Double sole

Etiology

• Most commonly a lesion secondary to one of the following:
  • Acute White line abscess White line disease, which extends under the sole before bursting out through the heel, coronary band or by draining through foot trimming.
  • Foreign body penetration (e.g. palm kernel, tooth, metal nail/screw or stone).
  • Abscessation following Sole ulcer Sole ulcer.
  • Footrot Footrot (foul-in-the-foot, interdigital necrobacillosis).
  • Acute necrotic hoof lesion  Necrotic hoof lesions (although the corium will remain inflamed and ulcerated until treated and so not a true double sole).
• It can also occur following to sole hemorrhage and bruising, with each layer of hemorrhage forming a double sole. Long standing times on concrete can be a risk factor, particularly around calving (which may indicate cubicle rejection, long penning times or low social dominance) or following periods of heat stress. (See related content for further risk factors related to sole hemorrhage and bruising).
• Disruption/cessation of horn formation can occur due to physiological or systemic disease-related stressors:
  • Metabolic disease associated with calving or Dystocia Dystocia.
  • Severe systemic disease like Toxic mastitis Acute mastitis or Metritis Uterine infections: overview.

Pathophysiology

• The sole horn is produced from germinal epithelium of the corium, and is produced at approximately 5mm per month.
• A double sole is formed when there is cessation of horn production followed by restoration of normal growth.
• Two or more layers of under-run sole horn can occur in the same claw (digit). If systemic disease is the cause, it can affect all eight claws in an animal simultaneously.
• Formation of underrun horn is exacerbated by the presence of fluid, most commonly occurring following sole hemorrhage, or from pus occurring due to sole abscesses or white line disease.
• Moisture and environmental contamination can wick between layers of sole from a focal defect such as a white line lesion.
• The size of the double sole depends on the affected area of sole corium.

Timecourse

• A double sole will become apparent from as early as 1 week following the initial cessation and re-start of the horn growth, but may not be discovered until the foot is trimmed at a later date.