The structure of the hoof wall

Introduction

The horse’s hoof is one of the most important structures in the animal’s body. It takes the weight of the horse, helps with movement, and absorbs the shock of every step. To do all of this, the hoof must be strong, flexible, and durable. Much of this strength comes from the materials that make up the hoof wall  mainly tubular horn, intertubular horn, and intratubular horn. These three types of horn work together to give the hoof its structure and function. This article will explain what each type is, how they are made, and why they matter for your horse’s hoof health.

External characteristics of the hoof wall.

The Structure of the Hoof Wall

The outside of the hoof, the part you see and touch is called the hoof wall. It doesn’t have blood vessels or nerves, and it's made up of hard, dead material called keratin, which is also found in human nails and hair. The hoof wall is divided into several layers, and the strongest layer is the stratum medium, which contains the tubular, intertubular, and intratubular horn (Bowker et al., 1998). This part of the hoof is made continuously by living tissue just above the coronet band called the coronary corium.

The hoof wall is not just a flat surface. It is made up of thousands of tiny horn tubes that run from the top of the hoof down toward the ground. These tubes are surrounded by a softer material that holds them in place. Together, these structures give the hoof its combination of strength and flexibility (Pollitt, 1990).

Tubular Horn: The Hoof’s Framework

The tubular horn is the main building block of the hoof wall. If you were to look at a cross-section of the hoof under a microscope, you would see many round or oval-shaped tubes. These are the horn tubules, and they run in the same direction as the hoof grows from the coronary band down to the ground. Each horn tubule is made by a finger-like structure in the coronary corium called a dermal papilla. As the cells at the base of each papilla divide and harden, they form a tough, keratin-rich tube (Floyd and Mansmann, 1996).

These tubes give the hoof its vertical strength. They act like tiny columns that resist pressure and stop the hoof wall from collapsing. The tubules are strongest at the front (toe) of the hoof, where the most pressure is applied during movement. As you move toward the quarters and heels, the tubules become less tightly packed, making the hoof more flexible in those areas (Thomason et al., 2005).

Healthy horn tubules are tightly packed, straight, and well-aligned. If the horse has poor nutrition, disease, or trauma to the coronet, the horn tubules may grow out weak, distorted, or loosely packed. This can make the hoof prone to cracks, chips, and flares (Douglas et al., 1996).

The composition of hoof wall - 1. Tubular horn 2. Inter tubular horn 3. Intra tubular horn

Intertubular Horn: The Glue Between the Tubes

The intertubular horn is the material that fills the space between the horn tubules. It is made by skin cells in the coronary region that are located between the dermal papillae. These cells don’t form tubes instead, they produce a more flexible kind of horn that acts like glue, holding all the tubules together (Reilly et al., 1996).

While the horn tubules give the hoof strength, the intertubular horn gives it flexibility. It allows the hoof wall to bend slightly under pressure without breaking. It also helps the hoof manage changes in moisture and temperature. Intertubular horn contains more fats and less tightly packed keratin than tubular horn, which makes it softer and better at holding moisture (Clark et al., 2006).

The health of this softer material is just as important as the hard horn tubules. If the intertubular horn breaks down such as in white line disease or seedy toe, the hoof wall can come apart. Microbes and dirt can get in through these weakened areas and cause infection (Colles and Jeffcott, 1977). Keeping this part of the hoof strong depends on good nutrition, proper trimming, and protecting the hoof from excessive moisture or dryness.

Intratubular Horn: The Filling Inside the Tubes

Intratubular horn is found inside the middle of each horn tubule. It is not as well-known as the other two types, but researchers now believe it plays an important role in hoof health. This material is formed from old skin cells and other substances that collect in the centre of the horn tubules as they grow. It’s softer than the outer layers of the tubule and may act as a cushion or filler (Bowker, 2003).

Although we don’t know everything about intratubular horn, it may help protect the tubules from damage or infection. It could also act like a shock absorber, reducing the impact when the hoof hits the ground. Some scientists think that the quality of intratubular horn might change with the horse’s diet, hoof loading, or overall health (Bowker et al., 2001).

While most hoof care focuses on the outside of the hoof, understanding intratubular horn might help explain why some horses have naturally stronger feet than others, or why some are more prone to cracks or horn defects.

What the Hoof Horn is Made Of

All three types of hoof horn are made mainly of keratin, which is a tough protein also found in your fingernails. In the hoof, this protein is arranged in long strands and then cross-linked by bonds between sulphur atoms. These cross-links make the keratin hard and durable (Linder and Horne, 2002).

The tubular horn has more of these cross-links, which makes it the hardest part of the hoof. The intertubular horn has fewer cross-links and more fats, making it softer and more flexible. These differences are important because they allow the hoof to be both tough and adaptable, it needs to be rigid enough to support the horse, but flexible enough to move and adjust to the ground (Whitaker et al., 2008).

Nutrition plays a big part in making good quality keratin. Horses need enough protein, as well as minerals like zinc, sulphur, and copper, to build strong horn. Biotin, a B-vitamin, has also been shown to improve horn quality in some horses (Comben et al., 1984).

How the Horn Grows

The horn of the hoof grows from the coronary band, which is located just below the horse’s hairline. Under the coronet is the coronary corium, which contains blood vessels and special structures that make the horn. The horn tubules grow from the tops of the papillae, while the intertubular horn is made by the skin cells between them (Pollitt, 1990).

The horn grows downward at about 6–10 mm per month, depending on the horse’s age, health, season, and nutrition. The quality of horn produced depends on many things  including blood supply, hoof balance, and how the horse is used. If the coronet is damaged, the horn may grow out misshapen or weak.

Different parts of the hoof wall grow at different rates. The toe usually grows faster than the quarters and heels. This natural difference helps shape the hoof, but if trimming is delayed or done incorrectly, it can lead to flares, imbalance, and stress on the horn structure (Thomason et al., 2005).

How the Horn Handles Pressure

The three horn types work together to manage the forces placed on the hoof. Every time the hoof hits the ground, it has to deal with impact, compression, and twisting forces. The tubular horn provides the upright strength to handle compression. The intertubular horn allows some movement between tubules, which helps the hoof flex and absorb impact. The intratubular horn, while not fully understood, may help reduce vibrations or stop cracks from forming (Bowker, 2003).

Areas of the hoof with more horn tubules, like the toe, are better at handling vertical forces. Areas with more intertubular horn, like the quarters and heels, are better at bending and adjusting to uneven ground (Douglas et al., 1996). This design helps protect the internal structures of the foot and prevents injury.

What Happens When Things Go Wrong

When the balance between the different horn types is upset, problems begin. If a horse suffers from laminitis, for example, the blood supply to the corium is damaged, and the hoof can no longer make strong horn. This often leads to weak, brittle horn that breaks apart or stretches at the white line (Pollitt, 1996).

White line disease and seedy toe often start with the breakdown of the intertubular horn. Fungi and bacteria can enter these weak areas and cause separation between the layers of the hoof wall (Colles and Jeffcott, 1977). In some cases, this leads to major structural failure.

Good hoof care including proper trimming, balanced shoeing, and good nutrition can help maintain the quality of all three horn types. Farriery that respects the natural shape and loading of the hoof will help avoid damage to the tubules and their surrounding horn. Diets rich in biotin, methionine, zinc, and copper can improve horn strength and moisture balance, especially in horses with naturally poor feet (Comben et al., 1984).

Trauma injury to the hoof wall due to this horse getting stuck in a fence.

Conclusion

The hoof wall is not just a block of hard material. It is a living, growing structure made of different horn types that each play a special role. The tubular horn provides strength and shape. The intertubular horn gives flexibility and holds everything together. The intratubular horn may act as a shock absorber and filler. When all three are working well, the hoof can support the horse’s weight, adapt to the ground, and stay healthy. But when one part breaks down whether from disease, poor nutrition, or injury,  the whole hoof suffers. As a horse owner, understanding these parts of the hoof can help you work with your vet and farrier to keep your horse sound, comfortable, and performing at its best.

References

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Bowker, R.M., 2003. Contrasting structural morphologies of “good” and “bad” footed horses. AAEP Proceedings, 49, pp.186–209.

Bowker, R.M., Van Wulfen, K.K., Springer, S.E. and Linder, K.E., 1998. Functional anatomy of the cartilage of the distal phalanx and digital cushion in the equine foot and a hemodynamic flow hypothesis. Equine Veterinary Journal, 30(S26), pp.46–55.

Clark, C., Mills, D. and Dyson, S., 2006. Equine Locomotion. 2nd ed. London: Saunders Elsevier.

Colles, C.M. and Jeffcott, L.B., 1977. The diagnosis of foot lameness in the horse: A study of 200 cases. Equine Veterinary Journal, 9(1), pp.31–39.

Comben, N., Clark, A. and Holt, D., 1984. Effect of biotin supplementation on equine hoof horn growth and hardness. Veterinary Record, 115(24), pp.642–645.

Douglas, J.E., Thomason, J.J. and Sears, W., 1996. Morphometric and material properties of the equine hoof wall: implications for the biomechanical function of the hoof. Equine Veterinary Journal, 28(5), pp.394–401.

Floyd, A.E. and Mansmann, R.A., 1996. Equine Podiatry. Philadelphia: Saunders.

Linder, K.E. and Horne, W.A., 2002. Immunohistochemical and histochemical comparison of keratins and proteins in the equine hoof wall. Journal of Anatomy, 201(6), pp.465–475.

Pollitt, C.C., 1990. The anatomy and physiology of the inner hoof wall. Equine Veterinary Education, 2(1), pp.26–33.

Pollitt, C.C., 1996. Basement membrane pathology: a feature of acute equine laminitis. Equine Veterinary Journal, 28(1), pp.38–46.

Reilly, J.D., Cottrell, D.F., Martin, R.J. and Cuddeford, D., 1996. Histological and histochemical aspects of the keratinization of the equine hoof. Equine Veterinary Journal, 28(1), pp.53–60.

Thomason, J.J., Douglas, J.E., Sears, W. and Bertram, J.E., 2005. Morphology of the internal structures of the hoof wall and its functional significance. Veterinary Clinics of North America: Equine Practice, 21(1), pp.15–31.

Whitaker, D.W., Hegemann, M. and Wagner, H.D., 2008. Mechanical and structural properties of keratin: effects of hydration and plasticisation. Journal of Biomechanics, 41(5), pp.1060–1065.