“Doc – Doc– What’s Canker and Can You Cure It?”
© A.J. Neumann, D.V.M.
published in The Draft Horse Journal, Spring 2000

Of all the diseases and conditions of the foot, equine canker is probably the least understood by veterinarians and horse owners alike, and its treatment is a long and arduous task.

Equine canker is a chronic, moist eczematous infection of the foot, with hyper-proliferation of inadequately keratinized epithelial tissue, which usually involves the frog, sole, and then the wall of the hoof, in this order, if the condition is allowed to proceed without adequate treatment.

Having said all that, let’s explain a little bit about what happens. In its early beginnings, canker is often mistakenly diagnosed as thrush. The condition usually begins in the cleft of the frog and occasionally in the cleft of the heels. Owners and farriers see and smell the diseased tissue and become aware of the problem. Beginning thrush and canker both have a very fetid odor, accompanied by decomposing moist tissue. Owners or veterinarians proceed to treat the thrush with various drugs and methods, and after a period of time, they find that these treatments are not working, and the condition has usually spread into the frog, to appear as a segregated “punched out” area of rotting, moist tissue with definite margins and a very rotten foul-smelling odor.

Oftentimes the frog will be intact, but has a ragged, rubbery appearance. This “horn tissue” of the frog will loosen easily, and under it will be a swollen, bloody corium covered with a very foul-smelling liquid, or white exudate. The corium is the horn-producing tissue of the frog, sole, hoof wall, ergot and chestnut.

When this extremely moist, liquifying or caseous material is removed, one will see strands of epithelial tissue spanning the area, resembling a huge spider web. Again, the odor is very foul.

The diagnosis of the condition by its appearance at this stage is very easy to the person who has heard of or seen canker. At this point a histological diagnosis can be made by taking a biopsy from the margin of the lesion, which should include the normal and abnormal tissues, and sending the samples to a laboratory. However, the need for this is almost nonexistent, as the general appearance and the foul smell of the area should be diagnostic in itself.

Historically, canker was most often seen in the hind feet of draft horses, but I have personally treated the condition in one adult Quarter Horse and one yearling Quarter Horse stallion. For some unknown reason horses, primarily drafts with flat feet, large fleshy frogs, heavy feather, and with white hoof bands and legs, seem to be the most susceptible to the condition. Of all the draft breeds, I have treated more Clydesdales than any other. At the present time I am involved with three Clydesdales and two Belgians in the treatment of canker.

There are two conditions which seem to be favorable for the onset of canker. One is dampness. The condition is rarely seen in high, dry areas, but is often seen occurring in low areas having wet pastures and long rainy seasons. Filthy stables and a horse’s long exposure to muddy environment are thought to be a predisposing cause, but this has not been proven.

The second circumstance seems to be injuries to the frog, whereby anaerobic situations are set up for the growth of certain anaerobic bacteria. Again, this is a theory and has not been proven.

Usually canker is found in only one foot, the rear feet being the most common. However, it may be present in two, three or all four feet at the same time. In some cases the disease may be present in one foot and then appear in another and then another until all of them have been involved.

Remarkably, in the early stages of this ailment, the affected animal will not be lame, even if the condition exists in all four feet. It is only when the canker has progressed to a stage where the sole and frog are largely destroyed and the infection has penetrated well up into the tissues above these structures that the animal will exhibit signs of pain and lameness. The lameness and pain which is then exhibited is not necessarily caused by the infection, but rather by the loss of protection to the tissues when portions of the sole and frog are destroyed. In mis-diagnosed or badly treated cases the disease can spread to the hoof wall and involve this structure.

The specific cause of this disease is believed to be an infectious agent or agents of an anaerobic bacteria type. This means these bacteria are capable of growing in tissue without oxygen. This fact is important and must be taken into consideration when treating the ailment. However, in my opinion whether anaerobic bacteria actually cause the disease or become involved after the fact is an open question.

Canker has been treated many, many ways over the years. The practice before the late 1800s was to strip off the entire sole and frog on the affected foot and cauterize the area deeply with strong acids or a hot iron. According to reports in old veterinary books the practice “was not attended with uniformly good results.”

About 1900 a different approach was in vogue. The affected horn tissue was pared away until only healthy horn borders were encountered. The foot was then dressed daily with various drying powders. It was a long process of changing dressings every day or two before the area was completely healed. Such powders as calamine, iron sulphate, and copper sulphate seemed to work well. Another often used remedy was the mixture of one part pine tar, eight parts turpentine and two parts carbolic acid.

Basically this was the only treatment horsemen had for canker until the advent of sulfa drugs and antibiotics. There are a few reports in the literature whereby some cases of canker were cured by the use of penicillin and tetracycline, which were applied topically, as well as given parenterally.

With the advent of chloramphenicol, I was in business to cure canker. I used it parenterally and topically, after removing the dead horn tissue. I also used calamine powder by making a paste and applying it on the affected areas and bandaging the paste in place. I would make a 2% chloramphenicol salve and use this product topically under a light bandage.

Chloramphenicol and calamine worked fine on these cases and all went well for me until chloramphenicol was removed from the market because of attendant human health risks. So I was back to square one, using formalin, calamine, and other astringent drugs, plus sulfa powders.

Then along came florfenical, the substitute for chloramphenicol. This drug was to do what its predecessor did, without the human risk of sickle cell anemia. It was packaged as an injectable product for use in cattle only. I made a 2% water-soluble salve and used it on horses. The salve worked wonderfully, but I soon learned it was difficult to use the drug parenterally in the horse.

By this time I knew from experience I had to treat the canker syndrome locally and parenterally, so I set my sights on another drug, metronidazole, which can be used as a 2% cream or salve or orally. I also have used TMS tablets for oral treatment. These are the drugs of choice today. So let’s look at a few ongoing examples and see how we are doing in treating these difficult cases of canker and what I have learned about their etiology or cause.

CASE #1

Case #1 is a Belgian gelding used for logging and general farm work in southern Indiana. The right rear leg has a black hoof and a white stocking. When stabled, he is in a tie stall in the barn. When the horse is turned out, he is in a pasture or yard with other draft horses.

The horse was in “poor shape” when he was purchased due to a “gravel” condition in the right front foot which, when healed, damaged the foot.

The owner noticed the horse being “off” in the right rear and examined the foot and saw what he and his local veterinarian believed to be some tissue growing up and out of the sole of the foot. The tissue was cut back. As the tissue continued to grow, the owner took the animal to a college of veterinary medicine where they cut out the diseased material. The wounds bled profusely. The owner was given some metronidazole salve or cream and instructed to bandage it on the hoof once a day, then every two days.

At first the horse seemed to do well, but after some time the canker began to invest more tissue. In about six months he took the horse back to the school for reassessment. The practitioners there wanted to cut out the rest of the foot, but the owner refused and brought the gelding back home.

At that time I was contacted. I put the animal on calamine packs to be left on one or two days. After a time the packs were to be left on for three days. Calamine is a powder consisting of zinc sulfate 98% and ferris sulfate 2%. It is water soluble and one can make a paste by adding water to the powder.

These applications got rid of the necrotic tissue and healing started.

According to the owner, people thought it odd he was spending so much time and money on the horse, but, as he told me, “he was a good worker and I just thought I should help him.”

After some time had passed, some “old horseman” told him about the turpentine-pine tar-carbolic acid salve. He tried it and alternated it with the calamine paste in packing and bandaging the hoof. He reported to me he was making progress, and the hoof was healing nicely.

As of the middle of January 2000, the Belgian’s right rear hoof is healed. The whole time span from when the first signs of canker were seen until healing was about one and a half years.

I might add, this foot lost the sole, frog and part of the rear side wall. This was a lot of damage to repair, but at no time were the coronet band, ergots or chestnuts involved.

CASE #2

Case #2 is a Clydesdale with canker in the right rear hoof. The hoof is white and so is the leg. Canker involved the sole, frog and medial side of the hoof wall.

Special shoe made to support wall, and pad the bottom of the foot.

This animal was treated with help and advice from a veterinary college. The drugs used were oral TMS tablets plus a 2% metronidazole ointment applied to the lesions of the foot.

This was done, of course, after the foot was operated on and all necrotic and diseased tissue was removed down to healthy corium.

This patient was shod with a supporting shoe and pad while it was treated because of the extensive damage done by the disease to the frog, sole and hoof wall. No ergot, coronet band or chestnut involvement was reported.

As of this writing, January 2000, the animal is cured.

CASE #3

Case #3 is a Belgian gelding used in the carriage business in California. The horse has four white feet and is a blonde sorrel. He was cared for extremely well. The horse had its feet trimmed regularly, was properly shod, was washed and curried daily, fed very well, and had his feet checked and cleaned daily. At no time was this animal exposed to mud or filthy stalls.

The owner came from her place of business to visit me about the horse when I was teaching classes just before Carlson’s sale at Turlock, California, the first week of November, 1999. If I remember correctly, at the time the diagnosis of canker had been made in all four feet of the horse, but no one knew what to do about it.

She told me the condition came on very fast. She first noticed a problem on the coronet band at the hoof head. The band seemed inflamed, and a white scaly substance was being produced there. She also told me the chestnuts, in her words, “just melted away”. In a phone conversation I had with her later she reported the ergots had also disappeared.

I believe at first they treated the animal for thrush, but soon realized this was not the problem.

Anyway, when I got home I sent her some metronidazole ointment, 2%, and instructed her veterinarian to treat the animal orally with metronidazole or TMS pills or both.

The veterinarian wanted to put her horse down on the premises to cut out the rotten tissue. She refused and instead, put the animal in her stocks, where the operation was done. The rotten, foul smelling tissue was cleaned out of the four feet and the cream applied under a bandage to each foot.

She told me she soon realized the animal’s tissues responded much better if they were bandaged at night and the wraps were off during the day. She actually saw the difference in the healing process. The reason being the organisms thought to be involved in the disease live without oxygen. Bandaging will keep out oxygen. Allowing the areas to oxygenate would in fact help destroy these bacteria.

She told me that she puts the horse in her stocks about every four weeks and removes any dead tissue she finds from the four affected feet.

To date, the end of January 2000, the animal’s front feet are cured, and the owner is still medicating the rears. Treatment did not start on this horse until about November 15, 1999, as I had to get home from California, ship her the medicine and instructions. All told, there were four feet to work on and recovery in two of them in 2–1/2 months.

CASE #4

This is a very interesting case involving a 10 year old Clydesdale gelding, Nickel, which the owner had just purchased. She lives in the state of Washington, just a few miles from the coast. She tells me they have a lot of rain, so consequently their horse is exposed to mud and wet pasture ground.

She also told me that she thought the horse had the problem when she bought it, and her veterinarian diagnosed it as thrush in the left rear foot. This diagnosis was made in March of 1998. The vet checked the horse in July 1998, December 1998 and May 1999. Diagnosis remained unchanged. The owner spent one year treating her Clydesdale for thrush, using many different products. As I understand it, other horse people also believed the animal had thrush.

Debridement of the foot. The canker was removed where the bleeding is visible.

She reported it was so bad that she could run a swab full of formalin down and under the frog, almost, as she stated, “clear through”.

In September, 1999, she found a veterinarian who diagnosed the problem as canker. Again it was occurring in a white hooved, white legged horse. This was on September 17, 1999. At the time the veterinarian and farrier trimmed the necrotic tissue away and left the healthy, but very bloody, corium in place. A biopsy was also taken.

A Nolvasan pack was placed over the foot and “duct taped” into place. This pack was removed on September 20, the area cleaned with soap and water, and a new Nolvasan pack applied.

On September 24, the pack was removed and deep surgical removal of the affected tissue was done. Cultures were made at this time which revealed four types of organisms present. X-rays taken showed no bone involvement. The Nolvasan pack was reapplied.

The Nolvasan packs were changed periodically, and on October 13, the veterinarian inserted a small tube into the pack, so that 60 cc. of a Nolvasan/Domso mixture could be infused daily.

The gelding had been put on SMZ orally in September and on October 2, was placed on oral metronidazole 500 mg.–20–twice a day.

On October 20, the owner called me and said the veterinarian felt the foot was 50% better. I told her to keep up the oral metronidazole, and I would send some 2% ointment of the same drug, which should be applied to the foot daily or every two days.

During this time the rains had arrived in the area, and the horse was sent to a stable where he could be kept dry for 30 days. The salve arrived on November 1 and it was used as the hoof dressing from then on. At that time the veterinarian thought the foot was 90% better.

As of January 2000, the horse is cured. In a recent phone call the owner told me that by Thanksgiving the animal was almost healed and, in her words, “he had a new foot.”

The Clydesdale, Nickel, probably had some extra help in that his owner placed him on “Red Cell”, “Nufoot”, and “Probios”, all products designed to build a stronger, healthier horse. She reported recently that Nickel is more “feisty” now than ever before, and that he has new living quarters, where he can be out of the rain and mud. Nickel was not lame through this ordeal, nor did he have any involvement of the ergots, chestnuts or hoof heads.

CASE #5

This is a very interesting situation concerning a 4 year old Clydesdale filly named Jazz. The owners are Jean and Jerry Lewis of Lewis Clydesdales, 7901 West A, Lincoln, NE 68532.

Cauliflower growth in the photo which looks like dirt, is the canker with its odd growing tissue. This tissue must be cut out.

I almost never use the names of clients or veterinarians when writing or speaking of clinical cases but these people wished me to do so. During their ordeal with Jazz they found that there is a definite lack of knowledge existing on all levels, in regards to canker in the foot of the horse. By using their names and address here they would be available for advice to anyone needing it, in regards to the diagnosis and treatment of canker.

On August 7, 1999, I first saw Jazz and her problem feet. The Lewises had trailered her to Orange City for me to look at her foot problems.

They had been treating all four of her feet for some time for thrush, with no improvement. Everything was getting worse rather than better. So they took her to a veterinary college and the diagnosis there was canker. At that time the clinicians debrided the four feet and told them not to bandage them, but to treat them daily with a topical application of a formalin product.

After a week the feet were all worse, and I got to see the animal. The frogs and heel areas were involved in all four feet. Mr. Lewis was removing any necrotic material he could find.

Upon close examination I noticed the area about the coronary bands seemed thicker than usual and had a heavy white accumulation of scaly material. When it was removed the area underneath appeared bloody. All of the ergots and chestnuts were missing. In their place were very red, almost bloody, stumps.

I recommended that they bandage the feet with a 2% florfenicol water-soluble ointment and change the bandage every day or two. I advised them to remove any separating tissue, and to stable Jazz in clean, dry quarters. I also placed the filly on a parenteral dose regimen of the same drug. This had worked well for me on two previous cases.

I informed them if this treatment did not work we would go to a 2% metronidazole cream and the same drug orally.

The florfenicol parenterally did not agree with Jazz causing her to go off feed and have a severe diarrhea. I got the diarrhea stopped and got her back on feed, keeping the same ointment on her feet. Jerry and Jean and I conversed over the phone many times until I examined the filly again on October 1. At that time I could see she needed extensive surgical debridement of all four feet, so arrangements were made to take her to the Veterinary Teaching Hospital at Fort Collins, Colorado.

All told, she was taken there a total of four times: October 5, November 17, December 16 and in January, 2000.

On the first visit all four feet were surgically debrided and all of the diseased tissue removed to the healthy corium. She was put down for this operation and a laser was also used in the surgery. She was placed on a regimen of 2% TMS tablets orally twice daily and one tablet of Butazalodine daily for seven days.

Bandages were changed every three days and the feet cleaned with Betadine before repacking with metronidazole 2% cream. Jazz was fed an all grass hay diet and bedded with straw to minimize any potential auto-immune factor.

At that time the coronary bands were much better, but still “bumpy”.

During the following three visits to the clinic at Colorado State University the mare’s feet were nerve-blocked and some surgical debridement of the feet was undertaken.

After the second trip it was decided not to bandage the feet, but to keep Jazz in a very clean stall and spray an iodine solution on the affected feet daily. This solution was strong tincture of iodine diluted with equal parts of water. This would be about a 3 1/2 % solution of iodine. Also at that time, drugs were given to activate her immune system and her diet was augmented with a hoof supplement.

On the third visit oral metronidazole was reinstated. The dose was 60 tablets orally, twice daily, for 21 days. If Jazz went off feed, this drug was to be stopped. The right rear foot was to be rewrapped with the metronidazole cream every three days and the left rear was to stay unbandaged. The iodine solution was to be used every other day lightly about the heel area.

The farrier came every two weeks to keep the area around the frogs cleaned.

On Jazz’s last visit to the Veterinary Teaching Hospital at Fort Collins on January 19, 2000, the medication to be applied to all four feet was changed to a Nolvasan solution diluted 1:2, and to be applied to all four feet twice a day with a spray bottle. Her feet are to be kept as clean as possible and the affected areas are to be debrided every two weeks, if need be.

Incidentally, the coronary bands have “cleaned up” and appear to be normal again. And through all of this, Jazz was never lame.

The Lewises report that Jazz’s feet look very well at this time and they expect a complete cure in a short while.

By the way, if anyone wants to know how to bandage a horse’s foot using baby diapers, duct tape and elastic bandages, I’m sure either Jean or Jerry Lewis can tell you how it’s done!

What have you learned about equine canker, and what questions about it should linger in your mind? A review is in order.

1) Equine canker is a strange disease or condition of the foot, primarily of draft horses, which is not readily recognized by horse owners, veterinarians or farriers when it occurs. It is often confused with thrush. Its cause is unknown and although wet conditions do not cause the problem, moisture in the form of muddy premises, wet pastures or filthy stalls exacerbate it.

2) The condition most often shows up in white hooves with attending white legs, as many old-timers have stated.

3) These afflicted horses are rarely lame, even after drastic surgery is performed on their feet to remove the affected flesh.

4) What role does stress play as a causative or supportive agent in the canker story?

5) As to the cause of canker, the five clinical cases bring up some very interesting observations. Is the cause an anaerobic bacteria or an immune reaction by the body of the horse which somehow involves the corium cells which produce the horn and growth of the hoof, frog, chestnut and ergot?

Remember the two horses with the condition in all four feet? Why did their ergots and chestnuts become involved, and also the coronary bands? Was it bacteria in the blood that caused the problem with the corium in these structures or was it some auto-immune reaction of the body which affected the horn-producing cells of these structures and the frog? If it was a bacteria or some infectious agent which circulated in the blood, why does the condition stay limited to one or two feet and not involve the chestnuts, ergots or coronary bands even on the affected leg or foot?

6) On the positive side you can now understand that we can employ several good drugs to aid in the healing of canker. From the case reports, you can become acquainted with the facts and realize there are several different ways to treat this situation with success, even by using so-called “old time remedies”.

7) Most important from the draft horse owner’s standpoint, it should be apparent that if a case of suspected thrush is vigorously treated without recovery in a relatively short time frame, one should be thinking about the possibility of canker. The thought should always be in your mind.

I wish to thank the owners of the horses involved in the five cases of canker discussed in this article for their cooperation in reporting the data, as well as for pictures needed to accurately report the progress and outcome of their individual horses. Each of these owners realized the importance of getting the correct facts out in the form of this article to educate other draft horse owners about equine canker. I sincerely hope my pen has done justice to them in passing this knowledge on to you.

Thank you again to every one of you who have contributed information to me about the strange subject of canker.