Heel erosion (and underrun heel and sole) is also called chronic necrotic pododermatitis, chronic foot rot, stable foot rot, and erosion ungulae. Most common in the hind feet. The erosive process begins at the heel bulb initially as pits and pockmarks, then parallel horizontal grooves develop filled with black necrotic material. Fusobacterium necrophorum and Bacteroides nodosus have both been isolated. The horn can seperate to form a flap which may extend to the toe with a new sole developing underneath. Debris can become packed down between the sole layers causing lameness. Erosion of the horn and undermining of the sole can also progress from the axial groove if the groove becomes packed with debris and anaerobic bacteria. Usually, underrun heels do not cause lameness unless there is infection of deeper structures or a lot of debris gets packed down between the sole layers.

Predisposing factors include:

• standing in wet lots
• weak pasterns or overgrown hooves shift weight to the heels
• chronic laminitis - decreases horn quality and causes foot deformities that shift weight to the heels

The abnormal horn and sole should be removed, and , grooves and ridges trimmed smooth. Prevention includes regular trimming, footbaths, and improved management of lots.