What do a dish, a crack, a flare, and a sheared heel have in common? All these problems fall under the hoof distortion umbrella.
“An undesirable shape change is a distortion,” which can lead to discomfort and lameness, said Scott Morrison, DVM, of Rood & Riddle Equine Hospital, in Lexington, Kentucky, during the 2017 Annual International Hoof-Care Summit, held Jan. 24-27, in Cincinnati, Ohio.
Morrison explained that hoof capsule distortion can have many causes:
- A conformation fault, which is the most common;
- Balance issues;
- Stress from certain types of work, such as repetitive speed training; and
- Diseases, such as laminitis, white line disease, or canker.
Early Hoof Morphology
Managing hooves to prevent distortions starts at a horse’s birth. When horses are born, their hooves are almost perfectly symmetrical. The foal’s hoof is covered with a soft deciduous (meaning it will eventually shed) material and a soft sole to protect the mare’s birthing canal. The hoof hardens after birth.
The typical newborn foal hoof is very contracted with underrun heels, which quickly shift back into the proper position, said Morrison. He also said it’s normal for foals to rock back on their heels, causing the toes to flip up slightly, and to be weak in the flexor tendons.
Hoof evaluation and care should begin within the first week of life with a minor trim, which the farrier should repeat every few weeks to help get the foot completely on the ground.
“That juvenile period is really important for the digital cushion and the collateral cartilages and all those things to respond to stress and develop and mature in a way so they are strong enough when they become adults and athletes,” said Morrison, emphasizing the importance of getting the proper proportions on the foal’s foot.
Morrison said he often sees changes in the hoof capsule after a few months as foals start to toe out naturally. But as the foal ages, the hoof capsule will become more symmetrical again. He advised the farrier audience to evaluate foal feet carefully and observe how the foal walks. When horses are young, farriery can help manipulate conformation for the better, at least until growth plates ossify (harden into bone), he said.
If a growing foal’s limbs become too crooked, Morrison will intervene with shoeing, using an extension to help straighten the limb by shifting the foot’s center of pressure. (This is the point at which the ground force reaction [GFR] acts upon the hoof.) He’ll use a pour-in pad to help support the sole to mimic the barefoot condition as much as possible.
Morrison said any outward limb rotation will usually self-correct as the foal grows into a yearling and his chest widens. “It’s normal for the foot to be loaded a little bit more medially than laterally (on the inside than the outside) resulting in the medial wall being more vertical or straighter than the lateral wall,” he said.
Shoeing and Trimming Basics
The way the hoof interacts with the ground impacts the whole limb (even the whole body), especially the coffin joint and the navicular structures. Morrison emphasized that farriers need to understand the front half of the foot’s role in establishing traction and supporting various inner hoof structures.
Morrison likes to mimic the barefoot condition as much as possible to minimize the effects of shoeing. He said farriers should be able to draw a line where the coffin bone is and then trim to the widest part of the foot, which is usually the center of rotation. Two-thirds of the coffin bone should be in front of the center of rotation and one-third behind.
He also recommended trimming the foot to create a positive palmar angle (the angle the wings of the coffin bone make with the ground), ideally 2-5 degrees, which he considers within normal range. The center of rotation should line up with the geometric center of the weight-bearing surface of the shoe. The ground surface of the heel should line up with the widest part of the frog, and there should be an adequate amount of sole depth, which varies based on the size of the horse’s hoof. Ideally, however, it should equal the width of the horn lamellar zone (the distance between the laminae and the outside of the hoof wall).
Morrison said the appropriate location of a horse’s breakover point—the forwardmost point of the foot or shoe’s ground contact—is hotly debated. He suggested it be at the apex of the coffin bone, unless he is treating a horse with problems.
Supporting Compromised Hooves
If a horse’s hoof capsule starts to distort due to imbalances, Morrison said he favors removing shoes when possible and letting the frog hit the ground, which stimulates hoof growth.
For horses with stressed feet that need axial (inner hoof wall) support, Morrison suggested supporting the frog with heart bars, heel plates, pour-in sole supports, or pads, or decreasing shoe thickness to allow the frog to contact the ground.
He said the most popular way to provide support is with a straight bar shoe, which puts weight on the base of the frog and, thus, unloads the heels. Additional options include an egg bar shoe, which is designed to provide limb support; a heart bar, which has a cutout “V” useful for treating thrush; or a short heart bar, which is safe for speed horses.
Pour-in pads provide support by allowing the horse to use his whole sole. A frog cradle is a safe way to support the base of the frog, he said. Farriers often use stabilizer plates on racehorses, but they can sometimes be difficult to clean out and can bruise the hoof bars.
Very compromised hooves are sore everywhere, making it difficult for farriers to provide any support, said Morrison. In these cases, he applies a heel plate shoe with some dental impression putty and rolls the toe and the heel to make the horse more comfortable.
“You have to look at distortions and keep in mind why they are there and why that foot is distorted and try to respect the lower limb,” said Morrison. “In trying to change hoof capsule distortions, you also want to think about how you are going to change the mechanics of the whole lower limb.”