Thrush in Horses: Advice, Diagnosis and Treatment

If you’ve been around or owned a horse long enough, you have most likely encountered one of the most common horse hoof issues called thrush.   Lucky for our equine companions and their owners, most cases of thrush are easy to treat, never cause lameness and are rarely ever life threatening.  You just need to be able to identify it early, if not take precautions to prevent it and treat it right away.

What is Thrush?

Thrush in horses is a degenerative infection of the central and collateral grooves of the frog that causes damage to the soft tissue in the hoof.One species of bacterium (Fusobacterium necrophorum) is particularly aggressive, invading and destroying the frog, sometimes exposing the deeper sensitive tissues.
The cause of thrush is sometimes debated as to whether or not it’s fungal or bacterial, but most think that the main culprit of thrush is ananaerobic bacterium bacterial called ( of Spherophorus neaophorus) in the frog (and in the grooves of the frog called sulci) of the horse’s foot.  Thrush is a bacterial infection that occurs in the tissue of the frog, the V-shaped structure located between the sole, wall and bars in the heel area of the hoof. The disease begins when bacteria penetrate the outer horn, or epidermis, of the frog. As it progresses, the frog tissue deteriorates, looking uneven and ragged and producing a smelly discharge. In severe cases, the bacteria can reach the inner dermis, the sensitive tissue beneath the frog, causing pain and lameness.  It starts out on the surface and works it’s way deeper into the hoof, and is typically caused by unclean, damp, and dirt packed conditions of that particular horse’s foot, or that the horse is standing/living in.

How do Horses Get Thrush?

While there are several situations and conditions that make horses more susceptible to thrush, it can happen to any horse no matter how well kept their feet or living conditions are.  It can also be a reoccurring issue for some horses.

Main Causes of Thrush

  1. Horses in unhealthy living conditions.  The fungus that causes thrush in equines thrives in filthy, wet barn and pasture conditions where the horse is kept.   Horses left in dirty stalls, saturated bedding or fields filled with manure or soaked with urine, are much more prone to getting thrush.
  2. Horses that wear pads.  When horses wear pads they become very prone to thrush because moisture, bacteria, fungus, dirt, manure and other contaminates can get packed into the pad.  Because the pad blocks off access to the bottom of the horse’s foot, it makes it next to impossible to clean out their feet properly.
  3. Horses that are inactive.  When a horse is ridden, or is very active, they naturally wear down their and clean their feet due to regular flection.  Movement helps to knock out the dirt packed into the frog, dry out their feet, and sand down or buff off surface contaminants.  When a horse is inactive, the fungus that causes it stays packed into the horse’s foot, allowing it to grow and spread.  Horses that are inactive due to lameness, or in small paddocks that don’t run or walk around that much are definitely at risk as well.
  4. Horses that do not get turned out enough.  A horse sitting in his stall all day, especially after soiling his bedding, will be more prone to get thrush.  Horses naturally clean out their own feet as they run and frolic in their fields or walk around on different surfaces.  Not only do they clean out their feet, the sand and grass also dries them out.  If a horse has been in his stall too long, either due to an injury, bad weather, or any other reason, their feet get moist and stay packed.  Horses constantly turned out in muddy or messy fields will get it for the same reasons.
  5. Horses who don’t get their feet cleaned out properly or regularly enough.  Unfortunately at times people may either not clean out their horse’s feet as often as they should, or they simply don’t clean out the horse’s feet as well as they should.  Taking the time to clean out your horse’s feet properly and often is actually one of the easiest ways to prevent thrush from happening in the first place.
  6. Excessively wet weather conditions.  Sometimes no matter how often you clean your horse’s feet, you still can’t control the weather.  Bacteria and fungus thrive in conditions that are really wet or moist, therefor causing an outbreak of thrush due to flooded fields, and damp barn conditions.
  7. Unhealthy Frogs or Frogs that are not shaped or maintained well by the farrier.  Measured at its base, the widest part, the frog’s width should be at least 70 percent of its length. A healthy frog shares the load-bearing function with the other structures of the hoof and helps to absorb concussion. This, in turn, stimulates continued frog health. A well-shaped frog also has a natural self-cleaning mechanism. When it comes into contact with the ground, it expands, pushing accumulated dirt and debris out of the frog sulci, the grooves on either side of the frog.  Frogs that are damaged or unhealthy are more at risk for infection.An unhealthy frog is recessed—shrunken inward from the surface level of the rest of the hoof—and is smaller in size than it should be. This can occur for a variety of reasons, including genetic abnormalities such as a clubfoot, and farriery issues such as a horse with sheared or low heels. The fundamental problem usually involves the frog and heels of the hoof capsule not being on or close to the same plane. This limits the frog’s contact with the ground and thus reduces the stimulation from the ground, causing the frog to atrophy. The recessed frog does not share in supporting the horse’s weight, so it shifts too much of the load bearing back onto the heels of the hoof capsule.

Meanwhile, as the frog atrophies, the sulci between it and the rest of the hoof structures deepen. Dirt and debris accumulate in these grooves, creating the anaerobic conditions in which bacteria thrive. Weakened by its reduced protective outer horn, the frog tissue becomes more susceptible to penetration by the bacteria and, consequently, development of the disease.

The best way to cure thrush and prevent it from recurring is to solve your horse’s original hoof-capsule abnormality. Your farrier will need to trim his hooves in a way that puts the frog and heels of the hoof capsule back on the same plane. Depending on your horse’s conformation and trimming history, this may just be a matter of rasping down his heels. Once the frog is level with the rest of the foot again, its restored function will promote new, healthy growth.

How to Identify Thrush

Identifying thrush is not that difficult.  One of the tell-tale signs of the infection is a foul odor coming from your horse’s feet.  You’ll notice this most when you pick your horse’s foot up to clean it’s hooves.  The infection itself looks like a black, pasty discharge.   For the most part, it’s a superficial infection, but it can go deeper into the tissues causing issues in the frog and even the heel.

Common signs include:

  • Smell: Hooves infected with thrush have a foul odor, far worse than the average hoof smell.
  • Discharge: In some cases of thrush, the frog will have discharge around it, usually black or dark brown in color.
  • Coating: Some horses will have a white coating on the hooves near the frog, indicating where the infection has taken hold.
  • Lameness or sensitivity: While some horses will be very sensitive if they have thrush or may even limp, others will seem completely fine.

 

How to Treat Thrush

Thrush can be stubborn at times to treat because it lives in the cracks and crevices of your horse’s feet and works it’s way deep into the foot if left untreated.  In most cases an over-the-counter thrush treatment you can find at your local feed store will do the trick but sometimes treatment will need to be a bit more aggressive.

You want to make sure your horse’s feet remain in clean and dry areas as much as possible.   Initially, your farrier will also treat the thrush much like a dirty wound, trimming away the loose, diseased frog tissue and possibly applying dilute bleach. You can follow this up with applications of a mild astringent, such as Betadine®, or another anti-thrush product.

Your farrier (or you if you are skilled) can help remove the damaged or infected areas of the foot or frog through trimming.  A hoof pick or wire brush can help to dig or clear out some of the infected area, but be careful not to make the infection worse by over scrubbing, scraping or cleaning.  Many times your farrier will notice the thrush before you do, and are able to remove it from the horse’s foot completely.

Diluted iodine tends to be a really good topical for treating thrush and for disinfecting the foot.  Some people even use a bleach/water solution, but this can lead to excessive foot drying or irritation.  Even iodine, if used to aggressively can cause other issues and irritation to the foot.  In some cases, it might be beneficial to treat the horse with poultice bandages and/or to soak their feet with antiseptic solutions.

However, treatment is not enough if you don’t clean up the areas where your horse is standing that he is getting infected with the fungus in the first place, like a dirty stall or muddy field.  The thrush will continue to return if you don’t get a handle on removing the contaminated conditions.

It is important to detect thrush early and to treat it thoroughly and consistently until it is gone so that it doesn’t invade deeper hoof tissues such as the frog or digital cushion.

Keep the stall bedding clean with fresh straw or shavings to prevent thrush from happening in the first place- switch from straw to shavings or sawdust to keep the enviroment and feet dryer.

One of my most effective treatments for potential or minor cases is a thorough hoof picking and a hoof wash/spray of a 50:50 mixture of water and either hydrogen peroxide or white vinegar. Clean the frog daily using a diluted agent of a substance such as apple cider vinegar, Borax powder, or Lysol.

Gently but thoroughly clean all of the deep crevices. Have your farrier trim away any loose flaps of dead frog. This will allow more air contact and easier cleaning. Take care not to poke and scrub too vigorously – infected frog tissue can be painful and can easily bleed. Use a squirt bottle of whatever solution you have chosen to irrigate the area and loosen debris (I re-purpose dish liquid bottles for this). An old cotton t-shirt cut into 4 or 5 inch squares is great for gently wiping through the sulci of the frog. The clean soft squares can “floss” the deep central crevice. Remember – gently! Follow this cleaning treatment with an application of healing salve or ointment to nourish damaged tissue.

 

If the appearance of the thrush seems extreme, abnormal, or worse than usual, or if it seems to be causing bigger issues such as tenderness or lameness in your horse, don’t hesitate to call the vet.

If the infection has become advanced, antibiotics may also be needed. Until thrush is eliminated, limit how often you ride, as the feet can be tender and your horse may not be as sure-footed as usual, making it dangerous for both of you.

 

Thrush Prevention

Prevention can help greatly reduce the occurrence of thrush in your horse.   To help prevent it, pick your horse’s hooves out every day, and provide clean, dry bedding at all times in their stall.  Daily cleaning of stalls and paddocks help to keep your horse’s feet in the best condition.  Make sure your horse has plenty of turnout to naturally exfoliate and clean out and keep their feet dry, and that they are kept away from over exposure to excessive moisture.   Ensuring good drainage in fields and paddocks will help keep the ground dry and bacteria and fungus free.