Thrush: Trouble in the Grooves of the Hooves

Thrush in Your Horse’s Hoof – Thrush can develop right under our noses . . . literally! Fortunately, it’s usually easily treated and managed. The worst thing you can do is ignore it, as serious thrush infections can cause injury and lameness. But fear not! You can head it off . . . at the frog. Download this article as a PDF.

Out-of-control thrush can open the door for more serious problems, like white-line disease.


Most of us recognize thrush as a smelly infection that eats away at the frog, especially down in the cracks called the sulci. When we sink our hoof picks into a thrush-infected crack, we drag out black, gooey, stinky crud. It can seem like there’s just no end to it! In some cases, the frog itself peels away, too.

Thrush predominantly occurs because of a nasty group of bacteria called anaerobes, and it can quickly appear on all four feet. Anaerobic bacteria grow in environments with little-to-no oxygen, like deep in the sulci, the crevices of the frog.

There can be dozens of different species of anaerobe involved in a thrush community, but predominantly we find a nasty little stinker named Fusobacterium necrophorum. In addition to bacteria, thrush has a fungal component. Fungi are hearty bugs that can be difficult to kill. They love environments that are moist with little air.

Even the most diligent hoof pickers can find a thrush infection. And that doesn’t necessarily equate to poor horse husbandry or hoof management. Factors such as anatomy, soil water content, lameness and hoof pads can stack the deck against us.

  • Environment:  If a horse lives in a perpetually wet environment, such as a swampy area, it can be an uphill battle. The constantly wet environment means air can’t get into the grooves of the frog and dry them out. Similarly, wet and soiled bedding provides all the substrate that thrush needs to thrive. In these situations, no matter how much you pick the feet, the odds are packed in favor of thrush.
  • Infrequent hoof picking: If your horse lives in a stall or small paddock, pick out his hooves daily. These horses have a higher risk of thrush. Horses who have room to run clear debris on their own. See How good are you at picking hooves?
  • Landing gear: Some veterinary podiatrists believe that when the horse avoids landing on the back of the foot, expansion and contraction of the frog doesn’t occur, and thus debris will accumulate there. Also, blood flow, which influences the health of all tissues in the body, is limited in the absence of concussion to the area. 
  • Horses with pads:  Farriers may place a hard plastic pad between the shoe and the hoof on thin- soled or foot-sore horses. While pads undisputedly make some horses more comfortable, they’re often accompanied by thrush because the pad prevents hoof picking and virtually cuts off air flow to the bottom of the foot. Most farriers combat this by placing chemical-soaked gauze pads in the cracks of the frog or tell owners to routinely squirt a desiccating agent under the pad.

Thrush can open the doors for major issues in some horses: 

1) White Line Disease/Seedy Toe:  This aggressive bacterial/fungal infection eats the hoof wall along the white line. Affected hoof tissue literally crumbles away from the hoof wall like chalk dust. It can result in compromised hoof stability and severe pain if the infection reaches live tissue.
White line requires both the veterinarian and the farrier. It involves removing the shoes, cutting away the infected hoof, and applying powerful medications to kill the infectious agents. Recovery can take months.
2) Canker: This problem is occurs more frequently in areas where soil is moist year round. Canker is a painful proliferative growth that originates in the sulci and grows like cauliflower out of the foot. Canker is like thrush on steroids!
Canker infections must be surgically removed and treated with aggressive, prolonged medical therapy in most cases. And it can recur. It’s a long haul with canker.
3) Hoof abscess:  If thrush burrows deep enough, it can contribute to the formation of an abscess. This occurs as the body attempts to battle the infection by walling it off. As the bacteria replicate and grow, pressure from the increased numbers cause extreme pain.

No, it can’t always be prevented. But you can lessen the odds: 

  • Pick hooves every day.
  • Keep stalls clean.
  • Lay base rock or decomposed granite in wet or muddy areas.
  • Sprinkle wet spots with powdered lime, Stall Dry, Sweet PDZ or Odor No More.
  • Have the farrier trim back the edges of the frog to open up the sulci to allow more air in.
  • Prophylactically apply a thrush remedy to the frogs weekly during wet times of year.

For mild thrush, apply a good commercial hoof product containing iodine or copper to the frog daily until the infection has cleared. Use it weekly and more frequently during wet times of the year. In addition, if another horse on the property gets thrush, all horses should be treated because thrush is bacteria and fungi, which can be spread. 

Get your farrier out at the first sign of thrush. You can get ahead of an infection physically by having the farrier cut away diseased and damaged frog tissue. As long as that tissue remains in place, it will serve as a nidus for thrush infection.

Hoof soaks can be used for extreme cases including white line disease, seedy toe and post op canker. However, we strongly advise you to only use hoof soaks under veterinary advisement. See our Recommended Thrush Products. Our top picks are Thrush Stop, D-Thrush and Keratex Hoof Wash.

As a rule of thumb, if your horse has thrush, your product should produce results in a week to 10 days. If the problem worsens or your horse becomes lame, it’s serious, so call your farrier and vet.

Work to prevent thrush with through stable management, hoof picking, trimming, and weekly application of a thrush remedy. 

Article by Contributing Veterinary Editor Grant Miller DVM.

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