The phrase “no hoof, no horse” was coined in England in the middle of the 18th century. Anyone who owns or works with horses has heard this phrase and adheres to a myriad of techniques to ensure that their horses’ hooves are always in excellent condition.
As nearly 80 percent of all lameness issues stem from problems in the hoof, the amount of attention directed to this anatomical structure is certainly warranted. “When considering the relative size ration between the hoof and the rest of the horses’ body, it is amazing that something so small can have the biggest impact on the total animal,” wrote S.E. Blackwell for a 2007 presentation at the North American Veterinary Conference. “From the continuous adjusting structure, to the shape and construction, the equine foot remains one of the greatest mysteries in animal science.”
Inside the Hoof
The equine hoof can be compared to a human fingernail – just one reason it is astonishing this structure is responsible for bearing all of a horse’s mass. The front hooves are typically a bit larger than the hind hooves, as they support roughly 60 percent of a horse’s weight. Every time a horse moves, the impact from its feet striking the ground send shock waves upwards through the legs. The concave shape of the hoof evolved to protect the foot from concussion, as well as the navicular bone, coffin bone, and laminae that are vital to how a hoof functions. Its role is to transmit moisture, stave off excessive wear or damage, and aid in the circulation process within the lower leg.
The hoof can be separated into two structures: the external hoof and internal hoof. The external hoof is the barrier and is in place to protect the blood-supplied tissues. “Although it is continually growing, the external structures are insensitive and have no blood supply,” wrote Blackwell. “They gain nutrients from the underlying blood supply that services the internal sensitive structures. This outer surface of the hoof consists of the hoof wall, sole, and frog. These are the only structures of the equine foot that come in direct contact with the ground surface.
“The wall is the tough, hard protective shell and is composed of protein keratinized epithelial cells. These tightly-packed, tubular-shaped cells are formed in the coronary band and run vertically down the hoof wall. The outside of the hoof wall is protected by the moisture-preventing varnish-like substance called the periople that is secreted by the coronary band. The main job of the periople and the tubular cells within the hoof wall is to monitor the moisture content within the entire foot. The periople protection extends from the coronary band down the hoof wall covering the heel and then blending in with the frog.”
The frog is constructed of nearly 50 percent water and is the spongy mass bound into place by the bars and sole. It operates much like a shock absorber when a horse’s foot hits the ground. The sole of the foot also functions in the same fashion and runs along the entire bottom of a horse’s foot. Its concave shape is essential for warding off undue stress and strain to the foot. The bar acts as support to the heel. All three of these structures work in conjunction so a horse can safely move.
“The internal workings of the hoof are extremely sensitive and consist of the coronary band, laminae, skeletal structures, and soft tissue supported by a continual blood supply,” wrote Blackwell. “The bones of the foot are not only sturdy enough to provide framework, stable enough for weight-bearing movements, but also light enough to facilitate locomotion. There are four boney structures in the horses’ foot, the second phalanx (P2 or middle phalanx) which extends distally from its connection with the first phalanx (P1 or pastern), the coffin bone (P3 or distal phalanx) which extends distally from the short pastern bone, and the navicular bone (distal sesmoid bone) located behind and proximal to the coffin bone. The bones of the foot and leg are connected by joints and ligaments, so any injury to one portion will have a directly negative effect on the other. The soft tissue structures consist of the extensor tendon, deep digital flexor tendon, navicular bursa, digital cushion, coronary cushion, and lateral cartilage.
“These inner structures are attached within and to the exterior surface structure by a middle interlocking, Velcro-type layer of mesh called the laminae,” Blackwell continued. “This laminae consists of thousands of tiny interlocking leaves or fingers that serve as an anchor that literally suspends the coffin bone within the hoof wall. It has a side-to-side concave shape that enables the weight of the entire horse to be distributed onto the hoof wall. Both the laminae and inner structures are serviced by a massive and complex network of vessels and nerves. This thin pumping mechanism that furnishes nutrition, blood, and sensitivity is facilitated by the compression of the horse’s movement.”
Common hoof issues
Understanding the physical structure and the amount of concussion a horse must sustain on a daily basis, it is clear that a healthy foot is essential to a horse’s overall well-being and how they perform.
“Caudal heel pain (which may or may not include navicular syndrome), thin soles, quarter cracks, and low heels/long toes are some of the most common performance issues related to the foot” explained Dr. Brent Barrett, a farrier who operates an equine podiatry practice that specializes in foot related lameness problems in Ocala, FL. “Although they are not typically life-threatening, some of these issues can be career-limiting. The lameness may either be within the foot itself or affecting other structures such as the suspensory ligament, deep digital flexor tendon, and superficial digital flexor tendons. Abscesses, foot infections, laminitis, and fractures often produce a more acute and intense pain and demand immediate attention. White line disease, sheared heels, and thrush are issues that are present, but don’t usually produce lameness unless a secondary complication arises.”
According to Dr. Mary Boyce from the University of Minnesota, there are a number of problems that can arise with a horse’s feet. The number-one recommendation for protecting and preserving a horse’s feet? “Regular trimming or shoeing,” she said. “You also seek to maintain good hoof balance, as well as the correct hoof pastern angle, break-over and medial-lateral balance. Next, heel support should be introduced if it is needed and appropriate shoes should be used for different weather as well as footing conditions. Also, the appropriate treatment must be used if a disease process occurs.”
In Boyce’s opinion, the most common hoof problems she encounters are simply caused by poor shoeing or trimming, as well as hoof cracks, thrush, solar abscesses, ‘hot’ or ‘street nail’ (nail driven into the sensitive structures of the hoof wall), laminitis, and navicular disease.
A 2013 article produced by Kentucky Performance Products points out a well-balanced diet and how much moisture a horse is exposed to have a direct impact on if that horse will develop foot problems. “A hoof that is constantly exposed to high moisture levels becomes increasingly soft and weak,” the article states. “The sole tends to flatten out and the hoof is no longer capable of properly supporting the weight of horse and rider. Soft feet can lead to lameness, particularly when a horse is asked to work on hard surfaces or is being exercised rigorously. Hooves that are continuously wet are also more porous and therefore more prone to bacterial and fungal infections. Soft hooves tend to develop deep cracks, chipped areas, and flat soles where bacteria and fungus set up housekeeping. The sole of the hoof, which is the most porous section of the foot, is particularly susceptible to disease.
“Often the outward appearance of the hoof is deceiving. Overly-moist feet tend to swell, so cracks are not as noticeable. The hoof may look shiny and healthy, but problems are brewing. It won’t be long before the hoof wall crumbles, clinches pop, and disease
Barrett discusses how radiographs are a very helpful tool in determining issues with the interior structure of the foot and can serve as a guide in how to treat any complications. He also advises that some breeds do have a disposition towards acquiring specific foot problems during the course of their lives.
“Thin soles, low and sore heels, and generalized caudal heel pain may all go together,” Barrett said. “Thoroughbreds are affected by low heels and thin soles more than most other breeds. Quarter Horses have the highest incidence of true navicular disease. This is due primarily to genetics and resulting hoof conformation tendencies. Typically, there is an imbalance in what is known as the dorsal palmar, or front-to-back plane of the foot. There are various ways of looking at what is the appropriate balance point of the foot, but typically it is considered to be the center of articulation of the coffin joint. This is also referred to as the widest point of the foot when looking at the ground surface. Ideally the ratio in front of and behind this point is 50:50. Quite often the cranial, or front part of this ratio, is much greater than the back [hence a long toe].”
Horse owners have a much larger range of therapeutic products available for managing foot conditions than in the past. “We have rapidly-developing technology regarding diagnostics leading to a better knowledge of the existing pathology,” explained Barrett. “Innovative products such as support materials, a huge variety of therapeutic shoes and boots, and new methods of attaching shoes to the foot provide options that weren’t present even 15 years ago.
“Additionally, education is growing in leaps and bounds. Every year brings more vet/farrier symposiums and clinics. The understanding of each other’s role allows for a much more effective environment, resulting in a more successful team for our patients.”
Barrett continued, “When a case requires work that does extend beyond the fundamentals, the farrier’s role is huge. Getting horses as comfortable as possible is our job and fortunately, veterinarians are relying more and more on farriers to help make that happen.”