The Science of Wound Ointments for Horses

A topical wound preparation can have a big impact--positive or negative--on the healing process. Here are tips from a wound-care expert for selecting the right product for your horse's injury.
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Your horse comes in from the pasture with a small cut on his chest. Maybe he hit the fence while playing or perhaps it was a tree.

In any case, the wound is fresh, clean and small. No need to call the veterinarian--you can handle this yourself. You reach for a tube of the thick wound ointment you've always used and smear a good-sized glob across the cut. That'll take care of it. Or will it?

Perhaps, says researcher Georgie Hollis, BSc, MVWHA, but it depends on what's in the tube.

The right preparation applied at the right time can protect a wound, support natural healing processes and minimize the risk of complications. But, warns Hollis, use the wrong type at the wrong time and you could actually slow down or even halt healing.

For the past three years, Hollis has been working to help make choosing the right ointment for each situation easier. A former podiatrist, she first observed the challenges of wound healing when she treated foot lesions in diabetic patients. In late 2006, Hollis, motivated by her personal interest in animals and horses in particular, began studying veterinary wound care. She now works with leading equine researchers, such as the University of Liverpool's Derek Knottenbelt, DVMS, MRCVS, in investigating and sharing information about how various treatment techniques affect healing.

Through her program, Intelligent Wound Care, Hollis maintains the Veterinary Wound Library, a database of individual research cases accessible to veterinarians. "There is quite a bit of science out there." says Hollis. "But there is also a tendency, even by veterinarians, to just put anything on the wound in the hopes that it helps. And there is no doubt that part of wound dressing is psychological. The creams cover up nasty-looking skin and make you feel that you've helped your horse in some way. I know as a horse owner, my first instinct is to cover my horse's minor scabs with a nice cream."

In the end, however, Hollis relies on her knowledge of the wound healing process to guide her selections. Here's what she has learned about how to use wound ointments to encourage healing.

A Fresh Start
The first step in treating any wound is a good cleansing. "Dilution is the solution to pollution," Hollis says. "Flushing the wound with large quantities of warm saline or water will loosen debris and dilute the bacterial concentration within the wound. This process alone is one of the most useful things an owner can do in helping a wound to heal."

Wounds that are particularly dirty may also benefit from antimicrobial wound washes, such as those containing povidone iodine or chlorhexidine, which kill bacteria on the surface of the wound while cleaning it (see "The Antibiotic Question" at the end). But small, fresh wounds often require nothing more than a standard cleansing, which removes bacteria mechanically.

As you clean the wound, do a thorough visual inspection to gauge its seriousness and your comfort level in dealing with it. Call your veterinarian about any wound that concerns you or that

  • is over a joint or could involve bone, tendons or ligaments
  • has embedded hair, debris or dirt
  • is estimated to be more than six hours old when it is discovered
  • "gapes" when the horse moves, with its edges pulling apart
  • is associated with any lameness or other obvious discomfort on the part of the horse.

Remember, says Hollis, some of the smallest wounds are the most dangerous: They are easily ignored and are sometimes very difficult to clean effectively. "The outside--visible--part of the wound may be small and 'insignificant,' but there may be contamination, tissue damage and even life-threatening infection present," she says. "It's far better to call for professional help immediately if you are even slightly worried."

Let the Healing Begin
Once the wound is clean, it's time to decide what to apply. "Your choice should be guided by what the body is doing at that point," says Hollis. During the initial phase of wound healing, the debridement stage, the body delivers white blood cells to the site to clean up damaged cells and foreign matter and defend against infection. These blood cells begin work within an hour of wounding, and for the next day or two the dead cells and bacteria are expelled from the wound as a clear or slightly yellowish discharge.

The sight of an oozing wound sends many people off-track. "There is a real instinct at this point to look at a wet, oozing wound and want to 'dry it up,'" says Hollis. "But that's the last thing you want to do. White blood cells are what trigger the 'cleanup' process and healing, and they need a moist environment to move in. If they do not have moisture to move around in, they get stuck and cannot work. So, if you 'dry up' a fresh wound, you hamper their work." Instead, she says, let it ooze, and even supplement its moisture with an ointment.

Thick creams, however, are not the best choice in this earliest stage of wound healing either. "Any dressing with a paraffin or petroleum compound can slow cell growth," says Hollis. This happens for two reasons: First, white blood cells are unable to move easily through the thicker compounds as they do through water-based products. Second, thicker compounds can cause a foreign-body reaction. "Essentially, the body sees these thick ointments as something to get rid of and mounts a defense against them," she says. "Instead of dedicating all resources to healing, the body is busy trying to get rid of what you are putting on the wound. It's counterproductive."

Nor are wound powders beneficial when a wound is just beginning to heal, says Hollis. "Not only do they dry out the wound, but the powder itself is essentially very tiny particles that the body will see as foreign."

Early On, the Choice is Clear
The best choice for the initial stage of healing is a hydrogel product, says Hollis. Chemically, hydrogels are superabsorbent polymer chains composed of up to 99 percent water. "These are the lighter, clear liquids that keep the wound moist so the white blood cells can easily get about their job cleaning things up," says Hollis. "We know that a layer of hydrogel ointment over a clean, fresh wound will create an ideal environment for healing without hampering the process." Hydrogel products are usually labeled as such or are described as "water-based."

As the body cleans up the debris, dead cells slough out of the wound, increasing the amount of exudates and causing the color to change. "This is a good thing," says Hollis. "Pus alone, without redness or smell or other signs of infection (see "Warning: Infection in the Works,"), is part of the healing process." To support the natural sloughing process, she advises gently wiping the hydrogel ointment from the wound once a day and replacing it. "This will assist the body in getting rid of debris and give you a chance to assess the wound."

In the next stages of healing, cells accumulate to fill in the depths of the wound (granulation), and layers of new skin cells grow inward to close the defect (epithelialization). These processes generally occur at the same time, making the wound progressively more shallow and narrow.

The danger at this point is the development of proud flesh, excessive growth of granulation tissue. A complication most often found in wounds of the lower leg on larger horse breeds, proud flesh grows more rapidly than normal tissue and doesn't stop even when it overflows the wound edges. This cauliflower-like tissue invariably slows or halts healing.

If you suspect your horse's wound is developing proud flesh, Hollis recommends calling your veterinarian. "There are lots of products out there marketed to reduce proud flesh, but some of them can actually make the problem much worse. It's safer to bring in your veterinarian.

He can confirm the problem and has many more options for fixing it, including surgically removing the unwanted tissue."

Support for the Rebuilding Process
Once a wound is nearly filled with new healthy tissue, a different type of support is needed from wound ointments.

Maturation, the reorganization of new cells laid down along collagen "scaffolding," is the last and longest phase of wound healing. "Once the wound has epithelialized, the replacement tissue cells--the scar tissue--will be visible as thick, nonpigmented, hairless skin," says Hollis. "This tissue is weak in the first few months and will not have much tensile strength." The maturation process makes this new skin stronger and reduces the appearance of scars over time. During this phase of the healing process, an emollient wound ointment is appropriate and helpful, says Hollis.

Thick and greasy creams, emollients soften and/or soothe tissues. Wound ointments containing lanolin fall into this category, as does ichthammol. "An emollient helps to maintain elasticity in the new tissues that are forming," says Hollis. "It helps them remain pliable so stronger, flexible, more functional scar tissue forms." An emollient works by creating a barrier of sorts on the skin surface, trapping moisture beneath it. By preventing dryness and irritation in new tissues, an emollient helps the maturation process proceed as quickly as possible.

"The thinner scar tissue in the early days of healing will be prone to drying out and may become flaky," says Hollis. "Emollients can help keep down the evaporation and reduce the flakiness, which can itself trap bacteria on the surface of the healed wound." Emollients also reduce the discomfort sometimes associated with new scar tissue. "If a horse finds the area tight and itchy as it heals, he may scratch, and the wound can easily open up again," she says, noting that emollients also help keep insects off tender new tissues.

In addition to their primary active ingredient, emollient-type ointments may also contain antimicrobial agents or extracts such as aloe vera. Read the label so you know what you are applying to your horse, and choose the simplest formula available, advises Hollis.

"Many products like this give with one hand and take with the other. They will provide protection to new skin, but also may have an antiseptic that particular wound doesn't need and is a potential irritant," she says. "The more complex the product--the more ingredients it contains--the more potential you have to take more than you give."

Also, be prepared to continue applying an emollient for several months. "Scar tissue in a wound will take up to a year to regain 80 percent of its original tissue strength," says Hollis. "Emollients can, and probably should, be used for several months after an injury to allow the tissue to reorganize and strengthen as much as it possibly can. Hair is more likely to regrow and scars will be less noticeable the longer you use an emollient."

Horses, more than dogs and even kids, seem to be prone to minor cuts and scrapes. Fortunately, these heal quickly with minimal care. All that's required is a thorough cleaning, followed by treatment to supplement the body's own resources and support its repair processes. Choosing the right ointment based on the specific wound and stage of healing will ensure that you help, rather than hinder, your horse's natural healing efforts.

Color Coded Wound Care
Ask your barn pals what they put on their horses' wounds and you may get a colorful answer: "The yellow stuff," or "that purple spray," is a common reply, with no further explanation.

The color of a wound ointment is inconsequential, of course, but what gives it that hue isn't. The "yellow stuff," for instance, is likely a nitrofurazone-based product. Nitrofurazone is an antibacterial agent, but some studies suggest it may actually slow healing--so before applying it to a wound talk to your veterinarian about whether it's advisable in your horse's case.

Moving to the other side of the color spectrum, the antifungal known as gentian violet gives some wound treatments a blue color. In between is a compound called Biebrich Scarlet Red, which gives preparations a red hue. Both of these are common ingredients in traditional wound care products, but their value is uncertain.

Read the label and consult with your veterinarian rather than relying on color alone.

Warning: Infection in the Works
Signs of infection can be similar to those of inflammation, which is necessary for healing. Distinguishing between the two depends on degree and timing--fresh wounds are more swollen and oozy than older wounds, and large wounds will remain in the inflammatory stage longer. Generally speaking, however, in small wounds more than a day old, any of the following signs may indicate infection:

  • heat
  • swelling, both in the wound and around its edges
  • smell, particularly the rotting "sweet" smell of necrotic tissue
  • an unusual color, such as green or bright yellow. "Healthy" slough or wound exudate usually has a creamy tinge to it. "It is easy to assume that healthy, sloughy tissue is infection when it is simply the natural expulsion of dead white blood cells and wound debris," explains Hollis.
  • increased exudates after the wound had naturally dried up a bit
  • fragile tissue that is prone to bleeding under "normal" pressure from your fingers.

The Antibiotic Question
Many of us have become accustomed to treating minor cuts and scrapes with over-the-counter antibiotic ointments. In England, however, horsekeepers don't have that do-it-yourself option. "In the United Kingdom antibiotic ointments are available only through prescription, and excessive use is linked with concerns about resistance," says Hollis.

Antibiotic resistance occurs when some bacteria survive a treatment and are left to multiply. A 2003 study showed that acne bacteria had developed resistance to topical erythromycin treatments, but a 2006 study of ointments containing neomycin, polymyxin B and bacitracin--so-called "triple antibiotic"--concluded that bacterial resistance to such products was rare in the United States.

Nonetheless, Hollis advises using antibiotic ointments with care: "It must be great to pick these up over the counter in the United States, but you still have to keep in mind that using them when they are not needed is just contributing to a bigger problem," she says. "Increasingly, antibiotics are thought not to be necessary unless signs of infection are present."

What's more, she says, several good alternatives are available: "Use of dressings containing ionic silver or manuka honey is now not unusual, and both are effective against a wide range of common wound pathogens including MRSA," she says.

Small, shallow cuts discovered and cleaned soon after they occur may need no topical antibiotic treatment at all, Hollis says, but tetanus remains an ever-present threat, so make sure your horse's vaccinations are current.

Hold the Cortisone
Hydrocortisone, a synthetic steroid that reduces inflammation, is available over the counter and is a staple in many equine first-aid kids. It may be tempting to put hydrocortisone on a wound to minimize swelling, but it's not a good idea.

Hydrocortisone treatment may make a wound look less "angry," but inflammation is needed to jump-start the healing process, delivering white blood cells and other materials to a wound site. Limiting inflammation in new wounds can delay or halt healing. Hydrocortisone is better used
in the treatment of inflammatory skin conditions, such as insect bites and rashes.

This article originally appeared in the April 2009 issue of EQUUS magazine.