each pinched vessel to help contain the damage and protect exposed tissue. Later, the fibrin will serve as the primary scaffolding for the regenerating tissue. On contact with air, the clot dries, forming a natural bandage, otherwise called a scab.
The blood vessels surrounding the injury have also swung into action, delivering inflammatory cells, called macrophages and neutrophils, that begin the cleanup effort. These cells migrate in from the edges of the wound to engulf and "digest" bacteria, forming pus and lifting out small foreign bodies, loose hair and dead tissue contaminating the wound.
Phase 2: Inflammation is simultaneously signaled by the first-response cells on the scene and typically lasts about six hours, barring complication such as infection. The effect is increased blood flow surrounding the wound to speed delivery of the materials necessary for the cleanup and repair activities. This localized flood of blood is responsible for inflammation's "cardinal signs": heat, swelling, redness and pain.
The common practice of using cold therapy or anti-inflammatory drugs to suppress the inflammatory reaction during wound treatment seems to fly in the face of all that's natural and necessary to healing, yet uncontrolled inflammation can become too much of a good thing.
"All wounds become inflamed, and the response corresponds to the degree of trauma," says Ted Stashak, DVM, professor of large-animal surgery at Colorado State University's College of Veterinary Medicine and author of Equine Wound Management. "We usually try to reduce the impact of inflammation because as long as the wound is inflamed, it delays the progress to the next phase."
Debridement is the removal of contaminants-continues in conjunction with inflammation. "White blood cells are brought in to engulf the bacteria and clean up dead tissue and foreign bodies," says Stashak. "This is the stage that [veterinarians] have the most effect on. We can lavage [wash] the wound and use a scalpel or scissors to remove dead tissue, allowing the wound to accelerate to the repair phase."
Phase 3: As decontamination proceeds, fibroblasts, cells that produce a raw, reparative matter, migrate into the area. Fibroblasts generate the mix of collagen fibers and ground substance, called granulation tissue, used to fill the wound site. "Fibroblasts put down an immature fiber called tropocollagen," says Stashak. "When it matures, it provides tensile strength."
During the granulation period, fibroblasts are converted into myofibroblasts that are capable of contraction and have the job of pulling the wound edges together to minimize the wound size. Granulation tissue also provides a surface for the next legion of cells-the initial skin cover-to enter the repair zone.
