White Line Disease: Progression and Identification
White line disease describes the result of an establishment of hoof eating micro-organisms within the hoof wall, usually concurrent with another hoof defect, imbalance or injury where the microbes gain entry. WLD feeds on the intertubular horn which fill the tiny voids between the strands of horn tubules. Affected areas begin as areas of wall/sole seperation. Untreated, these voids fill with the digested hoof material, manure and other debris combine creating ideal conditions for the proliferation of the microbes and more hoof loss
This article attempts help horse caretakers understand and identify white line disease in horses.
Tubular and Intertubular Horn
The hoof wall is composed of countless whisker-like horn tubules. These horn tubules are constantly produced at the coronary band by the horn papillae. Horn tubules provide structure, shape and resistance to vertical compression of the horse above. Intertubular horn is also constantly emerging from the coronary band, but from in the spaces between the horn papillae. Intertubular horn fills the gaps between all of the individual strands of horn providing cohesive stability, resistance to wear, and mass to the hoof wall. Both components are made the same keratinized horn material, but this matrix gives the hoof great strength while remaining flexible.
How White Line Disease Affects the Hoof
Many horses have a small degree of WLD , especially horses in wet environments. Any defect to the hoof wall not open to air flow such as nail holes or old abscess tracts will be prone to WLD invasion.
Grass cracks, named for the dewy fields that can lead to chronically overly wet hooves, describe numerous, small, superficial splits caused by the erosion of the binding intertubular horn beneath the surface of the wall from white line disease. Like grass, they start from the bottom and progress upwards. The loss of intertubular horn is what causes this delamination of the hoof wall and the weakened areas to fray and split.
Premature Loose Shoes and Clinches Due to WLD
Horseshoe nails, especially loose or ill-fitting can exacerbate WLD. When the wall looses it’s intertubular horn, it loses stability. The damaged wall near the shoe is the most damaged and will not resist vertical compression. Instead of growing down, it will flare out to the side. This causes the clinches to loosen. Loose nails move with each step, enlarging the nail holes, leaving even more weakened hoof for WLD to homestead. Clipped shoes that are not hot fit will also cause this sort of damage because WLD will invade the tiny crack between hoof wall and clip.
A toe crack will originate from the center of the toe where the WLD first gains entry. The weakness can be from an old abscess, laminitis, clubby foot, excessive length of toe or from an inherent weakness in some hooves associated with the mid-dorsal notch of the coffin bone.
If the hoof is not returned to a state of balance and the WLD isn’t addressed with methods I will cover a future article, the crack will get larger.
Until you have a full thickness crack extending upwards into the coronary band and inwards towards the laminae. This shearing will cause lameness and even rotation of the coffin bone similar to laminitis.
White line disease is a very common condition in horses, especially those that already have compromised hooves. Horses with WLD are easy to spot due to the predictable progression of these hoof-hungry microbes. Fortunately, most cases can be improved with best farrier practices, more frequent trimming/shoeing and environmental changes. I hope to share my thoughts and methods for the management of white line disease in an upcoming article, so please like, subscribe for updates.
UPDATE-Check out my article Hoof Cracks: 3 reasons why you have them and how to get rid of them for my methods of managing WLD.