Your horse's feet are some of the most important structures contributing to his performance ability, and most people do what they can to keep them healthy. Unfortunately, things can and do go wrong with your horse that can cause hoof cracks to form. Maybe he pulled a shoe in the pasture or grabbed his heel during a competition. Perhaps conditions have been muddy or icy. Sometimes you don't know what happened. Still, there it is: A crack. What can be done about it?
Most cracks are superficial and grow out without consequence. However, there are instances where the crack is more severe, or what appears to be superficial becomes more serious. Then you could be looking at lameness, infection, and a much longer recovery time.
The Normal Hoof
The hoof is composed of a number of regions, including the wall, sole, frog, and the white line. The hoof wall bears most of the horse's weight and is most vulnerable to wear and trauma. Directly inside the hoof wall is leaf-like epidermal that interlocks with the inner dermal laminae, anchoring the hoof to the coffin bone. This allows the hoof wall to grow down while still being attached to the third phalanx (coffin bone) inside the hoof.
The sole covers the bottom of the horse's foot and protects the coffin bone from injury. It should be concave, which keeps it from bearing weight and helps support the bony column. The frog, which is also on the bottom of the foot, is relatively soft and triangular and helps absorb shock and maintain traction. Finally, the white line is about an eighth of an inch wide and is the junction between the sole and wall. It serves as a guideline for driving nails between the sensitive and insensitive tissue.
In addition to the basic outer parts of the hoof, there are several inner structures as well. The digital cushion is a shock absorber located above the frog in the back half of the foot. The distal end of the second phalanx (short pastern), third phalanx (coffin bone), and navicular bone are the three bones located in the horse's foot. Finally, lateral cartilages are attached to the wings of the third phalanx and rise up above the coronary band.
Types of Cracks
Hoof cracks can occur at any time and are not breed or sport specific, notes Bill Moyer, DVM, professor and head of the Department of Large Animal Medicine and Surgery at Texas A&M University. Horizontal cracks, while more unusual, are usually due to injury or the result of an abscess that ruptures at the coronary band thus interfering with normal hoof wall growth. They are often minor and will grow out in time. Much more common are vertical cracks, which, according to Moyer, have not received much attention with regard to research and thus most "information" is based on experience. The cracks can be complete (ones that run from the coronary band to the ground), or incomplete (shorter ones), and they can happen at the toe, quarter, heel, or bar.
A crack can vary from only affecting the external wall to involving its full thickness and the underlying sensitive tissues, notes Moyer. The latter likely cause pain and lameness and can bleed and/or be infected. "Hoof wall cracks can occur suddenly and presumably from focal abnormal stress or the result of previous damage to the underlying horn making the wall more likely to fail (crack) over time," he added. "Previous damage could be the result of wall separation, laminitis, and other problems affecting the deeper structures.
"Hoof cracks create wall instability and thus motion at the crack site may occur," continues Moyer. "It is generally the motion (and thus need for stability) that can create the pain. The instability cause may allow what was a small crack to propagate and be more extensive with time."
Who is Affected?
Moyer says cracks are "reasonably common." He says, "The incidence in Standardbred racehorses is probably the highest within breed and sport types. This may be a function of the reasonably heavy workload and the fact that they are shod frequently and work on reasonably hard track surfaces. Because of the abrasive nature of some tracks, the shoes wear rapidly and thus there is the need for frequent shoeing. Racehorses in general appear to have a higher incidence, whether Thoroughbred or Quarter Horse. In my experience, the incidence in the winter is higher and further indicates that it may that the addition of chemicals to the surface to prevent surface freezing play a role."
Stephen O'Grady, DVM, MRCVS, who specializes in foot problems at Northern Virginia Equine in Marshall, Va., agrees that Thoroughbreds are very susceptible to hoof cracks, but it is due to more than just their job. "They come from the factory with feet that are less than ideal," he says.
Causes of Cracks
It is helpful, particularly when it comes time for repair, to know the cause of the crack. "You have to address the reason," O'Grady says. He mentions poor foot conformation, such as a club foot, long toe/low heel, sheared heels, and thin hoof walls with a flat sole as predispositions for cracks. In those situations, the foot's landing pattern causes inappropriate forces to be placed on it, which often leads to a distorted hoof capsule or a dished foot and eventually a toe or quarter crack.
"It is very, very rare to see a horse with a quarter crack that does not have a sheared heel," he says.
In addition, O'Grady cites trauma to the coronary band, pre-existing damage to the laminar corium from infection, focal foot imbalances, and short shoes as additional causes of quarter cracks.
Moyer says most central toe cracks have underlying damage and that the crack is a result of the weakened structure. This often is the result of damage via laminitis, club feet, or simply excessively long toes.
Moyer warns that damage resulting from previous injury to the coronary band or damaged horn can be difficult to repair, and permanent solutions are not likely. The amount of scar tissue growing down is proportional to the amount of damage that exists at the site of injury. Thus, these can only be managed, not cured.
While many hoof cracks are minor, repairing one should be considered when the horse is lame, the crack is infected, or the damage is extensive enough that lameness is likely to result.
Prior to determining the repair method, Moyer recommends noting the type, location, and degree of involvement at the crack site. The costs involved, time, and horse's job can also all impact the repair choice. Finally, it is very important that the vet and/or farrier have experience in the given technique because doing a poor job can do more harm than doing nothing at all.
Moyer also feels that the person holding the horse needs to be someone who can handle the animal appropriately, especially if the repair work is extensive.
Foot preparation is crucial to successful repair. The feet should be properly trimmed and balanced so that they strike the ground evenly. If poor landing pattern is not addressed, chances are the crack will keep breaking open. Then, every time it heals, it does so with more scar tissue.
After trimming, all dead or loose horn is removed. The crack is cleaned with a motorized burr or modified hoof knife and explored to determine the extent of damage and infection (if present) because that can have a significant impact on the chosen method. Any infection should be cleared up before attempting a repair.
There are many techniques and materials available to repair cracks, and no single technique will solve all problems. According to Moyer, the techniques currently being used for hoof crack repair include: "Remove hoof wall (make it non-weight-bearing below the crack); remove the offending wall and thus the crack; bum or rasp across the top of the defect; stabilize in one of a variety of means (nail across the crack, clamps of various designs, suture with various materials across the crack, patch the defect with various materials, placement of screws and wires to stabilize the crack); or apply shoes (a wide variety are used). There are also tapes and other methods I have failed to mention."
The list of repair materials, he says, is equally as extensive and includes "various metals, rubber compounds, epoxies, polymethylmethacrylates, plastics, fiberglass, 'space age' fabrics such as Spectra and Kevlar, suture materials of various description and types, and so on."
Moyer says "the goal of repair is to stabilize the crack, protect the damaged wall, eliminate pain and bleeding, and prevent further progression and possible infection."
Often, it is necessary for the horse to continue to perform. In that case, O'Grady feels that the repair must provide strength and stability for performance, while also promoting healing. He recommends placing an implant (wires) along with an acrylic patch.
The simplest and least costly repair technique that Moyer suggests is fitting the horse with a bar shoe (usually an egg bar) with or without clips to anchor the shoe to the wall for more hoof stability, reduced work/rest, and time to grow out with an anticipated average growth rate of one-quarter-inch per month. This method is relatively inexpensive and is best for reasonably stable cracks that are not extensive.
Other materials used to increase stability are various fabrics and adhesives. Different types of fabric are used because some are appropriate for cracks with small amounts of lost hoof wall, while others are intended for high-stress repairs. Some of the earlier acrylics didn't work well because they were too rigid and didn't maintain a consistent bond long enough. Fortunately, the newer adhesives on the market are more reliable. When covering an infected crack, inserting a drain under the patch might be helpful, but it is best to allow the infection to heal prior to applying a patch, noted Moyer.
O'Grady suggests that to fix a toe crack, one first needs to correct the hoof capsule distortion through proper trimming. Once the hoof wall is corrected, the crack might stabilize on its own, but he stresses that no stabilization will work if the distortion isn't addressed. If he chooses to repair a full thickness toe crack, O'Grady prefers a metal band with screws because the crack needs some kind of stability. However, he warns that the practitioner needs to be experienced to use these methods. Toe crack repair should be done with the foot off the ground so the crack is open to prevent pinching when weight is on the foot.
Horse owners can't necessarily keep their horses from getting hurt, so it might be difficult to actually prevent hoof cracks. However, both Moyer and O'Grady agree that supplements and topical applications have little effect on the quality of the hoof. Having a good farrier who properly manages the feet and maintaing plenty of exercise for the horse are the best preventive measures.
Even though the majority of hoof cracks are minor, they are still worth the attention of your farrier and sometimes your veterinarian. Addressing one promptly might prevent bigger problems. However, when a crack is severe, it is best to contact your farrier and your veterinarian. The two should consult on the best way to proceed. If the repair procedure is complex, make sure you find someone experienced and comfortable with the task.
Most of all, be patient. It can take a long time for hoof cracks to heal and grow out, but taking the appropriate amount of time will help ensure your performance horse is back on four solid feet.
"How to Repair a Quarter Crack," by Stephen O'Grady, DVM, BVSc, MRCVS, www.TheHorse.com/emag.aspx?id=6754.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.