The horse hoof ailment white-line disease has become a bit of a hoof disease du jour and has led to a near epidemic of intensive hoof treatments/soaks, ranging from a few days a week to several times a day. More often than not the treatment doesn't have the desired effect on this horse hoof ailment, and there's a good reason why: The horse didn't have the equine hoof problem of white-line disease in the first place.
The layers of the hoof wall, from outside working in, are the pigmented horn, nonpigmented horn, the white line then the sole. The white line contains the live/sensitive laminae and the dead/insensitive laminae along the inner layer of the nonpigmented horn. Once the hoof wall has grown past the level of the live sole tissue, all laminae in the white line are dead, just like white tips of our finger nails.
The term "white-line disease" refers to a specific condition where an infection has invaded the tissues of the white line and is causing destruction of the tissue that extends for variable distances up past the live tissue level. It may often begin as a crumbling of the stratum medium. At that stage it isn't painful, but it soon begins to weaken and stretch the white line as the hoof wall flares away. Then, it hurts.
The things that distinguish white-line disease from other conditions along the white line are:
1) There are no other underlying conditions, such as an abscess.
2) There is active infection.
3) The loss of white-line tissue extends well into the live tissue of the white line.
White-line disease is often misdiagnosed when there's crumbling of the white line and chipping or cracks. However, the white-line crumbling stops at the live tissues. The most common cause of this is going too long between trims. As the hoof wall grows away from the coffin bone, it puts more traction on the white line, causing it to crack and crumble.
Dietary deficiencies or imbalances (see May 2009) also lead to poor integrity and crumbling of the white line. Laminitis weakens the laminar connections, making the wall more likely to tear the white line. A hoof-wall abscess or keratoma will also cause the white line to spread.
BottomLine. True white-line disease can be determined by probing how deeply the crumbling tissue extends. When in the stratum medium stage, the loss of horn will extend above the sole and the hoof wall sounds hollow on tapping. White-line crumbling extends into sensitive tissue. Many different types of bacteria and fungi have been cultured, often working together to cause the destruction.
This isn't a do-it-yourself problem. You need to work with your vet and farrier. Treatment involves removing the hoof wall overlying the infected tissue to expose it to light and air. The exposed area is treated daily or several times a day, usually for two to three weeks.
A bar shoe may be needed to hold the hoof. Acrylic hoof patching material may be used, however, it's controversial due to the risk of trapping organisms under the patch.