Can foot shape offer clues about a horse’s potential to stay sound? Dr Sue Dyson explains how research is attempting to quantify the link between poor foot conformation and lameness
Foot pain is the most common cause of lameness in horses from all work disciplines.
Some lameness is due to an obvious cause, such as a bruised sole or poor trimming and shoeing, and can be readily resolved. But a large number of horses have chronic foot pain because of more serious underlying injuries.
It is generally accepted that poor foot conformation and/or balance are associated with an increased risk of foot-related lameness. However, there is only limited factual scientific information to support this.
Since the advent of magnetic resonance imaging (MRI), we have become much better at making accurate diagnoses of these injuries, such as deep digital flexor tendon injury. Yet to determine if there are ways of predicting or preventing these injuries, we need a better understanding of why they occur.
What makes a ‘good’ foot?
In an ideally conformed horse, free from lameness, it is thought that the pastern-hoof axis should be straight and the front aspect of the hoof wall and the heel should be parallel.
The horn tubules — the thin, vertical “tubes” that make up the hoof wall — should be parallel with one another, as should the horizontal growth rings (which may have variable separation). The coronary band should be symmetrical, so that a line drawn between any two comparable points on the band is parallel to the ground.
While there is a lack of evidence-based information concerning foot conformation, some studies have revealed that deviation from this ideal conformation increases the likelihood of foot pain. A large-scale German study, for example, showed that horses with left and right front feet of different shape and size leave the sport horse population earlier than those with symmetrical feet.
To investigate further, researchers at the Animal Health Trust (AHT) in Newmarket performed a study in 2011. They documented photographically the foot shape and external hoof characteristics of approximately 350 lame and non-lame horses. The duration of the lameness was defined as acute (less than 3 months), intermittent (difficult to determine accurately), or chronic (more than 3 months).
All feet were photographed from the side and the photographs were assessed to determine the shape of the coronary band, which was described as straight or curved. The orientation of the horn tubules and the growth rings was also recorded.
The front of the hoof wall was described as straight, concave or convex, and abrupt changes in hoof wall alignment were recorded. Various length and angle measurements were made to describe the shape of the hoof capsule.
Causes of pain
Some of the results surprised us:
- Just half of the feet of “normal” (non-lame) horses had a straight wall — in a third of these, the wall was concave and in a fifth it was convex. In almost half of these curved walls, the angle changed abruptly part way down, usually coinciding with a prominent growth ring. This lack of straightness may reflect, at least in part, previous trimming techniques.
- Just half of the feet of normal horses had a straight coronary band — a third had an overall concave shape and a fifth had concavity in the back half of the foot. The incidence of curvature of the coronary band was significantly higher in lame horses. Moreover, a concave coronary band was associated with persistent lameness.
- One of the most unexpected observations was that a large proportion of non-lame feet had divergent growth rings at the heel and non-parallel horn tubules. Divergent growth rings have previously been considered to be a hallmark of laminitis, but it seems unlikely that such a high proportion of horses had previously suffered from it.
- The average angle of the front of the hoof wall was consistently greater than the average heel angle in both lame and non-lame feet, so the front aspect of the foot and heel were rarely parallel.
- Only the ratio of the height of the coronary band at the front and back was significantly different between lame and non-lame horses, being greater in lame horses. But there was no significant difference in the frequency of occurrence of a collapsed heel between the feet of non-lame and lame horses.
- Some 23% of lame horses had well conformed front feet. In 22% of those lame in one foot, the affected foot had a taller, more narrow and upright conformation. In 10% the lame foot had a long toe and a low, collapsed heel.
A combination of a long toe and a low heel results in greater contact pressure on the navicular bone, increased strain in its supporting ligaments and the deep digital flexor tendon. This is subsequently associated with increased extension of the coffin joint.
But chronic — long-standing — lameness may result in the development of an upright foot conformation over time, irrespective of injury type. This reflects lack of normal foot function and altered biomechanical loading.
What can we learn?
This study confirmed that asymmetry of foot shape may be present in foot-related lameness.
There is an overlap between the foot shape of normal horses and those with foot pain. But the presence of asymmetrically shaped feet, a curved coronary band, a low collapsed heel or non-parallel growth rings or horn tubules are potential indicators of a risk of foot-related lameness.
The presence of any of these at a pre-purchase examination should alert you that there may have been previous lameness.
Because this study focused on the foot from the side, however, there are other factors regarding conformation and foot trimming, which may be related to lameness, that were not investigated.
Markedly pigeon-toed conformation or obvious asymmetry of the foot from the inside to the outside are likely to result in asymmetrical loading of the bones and soft tissues of the foot, therefore predisposing the horse to injury.
All horses tend to land on the outside of each foot slightly in advance of the inside. If the foot is not symmetrically trimmed so that one side is higher than the other, the tendency to land on one side first may be accentuated.
The saying “no foot, no horse” holds ever true, and the importance of good trimming and shoeing cannot be overemphasised. Although there are clearly multiple causes of foot pain, good foot conformation, which is symmetrical between right and left limbs, may reduce the risks of the development of foot pain.
Foot pain: which horses are most at risk?
The large number of cases seen at the Animal Health Trust in Newmarket provides it with a significant database from which to identify lameness trends.
Some interesting facts emerged when the AHT reviewed all horses examined between 2001 and 2010 for investigation of lameness, poor performance or as part of a pre-purchase examination.
Advanced statistical analyses were performed on 4,618 horses, 1,132 of whom had foot pain. The results revealed:
1. There was increased risk of foot pain in horses aged from 6 to 9 and 10-15, compared with horses less than 6 years old. Horses older than 15 were protected, indicating a “healthy horse” effect (meaning that although one would expect older horses to have more degenerative-type injuries, some animals are simply less injury prone).
2. Showjumpers were more at risk of chronic foot pain compared with dressage horses. This is probably related to the higher forces transmitted through the foot when landing over fences, and the strains placed on the soft tissues of the foot when performing the quick turns that are very much part of showjumping.
3. Thoroughbred cross-breeds had a higher risk compared with warmbloods.
4. Horses with a high bodyweight to height ratio, indicating that they were overweight, were more at risk than horses in leaner bodily condition. This may reflect the relative loads transmitted through feet of similar size, with higher loads in the overweight horses.
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