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Underrun Heels in Horses

Hooves where the angles of the toe and heels don't match can't bear weight properly.

underslug heels, crushed heels
Red lines illustrate the multiple unhealthy angles this foot has developed. I replaced the horse's too-small shoes (upper inset) with rolled-toe heart-bar shoes (lower inset) so his feet can begin to grow at a normal angle (yellow line) that matches the slope of his pastern.
© Practical Horseman

Your horse's hooves should not look like the one in the large photo at the right. This "patient" of mine, a 5-year-old Thoroughbred recently off the track, has major hoof problems created by years of shoeing for speed: drastically underrun heels, long toes and too-small shoes (see the upper inset photo) that caused painful abscesses and bruising in his feet.

Correcting his problems will take months. In the meantime, his feet make a great case study both of the problems that exist and the way his hoof-growth pattern tells the tale of what is happening.

The first thing I noticed was that this horse was short-shod, meaning that his shoes were too small: Although they'd been fitted to his long toes, they didn't cover or support his heels. Because of that, the shoes' heels were resting against the soles of his feet rather than the walls. The pressure of his body weight bearing down on his heels and soles caused serious soreness, bruising, and at one point—as I can tell from a scar line on his heel—an abscess where his entire heel detached from the coronary band.

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The combination of long toes and short shoes that didn't extend far enough back to support to the heels led this horse to develop badly underrun heels. On a healthy foot, heel and toe grow from the coronary band to the ground at the same angle; when the angle of the heel is less than that of the toe (making it look flattened out), the heels are considered "underrun." Here the angle of the toe is already far too flat, and the angle of the heel is even flatter—to the point that these heels can't bear weight as they should.

Note the way that, a little more than halfway across the lateral coronary band, the hairline rises, then drops steeply to the heel. It's dropped because none of the horse's long, flat heel behind the heel of the shoe has been supported. In conjunction, the horn tubules—the structures that make up the hoof wall—have started to buckle from the pressure being exerted on the heel and have actually wrapped under, so that the horse is now walking on the sides of the horn tubules instead of the ends.

Now look at the wavy ridges running horizontally around the hoof wall. They're signs of irregular hoof growth, and they take a long time to develop, indicating the mounting damage this type of shoeing has done. Because the shoe is too small, it's turned into a lever, with its heels jamming up into the foot every time the horse puts weight on that foot. Notice that the heel of the shoe is directly underneath the high point in the coronary band; the pressure it's caused has created distorted hoof growth and almost led to a quarter-crack.

Perhaps the most obvious problem with this horse's foot, related to everything else we've discussed, is the excessive length of his toe. Throughout his racing career, he was probably shod to encourage the long toe he has now, because some track folks believe that long toes help make a horse faster by giving him a longer stride. Unfortunately, long toes also put a lot of stress on the hoof capsule and on the tendons and ligaments of a horse's legs because they move his weight-bearing surface far out in front of his center of gravity.

On a healthy foot, the angle of the toe from the coronary band to the ground matches the angle of the pastern bone. On this horse's foot, there are three distinctly different angles:

  • Just below the coronary band, the hoof angle does match that of the pastern. This is new hoof growth that hasn't yet been distorted by the stress of his long toes. It tells me that, without human interference, his toes would grow on a naturally healthy angle. (His back feet, which had been trimmed and left barefoot, have worn away naturally and are healthy: reaffirmation that bad shoeing hurts horses far more than it protects them.)
  • The long plane at the middle of the anterior (front) hoof wall juts forward at a much shallower, distorted angle. As the horse breaks over his toe with each step, the toe's excessive length causes the laminae to be pulled away form the foot. That causes bruising and, over time, creates the dished, distorted angle we see here.
  • Near the ground surface, the angle gets steeper again. This is from a farrier's "dubbing" the toe- setting the shoe back slightly and rasping the toe to meet it- in an attempt to shorten the toe. Dubbing is a short-term fix, and not a very good one: It doesn't fix the angle at which the toe is growing; and because so much rasping is involved, it thins down the horn, making it weaker and more likely to dish.

To make this horse's sore feet more comfortable in the short term and help correct them for the long run, I rebalanced him by moving the weight-bearing surface back closer to his center of gravity and gave him the pressure relief and posterior support he needs to allow his hooves to grow normally again. How?

Correcting his underrun heels required, in part, trimming them back to where the horn was still growing straight. However, this horse's problem was severe enough that I couldn't do that all in one shoeing. Instead, I started by trimming from his heel as much of the wrapped-under horn as I could.

Then I shod him with heart-bar shoes (see lower inset photo). The frog plate of the heart-bar shoe allows him to bear weight on his frog rather than his heels. The bar shoe also allows me to take his body weight off his very sore, bruised heels by "floating" part of the foot (creating a depression in the hoof-facing surface of the shoe, so that it doesn't actually touch his foot at the heels). Not only will that pressure relief make him more comfortable; it will allow his hoof capsule to open up and unfold. Also, the rear surface of the bar shoe helps balance him by providing extra posterior support to compensate for how long his toes are right now.

I rolled the toes of the shoes (cut away their ground-facing edge at a 45-degree angle) and set them back as far as I could to help ease the horse's breakover. Over time, he'll begin to grow more upright feet because he won't be tearing the horn and causing the hoof to dish as it grows.

This horse jogged away from his shoeing sound, but he'll need at least six months for the problem areas to grow out entirely.

Certified Journeyman Farrier R. Vance Glenn has shod sporthorses for more than 25 years. His clients include world-class competitors in eventing, dressage, show jumping and driving. A member of the American Farriers Association, Vance often partners with veterinarians on lameness issues that require state-of-the-art therapeutic shoeing. Based in Chester County, Pennsylvania, he travels to regular appointments in South Carolina, and seasonally to Florida.

Read more about underrun or "crushed" heels in the July 2011 issue of Practical Horseman magazine.

Posted in Anatomy, Health, Hoof Care, Lameness | | Leave a comment

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