Canker In Horses: An In Depth Look

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What is Canker?

In a nutshell Canker is a disease that causes the tissues in and around a horse’s frog to grow excessively. In more technical terms canker is:

Canker is a chronic hypertrophy and apparent suppuration of the horn-producing tissues of the foot, involving the frog and the sole.

(https://www.merckvetmanual.com/musculoskeletal-system/lameness-in-horses/canker-in-horses)

History

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The name canker comes from the early belief that the conditions was cancerous in nature. However, current knowledge is that canker is an anaerobic (grows in the absence of oxygen) infection in the superficial tissues which produce the horn of the hoof.

Cause

Currently the cause is unknown. It is only briefly discussed in veterinary textbooks. Most books suggest that it is caused from housing a horse in unsanitary conditions but farms with both the best of stable management and the worst can both have horses with the disease. In attempts to recreate the disease, Dr. Tracy A. Turner, DVM, have packed a horse’s frog with manure after injecting it with what they believe are the causative bacteria. To date is has not been possible to prove that canker is due to unsanitary conditions. Another theory as to the cause of canker is that development might instead be influenced by how the horse is used. Corralled horses will little exercise seem to be more predisposed to the disease than horses that are active and kept outdoors. The causative bacteria is unknown, but some researchers have suggested that the organism is part of the Bacteroides species, which is similar to what causes “foot rot” in sheep. In a study that was completed more recently, researchers found spirochete (spiral shaped) bacteria in the epithelium, which was similar to what they found in cows and sheep with digital dermatitis. Dr David Wilson, professor of large animal surgery at the University of Saskatchewan, explains that when the horse’s hooves are wet for an extended period of time, the keratin in the foot structure softens, making it easier for bacteria to enter. Because the bacteria found in hoof canker cases lives in the soil, the best way to prevent the condition is to keep the hoof clean and dry.

“Daily picking out of the horse’s hooves will likely prevent the condition from developing, and this may be especially important for horses in wetter environments”

https://horse-canada.com/magazine_articles/hoof-canker/

In the end nobody knows exactly what causes the conditions. What I have presented here are the theories that may vets and researchers have formed over the years. I hope that soon they will be able to figure out exactly what causes this terrible disease and can then focus on finding a way to cure it without fail.

Where is Canker Found

Typically equine canker cases are found in the southeastern United States due to its higher moisture content and heat. However, there have been diagnosed cases of canker all over the country. The reason it is more common through the Southeastern United States is due to the widely held belief that moisture is a contributing factor to the cause of the disease.

What does Canker Do

The microorganism that is associated with canker causes abnormal keratin production, or overgrowth of the horn. This excessive growth occurs underneath the horn, as the infection spreads throughout the epithelial layer. Commonly, an affected horse will have white or gray matter that is spongy and moist appearing in the sulci region (grooves on either side and in the center of the frog) of the hoof. This growth’s appearance has been described as looking similar to wet cauliflower with cottage cheese like emission. If an extreme infection is present then heat may be felt in the hoof, but this is only in extreme situations. I noticed when my wife had her horse treated that the growth itself was extremely fibrous. When the vet was cutting through the grown you could hear each cut as it was made. The growth itself felt a lot like a piece of grizzle from a steak. In the early stages canker can appear to be thrush or abscesses that will not go away.

Is Canker Like Thrush?

Not really. Unlike thrush, which is a necrotic or tissue-destroying process, canker creates abnormal tissue grown and is described as a hypertrophic pododermatitis. Thrush and canker are both found in the same region of the foot but thrush is more of a tar like substance. While thrush eats at tissue, the inner tissues of the foot are protected until bacteria get deep enough to deteriorate the more sensitive structures. Canker, on the other hand, spreads in live tissue, without the help of oxygen.

Is there treatment for canker?

Treating canker can be a challenge as most of us who have experienced it know first hand. Many Vets have suggested a variety of medications and treatments but the most successful therapy is based on the following:

  1. Superficial Debridement (cutting away abnormal tissue) over the entire affected area. This process can be done by putting the horse to sleep with the use of anesthesia or by using a nerve block. Only the superficial layer of the infected tissue is usually removed because excising too deeply can slow down healing and also drive the infection into deeper tissues. Some vets follow the debridement process with two or three superficial freezes of the affected area to further kill off the diseased tissue.
  2. Canker prefers moist conditions, so make sure you keep the treated area very clean and dry.
  3. Topical Treatments. Veterinarians have suggested several treatments but two of the most effective topical therapies are the antimicrobial drug metronidazole and 10% benzyl peroxide solution. Metronidazole is usually ground into a powder and spread over the affected area. Benzyl peroxide is a potent astringent commonly found in acne medicine. It is soaked into gauze sponges and applies as a wound dressing. Although, no medicine will cure canker if superficial debridement is not performed.

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email: support@well-horse.com
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It is also now available on their website.

After applying the topical medications, you want to apply a clean, dry, waterproof bandage. A number of Vets recommend using shoes with treatment plates, which are more convenient than bandaging the entire hoof. Dr. David Wilson says he has never seen a case of canker recur in a horse that has been successfully treated. A large number of people have reported success in treating their horses for canker by using a product called “Purple Mush”. This product is from well-horse.com but is not available on their website. It is a salve made from plant resin and is supposedly easy to apply and affordable. I have not tried it but my wife has been trying to find it for a while. I managed to find it yesterday so I’ll post the information for anyone else who may be interested in trying it. Please let me know if you have success with it so I can update this article with the information so more people can benefit from it.

How do horses respond to treatment?

Every horse is different so there isn’t a sure answer. Some horses will heal within a week or 10 days and some cases last for months. With good, aggressive treatment, a week to 10 days of intensive therapy should be enough to get the canker under control. Once the tissue has healed, it is very rare for the disease to reoccur. However, the canker can return before the healing is complete. This is what led many to believe that canker was a cancerous disease.

How can I identify Canker?

In the early stages canker may present itself as a focal area of granulation tissue in the frog the bleeds easily when cut. If you look closer you will typically see a light brown or gray tissue that will surround this focal area. If it is not treated, the disease will become more distributed and involve the frog, bars, sole and the stratum medium of the hoof wall in the plantar aspect of the foot. The infection itself results in abnormal keratin production, which is seen as filamentous fronds of hypertrophic horn. Canker is characterized by a number of small, finger-like protruding growth of soft off-white material that appears like cauliflower. This condition is often, but not always, accompanies by a foul odor and is covered with a caseous white emission that resembles cottage cheese. The frog itself is often undermined with the horny frog covering the bulk of the disease. The affected tissue will bleed very easily if cut and may be extremely painful when touched. Varying degrees of lameness will be present depending on the extent and the depth of the infection. Most horses are not lame when the disease is first recognized and treated early. If the horse is lame it indicates that the disease involved more than just the superficial horny frog and needs an aggressive approach to resolving the problem.

Diagnosis

An early diagnosis of canker is based on the general appearance of the affected horny tissue along with a rancid odor. However, a definitive diagnosis may be confirmed with a biopsy. Biopsy is the most useful in recurrent cases or when the lesions do not have the signature appearance or they appear in unusual locations of the foot. Caution must be used when removing the superficial necrotic tissue before the biopsy is taken from the margin of the lesion. The biopsy should include both normal and abnormal tissue. A 6 mm biopsy punch works well for this purpose. Histologically, the lesion is read as a chronic, hypertrophic, moist pododermatitis of the frog. It is characterized by a proliferative papillary hyperplasia of the epidermis with dyskeratosis, keratolysis and ballooning degeneration of the outer layers of the epidermis. A mixed population of bacterial organisms are observed in the stratum germinativum layer of the epidermis of the frog. Normally cultures are useless as they produce an assortment of environmental organisms, bacteroids sp. and Fusobacterium necrophorum. Benzyl Peroxide is easily purchased at places such as Wal-Mart or your local drug store.

Discussion

The treatment of equine canker has always presented problems for veterinarians and the farriers due to the poor prognosis. The cause of canker remains unknown; however, the disease as seen by authors differs in some respects from the disease that was described in the old surgical texts. It does not appear to be a disease that only effects poorly kept horses. Many studies have shown that horses that are in very well kept conditions and receive routine hoof care can still be affected. While the hind legs seem to be more frequently affected, front leg involvement is common. In the majority of cases, the condition starts on the frog near the heel lateral or medial to the sulcus. From there, it can extend anywhere on the foot and even break through the hoof capsule. In 1997, one author began using a topical therapy reported by a Texas farrier consisting of benzyl peroxide in acetone and metronidazole. Since that time all horses have been managed with surgical debridement followed by this combination of topical therapy with excellent success. The combination of careful debridement along with topical benzyl peroxide in acetone and metronidazole have yielded consistent predicable results in 56 cases. Even though the cause of canker is still unknown, there are several principles of therapy for the condition for which authors consider to be important. Thorough debridement of the lesion is essential. The method used to achieve this is probably of less importance. Electrocautery or cold steel excision followed by cryotherapy both cause tissue necrosis away from the surgical margins ensuring complete resection of the growth. It is critical that the growth is followed to is root and that the entire growth is removed. Finally, methodical topical treatment is important. Cleaning the affected area with an antiseptic solution daily removes the surface bacteria and provides and environment where the wound can heal properly. 10% benzyl peroxide in acetone is an excellent astringent and keeps the tissue dry with no caustic effect and finally the bacteria cultured from canker cases are usually anaerobic making metronidazole a good choice as a topical antibiotic. Attention must be placed on keeping the surgical wound clean and dry until the wound begins to heal. The horse owner’s compliance to perform the daily foot care is another essential element in the treatment of equine canker.

Our Canker Story

Canker is pretty rare in Arizona so when my wife’s thoroughbred came up with it about 2 years ago we had no idea what it was. It started as thrush then abscesses which we were unable to get rid of. Eventually our farrier pulled a horseshoe nail out of Tiz’s frog (which had to have been there for a long time due to the condition of it) which we believe is what gave the canker a path to follow out of the frog.

When we first saw it we had no idea what it was so we immediately started researching it and finally was able to figure out what it was. We decided to hit it aggressively right from the start so had our vet do a debridement on his hind foot. To get the entire growth removed involved our vet following the growth all the way to the coffin bone and hollowing out our boy’s hoof. It literally looked like a bowl. After that we used crushed up metronidazole mixed with 10% benzyl peroxide on cotton and packed his foot with it.

This process went on for months. Our farrier at the time had no experience with this disease and had no idea how to treat it so we ended up contacting a specialist in Scottsdale. The specialist came up and evaluated Tiz and explained to us what we were dealing with in better detail than what we had been able to find. At this point we knew he was the guy to help Tiz if anyone was so we immediately swapped farriers. Tiz has this issue where he doesn’t like to pick his feet up.

When you do finally get them up you have to really keep a close eye on him because he will try and lay down on you. So dealing with his feet in any capacity takes two people, one to deal with his feet, and one to keep him standing. The first time this farrier came out he spent the better part of 8 hours treating the canker and dealing with abscesses that Tiz had in his front. This is the first thoroughbred we have owned and probably the last from what we’ve been hearing. They are amazing horses but do tend to have tons of feet issues. After the Farrier was done that first time he suggested we keep Tiz on a schedule to get trimmed every 4 weeks and deal with the canker as it returns. Now it’s been over a year and every four weeks the farrier is out taking care of Tiz’s feet and removing the canker as it returns. While doing research for this article I have found that we may not have handled the after-care of his surgery properly and now are going to be trying some other techniques to try and eliminate the canker. Since we made the switch to the farrier we are currently using, Tiz has made improvements by leaps and bounds. He has very little issues with his back feet which is where the canker first popped up. Since that time it has appeared in one of his front feet as well but the farrier caught it immediately and we were able to get it dealt with. The current issue with him is abscesses which we believe to be the sign of canker. Much of the information I found while researching this article says that canker usually starts off like thrush. In our case it was more abscesses that we couldn’t get rid of so we believe this is one of the signs that canker is present.

Canker is pretty rare in Arizona so when my wife’s thoroughbred came up with it about 2 years ago we had no idea what it was. It started as thrush then abscesses which we were unable to get rid of. Eventually our farrier pulled a horseshoe nail out of Tiz’s frog (which had to have been there for a long time due to the condition of it) which we believe is what gave the canker a path to follow out of the frog. When we first saw it we had no idea what it was so we immediately started researching it and finally was able to figure out what it was.

We decided to hit it aggressively right from the start so had our vet do a debridement on his hind foot. To get the entire growth removed involved our vet following the growth all the way to the coffin bone and hollowing out our boy’s hoof. It literally looked like a bowl. After that we used crushed up metronidazole mixed with 10% benzyl peroxide on cotton and packed his foot with it.

This process went on for months. Our farrier at the time had no experience with this disease and had no idea how to treat it so we ended up contacting a specialist in Scottsdale. The specialist came up and evaluated Tiz and explained to us what we were dealing with in better detail than what we had been able to find. At this point we knew he was the guy to help Tiz if anyone was so we immediately swapped farriers. Tiz has this issue where he doesn’t like to pick his feet up. When you do finally get them up you have to really keep a close eye on him because he will try and lay down on you. So dealing with his feet in any capacity takes two people, one to deal with his feet, and one to keep him standing.

The first time this farrier came out he spent the better part of 8 hours treating the canker and dealing with abscesses that Tiz had in his front. This is the first thoroughbred we have owned and probably the last from what we’ve been hearing. They are amazing horses but do tend to have tons of feet issues. After the Farrier was done that first time he suggested we keep Tiz on a schedule to get trimmed every 4 weeks and deal with the canker as it returns.

Now it’s been over a year and every four weeks the farrier is out taking care of Tiz’s feet and removing the canker as it returns. While doing research for this article I have found that we may not have handled the after-care of his surgery properly and now are going to be trying some other techniques to try and eliminate the canker. Since we made the switch to the farrier we are currently using, Tiz has made improvements by leaps and bounds. He has very little issues with his back feet which is where the canker first popped up.

Since that time it has appeared in one of his front feet as well but the farrier caught it immediately and we were able to get it dealt with. The current issue with him is abscesses which we believe to be the sign of canker. Much of the information I found while researching this article says that canker usually starts off like thrush. In our case it was more abscesses that we couldn’t get rid of so we believe this is one of the signs that canker is present.

The specialist came up and evaluated Tiz and explained to us what we were dealing with in better detail than what we had been able to find. At this point we knew he was the guy to help Tiz if anyone was so we immediately swapped farriers. Tiz has this issue where he doesn’t like to pick his feet up. When you do finally get them up you have to really keep a close eye on him because he will try and lay down on you. So dealing with his feet in any capacity takes two people, one to deal with his feet, and one to keep him standing.

The first time this farrier came out he spent the better part of 8 hours treating the canker and dealing with abscesses that Tiz had in his front. This is the first thoroughbred we have owned and probably the last from what we’ve been hearing. They are amazing horses but do tend to have tons of feet issues. After the Farrier was done that first time he suggested we keep Tiz on a schedule to get trimmed every 4 weeks and deal with the canker as it returns.

Now it’s been over a year and every four weeks the farrier is out taking care of Tiz’s feet and removing the canker as it returns. While doing research for this article I have found that we may not have handled the after-care of his surgery properly and now are going to be trying some other techniques to try and eliminate the canker. Since we made the switch to the farrier we are currently using, Tiz has made improvements by leaps and bounds. He has very little issues with his back feet which is where the canker first popped up.

Since that time it has appeared in one of his front feet as well but the farrier caught it immediately and we were able to get it dealt with. The current issue with him is abscesses which we believe to be the sign of canker. Much of the information I found while researching this article says that canker usually starts off like thrush. In our case it was more abscesses that we couldn’t get rid of so we believe this is one of the signs that canker is present.

Another Quick Theory

My wife was telling just this morning how two friends of hers had horses they couldn’t get rid of thrush in. The boarding facility they were at had cattle grazing nearby when the thrush popped up. They tried all the equine thrush medications with no luck. Eventually they picked up some thrush medicine for cattle and used that which effectively got rid of the thrush.

This story leads me to believe the theory that I stated earlier in this article that the bacteria that causes thrush and foot rot in cattle and sheep may have something to do with the cause of canker. I still have plenty of questions that I haven’t been able to find answers to yet but hope to in the near future. As I am able to obtain more information I will post more articles on this topic. I have reached out to a vet in New York who is currently researching canker to see if she can shed some more light on the subject and maybe somebody, somewhere can finally find a lasting cure for this disease.

There are a large number of people from all walks of life who have had to deal with this disease in their horses. Some of these stories have happy endings and some of them do not. I am reaching out to a number of people to share their experiences with this horrible disease. If you have ever had to deal with it or have more information about this disease please use the Contact Us form at the bottom of the page to let us know. By sending us your story you authorize us to use your name and the contents of your canker related email to publish on our site.

I hope this article was helpful to you. If it was I would be appreciative if you would share it with your friends and on your favorite social media pages. Leave a comment in the section below and let me know hat you thought.

References
1) Moyer, W.A., Colohan, P.T.: Canker. In Equine Medicine & Surgery, 5th edition, Mosby, St. Louis (1999); 1544-1546.
2) Reeves, M.J., Yovich, J.V., Turner, A.S. Miscellaneous Conditions of the Equine Foot. In Veterinary Clinics of North America – equine practice. Vol 5 (1) (1989); 236-237.
3) Wilson, D.G.: Equine Canker. In Current Therapy in Equine Medicine 4. Edited by Robinson, N.E., W.B. Saunders Co., Philadelphia (1997); 127-128.
4) Steckel, R.R.: Puncture Wounds, Abscesses, Thrush, and Canker. In Current Therapy in Equine Medicine 2. Edited by Robinson, N.E., W.B. Saunders Co., Philadelphia (1987); 271.
5) Turner, T.A.: Treatment of equine canker. Proc 34th Annu Conv Am Assoc Equine Pract, 1988, pp 307-310.
6) https://www.equipodiatry.com/canker1.htm

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