Infections of the Equine HoofPosted by Rood and Riddle on October 31, 2011
The equine hoof is a unique structure composed of bone, connective tissue, and an extensive vascular pattern. The keratinized tissues of the hoof wall, sole, and frog protect the sensitive structures of the hoof and provide a barrier against invading microorganisms. The sensitive structures of the foot are susceptible to infection if any of these structures are damaged or weakened. Typically, causes of foot infections can be broken down into:
1. Environmental- puncture wounds or gravels
2. Hoof Capsule Defects- cracks, flares, cracks, contracted heels
3. Digital Instability- laminitis
4. Systemic- bacteria invade the hoof through the blood stream
The severity of the infection and prognosis of the patient depend on the structures of the hoof involved. Infections of deep structures such as the coffin bone, coffin joint, navicular bone/bursa, digital tendon sheath, or collateral cartilages require more care and intense treatment than infections of superficial structures.
Early identification of hoof infections can greatly improve the case outcome. The longer the infection goes untreated the more damage the foot will suffer. Many times a serious puncture wound to a vital foot structure can heal uneventfully if treated appropriately and in a timely manner. Identifying the lameness and a good examination of the injured foot are necessary. Often, the injury or insult is obvious such as a puncture wound with the foreign body still in the foot. Puncture wounds to the central region of the foot should be treated as a medical emergency due to the risk of involvement with deep structures such as the navicular bursa, coffin joint, and the tendon sheath. When the problem is not as obvious hoof testers can be useful to localize the affected area. It is very important for the veterinarian to obtain good quality radiographs of the injured foot. If there is a foreign body in the foot, it is important to take radiographs to outline its location. If the foreign body is not present a radiograph can be taken, with radio-opaque dye injected in to the defect or puncture site to outline the tract. This technique is called a fistulogram (Fig. 2). Other advanced imaging techniques such as MRI or CT may be useful to localize the diseased area. Getting the cases proper treatment early is imperative for a successful outcome.
Foot abscesses are a very common problem in the equine patient and if not identified and treated properly may develop into a more serious problem. The best approach to hoof abscesses is to establish drainage, protect the sensitive area, and provide a clean environment. Topical antiseptics such as iodine-based solutions are commonly used over the abscess site. If the abscess does not resolve easily and is draining excessively, additional measures should be taken. Your veterinarian should culture the site and an antibiotic sensitivity test performed. The draining tract should be thoroughly cleaned and radiographs taken. If the coffin bone is infected, it may be necessary to perform surgery to remove the dead and infected tissue. Broad-spectrum systemic antibiotics should be initiated.
Larval debridement therapy is the use of sterile Phaenicia sericata fly larva to debride necrotic tissue in hoof infections. This method of treatment has long been used in human medicine and more recently in veterinary medicine. The larval secretions liquefy and ingest the dead tissue, disinfect the infection and stimulate wound healing. It is a minimally invasive method to remove dead tissue without disturbing the normal architecture of the internal structures of the foot. We commonly use this as part of our treatment regimen on serious foot infections.
Quittor is the horseman’s term for an infected collateral cartilage. This type of infection can occur due to an abscess, puncture wound, laceration, or even pressure necrosis from blunt force trauma. This condition presents as a draining tract from the coronary band or just above the coronary band. The treatment is to remove all of the dead/infected tissue and begin antibiotic therapy.
Thrush is a term used to describe an infection of the frog of the foot by keratolytic bacteria. Fusobacterium necrophorum is a gram-negative obligate anaerobic bacillus that has been associated with this type of infection. Thrush usually presents as foul smelling black matter in the sulci of the frog. Thrush commonly occurs as a result of poor environmental conditions but may occur in horses that are well kept. If the hoof has abnormalities such as excessive length, contracted heels, or shod with a full pad thrush may be more likely to develop. Horses may have thrush but not show lameness until the sensitive structures are involved. To eliminate thrush it is important to provide a clean environment and give the hoof a balanced trim to remove the necrotic tissue. Most mild cases respond to topical treatment with antiseptics. There are many topical agents available that are effective in treating this condition. Severe cases may need surgical debridement and more aggressive treatments.
Canker is an uncommon infection seen in poor environmental conditions and usually associated with draft breeds. Canker is thought to be an intracellular microorganism infection of the hoof usually affecting the frog and heel bulbs. Canker is a proliferative painful mass which usually outgrows its own blood supply and develops necrotic areas. The characteristic yellow-white tissue covering the frog and heel bulbs is caused by abnormal keratin production. Treatment of this condition consists of surgical debridement of the abnormal tissue followed by cryotherapy, thermal cautery or lazer to kill the remaining canker tissue at the margins. A paste of metronidazole and oxytetracycline seems to be useful in the treatment of this disease following debridement. While treating this condition, it is necessary to keep the foot clean, dry and protected. Some severe cases may have an unstable hoof capsule which may need support with special shoeing while healing.
White line disease is believed to be caused by keratinolytic fungi found ubiquitous in the environment. The pathogenic organisms digest the keritanized tissue between the stratum medium and stratum internum of the hoof wall. This type of infection is usually associated with abnormalities or defects in the hoof. Chronic laminitis, excessive hoof length, flares, hoof cracks, and poor quality horn are all conditions that give the organism an opportunity to invade the hoof capsule and set up the infection. This type of infection may go unnoticed until lameness is apparent or the hoof capsule damage is severe. Severe cases can develop instability and displacement of the coffin bone, very similar to laminitis or founder. Special shoeing is required in some cases along with treatments to kill the fungus. Chlorine dioxide is often used to treat this disease once debridement has been performed.
Keratoma is a tumor of the keratin producing epidermal cells of the inner hoof wall. They can be cylindrical or spherical in shape. The growth of the tumor beneath the rigid hoof wall or sole will press into sensitive tissue and the coffin bone causing pressure necrosis resulting in chronic recurrent abscesses. Abnormal hoof growth is also evident in some cases. Surgical removal of the keratoma is usually recommended in theses cases.
In conclusion, early identification and treatment are the keys to resolving hoof infections. It is important to remember that the hoof like any other injured or infected area needs a clean dry environment to heal. This can be accomplished in many ways such as a treatment plate shoe, foot cast, or a simple foot bandage in some cases. We must also remember that stabilization of the foot is necessary if the supporting structures of the hoof have lost integrity. Finally, a regular trimming/ shoeing schedule of ~6 weeks will help maintain the integrity of the hoof and help prevent unwanted infections.
Common Ailments of the Foot