| Your One-Stop Farrier and Hoofcare Portal - Hoof Pathology Wed, 22 Nov 2017 09:12:27 +0000 Joomla! - Open Source Content Management en-gb Hoof Wall Separations

I'd like to know exactly what causes hoof wall separations. I can delineate the obvious, the same factors sometimes cause cracks in the hoof wall: poor farriery, genetics, imbalance, mechanical pressure, failure to maintain moisture equilibrium, trauma, and pathology. But, what triggers the phenomenon?

Why is it that two horses standing side-by-side, full siblings and indistinguishable in most all respects, often have feet so different from one another that they might as well belong to horses from different planets? ¿Quién sabe?

We do know a little about how hoof wall separations are formed after whatever triggering mechanism has occurred.

The horny covering of the horse's hoof capsule we call "hoof wall" is anatomically analogous to a human's middle fingernail. The hoof wall consists of three main layers, the stratum externum, the stratum medium and the stratum internum. Technically, the hoof wall consists of parallel strands of keratinized epithelial cells that arise on the coronary corium of the coronary band. The hoof wall has no nerves or blood vessels. Put another way, the hoof wall is a modified hair.

The stratum externum is the outermost layer and serves mainly to help maintain moisture equilibrium within the inner layers of the wall by retaining moisture. Most of this layer is routinely rasped off in show horses, worn off in horses at liberty, seemingly without ill effect.

The middle layer of hoof wall, the stratum medium, forms the bulk of the wall. It plays an important role in the way the horse disperses shock and in the horse's blood circulation.

The innermost layer of wall is called the stratum internum. This structure provides the means, laminae, by which the coffin bone is attached to the hoof capsule.

For whatever of the reasons mentioned, and goodness knows how many others, the rows of parallel epithelial cells in the stratum medium sometime part company. This phenomenon is called a "wall separation." Wall separations can have far- reaching consequences and, if not addressed on a timely basis, can compromise the hoof's ability to function normally. Wall separations can and do occur in both shod and unshod horses, but are more often found in barefoot horses. The most insidious part about wall separations is that they very seldom get better without mechanical treatment because, once begun, their growth is accelerated by mechanical means. Once started, the separation, however tiny, fills with dirt, rocks, ****** matter, etc. Whatever the material filling the crack, when the foot is weighted ("loaded"), the material exerts mechanical pressure on the strands of keratinized epithelial cells forming the wall, which causes more tearing, allowing more dirt, rocks, ****** matter, etc., to enter the crack, causing more mechanical pressure, ad nauseam.

In addition to becoming somewhat of a self-perpetuating phenomenon, wall separations create the anaerobic conditions conducive to the growth and proliferation of the pathogens responsible for the pathology sometimes called "White Line Disease." Actually, this pathology does not affect the white line, it affects only the stratum medium of the hoof wall, and is much more accurately described as "Hoof Wall Disease." HWD is epidemic on the Texas Gulf.

Wall separations are most often successfully treated mechanically by unloading the affected area. "Unloading", translated from farrierspeak, means that the affected portion of the hoof wall is not allowed to bear weight ("load") when the wall bears weight (is "loaded").

How is this accomplished?

One unloads a portion of the hoof wall by cutting it away until that portion of the hoof wall affected is no longer an integral portion of the perimeter of the ground surface of the hoof. In other words, hoof separations are treated by stopping their tendency to self-perpetuation by negating the mechanical forces which separate the strands of epithelial cells and push them outward.

The extent of this cutting away, or debridement, is governed by the following axiom: "New growth follows old." Unless all the aberrant growth is removed, all new growth will follow the old; therefore, the wall must be removed to a point above the separation or the treatment will be unsuccessful. If known, the original cause of the separation is not addressed until after mechanical treatment is initiated. Most often, the affected hoof is shod in order to better distribute the stresses normally taken by the portion of the wall debrided and, in the case of extensive debridement, to maintain the structural integrity of the hoof capsule. In the case of small separations, especially at the quarters, the foot is sometimes left bare after debridement.

At times, the separation is so extensive that the affected area of the wall cannot be debrided without compromising the function of the hoof capsule and the procedure must be done in stages, with the most affected portion of the wall usually debrided first.

Tom Stovall is an American Farriers Association Certified Journeyman Farrier since 1983, a Member of the Texas Professional Farriers Association, and a Member of the Artists-Blacksmiths Association of North America. Thanks to him for his permission to post this article.

]]> (Tom Stovall, CJF) Hoof Pathology Thu, 28 May 2009 07:06:40 +0000
Hoof Wall Disease Update

This article does not recommend the application of any of the techniques or preparations discussed here. This is merely a report on a research project involving a problem that has reached epidemic proportions in some areas. The disease could become life threatening to a number of equines without a massive research and education effort. Before you try any non-conventional treatment, consult a veterinarian who is knowledgeable on this disease.

We've now heard about 16 different names which are supposed to be scientifically correct for this problem . Every time we think we have it, the research points to another direction. I've finally decided to just call it "hoof wall disease".

About half of most research (including mine) is verifiable facts and data. The other half usually consists of "SWAGs" (scientific wild ass guesses). In the case of hoof wall disease, it's probably more of the latter, due to the relatively little research that has been done.

At this point, it might be time to take a look at our adversary and some of the myths that have surrounded the disease. During my research on hoof disease, I've heard and read a number of statements regarding the problem. Of course, some of them are true, but a number are pure myth. Some of the myths are the result of innocent misinformation or "old wives tales." Incidentally, the term "old wives" is no longer valid. The politically correct term today is "aging spousal units". Some of the misinformation is perpetrated and perpetuated for the purpose of selling products which may or may not help treat the condition.

It's important to know something about your opponent, whether it's a game, business, war or, in this case, a biological battle. It isn't necessary to know the names of each soldier, but it's important to know how they work, reproduce and where their strengths and weaknesses are. This is why I haven't spent a lot of time trying to identify individual species. Not only am I not trained to do this, but, I'm leery of cultured results taken from equine hooves. If you look for fungus, you'll find fungus. If you culture using a medium that favors bacterial growth, that's what you'll find. There has been some work done in identifying the supposed culprit here (Chapman, et al). They feel it is the same organism responsible for nail disease in 20 million Americans. If that is the case, we may not be dealing with a fungus at all.

Dr. Richard Sher, Professor of Dermatology at Columbia University says that fungal infections (human) of the nails are uncommon. In the vast majority of cases it is a bacterium which is responsible. Pseudomonas is the offender most of the time. Having said that, I will still refer to the organism as fungus, but the control measures I've used are also effective against bacteria, including pseudomonas.

There are literally hundreds of thousands of different fungi in the world. They range in size from microscopic one celled organisms to the earth's largest living things. A single individual fungus recently discovered in Michigan was measured in acres. The identified fungi associated with hoof problems seem to be of the class oomycetes. These organisms reproduce using spores and, as many other fungi, can generate a new individual from a small shred of itself. Spores are the most difficult phase of a fungus to control; followed closely by mature dormant individuals. Growing fungi are the easiest phase of the organism to kill. This is one reason that laboratory inhibition tests are sometimes inconclusive. In controlling a biological organism, it is important to realize that some individual cells or fungal units are dying while others are being created through various means of reproduction. These might include ******, a******, cell division or regeneration. Some of the organisms we are dealing with are capable of at least three.

What is important is that we can never kill all of them. What we must do to maintain a controlled situation is to effect a negative growth to death ratio. That is for more to be dying than are being produced. The speaker at a I attended in Florida was adamant that a (fungi) static situation be maintained. That would mean equal numbers dying to those being produced. I would strongly disagree with that position. To begin with, it is an extremely difficult balancing act and would be virtually impossible to maintain. But, more importantly, I want to be way ahead of the curve in this disease. An organism is eating away the hooves of that mule or horse and threatening his very existence. We need to do everything possible to (safely) eliminate the fungus.

Among the more common myths surrounding this problem is the belief that exposure to oxygen kills the fungus. This is incorrect. Virtually all fungi are aerobic organisms. This means they require oxygen to thrive. Exposure to air seemed to help in my earlier work, but, it appears to be the drying action rather than the presence of oxygen which affected the disease. When you think about the fact that this group of fungi inhabit the soil on or near the surface, it stands to reason that they would not be killed by exposure to the air. They are also instrumental in the breakdown of organic matter into basic elements. Consequently, there may be from one thousand to several hundred thousand individuals in a pinch of soil.

Some other fallacies include: "This is a very contagious disease and people can get it too." Chances are, if you are going to get Onychomycosis, you probably already have it. I've even heard of people wearing masks and rubber gloves while working on infected feet. If you are working on a farm, it probably does little good to clean tools between animals. Virtually every step the horse takes exposes it to the fungi which inhabit the soil. It wouldn't hurt for a farrier to clean up between farms; especially if the next farm doesn't have a problem with fungus. Some of the fungi identified are always present on human skin.

I had gone to the aforementioned Farriers "seminar" in Florida hoping to get some helpful information. Unfortunately, it turned out to be a pseudo-scientific sales pitch for several products the speaker was representing and touting as effective against the disease. One statement that he made which I had heard before was that we have destroyed our animals' immune systems with fly sprays and wormers. While not specifically expressed, it was implied that ivermectin was a prime culprit. I guess the scientific term for this would be "hogwash". Why are the equines with the reputation for vigor, mules, the most frequent victims of this fungus? Why do animals who have never been fly sprayed and are rarely wormed just as susceptible? This includes mustangs fresh off the range as well as burros with "iron" feet. Horses and mules that have never had a sick day in their lives have this problem as often as any. If their immune systems were depressed, logically, they would also be susceptible to other ailments such as viral infections. This does not appear to be the case.

Ivermectin is probably the least invasive to the equine "system" of any anthelmic we've ever had. It works on the motor neurons of worms, as I understand it. Huge overdoses had no adverse affects on the horse's system in extensive testing.

Another point made to justify the "antifungal" feed supplement was that feedlot cattle don't have this problem. I would like to see an impartial study of that conclusion which the speaker attributed to the practice of mixing choline and iodine in the cattle's feed. In looking over the content of the supplement being promoted, I noted that it contained 20 milligrams per pound of iodine. If you look at almost any equine supplement, including those being fed to horses with hoof problems, you'll probably find those ingredients. The one I use, SHO-GLO by Manna Pro, has over 3 times the iodine (4.6 MG/Oz) and choline. As far as I can tell, it hasn't helped my animals feet. I have given it to brood mares and weanlings as well as those in training, while the remainder of the mules and horses get no supplement. They all share in the foot fungus problem equally. The point was made that chlorine (bleach) inflames the problem. Knowing that bleach is a biocide which is used in swimming pools among other applications should lead you to discredit this myth. While I didn't find it particularly effective, it certainly did not aggravate the problem. I also know of at least one severe case in a mule which was brought under control by conscientious applications of bleach and iodine (alternating). There has also been a belief that this condition is a malady only suffered by stalled horses. While those kept in stalls may have a slightly higher incidence and severity of the disease, pastured animals also very susceptible.

Another suggestion has been made to "go back to liming the pastures". The problem here is that, to raise the pH enough to effect a kill of the organism similar to stall liming, you would need to raise it above 9 or 10. It would require around 2400 pounds of lime per acre (depending on the soil) and, unfortunately, the grass would also be killed.

So what has all this research brought out so far?

  1. This fungus can be controlled by a number of microbicides if they are applied to it.
  2. We will probably never be rid of this problem. Like other parasites, we will simply have to take preventive measures once the disease is under control.
  3. The geographic range has apparently expanded dramatically. I received calls from California to Maryland and the northwest following the publication of the first research report. There was even a letter from a farrier in Ireland.

Enough of the bad news; what about the good?

Some of the new control regimes I'm working with are showing great promise. I've also modified some of the previous ones to make them more effective and/or less toxic.


One of the questions I have been asked is: why don't you just use the products advertised for the disease instead of working with all these chemicals which are hazardous to your health and the environment? Good question. First off, they didn't work. Second, all the chemicals I've used, with a couple early exceptions, can be handled safely if precautions are taken. I would not use any chemical which I felt would harm the environment (or the animal). Many of the products I tried are used routinely for microbiological control and are registered with the EPA for that pur pose. Others are used in foods and cosmetics (at much lower dosages). Mercury based compounds are being phased out by regulatory agencies in their infinite wisdom. Formaldehyde is used in a variety of products we use every day. Of course many of these chemicals are hazardous. What isn't these days? I guess the bottom line is, that the animal is suffering from a malady that is threatening it's life and, the first order of business is to get control. If any of the products sold for the purpose of solving this problem had worked, you would not be reading this now and I would never have begun this project. Some of the store remedies appear to be thrush preparations which have been relabeled, but not necessarily developed for hoof wall disease. A number of the people who have called in response to the first article had the same luck with OTC products I had. Some of them were owners or farriers at the end of their rope trying to find some relief. I have offered to share my data with one well known company which contacted me and is interested in developing and marketing an effective product. I believe we need to get the universities and other well equipped institutions involved with this effort. I will also share what I've learned with any other reputable company that's interested. We all need to help find a cure that is available to the public to stop this disease or, at least, control it.

I don't like to test anything that I don't know the ingredients of. I generally don't trust them. However, the Sav-A-Hoof line of products is promoted specifically for the hoof fungus problem. The people who make it wouldn't tell me what is in the product but I think I have a pretty good idea after talking with them and some veterinary pharmacologists. My skepticism (in not trusting a company that won't give out the ingredients of their product) lies in the fact that anyone with the capability of duplicating it for sale on the market is also capable of analyzing it for the ingredients. The secrecy must, therefore, mean they have something to hide from the user. I am even more leery when the price for these products is very high. After reading their Material Safety Data Sheets (MSDS) and talking with their employees and reps concerning the other uses of the active ingredient (Methedyne B), I can guess at the ingredients. I would bet that the liquid Sav-A-Hoof contains about 3% chlorhexidine along with 70% isopropyl alcohol and a little brown dye.

Methedyne B is not found in any veterinary pharmaceutical abstracts or chemical abstracts. It appears to be a name coined by the makers of the product. They did say that it was used to treat gingivitis. The primary antiseptic used for that purpose is chlorhexidine gluconate. I found it to be somewhat useful in my tests but it was not quite as effective as strong iodine (7% tincture). I feel that it would also require more frequent application than iodine. The "gel" product probably contains some glycerin (from the texture) and a thickener which helps it to remain in place longer.

One problem with these products is cost. They are quite expensive. Another drawback of chlorhexidine is that it's not sporicidal. Some solutions of chlorhexidine have even been contaminated with pseudomonas bacteria. It is very important that some phase of any control program contain a sporicidal microbicide. If you want to try a hlorhexidine\glycerine treatment, buy some Nolvasan Teat Dip Concentrate (4% chlorhexidine) and use it full strength or cut it with 1 part alcohol to 3 parts Nolvasan. This will give you a 3% solution which has been used successfully as part of an overall control program. I prefer to use it as a preventive measureby painting it on the bottom of the hoof once a week or more. The glycerine seems to "wick" up into the hoof fibers and bond with them while keeping the biocide in place. This is about one fourth the cost of the other product and seems to work as well. A pint of Nolvasan runs about 10 bucks at the discount vet supply houses.


After trying about every known microbicide that was reasonably safe, I believe that this may be the very best weapon against hoof disease. It is fungicidal, bactericidal, sporicidal, viricidal etc, etc.. It does not contain or release formaldehyde although it is a member of the same family (alde hydes or alkylating agents). Of course, getting the treatment to the root of the organism is a major part of it and we'll get to that in a moment. Some of the early successful remedies included formaldehyde. They actually contained formalin: an aqueous solution of @ 40%formaldehyde, which is a gas. The major problem with formalin is it's toxicity. It is also a suspected carcinogen. Glutaraldehyde is about four times more effective (depending on the organism) than formaldehyde, and relatively less toxic. It will kill fungi and bacteria in all phases of their life cycle. The efficacy can also be changed along with it's active life by simply adjusting the pH.

I've been using different solutions up to 5% in alcohol, but, a 2% solution is probably fine. Glutaraldehyde is a widely used disinfectant which is found in hospitals and industrial locations. It is often used to sterilize equipment which cannot be autoclaved (heat sterilized). In it's pure form, it is an oil which is readily soluble in water or alcohol. You might be able to talk your veterinary or hospital supply house out of some. This product is also used in cosmetics and packaging for various products as a preservative. One of it's strong points is effectiveness at very low levels and in the presence of extraneous organic matter.

The best biocide in the world does little good if it doesn't reach the organism it is being used to control. We need to devise a way to "map out" the extent of involvement on the hoof wall. This is a challenge to you "techies" out there with access to equipment. Perhaps we could put the hoof in cold water and then take a thermographic picture of it. There may be some way to use radiology or ultrasound to find the point at which the fungus has invaded the wall without cutting away the horn of the hoof. I would not allow the entire wall of my animal's hoof to be removed except as a last resort to save it's life. I've heard horror stories of horses having to be destroyed as a result of infection or irreversible damage to the foot structures. I have also seen horses which have been extensively debrided of hoof wall that could barely walk. At best the animal will be unusable for up to a year or more. I try to clean out the area between the hoof wall and the foot as well as possible with a small flat spoon or pointed tool. After applying the biocide into the cavity, I hold the foot upside down for a minute or so to allow as much gravity penetration as possible. If we know where the fungus is, we should be able to go in through the outside of the wall at the highest point of involvement and inject biocide through a series of small holes which could then be closed with Keratex putty.

I have done this after probing to find the depth of the affected tissue but I didn't feel comfortable in my location of the hole(s) as being the true upper level. Unless you're experienced at drilling a hoof wall, it is important that you never use an electric drill. The tissue will pull the drill bit deep into the foot and you are in deep trouble at that point. If you decide to try this, do it with a veterinarian handy and turn the bit with your hand. You can epoxy a 5/32" bit into a 2" piece of broom handle. This size bit provides a press fit for a standard Luer slip syringe tip. Be careful to only go through the outer hoof wall. You may have to clean the area inside the hole with a dental pick to make room for the biocide. After you inject the solution, plug the holes with Keratex. You can later remove the putty for additional applications.

Moisture is clearly an ally of this disease. You should try to keep the feet as dry as possible during treatment.


Wouldn't it be nice if we could just paint the stuff on the hoof, confident that it would slip in through the fibers and hunt down the little varmints and kill them? One preparation claims the ability to do this. It didn't work for me and I would question the claim. This goes back to ole Grampa's advice... "If it sounds too good to be true, it more'n likely is." I have been looking at some penetrants which might be able to do something akin to the opening sentence of this para graph. There is a family of gaseous sterilants which can penetrate through bundles of cloth, paper and even some plastics. They are used for various sterilizing tasks and are sporicidal. Ethylene Oxide is one of these disinfectants and is used for sterilizing instruments which are packaged. It is also used for sterilizing some food products. This could probably penetrate the hoof wall and neutralize the organism within it if a delivery system could be devised. A problem here is stability. This stuff is very combustible and forms a gas (boils) at 51 degrees F.

If a device could be designed to seal the hoof while this gas is placed around it under pressure for half an hour or so, we may have another weapon to use in our fight. Currently, I'm working with a member of the same family called propylene oxide which is relatively more stable (but still very hazardous). This chemical has a boiling point of 93 Degrees F and does not have the penetrating power of ethylene oxide. I do believe that it will penetrate much better than any of the aqueous or alcohol preparations I've used. Because the effects of these are temporary, they would be part of a program. The method for applying it is to wrap the hoof in duct tape or packing tape leaving an access point into the hollowed out hoof wall. There would be cotton in the recess. A couple cc's of propylene oxide (at 32 Deg. F.) would then be placed into the cavity and it would be sealed with tape. The sterilant will quickly form a gas, as it warms, which penetrates the hoof fibers as well (hopefully) as any debris to effect a kill of the organism. The tape could be left on for an hour to overnight. This would be done in extreme cases and before returning to one of the other effective control biocides. Note: a farrier from Seattle had good success with the above technique using 10% formalin solution (overnight).


This is a wide range of microbicides generally referred to as "quats". They are marginally effec tive in a .5% (or even less) solution. I used alcohol to minimize surface tension and help penetrability. These are very cheap to use and can be found at swimming pool supply stores under the chemical name di-methyl ammonium chloride (or very similar). They are not sporicidal and work best against growing fungi and somewhat against mature ones. This chemical affects the permeability of the cell wall, interfering with it's metabolism. Another source for quaternary ammonium is a product for disinfection of poultry areas called Germex. It is available as a 20% solution from Jeffers Vet supply or a number of others. A gallon would probably last a lifetime when it's cut to .5%. It may also be a useful stall spray at the manufacturers recommended dilution ratio.


Strong tincture iodine is still one of the best treatments available. Be sure to use a 7% product which also contains potassium iodide. A pint of this costs about 4 bucks and is a very good preventive as well as a treatment. This chemical belongs to a group called halogens. They have some sporicidal action and also help as a desiccant (drying agent).


This method remains one of the most effective control techniques, although I've modified the solution in recent use. I now add 1/4 cup of citric acid and 2 cups of copper sulfate per gallon of water. You can also use straight vinegar without the citric acid by adding the copper sulfate to it. This bath should be used on each affected foot for about 5 minutes every other day. If all else fails, this should work. A farrier called me after the initial article and suggested that I use a section of inner tube to hold the solution in contact with the foot. He said that he slipped the tube half it's length up the leg and poured in a cup or so of the solution and folded the rest up around the pastern. It can be secured with a vetrap or a single hobble. The horse is then walked around for awhile. The walking action forces the solution up into the affected area. It certainly sounds reasonable to me. I would be sure to keep the pH of your solution around 4 or a little higher with this method since it will come into constant agitated contact with the skin. You can adjust the pH upward with baking soda.


There has been some speculation regarding systemic medication to treat hoof fungus. The preferred treatment regime for human onychomycosis is oral antibiotics. I believe that the equine situation is quite different in that the point of infection is much farther from the vascular tissue (charged with blood) which could deliver the antibiotic to the disease. In humans the fungus inhabits the nail bed which is quite vascular. Two antibiotics are currently favored to treat the human condition: Griseofulvin and Ketoconozole. Both are very expensive. Since they would probably be given based on body weight, the cost for a horse could be astronomical. Emory University in Atlanta is currently conducting research on oral medication for control of nail fungus but, I have no idea which direction they are going.


Once you have the problem under control, how do you prevent it from recurring? There are a number of things you can do. One of the most vulnerable points in the foot is the nail hole. I tried to think of a good way to prevent the invasion of the nail holes by the fungus and the answer was quite simple: copper plated nails. If you grow almost any fungus in a petri dish with a penny in it, you will notice that the fungus will not come close to it. This is called the zone of inhibition. Before you start worrying about where to find copper plated nails in your preferred style and size, I'll tell you. You plate them yourself. It takes about 5 minutes to plate five hundred nails using supplies you can probably find around your shop. Make a solution of 24 ounces of copper sulfate, 6 ounces of sulfuric acid and enough distilled water to make a gallon. Use a plastic bucket and suspend a piece of steel wire screen by a piece copper wire. Suspend another piece of copper bar by a length of copper wire and hook it to a six volt battery positive post. Attach the negative post to the wire on the screen and stick as many of your favorite shoeing nails (new & clean) as you can through the screen and add plating solution to cover both suspended parts. In 2 to 5 minutes you should have a good supply of copper plated nails. Even after removing these nails for reset ting the shoes, enough metallic copper should remain in the holes to inhibit fungal growth until they are trimmed off. Keratex putty which has copper and pine tar will also help keep fungus out of the holes.

All this may seem confusing, and I can't specifically recommend a treatment because of the liability nonsense that has permeated our society. I will, however, list the control programs I tested in order of effectiveness. I've added some strong and weak points associated with them.

  • Glutaraldehyde 2.5% in 70% Isopropyl alcohol: Best overall, poor availability.
  • Copper sulfate bath at pH3: Labor intensive but relatively safe, seems to provide extended inhibition and toughen the hoof wall.
  • Iodine, or Formalin in combination, Iodine oxidizer, formalin requires careful handling.
  • Chlorhexidine based inhibitors and over the counter preparations, Not sporicidal, can be expen sive, easy availability.
  • Quaternary Ammonium Compounds, not sporicidal, inexpensive may be good stall sanitizers.
  • Fumigants, very hazardous and difficult to obtain.
  • There are some other microbicides IE: Isothiazoline, that worked at least as well as the quats but because of similar action and relative unavailability, they are not discussed here.

We still have a long way to go in this war, but I feel that the tide is beginning to turn our way.

]]> (Greg Sefton) Hoof Pathology Thu, 28 May 2009 07:02:44 +0000
Considerations on the Pathogenesis of Cracks in the Hoof Wall

Toe and quarter cracks starting at the coronary band – the more common and clinically important form of cracks - are a direct result of disruption/damage of the coronary band . With such damage, vialis 40mg of course, ****** sale the process of tubular horn formation is interrupted , for sale and a defect appears in the hoof wall as the adjacent, normal coronary band continues to produce new horn tubules. Usually such interruptions of growth are temporary with the crack eventually disappearing as the coronary band is repaired and resumes growing with the hoof growing out.

Direct trauma to the coronary band is a clear example. Such trauma occurs for a variety of reasons: interference by another foot, wire cuts, treading by the same or another horse, etc.

The purpose here is to consider the role of the horseshoe in the pathogenesis of quarter and toe cracks not attributable to such direct trauma.

As the bare foot is loaded the quarter moves outward in a smooth curve as indicated in the drawing. When the horse is shod, the quarter is constrained by the nails and will bend at or near the last nail. This bending can cause tearing and bruising of the laminae along the bend line and at the coronary band. “Crack,” then, is a misnomer. There is, in fact, failure of production of new horn tubules in an area of the coronary band (the area of the asterisk in the drawing), and this appears as a defect in the wall.

A similar mechanism holds for toe cracks. Because of the restraint imposed by the nails and shoe the toe bulges out and forward as shown by the asterisk in the drawing. In this case , the bending is in the opposite sense but still could cause damage as discussed.

An interesting feature of many toe cracks is that, if not too large, they tend to close when the foot is loaded and open when unloaded. This clinical observation has been confirmed by Thomason et al 1992. They showed with strain gauges that there is biaxial compression (two compressive loadings at right angles to each other) of the toe portion of the hoof wall. The major compression is vertical while that at right angles is caused by the circumferential bending of the hoof wall. It is this circumferential bending which tends to close the gap when the foot is loaded. The old literature also indicates that toe cracks were more common in the hind feet of draft horses. One may speculate that the damage could be done when the foot if lifting from the surface with the compressive force concentrated on a decreasing surface area. Even though the total force would be decreasing as the foot lifted off the surface, the force per unit area (the stress) at the toe could be increasing.

Given that the above hypothesis is correct or nearly so, one is faced with an age-old dilemma: why don’t all shod horses crack their hoof walls? It is not possible to answer this question here in a general way. To find an answer one must consider a variety of factors for the individual horse. A few of those factors: genetic (or otherwise) quality of hoof horn, frequency of trimming/shoeing, surfaces upon which horse habitually moves, body weight (more weight=more load=more movement of hoof wall), misplacement of nails, state of hydration of the hoof wall, contracted hoof, etc. The important point is that one can provide a reasonable general pathogenesis applicable in all cases but cannot provide general statements about other, contributing factors. Those can only come with evaluation of the individual horse.


]]> (James Rooney, D.V.M.) Hoof Pathology Tue, 12 May 2009 06:43:23 +0000