Understanding Underrun Heels in Horses: A Complete Guide

What Are Underrun Heels in Horses?

• When viewed from the side, you can see the angles of the toe and the heel. When the heel angle is less than the toe angle, that hoof is underrun.

• A low heel in horses means the back of the hoof is closer to the ground, but not underrun (yet). A true underrun situation occurs when the heel angle approaches the ground. Think of it as the heel sliding under the hoof and becoming flatter, rather than more supportive. The heel of the hoof wall will collapse and flatten under the hoof.

• Inside the hoof, the tubules that make up the structure of the hoof wall are usually vertical. As the heels collapse, the tubules become more horizontal and parallel to the Earth.

Peep some diagrams here.

This article has comparative photos of hooves.

Identifying Visual Characteristics of Underrun Heels

• You can see underrun heels, especially from the side view. You will usually see:

• Long toes. This length pulls the heels forward and stretches the tendons and ligaments at the back of the leg.
• Growth rings are usually uniform on a health hoof, but will be closer together around the heels.
• The heel bulbs look squashed.
• The end of the heel has slipped forward.
• Some horses will have a convex (dished shape) hoof wall.

This article includes helpful diagrams of horse hoof anatomy.

Differences Between Underrun Heels and Low Heels in Horses

• While the terms “low heels” and “underrun heels” are sometimes used interchangeably, they refer to distinct structural issues. Low heels mean there isn’t much vertical height to the heel structures. This can be a conformational trait and may or may not cause problems.

• In contrast, underrun heels are a more serious distortion. The defining feature is the forward migration of the heels. The horn tubules that make up the heel wall bend and grow forward, becoming almost parallel to the ground instead of growing downward. This collapse weakens the entire back part of the foot.

• A horse can have low heels without them being underrun, but underrun heels almost always result in a low, collapsed heel structure. The table below highlights the key distinctions.

Common Causes of Underrun Heels

• Several factors contribute to the development of underrun heels and low heels in horses. First, and sometimes most powerfully, are genetics. Other factors include mechanical forces, your horse’s environment, and hoof health care practices.

Mechanical Factors Impacting Heel Structure

• Long toes help create heel problems. The elongated toes act like levers, pulling the hooves forward.

• Short shoeing is also a factor. Short shoeing occurs when the horseshoe is too small or fails to support the heels adequately.

• Waiting too long between farrier visits also creates short shoeing as the foot outgrows the horseshoe.

Read this case study of a young OTTB.

It’s hard to tell on this horse if the heels are low or underrun. But clearly they are due for some care!

Conformation Traits and Genetics

• A horse’s natural conformation and genetics can predispose it to developing underrun heels. Some horses inherit hoof shapes that are more prone to this condition.

• Thoroughbreds, particularly those from the racing industry, are frequently affected, suggesting a genetic link or a consequence of industry practices that often encourage longer toes in an effort to lengthen their stride.

• Injuries or conformational traits can encourage a horse to seek comfort, and the resulting stances may place more stress on the heels, causing them to be pushed forward.

• Some horses may also influence their foot shape by the way they stand while eating. The forward foot may grow a longer toe, while the other foot may become more vertical or clubby.

Environmental and Management Influences

• Routine farrier care should include the following:

• Regular X-rays to ensure the external angles are healthy and supportive for the internal structures of the foot.

• Appropriate trimming intervals. Waiting too long allows the toe to lengthen. In the summer, most horses grow faster and may require their interval to be adjusted.

• Proper shoeing to protect the hoof while preventing the heels from slipping under.

• Horse owners should pick their horse’s hooves several times a day and take photos to document hoof growth and changes over time.

• We can’t always control wet or dry conditions, but we can ensure the lower legs and feet are clean and dry when in the barn. For those tricky wet/dry cycles that abscesses and white line disease love to take advantage of, using vet and farrier-approved products to avoid softening of the hoof is best. Boots are another option.

• Be mindful of the conditions and footing when riding or lungeing. Avoid hard and deep surfaces for prolonged periods. There are some days when the footing is only suitable for walking. It’s a great idea to vary the surfaces your horse exercises on, but there’s also a happy medium.

How Underrun Heels Affect Equine Movement and Performance

• Underrun heels do more than change the shape of the foot – they dramatically alter how your horse moves. In a healthy hoof, the heel structures, including the digital cushion, are designed to absorb the impact of a heel-first landing. When the heels collapse, they can no longer handle the horse’s weight effectively. The weight-bearing aspects of the hoof have shifted, potentially causing pain.

• This forces the horse to change its landing pattern to avoid pain, often shifting to a toe-first landing. This unnatural movement places tremendous strain on other soft tissue structures, tendons, and bones, like the navicular bone.

Changes in Gait and Stability

• A horse with underrun heels will often exhibit noticeable changes in its gait. The most significant change is a shift from a confident, heel-first landing to a tentative, toe-first one. This happens because the crushed tissues in the heel area are painful, and the horse alters its movement to avoid pressure there.

• This action creates a choppy stride that is uncomfortable for everyone. You will also notice that the usually smooth rolling-over motion is now rough. You are more likely to see this in the front feet, but it can certainly happen in the hind legs, too.

• Overall, there’s a lack of fluidity to movement.

Risks for Tendon and Ligament Strain

• Leaving underrun heels untreated poses significant long-term risks to the soft tissues of the lower leg. The broken-back hoof-pastern axis created by the collapsed structure places constant, abnormal strain on the deep digital flexor tendon (DDFT). This tendon runs down the back of the leg and under the navicular bone. Excessive stresses and tension here can lead to inflammation and injury.

• The pain associated with this condition is a significant concern. The crushing of the soft tissues in the back of the foot can cause soreness and inflammation in the navicular region. Over time, this chronic inflammation can contribute to the development of navicular disease, a degenerative condition that causes persistent lameness.

• When these excessive forces compromise the structures, any disruption to the hoof, due to an abscess, laminitis, or injury, makes the situation even more dangerous and may further damage the tendons or ligaments.

Signs of Lameness Related to Under-Run and Low Heels

• It’s never easy to discern subtle lameness in horses, especially in the hind legs, as any changes can be associated with hocks, stifles, backs, saddle fit, and more. This is because the distortion of the hind feet affects the horse’s entire posture and gait.

• The foot pain may be the primary cause of lameness, or there may be pain further up the compromised soft tissue structures. And just like all things lameness-related, the signs can point to underrun heels or a bevy of other conditions that your vet can sort through.

You may see:

• A reluctance to stand on one foot when the opposite limb lifts while picking hooves.
• A painful response when hoof testers are applied to the heel area.
• A shortened stride or choppy gait.
• Hesitation or resistance when asked to move forward.
• A subtle, shifting lameness that is difficult to pinpoint.

Diagnostic Approaches for Underrun Heels

• Diagnosing underrun heels starts with a thorough hoof examination. A skilled farrier or veterinarian will assess the overall hoof conformation, looking at the angles of the dorsal hoof wall and coronary band, the position of the frog, and the health of the sole wall junction.

• There will be differences in conformation of the hind foot compared to the fore feet, which is to be expected.

• X-rays from your veterinarian will always help assess the overall condition of the hoof, both inside and out.

• Radiographs also provide your farrier with a clear visual of the coffin joint and coffin bone, toe wall, sole, pastern angle, and internal structures, which help them create the best trimming and shoeing plan.

• Your vet will also examine the sole depth and frog to determine if it’s shifting lower during a clinical examination of the foot. Hoof testers can assess pain levels around the heels, and a visual exam, along with watching your horse jog, can help them see how the hoof lands.

Corrective Farrier Work and Horseshoes

• The goal of corrective shoeing and trimming is to help the exterior hoof angles return to a more comfortable place. The first part of the farriery process is working toward a more balanced hoof, without causing discomfort from a sudden change. You don’t always want to rush the amount of time it takes for drastic changes, but that may be necessary.

• The toe area needs addressing, and for the under run heels, a wedge pad or specialty shoe may be necessary. The goal is to change the angle of the heel, but that requires some clever planning.

• Some good-intentioned methods of corrective shoeing may do more harm than goo. Sometimes elevating the heel pus more pressure on the area. 

This article has great information about shoeing options.

By recognizing the signs and causes of this condition, you can take proactive measures to mitigate its effects. Regular hoof examinations, proper management, and collaboration with experienced farriers and veterinarians are key components in addressing undervalued hoof issues. Remember, each horse is unique, and tailored care is crucial for their well-being. If you have any questions or need assistance with your horse’s hoof health, feel free to reach out for a consultation. Your horse deserves the best care possible!

This horse has low heels, and you can clearly see the rings stay evenly spaced toward the heel on the white hoof. 

Key Highlights

• Underrun heels occur when that angle becomes lower than the toe angle, causing the structures to collapse forward.
• This condition compromises the integrity of the hoof capsule, leading to a weaker foot that cannot properly absorb impact.
• Key causes include improper farrier work, genetics, and environmental factors that put excessive pressure on the heels.
• Identifying any foot issues also involves looking for a “bull nosed” hoof wall, uneven growth rings, and a broken-back hoof-pastern axis.
• While serious, this condition can be managed with corrective trimming and shoeing, which can prevent chronic lameness.