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Is it just lameness?

Does your horse have a problem with lameness? Does its hoof show chronicle signs of being fractured and poor looking, with the hoof wall actually peeling away? The cause could be a condition commonly known as white line disease (WLD).

WLD had been thought to be caused by the presence of a fungus that exists in dirt. However, research has now determined that it is caused by at least two different types of opportunistic 

microorganisms that exist in a symbiotic relationship. Together they produce enzymes and exotoxins that break down the protein and collagen of the hoof wall. This dynamic colony of microorganisms consists of at least one type of destructive bacteria and at least one fungus.
Since it is not caused by a single organism, WLD may appear different from horse to horse and even from hoof to hoof, depending on the particular makeup of the colony of microorganisms present. For example, if there is a very aggressive fungus present mixed in with a virulent bacterium, a fast-growing, hard-to-treat case will result. Conversely, if a slow-growing, less invasive fungus is paired with a more benign bacterium, this case can be treated more easily. There may be two or more destructive bacteria or fungi present in the same hoof. An infinite number of combinations can result. This explains why a certain treatment may work effectively in one case and fail miserably on the next. To add another variable to the mix, these colonies are dynamic and grow faster when the environment is wet and warm, and slower when it is cold and dry.

In WLD, bacteria and fungi live within the confines of the hoof wall in a symbiotic relationship. That is, they can live independently, but mutually benefit by each other’s presence. Each organism breaks down the hoof in a different manner while providing metabolites for the other. The fungi can be heterotrophs, obtaining their food from nonliving organic matter, or saprophytes, feeding as parasites on living hosts. They become deeply imbedded within the hoof wall and send out threadlike filaments called hyphae that absorb nutrients much like roots of a plant. The bacterium reproduces more quickly by dividing, but the fungus can produce spores that makes it harder to kill. Treating for bacteria or fungus alone is useless because when one is eliminated, the other will continue to grow unabated. You must control both at the same time.

The disease process occurs secondary to a primary hoof problem such as laminitis, abnormal hoof conformation, hoof imbalance or any other condition that causes a hoof wall separation due to the fact that these microorganisms are opportunistic in nature. That is, they ordinarily will not attack perfectly healthy hoof tissue but will enter into a small crack, nail hole, or fissure at the white line of the hoof. These problems commonly occur at the stratum medium because this is where the horny laminae interlocks with the sensitive laminae. There is a rich blood supply here, and wherever blood is present in nature, there is a possibility of infection. 

Obviously a quick is an open invitation for infection. Even subclinical cases of laminitis, although not severe enough to cause lameness, could result in small tears at the stratum medium. Even bruising this area can lead to problems. Any trace of dried blood from the bruise makes a perfect nutrient for growth of these microorganisms. Shod animals typically develop a worse case, as the nail holes provide an entrance, while the shoe caps the foot and provides an excellent environment in which the fungus can thrive.

Although unsightly, this disease does not usually cause lameness. However, if the hoof wall chips so that the horse is walking on his sole the owner will probably notice tenderness. Problems will also arise if the cracking and chipping extend up to and involves the coronet band. Be suspicious of any injury in the area of the white line, however minor. A single horse may show signs in one, two, three or four hooves; in a herd, any number of horses may exhibit the characteristic chips and cracks. Horses that previously had strong healthy hooves can show signs of infection, as well as those who have had problems with hoof quality in the past.

The condition usually initiates in the quarters of the hoof and works forward to the toe area. In its early stages, WLD usually evidences in the quarters of the hoof, generally appearing as a white, gray or black crumbly area, with a consistency similar to grated Parmesan cheese. Externally, the hoof will occasionally show signs of stress and breakage, and it will often become challenging to keep shoes attached even when the nails have been appropriately started in the white line of the hoof. 

At this stage, WLD can often be arrested through good maintenance practices: keeping the hoof balanced, clean and dry; encouraging circulation through turn-out and exercise; and applying appropriate medications. Although applying an affixed pad is occasionally suggested at this point, traditional approaches usually prove counter-productive in this situation since WLD thrives in an anaerobic (dark, wet, airless) environment.

In its more advanced stages, WLD will actually undermine the hoof capsule. Often, a visual inspection of the outer wall and ground surface of an affected hoof will reveal no apparent abnormalities; a cavity may not be visible until the hoof is trimmed. Even then, it may appear as only a small opening, but it will often open into a large area, revealing that much of the hoof capsule has been undermined and compromised. Once the condition reaches this point, it’s more than the nuisance of nasty looking, shelly walls and shoes that are difficult to keep on. At this stage, there’s a potential for intermittent lameness and, worse, a potential for remodeling of unsupported internal structures.

It is best to treat WLD aggressively and early. The best way to treat WLD is first to recognize it early and then treat it with a product that is a broad-spectrum bactericide as well as a fungicide. You must remember that dry, cool conditions are your ally and that warm, wet ones are your enemy. 

Because some of the different organisms present are capable of producing spores, you must choose a product that is powerful and stays active for a long time. It takes time and patience to treat these infections once they gain a foothold. Even if you don’t kill all the organisms initially, you may kill enough of them to slow the advancement of the disease to the point that it may grow out with successive trimmings. Remember that it takes a full year for the hoof to grow down, as it begins at the coronet band, so it will take time to evaluate the results of the treatment.

Prevention is the best form of protection. Good quality hooves are an inherited trait but a bad diet and poor management can ruin even the best foot. Top of the list in hoof care is diet. Horses need adequate protein and trace minerals to build a healthy foot. The quality of the protein is critical because certain amino acids such as methionine are especially important. 

Simply feeding a high protein feed does not guarantee the correct balance of amino acids and, in fact, excessive protein in the diet can damage the feet. If the diet is higher in protein that what is needed the extra protein is excreted in the urine. A horse on too high a protein diet will urinate more causing a wet stall and the ammonia in the urine is caustic to the hooves. 

Trace minerals such as sulfur are also important for hoof quality. These trace minerals must come in a form that is digestible for the horse. Most free choice mineral blocks or powders are designed for cattle not horses. Also some minerals are more expensive than others, so most formulated supplements have more of the cheap minerals and less of the expensive ones. This can throw the horses’ mineral balance off creating deficiencies even with adequate intake. There are numerous supplements on the market which claim to improve hoof quality. 

If your horse is on a good whole grain diet and a good supplement but still has bad feet you may want to add a probiotic. Biotin is a vitamin that is essential for healthy hooves. The beneficial bacteria in the horse’s large intestine produce this vitamin for the horse. If your horse is stressed or, for whatever reason, does not have good bacteria, he will be deficient in biotin. It is much better to maintain healthy bacteria than to try and supplement single nutrients. If your horse still has bad feet despite good feed, it is necessary to look at his assimilation of nutrients. The best way to address this is through homeopathy. 

Homeopathy will improve your horse’s digestion by bringing his whole system back into 

balance. Excessive vaccination has been found to be one of the most common causes of poor assimilation of nutrients.

Hooves are easiest to maintain under dry conditions as it is easier to add moisture to the foot than take it away. Repeated wet and dry cycles are the hardest on the hoof. Try to keep your horses feet as dry as possible and if that is not possible, keep the foot as clean as possible. A soft foot is more prone to infection from bacteria and fungus in contaminated bedding.



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Date Last Updated January, 2006