Heel horn erosion is seen as a change in the appearance of the surface of the bulb of the heel. Because heel horn erosion alone does not always cause lameness, the true incidence is unknown. However, subjective observations suggest that once cows have been exposed to copious slurry, the incidence of heel erosion rapidly approaches 100%. In some cows, heel horn erosion advances to a point at which complications develop and lameness may be apparent.
The etiology is unknown. Heel horn erosion is perhaps more commonly seen in herds in which subclinical laminitis has been diagnosed and in herds affected by digital dermatitis. It is also more commonly seen during the winter, particularly when the claws are exposed to an unhygienic, moist environment (eg, intensively managed dairy units).
The first lesions seen are small circular erosions <0.5 cm in diameter. As the condition advances, these lesions merge, and ridges form parallel to the hair line on the axial surface of the bulb. Invariably, the color of the roughened area is black. At this stage, the cow is not lame.
In the secondary phase, the appearance of the heel varies. In some cases, there is a buildup of horn beneath the heel. Simultaneously, there may be a loss of horn under the axial part of the bulbs. The excessive accumulation of horn is often more pronounced in the lateral claw and causes the hock to turn in (cow-hocked stance). This stance resolves after therapeutic claw trimming. Generally, the condition is progressive unless corrected. The disturbance interferes with shock absorption, and the animal throws more and more weight forward. A common concurrent lesion is a sole ulcer. In other cases, erosion completely denudes the heel of horn—a process that also interferes with shock absorption and can be associated with a sole ulcer. Treponema-like organisms have been observed in microscopic samples of heel horn.
Heel horn erosion must not be confused with separation of the heel, which is the result of the escape of pus from an abscess close to the heel.
Both heels should be reduced to the same height by paring away excess horn. Careful attention must be paid to maintaining the bearing function of the abaxial wall and sloping the sole toward the axial border.
Attention to hygiene and reduction of slurry are essential. The claws of dairy cows should be trimmed twice each year. A weekly footbath (where permitted, 3%–5% formalin), starting no later than October in the northern hemisphere, should be provided.