Thrush is something that at one time or another all horse owners will likely have to deal with. It is not a product of neglectful horse care, nor is it a product of unsanitary living environment etc. Thrush is a combination of bacteria and fungus that can eat away at the frog tissue in the hoof. These bacteria and fungus are more prominent in wet conditions and thrive in moist ground, but can also be a problem in dry conditions. In the image above you will see the healthy frog on the right, the thrush infected frog on the left. You will notice that the central sulcus, the area at the rear of the frog in the middle, in the healthy hoof is just a small indent, but in the affected hoof it is a deep crack. This is the first area that thrush usually starts to affect. What happens is the the thrush eats away at the healthy tissue and creates a "home" for itself withing the sulcus of the frog. The deeper the crack, the better the hiding spot for the thrush to thrive and eat more healthy tissue. It is a vicious cycle and can be extremely hard to beat once it gets to this advanced stage.
Minor surface thrush is much easier to deal with. Some ratty tags on the frog, or a small infection of the central sulcus can usually be treated with diligent hoof picking and 2-3 times a week topical treatments. More severe thrush can take weeks or even months to clear up and can require soaking, topical treatments, booting and even diet/nutrition changes.
So why is thrush an issue? At the start with a minor case, thrush doesn't really alter the horse in any way. If we catch it early enough and treat it then it is a non issue. If thrush persists and manages to eat into the frog tissue deeper it can cause the horse to feel some sensitivity when loading the back of their hoof and can cause them to land flat or toe first as opposed to heel first as they are intended to land. Horses land heel first in order to use the frog and its underlying structure, the digital cushion, to absorb impact and dissipate energy vibrations. When the horse alters its movement and doesn't land heel first that impact energy travels up the leg into the joints, shoulders/hip and back and causes excess strain on the body. This can create a cascade effect that can significantly affect the performance of the horse and in serious cases can even lead to lameness.
When the thrush eats through the frog and into the sensitive digital cushion it is extremely painful for the horse. The hoof and its outside structures are designed to protect, and are insensitive structures, meaning they do not have nerves and blood supply directly within them. The nerve receptors and blood supply are located within the sensitive structures: the digital cushion, solar corium and lamina. So this means that a minor surface infection of the frog really won't cause much pain, however once the thrush eats into the digital cushion it is in fact an open wound of the horse, and is painful when impacting the ground. The horse then alters their movement to avoid loading the frog as much as possible. This is an issue because of the previously mentioned strain on the body, but also because healthy frog tissue is generated because of positive impact forces, and without the horse loading the frog it won't receive these forces. This creates a long term problem as the frog and digital cushion will atrophy over time due to lack of stimulation and will alter the shape of the hoof capsule. You then have a significant reduction of impact energy dissipation and a horse that is absorbing that impact in their joints, therefore more prone to develop arthritis and other joint related conditions.
The pictures below show you the severity of a thrush infection once it gets into the digital cushion. These cadavers have the outside structures removed and the one on the left has an infection so deep that a hoof pick can be inserted into the crack approx 1/2 an inch. This is a deep open wound for the horse and extremely painful. The cadaver on the right shows a healthy digital cushion with a normal central sulcus without infection.
So what can we do about it? For minor infections treating topically is easy. Your local tack store will have several products available that are designed to kill the harmful bacteria and fungus that cause thrush. My personal word of of caution would be to read the ingredients label on those products. What you want is something that will kill the harmful bacteria and fungus, but not the healthy tissue. A lot of commercially made thrush products have ingredients like formaldehyde, formalin, turpentine etc. These substances are toxic to healthy tissues and will indeed kill the thrush but also the regenerating frog tissue. My favorite for minor surface thrush are tea tree ointments, gentian violet treatments or zinc oxide cream marketed as diaper cream for babies.
Think about a deep thrush infection like an open wound on your own skin. Use products that will keep it clean but also encourage healthy growth. Products such as antibacterial wound scrubs used in human medicine, as well as barrier creams and ointments. My personal method for treating for this type of infection is as follows:
Easyboot Cloud therapy boots are also a great rehab boot. I sometimes use these if I need more protection for the hoof and a thicker padding. These are not suitable for riding so it makes them strictly a turnout/therapy boot. If you are looking for Cloud boots contact me as I can special order them.
Published in Saddle Up Magazine December 2014
Maintaining frog health through the winter can be a challenging task in our climate. A healthy robust frog is one of the main supporting structures in the back of the hoof. As the horse strides out the heels and frog impact the ground first, absorbing the impact energy and dissipating the forces on the horses’ joints. A weak or infected frog will cause the horse to alter its stride and can cause the horse to land toe first. This is detrimental to the functionality of the limb and can wreak havoc on hoof health as well as cause a myriad of body issues.
A healthy frog is calloused and firm to the touch with no snags, flaps or crevices for debris and manure to get trapped inside. The central sulcus (small “V” shaped crevice at the rear of frog) should be shallow and wide. The collateral grooves (indented area on each side of frog) should be open and be easy to slip a hoof pick in for cleaning. If they are too tight your trimmer might open them up to allow you better access for cleaning during the wetter months.
An unhealthy frog is one with flaps and tags of material that appears ratty and loose. In many instances thrush and other fungus and bacteria can get trapped in deep grooves and fissures creating further infection inside the sensitive. Once the frog and its underlying structures become infected it can be very hard treat and heal. A balance of cleaning with topical anti-fungal and anti-bacterial solutions as well as keeping the hooves clean and dry is the best remedy. In the winter with the mud and snow manure management can be difficult, but keeping your horses’ heavier trafficked areas clean and dry is a priority as well as picking their feet regularly.
A great strategy is to treat the horse preventively twice a week as the ground becomes wet with a mild anti-fungal like apple cider vinegar. The vinegar kills the bacteria and fungus but will not harm the healthy tissues. There are many products on the market for treating thrush, but whenever possible I prefer to recommend something natural when using it as a preventative measure. If you are dealing with an active surface infection the apple cider vinegar is still effective, but more frequent treatment is needed. My preferred method of application is to put the vinegar in a spray bottle or a bottle with a pointed tip to apply it only to the infected area. After applying I use an old toothbrush to massage the vinegar into any small cracks or crevices. Too much vinegar on the skin or heel bulbs could cause irritation or sensitivity and should be avoided. The aim is to apply only to the infected areas of the frog or hoof.
For deep central sulcus thrush causing toe first landings or altered stride serious effort must be put into healing the hoof before lasting damage is done to the horse’s hoof, joints and body. In this instance I recommend a soaking boot and a solution called White Lightning. White Lightning is a liquid that when mixed with equal parts white vinegar creates a Chlorine Dioxide Gas. This gas kills the fungus and bacteria on contact without irritating the sensitive tissues that could be sensitive from the underlying infection. Soaking is recommended daily for 20 minutes until the infection is starting to dry up and the cracks can start to close. As the infection starts to clear treatment can be gradually reduced until the crack is healed. A word of caution: During soaking keeping the solution low on the hoof so that is does not irritate the skin is of great importance. The liquid can discolor the hair and can irritate the skin if left saturated for too long. A little solution goes a long way, on average I use 2 tablespoons of WL mixed with equal parts vinegar. It is also important to note that this solution must be mixed up on an as needed basis and will not be effective if mixed ahead of time. It is the chemical reaction that causes the gas and so the soaking boot should also be wrapped to trap the gas inside while soaking. An old polo wrap or vet wrap works well for this. With any medical treatment, consult your veterinarian or hoof care practitioner if you have any questions or concerns or if the infection persists.
More Ideas for treating thrush
Another product that I recommend for thrush is No Thrush powder. It is the only thrush product on the market (that I know of) that is a dry treatment for thrush. The powder comes in a bottle with a pointed tip so that you can insert the tip into the crevices and expel the powder. This needs to be done daily, or in some cases multiple times per day in order to treat severe infections. I like to use this powder on an infected hoof and then as a base in a hoof boot in wet or muddy conditions in order to keep the hoof clean and dry.
For central sulcas thrush with deep cracks I also use a cream made up of equal parts clotrimazole and triple antibiotic ointment. The clotrimazole is used for athletes foot infections and can be found at most pharmacies. I mix both creams together and put the mixture into a large syringe with a pointed tip. The syringe allows me to inject the cream deep into the crack in the frog and the cream kills the fungus and bacteria. This treatment is effective long term, but needs to be done daily and the hooves kept clean and dry.
A liquid thrush product I use regularly to treat thrush and as a preventative is No Thrush. It is a deep purple color and works very well for surface thrush and as a preventative. I apply it to a clean, dry frog with a toothbrush so that I can scrub it into the frog and any cracks and crevices. Be sure to wear gloves and don't get it on your clothes as it stains everything it touches!
Kristi Luehr is a barefoot trimmer, author, and founder of the Okanagan School of Natural Hoof Care. She is certified by the Canadian Farrier School as well as the Oregon School of Natural Hoof Care, and also has certification in equine massage and dentistry. Her focus is to educate owners about hoof anatomy, function and proper barefoot trimming that supports and grows healthy and functional hooves specific to each horse's individual needs. She is the author of two online courses specific to hoof care and is always striving to create more educational content for students to learn from.