White Line Disease Concerns: Letter To The Editor

There has not been enough room to publish some of the longer letters to the Editor in the print issue of The Horse, therefore we will be placing some of them online in the news section. This letter makes reference to an article which can be viewed at http://www.thehorse.com/ViewArticle.aspx?ID=248

White Line Disease Concerns

I enjoyed Dr. Ball's article on problem feet--

I have written a condensation of his article and a very personal experience with the disease for our local newsletter. A copy of which I am enclosing.

Incidently, Mucor can be a fatal human pathogen in humans with a compromised immune system as I had a diabetic patient die from Mucor. (Comments are welcome.)

Sincerely, R.T. McDonald, MD

(enclosed article) White Line Disease

What Is It and What Can We Do About it?

Until about three years ago, I had never heard the term "White Line Disease" [WLD]. I'm sure our horses had it but it was never enough of a problem to even hang a name on it. I had noticed that certain horses, where they should have had a nice white line between the hoof wall and the sole, had a cleft filled with dirt. When you dug this out, you got down to the white line. Instead of being firm and white it was an off-color gray and crumbly. Now I know this is mild white line disease. Since then I have observed dissolution of the white line of over an inch in depth. When it is of this severity, it can cause the horse to become unsound and unusable. Whenever I asked veterinarians about the causative agent, they replied, "some bacterial fungus" and that was about as far as it went. Finally, in the January issue of The Horse, Michael A. Ball, DVM, has published a nice article on problem feet where he has fairly conclusively shown that the causative agent is a fungus. What his group did after sterilizing the hoof wall of an individual suspected of having WLD using sterile techniques, drilled a hole through to the white line and cultured this area. In all the control horses there was no growth. In the horses suspected of WLD, all cultured a fungus, but none cultured bacteria. They isolated Trichoderma, Mucor, Aspergillus, and Gliocladium. [Don't be turned off by the big names, all they are talking about is a fungus like the one that causes Athlete's Foot.] At last we have a name for the causative agents. All these incriminated fungi are common soil inhabitants and none are thought to be able to cause primary disease. Translation: they act in conjunction with some other condition such as poor hoof hygiene or poor nutrition.

How can we treat it? First off, we need to be sure that the affected horse is receiving an adequate diet to sustain normal hoof growth. Since that is probably impossible to ascertain, the simplest thing to do is to start feeding one of the commercially available supplements. If the horse is unshod, his hooves should be cleaned meticulously, all of the clefts scraped out to the bottom with a pointed object. [An unused horseshoe nail works for me]. After all the debris is removed, the cleft can be saturated with an antifungal agent such as 7% iodine, clorox, mercurochrome, or Coppertox. All of these agents seem to work. I prefer iodine. Betadine doesn't seem to work for some reason. The treatments have to be carried out until the cleft has been obliterated and the white line is flush with the hoof wall. Generally what happens is you stop the invasion of the fungus and the hoof grows out and eventually you have a healthy white line. Efforts that stimulate the coronary band and make the hoof grow faster are probably also worthwhile.

When you have a shod horse the problem is much more comoplicated ecause of lack of access to the diseased portion of the hoof Before the shoe is applied, the bottom of the hoof should be drenched with iodine and maintained in this position for several minutes so the iodine has a chance to penetrate into the diseased area. If there is a large cleft, cotton can be rolled up and packed into the cavity and saturated with iodine. The shoe is then nailed in place over the cotton. A small triangular opening can be made in the hoof wall at the junction of the hoof and shoe so daily applications of iodine can be made through the opening, resaturating the cotton and carrying the iodine into the depths of the cleft. This method has proved successful and avoids removal of large portions of the hoof wall, as has been previously done. The shoe should be replaced after three or four weeks to check and make sure that the treatment is working. The process is repeated as often as necessary until a cure is affected. If you are not able to control the program, you may have to leave the shoe off so you can directly treat the lesion until you can gain control.

There are a number of systemic fungicides that can be considered such as miconazole, but I have never had to resort to these agents.

R.T. McDonald, MD
Camp Verde, Arizona
