Many farriers have a tried-and-tested method of working with microbial issues on a horse’s feet. But from time to time, a case might come along that is particularly stubborn —when nothing seems to work or it just keeps recurring, despite a hoof-care professional’s best efforts.

Sam Austin, from Red Horse Products in the United Kingdom, shared his treatment protocol for microbial infections during a How-To Hoof-Care Product Knowledge Clinic, sponsored by Equine Digit Support System, at the 2020 International Hoof-Care Summit in Cincinnati, Ohio.

The type of microbial infection —
bacterial or fungal — will depend largely on geographic location but the most damaging microbes are keratolytic, which means that they feed on hoof matter or keratin. Microbial infections can include thrush on the surface of the foot or the deep central sulcus, white line disease, seedy toe and, in extreme cases, canker.

“I don’t like to get too hung up on what the exact microbe is because we often find that the same treatment protocols tend to work with all of these particular microbes,” Austin says.

“Canker we’d leave as a veterinary issue, but the protocols work quite similarly.”

Common Causes

For the origins of microbial infections, look no further than a horse’s immediate environment. Organic matter, moisture and a limited oxygen supply converge to provide ideal conditions for microbial proliferation. Likewise, the moist, anaerobic cavities within the horse’s foot — the white line and central sulcus — are an attractive habitat for microbes and offer the added bonus of warmth provided by the proximity of the hoof’s blood supply. A foot that’s weakened by poor care or improper hygiene is an open invitation to infection.

“Dead sole tissue and dead frog tissue not being removed, and poor hoof picking on the part of your clients, create an anaerobic plug and cause the foot to become more porous than hard,” Austin says. “Think in terms of what supports bacteria best: a damp sponge or a dry marble worktop? You want to always be erring on the side of a tough foot that isn’t an easy target for microbes.”

Nutrition is also cited as a cause of microbial infections, Austin says, specifically deficiencies in minerals or a nutritional imbalance, although he is wary of suggesting supplementation without having more in-depth knowledge about a horse’s current diet.

“Often you will have balancers that are supposed to help feet that have a high level of a specific mineral, but you can be feeding that to a horse that already has a high level of the mineral in its diet, leading to greater mineral imbalance,” he says. “You’re just making the feet worse the more balancer that you give it.”

Another consideration is microbial imbalances. “Good” and “bad” bacteria live in the gastrointestinal tract, as well as on the skin and the foot. The “bad” bacteria are the disease-causing pathogens while the “good” bacteria are those that keep them in check, creating an environment in which the bad bacteria are unable to proliferate.

When using treatments on the foot, it’s important not to do too much harm to the good bacteria, Austin says, because that’s what often stops a massive flourishing of bad bacteria.

Treatment Pitfalls

Austin’s guiding principle for treating microbial infections is “do no harm,” which might appear obvious, but in practice it could feel counter-intuitive. Fast-acting microbial treatments can be effective but also damaging. To avoid common treatment pitfalls, here are his suggestions:

Think in terms of the “long game.” Some treatments that work very rapidly can damage tissue. Damaged tissue perpetuates an environment where microbes can grow. “Everything looks good for a little bit and then the infection comes back worse than it was before,” he says.

Consider active ingredients. Formalin and iodine can dry out the foot and cause microscopic fissures. Peroxide and copper sulfate both burn and damage tissue when used in an effective concentration. Tea tree oil can be allergenic and aggressive toward “good bacteria.”

“Even though it’s natural doesn’t mean it’s good and if it’s synthetic that doesn’t necessarily mean it’s bad,” he says. “You have to keep an open mind.”

Be wary of oils and strong solvents. Oil-based products can trap moisture into the foot. That might sound like a good thing, Austin says, because when the hoof wall has the correct level of moisture in it, it doesn’t crack. “But if you trap moisture in fissures in the sole of the foot, you’re absolutely playing into the hands — if they had hands — of the microbes that want to live in there. And you’re blocking out oxygen, so the anaerobes love it,” he adds.

Strong solvents are problematic because they can damage the lipid barrier inside the horse’s hoof tissue, which prevents too much moisture from being absorbed. There may be occasions when a strong product is needed, Austin says, but it doesn’t need to be the default option.

Thrush that has worked into the surface of the foot, burrowing away from air and oxygen may produce veins.

A Protocol that Works

Although the list of potentially damaging ingredients might seem long, there are plenty of active ingredients that can work very effectively in the short-term while having long-term benefits, Austin says. Here is the protocol he has found effective for treating most microbial problems.

Step 1: Remove packed dirt and dead tissue. Not only do dirt and dead tissue harbor bacteria that will attack new tissue, but deep in a white line cavity they will also keep the active ingredient away from the area that needs to be treated.

Step 2: Eliminate surface pathogens. Choose a product that is an effective antimicrobial but minimally damaging. Austin recommends zinc sulfate, which scientific studies have shown is as effective an antimicrobial as copper sulfate in the same concentrations but less harmful. Eucalyptus oil, thyme, oregano and rosemary also can be very effective. “It all sounds very natural and very fluffy but they are excellent antimicrobials and they don’t do damage,” he says. Zinc oxide and medical grade honey are especially useful because they are very aggressive against anaerobes.

Step 3: Draw out the infection. The type of infections will vary — it could be thrush that has worked into the surface of the foot, burrowing away from oxygen in the air that will kill it. If it’s made a cavity for itself, it will produce veins (see Figure 1). Austin recommends mineral clays such as kaolinite and bentonite. “It must be mineral, not cereal,” he cautions, “as doughs or pastes can harbor microbes.” Salts can also be effective drawing agents, especially traditional magnesium sulfate, Epsom salt. Wet poultices can also be effective, but used too regularly can soften the foot, making it more porous and introducing a lot of moisture.

“If using a wet poultice, I usually put Epsom salt in them as well to try to help make sure that the moisture is still coming out of the foot rather than all going in,” he says.

A radiograph shows how Red Horse’s Artimud on the toe in the white line cavity keeps foreign bodies out of the foot while treating the existing microbes.

Step 4: Create a barrier against dirt and microbes. Clays are ideal barrier builders, Austin says. One option is Red Horse Product’s Artimud, which consists of zinc oxide, honey, eucalyptus and clay. Figures 2 and 3 are radiographs showing the Artimud on the toe in the white line cavity, keeping any foreign bodies from going in while treating microbes that may be inside already.

This crack is packed with medicated cotton to provide growth simulating pressure, but any medicated fibrous material, including hemp, will also work well.

Step 5: Promote regrowth. “We’ve probably all seen the deep central sulci that we’ve thought, ‘There’s nothing going on in it. There’s no bacterial presence.’ But it just won’t grow out,” Austin says. That’s because there is no pressure in the cracks to create stimulation or growth. Austin recommends packing cracks with a medicated fibrous material. Figure 4 shows a cotton fiber, but hemp also works well.

“You can impregnate that with your active ingredient of choice,” he says. “Pack that into the crack, it treats the microbes, it stays in place and it produces pressure to stimulate regrowth.”

Clays and pastes will stay in place longer under shoes. Artimud was put on before the former shoe was applied (left) while the other (right) did not. The longer a preventative measure lasts, the less concentration it needs to be, so it’s less damaging.

Step 6: Apply a tissue healing agent. Exposed live tissue can benefit from honey to promote healing. Zinc oxide and aloe vera are also options, but with the aloe vera, Austin says, make sure to apply it at a 1:1 concentration or you’ll run the risk of introducing too much moisture.

In an effort to provide air to the white line cavities, another step that some farriers may consider at this point is a resection. Austin advises against it if possible because resecting the white line will remove any pressure that movement of the wall creates and you don’t have an outer wall that you can pack into.

“The outer wall keeps packing material in there, which keeps providing pressure,” he says. “Unless you really aren’t convinced that you can remove all the dead tissue, I recommend not to resect, in the first instance, at least.”

April 2020