What is Thrush in Horses

When thrush is found in humans, it is a yeast-shaped fungus that causes growth in the throat and mouth. It can be caused by a number of factors, from illness to smoking to wearing dentures.

When thrush is found in horses, it is an infection that affects the frog of the horse. The frog is the support portion of the hoof that provides traction and balance. It is a condition that horses and humans share in name, but not in location or for the same reasons. That is why it is important to distinguish one from the other. 

The infection is usually caused by the presence of frequent or prolonged exposure to wet, damp, and dirty stable conditions. Horses turned out into damp, dirty conditions can also develop thrush. There are also some instances when thrush is able to form when none of these common conditions are present.

What is problematic about thrush in horses is that most cases of it are discovered by a farrier or a veterinarian and not the owner or handler of the horse. 

What Is the Cause of Thrush in Horses?

Thrush can be a bacterial or a fungal infection in horses, though bacterial infections are the most common. One bacterium, called fusobacterium necrophorum, is very aggressive when it causes an infection and it can quickly destroy the frog and the deeper tissues of the hoof and foot.

Severe cases of thrush have caused swelling in the upper leg and infections of the hoof wall, heel bulb, and digital cushion. 

Horses that have an imbalanced food or have a frog that is deep and narrow have higher risks for a thrush infection, but any horse can develop thrush if the environmental and health conditions are just right.

Back feet tend to be more affected than the front feet in many horses. One or more feet can become infected with thrust at the same time.

If left unrecognized or untreated, thrush becomes a degenerative condition.

Poor bedding is the most common cause of thrush in horses. Being stabled on sodden and soiled bedding for a prolonged period is an almost guarantee that thrust will eventually develop.

Poor foot care is another common reason for thrush to develop. If a horse’s feet are not regularly picked out and cleaned, then the bacteria can make its way into the frog and start an infection. Trimming and shoeing activities that are incorrect or done with poor skill can also encourage the development of thrush in some horses.

Although bad stable management is usually blamed for thrush, some horses tend to be more susceptible to it than others. Some cases of thrush are thought to be caused by too much aggressiveness with a hoof pick as well. 

How Can Thrush Be Diagnosed in Horses?

One of the issues that owners and handlers face when dealing with thrush is that a horse affected by this condition will often show no signs of discomfort. Even if there is discharge present, the horse will normally experience no lameness or discomfort. 

When thrush is present in the frog, the infection creates a very foul odor that is quite recognizable. A black discharge that also smells foul will come from the sulcus of the affected frog. Horses that are dealing with thrust will also show discomfort when direct compression is applied to the affected area.

There are other indicators which can indicate thrush is present, even if the discharge has not yet formed. The central sulcus on inactive horses or those experiencing health issues can be deeper than normal, which limits air access to that region. If there is debris found in this area, there is a good chance that bacteria will also be in that area and the tissues are beginning to degrade.

Severe cases of thrush are sometimes confused with another infection that is called “Canker.” This type of infection is more severe than thrush and can cause bleeding with simple pressure to the affected area. Tissues that are affected by canker look like a cauliflower that has rotted and will have a sponge-like texture to them. 

How Is Thrush Treated in Horses?

To treat thrush in horses, the underlying cause of the infection must be removed. Environmental conditions that could encourage the infection to survive must also be properly managed. For most horses, the first steps in treating thrush involve being moved to a stable or environment that is dry and clean. Their feet should be cleaned every day.

In some instances, a farrier or veterinarian may also need to directly treat the foot if there is tissue damage present. Any tissues that are dead or damaged must be cut away so that the healthy tissues can be reached. This cutaway process may need to be repeated for some horses, depending upon the severity of their condition.

Once the dead and damaged tissue has been removed, a topical treatment is usually applied to the area experiencing the infection. It is usually a caustic combination that involves iodine, formalin, or even chlorine bleach. A farrier will likely need to trim the affected hooves so that new frog growth is promoted. 

After the frog and the rest of the affected hoof has been cleaned, an antibiotic solution is usually applied to the area. Bandaging may be necessary to promote the healing process if the amount of trimming required to reach healthy tissues was extensive.

Dry and clean bedding is mandatory. It may need to be changed daily.

Should the thrush infection spread to other parts of the horse’s body, prescription antibiotics may be required to restore health.

Picking out the hooves carefully will encourage healing as well. The bacteria which cause thrush are killed when exposed to oxygen. By using the hoof pick properly, the hoof will experience better air flow levels and that will reduce the chances that the bacteria have to thrive.

Why Does Thrush Return So Often in Horses?

A horse may be responding very well to its thrush treatment, but after a few days, the problem comes back with an even greater ferocity. Why do some horses experience a return of the infection immediately after it has been treated?

It depends on the condition of the hoof itself. Many horses have crevices in their hooves that an antibiotic paste or caustic solution will not reach. Even though a majority of the infection is treated and removed, the bacteria is allowed to linger and will take over once the treatment efforts are stopped.

Cracking in the keratin of the horse hoof is also quite common. These cracks may be very fine and not even allow the caustic solution to flow through them, but they’ll still be large enough for the bacteria to find a home.

At the same time, packing the hoof with antibiotic products isn’t usually an option because the extra pressure on the frog can be painful to the horse. Too much pressure on the frog for an extended period can even kill the frog tissues and prolong the course of treatment.

If you are administering the treatment course for your horse, be sure to use a swab that can reach all areas of the hoof. Applying a cotton swab to the end of a hoof pick can be an effective option. Then soak the swab in the treatment solution and wash the sides of the frog down first, just like you’re going to pick out the hoof. That will let the solution get into the cracks and prevent the bacteria from finding a place to wait out your treatment efforts. 

Is It Possible to Prevent Thrush in Horses?

In most cases, thrush is an entirely preventable condition. Horses that are kept in dry and clean conditions, receive regular foot care, and see a farrier regularly have a much lower risk of developing thrush compared to other horses. Although some horses have hooves that increase their risk of developing thrush, good stable habits can dramatically lower the risks for a horse.

It is important to remember that if the frog is compromised, it becomes an entry point for other dangerous bacteria. The bacteria that causes tetanus is known to use an infected frog to afflict horses. If thrush is present, speak with your veterinarian about taking precautions against tetanus.

For most horses, a case of thrush is usually fairly easy to treat. Keep the stable clean, keep the foot clean, and pick out the hoof each day. Despite your best efforts, even with a perfectly clean stable, some horses are just prone to this condition and will require ongoing treatment. 

If the infection is not responding to your treatments or you have specific questions about the health of a horse, always consult with a veterinarian as your first course of action. Rapid recognition can lead to a rapid response and that will help to decrease the discomfort a horse experiences from this condition.