Next, Taylor described the heel base, which includes the hoof wall, buttress (the back the part of the hoof that makes initial contact with the ground from a heel-first landing), sole angle (the degree between the coffin bone and a straight horizontal line), and bars. In a healthy hoof, she said, the heel bulbs shouldn’t touch the ground, and the heel tubules should be straight and nearly parallel (within 5°) to the tubules in the toe region. The heel tubules’ most palmar (furthest to the rear) weight bearing surface should be at the base of the frog.
Underrun heels—which can be caused by a variety of issues ranging from a horse’s conformation to improper trimming aand/or shoeing—can lead to an array of problems. “Underrun heels that grow forward towards the widest part of the foot often collapse under the weight of the horse, causing heel tubules to run nearly ground parallel,” Taylor explained. “The bars and the angle of the sole may be crushed, deformed, or injured as a consequence of the severely underrun heel.”
Additionally, Taylor said, researchers have recently postulated that inadequate fibrocartilage development in the digital cushion (a soft tissue structure in the hoof capsule, above the frog) is a precursor to tissue injury and lameness. She recommended practitioners become familiar with what a healthy heel looks and feels like. “A sense of normal can be learned by palpating the digital cushions of sound horses with good feet and comparing those findings with those of horses with poorly conformed feet,” she said.
In a healthy hoof, the combined tissues of the frog and digital cushion should measure about two inches, she said; hooves with combined tissues measuring less that that will likely be predisposed to injury. Underrun or collapsed heels with underdeveloped digital cushions deform easily when you apply thumb pressure, while healthy heels will not give way as readily. Horses with suboptimal digital cushion volume and fibrocartilage usually have either narrow, contracted or wide, thin underrun heels, and they likely are at risk for lameness, she said.