The Lowdown on Thrush

For years, thrush was thought to be a fungal disease, but we now know that the thrush we find in horses' hooves is bacterial. In fact, we know that it's an anaerobic bacteria (bacteria that is most suited for living in an environment without oxygen), Fusobacterium necrophorum, which is present in animal feces and most soil samples.

When it sets up residence in the horse's hoof, F. necrophorum generally localizes near the frog and is usually most prevalent in the collateral sulci (the grooves adjacent to and in the middle of the triangle-shaped frog) and/or in the central sulcus (the cleft between the heels). Because it's anaerobic, it thrives in a moist, dark, poorly oxygenated environment. Once the bacteria are established, you can recognize their presence from many clinical signs typically associated with thrush infections:

  • Repulsive odor;
  • Watery or oily discharge (often black in color);
  • Tenderness in the frog region;
  • Fissures or deep pockets extending to the heel bulbs; and
  • Loss of frog shape and integrity.

Standard texts on equine health will tell you that horses develop thrush because they're being kept in a sub-standard environment, and there's no doubt that poor conditions, especially wet conditions, will promote the problem. But most farriers will agree that it's a more complicated issue that simply can't be explained away by pointing at dirty stalls and mud puddles.

They'll say they've seen horses with thrush in pristine barns. Likewise, they'll say they've seen other horses with no thrush despite their living fetlock-deep in manure and mud. Thrush management involves performing regular maintenance to maintain the hoof capsule in a balanced, supportive manner, and allowing the horse sufficient exercise.

One of the most important factors in avoiding and/or eliminating thrush is exercise. Even horses living in manure and mud might be working hard all day, getting a lot of activity and moving in a natural manner that promotes good vascularity (level of blood supply) in the foot, which is key to keeping the hoof healthy. The horses standing in those pristine stalls are simply standing, so they are not promoting the same kind of vascularity to generate a healthy foot. 

Likewise, the horse that is receiving regular maintenance from a farrier will maintain a more balanced and supportive hoof. And that balance lends itself to even loading, compression, and concussion, all of which promotes good vascularity and overall health.

Thrush treatment will vary according to the severity of the condition. Should the thrush be advanced to the point that the horse is lame, blood is present, and/or puss or proud flesh is present, a veterinarian should be contacted to debride the infected area and administer appropriate medications and possibly a tetanus vaccine or booster.

Less advanced cases (i.e., ones that are not invasive of sensitive tissue), should be debrided and treated aggressively with commercially available products or with a medication obtained from a veterinarian. While home remedies and recipes abound, many are simply inappropriate. For instance, some texts advocate the use of bleach on thrush. The authors of these treatises would likely never pour bleach on an open wound of the hip, yet they willingly recommend that you soak an open hoof wound and its exposed sensitive tissue in bleach.

A good thrush prevention plan includes trimming or shoeing horses properly, exercising animals regularly, and keeping a good horse maintenance plan that includes regular hoof care and a clean living environment.

Reprinted with permission from the Kentucky Horse Council.

About the Author

Danvers Child, CJF

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