Thrush describes an infection that develops in the frog of one or more of the horse’s hooves, caused by a fungal or bacterial pathogen. Fusobacterium necrophorum is the bacterium most often associated with thrush infections. 
Hooves with frogs that have deep sulci are prone to becoming infected with pathogens that cause thrush. Wet and dirty environments contribute to the development of this infection as thrush-causing pathogens flourish under these conditions.
Typical signs of a thrush infection include hoof tenderness and a foul-smelling discharge from the hoof. The condition is often diagnosed by visually assessing the hoof and checking the health of the frog tissue.
Thrush can progress to cause permanent lameness if it results in extensive damage to hoof tissues. Prompt treatment is necessary to stop the spread of the infection.
Treatment of thrush involves removing necrotic tissue from the hoof, disinfecting it, and keeping it clean during the healing process. Management strategies to prevent thrush and support recovery aim at keeping the horse’s living environment clean.
What is Thrush in Horses?
A relatively common bacterial infection of the horse’s hoof, thrush can affect one hoof or all four at once.
Thrush typically affects the center and grooves (central and lateral sulci) of the frog – a triangular structure on the underside of the hoof. It can also occur in the heel of the hoof.
Several bacterial and/or fungal microorganisms can cause thrush, but the bacterium Fusobacterium necrophorum is most frequently involved.
Thrush infection can cause minor to significant damage to hoof tissues and requires treatment to prevent it from spreading. If left untreated, the infection can damage the sensitive structures of the hoof including the laminae and digital cushion, and result in temporary to permanent lameness.
A common symptom of thrush is a foul-smelling discharge emanating from infected hooves. Horses with thrush may exhibit tenderness when pressure is applied to their affected hooves.
Damp and dirty environmental conditions are known to promote thrush infections as they create an environment where bacterial and fungal organisms can thrive.
The exact number of horses affected by thrush is unknown. Thrush affects all breeds and ages of horses.
A study conducted in the Netherlands determined that out of 942 randomly selected horses that were assessed, 45% had thrush. 
Signs of Thrush
Depending on the severity of the infection, thrush can cause a range of clinical signs including:
- Hoof sensitivity or pain
- A pungent smelling, tar-like discharge emanating from the infected hoof tissues
- A softened frog
- Necrotic (dead) tissue in the hoof
- Swelling in the lower limb if the infection is severe
- Lameness in advanced cases
Pain caused by thrush increases as the infection spreads deeper into the tissues of the hooves.
Causes of Thrush
Thrush is caused by bacterial or fungal organisms that enter the hoof tissue. An anaerobic bacterial species, Fusobacterium necrophorum, is the bacterial pathogen most often involved with thrush infection.
The following factors can promote a thrush infection:
Hoof Conformation with a Long Heel
Horses with a long heel conformation that results in deep, narrow frog sulci may be at an increased risk for thrush infection when exposed to damp and unclean environmental conditions.
Hooves with a recessed frog are prone to collecting more mud and dirt compared to those without. Deep and narrow sulci trap moisture and bacteria-laden debris in the hooves and create an ideal environment for infection to develop.
The microorganisms that cause thrush can propagate in conditions including deeply soiled bedding, mud, or very wet pastures. Horses living in these conditions may be at risk of developing thrush.
Not picking your horse’s hooves out daily can increase the risk of thrush infection. Overgrown or poorly trimmed hooves can increase the amount of moisture and mud/dirt than can lodge in the sulci.
Wearing hoof pads continuously may promote thrush-causing bacteria to accumulate in the sulci because they trap moisture against the bottom of the foot.
If you suspect your horse has thrush, consult with your veterinarian to confirm a diagnosis of the condition. A physical examination of the hoof is necessary to determine if the infection is present in the frog.
Your veterinarian will check for signs of infection such as discharge, odor, and necrotic tissue. They will also check for lameness and assess your horse’s response when pressure is applied to the frog to determine if the hoof is painful.
With appropriate treatment, horses diagnosed with thrush have a good prognosis for full recovery. Treating thrush infection promptly is important to prevent it from spreading deeper into the hoof tissues.
If thrush infection has progressed to the point of becoming chronic and/or the deeper tissues of the hooves are involved, lameness may result from the condition due to the destruction of tissues.
Treating Horses with Thrush
Mild to moderate thrush infections may take 7 to 14 days to resolve in affected hooves. Horses with advanced infection may require a longer period of treatment to recover fully.
Removal of Necrotic Tissue:
Treating thrush requires the removal of dead tissue from the hoof by a farrier or veterinarian. Sedation and or local anesthetic may be necessary to complete this process.
If a significant amount of hoof wall must be removed, your farrier may use an acrylic material to fill in the defect once the infection has been treated.
After any necrotic tissue has been removed, treated hooves should be disinfected with an iodine solution to destroy the microorganisms causing the infection. Daily cleaning is necessary to help treat the infection.
Daily Cleaning and Soaking:
Affected hooves should be cleaned daily using a hoof pick to gently remove debris and dead tissue from them.
A soft brush and or cotton swabs soaked in diluted iodine or other antiseptic solution are ideal to use for cleansing the hooves after debris and dead tissue have been removed. Avoid using acidic solutions to cleanse the hooves as they can destroy healthy tissue.
Soaking the hooves for 20 to 30 minutes each day may aid in clearing the infection. Epsom salts can help to draw the infection out from the hooves.
After cleansing/soaking the hooves, they should be thoroughly dried using clean swabs.
After cleaning the affected hooves daily, they may need to be bandaged between soakings until new and healthy tissue can regrow in the frog. Packing the cleft of the frog with cotton soaked with a disinfectant solution can help to eliminate the infection.
Using a hoof boot can aid in keeping the hooves clean while the inner tissues heal. Hoof boots are available at many tack stores and come in a range of sizes and styles.
Shoeing the affected hooves may be beneficial if they are imbalanced or have unstable heels. Shoes also improve the flow of air under the hoof.
Horses with advanced cases of thrush may be administered oral or injectable antibiotics to treat the infection and analgesics to relieve pain.
Topical medication may be used to treat the infected hoof tissue. These applications should only be applied to a clean, dry frog after it has been cleaned.
Horses that are not up to date with their tetanus vaccine should be administered one to reduce the risk of this disease developing. Tetanus is a serious disease of the nervous system that can be fatal.
Clostridium tetani is a spore-forming bacterium found in the soil that is responsible for causing tetanus. This microbe can enter the body through compromised hoof tissue.
Because exposure to wet environmental conditions can promote bacterial/fungal growth, horses should be kept in a clean and dry environment as they recover from thrush.
Contact your vet if your horse’s thrush is not improving with treatment and if lameness develops or worsens.
When handling hooves infected with the bacteria that cause thrush, consider wearing personal protective latex gloves and cleanse your hands afterward to prevent spreading the bacteria.
You can prevent or reduce the risk of thrush in your horse through the following management practices.
1) Maintain a Clean, Dry Environment:
Maintaining the cleanliness of your horse’s turn-out area and stall is essential to prevent thrush. Make sure that the turnout area where your horse spends the most time is dry.
Keep stalls clean by removing wet spots and manure daily. Clean outdoor run-in sheds/shelters weekly to prevent manure from accumulating in areas where your horse stands.
Manage mud in your horse’s turnout area. Eliminate water and mud accumulation in low-lying and high-traffic areas by filling them in with sand, wood bark, sawdust, gravel, or crushed asphalt.
Consider laying down a gravel base and filling it with round, pea-sized gravel to a depth of approximately four inches to create an area in your pasture that can drain away excess moisture.
Consider changing feeding spots in your horse’s turnout each day to help prevent mud from developing in these high-traffic areas.
Establish efficient drainage in paddocks and around the stable to prevent water and mud from accumulating.
Enhance ventilation in the stable to prevent moisture accumulation and dampness. This will also support your horse’s respiratory health and overall immune system.
2) Clean and Inspect Hooves Regularly:
Keeping your horse’s hooves clean is essential for preventing thrush. Remove dirt, debris, and excess moisture by picking your horse’s hooves out daily.
Check the structural integrity and overall health of your horse’s hooves each time you clean them. Check for signs of abscesses and white line disease which are also caused by infectious agents entering the hoof tissues.
3) Provide Regular Farrier Care:
Provide your horse with regular farrier care (every four to six weeks). Hoof issues are more likely to be caught early if farrier sessions occur at shorter intervals.
Ensure the hooves are properly trimmed and balanced to avoid long heels and deep sulci from developing. The frog should be trimmed to remove torn or jagged pieces that provide space for bacteria to propagate.
When the frog is properly trimmed, debris is naturally removed from the hoof more easily as the hoof expands and contracts during exercise.
4) Use Hoof Care Products:
Hoof hardening products can help to dry the sole of the hoof i