Far too often when discussing a horse’s foot, we use the word "normal" as a reference point to determine its state of health. But what is the "normal" we are comparing it to? Normal refers to a single foot on a specific horse, nothing more or less, because all feet are not born equal. Let’s throw out the term normal and instead talk about "healthy." Whether a foot’s shape, angles, and symmetry match a textbook ideal has little bearing on whether that foot is healthy. In fact, taking a foot that deviates from one’s concept of normal and forcing it to meet those standards frequently causes far more harm than good.
Healthy feet can be remarkably different in many ways, but they do share some common features. For instance, a healthy foot can replace sole and horn as required, regardless of whether it is shod or barefoot. The healthy hoof also can maintain appropriate palmar/plantar angle (the angle the wings of the coffin bone make with the ground) with only subtle farrier intervention; maintains adequate medial/lateral (inner/outer) balance relative to the articular (joint) surface of the coffin and pastern joint; sustains digital cushion mass, which is responsible for shock absorption; and helps maintain healthy heel tubules (which grow downward from the coronary band and provide strength and resistance, protecting them from excessive loading and inevitable crushed heel syndrome).
The differences between this horse's front feet are typical variances that occur within healthy feet of most breeds.
Courtesy Dr. R.F. Redden
Feet can remain within these healthy boundaries, though they can also deviate from this natural range for a variety of reasons, many of which we can identify, predict, and manage. The most important aspect of a healthy foot is overall mass (e.g., sole depth, hoof wall thickness and strength, and optimum frog and digital cushion function). If a foot has adequate mass, the qualities of strength, durability, and balance will follow.
To illustrate hoof differences, let's look at the healthy front feet of a Thoroughbred race mare.
In Image 1 the heel bulbs are asymmetrical, and the left front foot has narrower heel bulb conformation than the right. Also in the left foot, the heel height from ground to hairline is greater, the frog width is narrower, and the frog sets deeper into the foot than the right. The wall angle at the quarters is steeper and the diameter and circumference of the coronary band is smaller on the left than the right. Notice the sagging effect of the right frog and buttress (the farthest weight bearing point of the heel).
In Image 2, the right front has smaller toe and heel angles and lower heel height than the left. The tubules in contact with the ground surface of the right front are farther under the heel bulbs than those of the left. The growth ring patterns indicate the right front grows slightly more toe than heel while the left front grows slightly more heel than toe. This slight growth discrepancy is well within healthy parameters, as adequate mass and balance are present. The single set of nail holes indicates the foot is capable of replacing sufficient horn and sole every four to six weeks, even though the feet are mismatched.
The majority of the differences between this horse’s front feet are typical variances that occur within healthy feet of most breeds. Each foot's internal and external characteristics are essentially shaped by genetics, but they constantly change with the effects of age, use, farrier care, management, environment, and normal wear and tear. Healthy feet are as different as our faces. They all have a range of functional limitations and the ability to adapt as well as heal and replace overly stressed and damaged soft tissue and horn. Trying to define the normal foot limits us to speaking about a particular foot on a specific horse. Observing the strong and durable features of healthy hoof capsules helps us better understand there is not a single standard image for all feet.
R.F. Redden, DVM, is an equine veterinarian, farrier, and founder of the International Podiatry Center, based in Versailles, Ky.
Originally published in the May 2013 issue of The Horse: Your Guide To Equine Health Care