Q My horse has a horizontal crack in his hoof, up by the coronet band. I’ve heard conflicting explanations of the cause of this crack. What is its most likely cause? How should I treat it, and can it be prevented in the future?
JESSICA DOON, New Jersey
A Horizontal cracks in the hoof wall are often thought to be caused by injuries at the hairline (coronary ridge) that are growing out. However, a split in the wall that develops as a result of trauma at the hairline will be vertical, typically, and nearly always becomes a permanent fixture of the wall.
By contrast, short (1- to 2-inch) horizontal cracks are most often caused by abscesses affecting the white line (the junction of the hoof wall and the sole, visible as the narrow, light-colored band on the underside of a freshly trimmed hoof). Such abscesses rupture at the hairline; then the resulting crack migrates with the wall growth to be trimmed off eventually. Abscesses often affect hooves that have been neglected, or that are trimmed regularly but incorrectly, whether shod or unshod.
The hoof wall, if allowed to flare, creates leverage on that connective tissue between the wall and the sole of the hoof. In turn, this can cause stretching of the white line. That connection can only stretch so far before we see separation, which causes the death of the connective tissue and may allow foreign matter to invade the hoof at this point. The formation of pus (dead tissue) tracks up the inside of the wall, leaving a trail of dead lamina in its wake as it takes the path of least resistance up the wall to the soft hairline.
When the abscess reaches the narrowing space just below the hairline, the pain will be at its worst as pressure builds, just prior to rupture. Lameness usually ensues to varying degrees.
Lameness caused by white-line abscesses is frequently misdiagnosed because it’s difficult to identify an abscess until it ruptures. Radiology and even MRI often won’t pick up the track of the abscess, though it usually can be located with thermal (heat-sensitive) imaging.
After rupture, as the wall grows out, well-connected lamina develops above the now-visible crack and takes the place of the damaged tissue. Lameness soon subsides. As the crack gets closer to the ground, the area below the crack may snap off due to the detached lamina below the rupture site. This doesn’t require soaking or special shoes, just time to heal and frequent trims.
The bars of the hoof are an extension of the hoof wall. So abscesses can develop in the white line of the bars, too, tracking up to rupture at the hairline of the heel bulb—often described as “mystery lameness.” The resulting horizontal splits in the back of the hoof are typically misinterpreted as injuries. Abscesses of the bar are more serious and painful than those of the wall, as invasion of the white line of the bars can spread and affect areas of the solar connective tissue (papillae), causing eventual detachment of the sole.
Often, abscesses are thought incorrectly to be caused by trauma to the sole. Sharp objects may strike the sole of a soft-soled hoof, but the result will be a wound. Practitioners need to be able to distinguish between sole trauma and white-line abscesses to avoid confusion.
Once the white line has been invaded, there’s no immediate cure for an abscess; the condition must run its course. Epsom-salt soaks may help soften the coronet band to encourage the abscess to erupt, while pain medications and padded boots can offer relief post-rupture.
Skilled veterinarians have drilled tiny holes in the outer wall in the path of the abscess, enabling discharge and relieving pressure and pain. But even when so drained, the abscess will still rupture at the hairline in most cases. To dig into the sole is a common approach to relieve pressure, but that procedure can cause further trauma to a hoof rather than relieve pain.
Preventing abscesses of the white line is as simple as making sure your horse’s hooves receive correct trimming at regular, 4- to 6-week intervals. Trimming strategies (whether or not the hooves are shod) should produce healthy hoof horn (no flare) and well-maintained bars with tight connecting tissue (lamina/white line); this, in turn, will reduce or eliminate abscesses.
Hoof Rehabilitation Practitioner