You start to pick out your horse’s hoof and get a nasty whiff of what can only be described as rot. As you continue, you notice a black, tarry substance coming off on your hoof pick that seems to be the source of the odour. Your horse has thrush.

Thrush is a common bacterial infection that softens the frog area of the hoof causing it to disintegrate, essentially rotting it away. The black goo is dead frog tissue.

Thrush mainly occurs in the collateral sulci (the clefts – or grooves – on either side of the frog) and the central sulcus (the centre of the frog). It’s not usually a serious condition, and minor cases can be easily treated. But, if allowed to develop, it can penetrate and destroy the deeper, sensitive tissues of the foot. Depending on the extent of the infection, thrush can cause varying levels of lameness and, at its worst, permanent damage.

Some of the signs your horse has thrush:

  • Foul odour
  • Discharge – generally black, sometimes with pus
  • Ragged, cracked frog
  • Tenderness upon pressure
  • Swelling of the lower leg
  • Lameness

How Did My Horse Get a Stinky Foot?

The primary bacterium that causes thrush already lives naturally in the soil, mud, manure and stall areas of a barn environment. Fusobacterium necrophorum is anaerobic, meaning it doesn’t like air. For this reason, it thrives in the damp, dark nooks and crannies of the hoof bottom, particularly if the hoof remains mired in damp or wet ground conditions or stalls, although it can occur in horses that stand in predominantly dry environments too. While F. necrophorum appears to be the main culprit in causing thrush, other anaerobic bacteria and the fungus Candida albicans are also suspected in playing a role.

Thrush develops more readily in horses that have certain types of hoof conformation. Contracted heels, for example, creates deep and narrow sulci where dirt, manure and other debris tends to lodge, creating a heavenly environment for the bacteria to proliferate.

As well, horses that don’t receive enough exercise either through workouts or turnout are prone to thrush. The circulation of blood during exercise helps keep the foot healthy.

Proper and regular farriery is also key. Not only does a good trim keep the foot healthy by providing balance and support, it also removes dead frog growth, allowing air to circulate and kill off the bacteria.

In many cases, it’s simply a matter of not hoof picking regularly.

Getting Rid of the Rot

No matter how severe the thrush, the horse first needs to be moved to a clean, dry environment. Hoof pick and then scrub the frog with a stiff brush, warm water and an antiseptic soap such as Betadine. Let the frog dry before moving on to the next step.

Any loose flaps of the frog need to be trimmed away with a hoof knife to remove infected tissue and allow air and any anti-thrush treatments to reach the infected areas and facilitate healing.

If the thrush doesn’t appear to be causing your horse lameness or discomfort, treating the thrush yourself by applying topical preparations that will kill the infection is a feasible option. Opinions differ, however, on which anti-thrush preparations are most effective and safest.

Some people swear by homemade concoctions made with ingredients such as bleach, formaldehyde, hydrogen peroxide, iodine, antibiotic ointments and athlete’s foot creams. These preparations should be used in consultation with a veterinarian or a farrier, as not only are some mixtures ineffective, others create too much of a drying effect on the hoof and frog and can damage to internal structures if the thrush has penetrated to deeper tissues.

One popular self-made mixture – sugardine – combines one part white, granulated sugar (used for centuries in wound healing) to two parts povidone iodine or Betadine. The non-damaging paste is packed into the sulci using small brush (an old toothbrush is great for getting into flaps and crevices).

Hundreds of readily available commercial products such as Kopertox, Copper Sept and Thrush Buster are specifically made for this purpose. Most commonly, they come in liquid form, but pastes, creams, aerosols and hoof packings are also available. Depending on the product, they contain active ingredients such as copper napthenate, iodine and gentian violet (used for years to threat oral thrush in human babies).And, a new dry thrush treatment made of a blend of clays, salts, diatomaceous earth, and oregano, is now available in Canada. Called No Thrush, it claims its goal is to attack thrush while wicking excess moisture.

The author, a long-time horse owner and stable operator, has had great success with over-the-counter products for minor thrush. As with some of the homemade thrush creations, these products can dry out the hoof and should be used carefully. Some are also strong smelling and highly staining, although this can be beneficial in that you definitely know where the product has been applied.

There are several ways to apply your preparation, whether homemade or commercial. You can squirt it right from a bottle into the fissures and cracks to reach deep into the affected areas. Another method is to use a spray bottle, but it’s difficult to achieve a truly targeted application this way. One of the author’s favourite techniques was suggested by her farrier when one of her horses had a crack in the central sulcus. He said to put the product in a small syringe that would allow direct application without creating a mess. He also advised soaking a small gauze square or cotton ball in the remedy, wrapping it around a hoof pick and inserting well into the grooves, leaving it to fall out on its own.

The duration of treatment will depend on the extent of the infection, but expect to be diligent in treating/monitoring daily for a few weeks to a month.

Never hesitate to call in your veterinarian and/or farrier, who will be able to guide you as to what they feel is the best way to tackle your horse’s thrush, particularly if you are confused as to whether to turn to over-the-counter products or to use something out of your own cupboards; you simply aren’t comfortable with removing dead frog tissue; or if the thrush has progressed to the point where the horse is sore, the discharge is profuse or blood is present.

Keeping Thrush at Bay

Prevention is paramount when dealing with thrush.

At least once a day, thoroughly pick the hoof, paying special attention to the sulci. This not only exposes the frog to air by removing the debris that invariably gets pushed into the hoof, but also gives you a chance to assess whether thrush could be taking hold. Yet, as thorough as you want to be, avoid over-excessive use of the hoof pick. This can create nicks and abrasions in the frog where thrush can set in.

Regular exercise and turnout keeps the blood flowing to the foot and promotes healthy hoof growth.

Make sure the horse is properly trimmed and/or shod on a regular basis to ensure a balanced hoof that supports the horse.
Although it can be difficult in Canada, especially during spring and fall, try to provide a clean, dry environment. Strip stalls and provide fresh bedding daily. Remove manure from paddocks regularly and keep watering areas as dry as possible.

But, even if you take all the precautions possible, your horse will still likely get thrush at some point. Don’t despair. Recognizing its onset and taking measures to eradicate it will ensure thrush doesn’t turn into a more severe and possibly debilitating problem.