Canker in Horses

The etiology and pathogenesis of canker in horses remain unknown. Anaerobic bacteria, spirochetes, and bovine papillomavirus have all been suspected as possible etiological agents.

The disease is characterized as proliferative inflammation of the epidermis and dermis.

Canker in horses usually starts in the central or collateral sulci of the frog, then generally spreads rapidly to the main body of the frog. Canker may extend to the sole and heel bulbs, and it occasionally involves the hoof wall and coronary band.

Poor hygiene and being housed in warm, moist environments are thought to be predisposing factors for canker; however, the disease can occur in horses that undergo regular hoof care and live in ideal conditions.

Canker has historically been reported most commonly in draft breeds, but it can occur in any breed of horse.

Whether canker causes lameness in horses depends on the chronicity of the disease. It can be present in one or multiple hooves, and affected limbs may have a palpable increase in digital pulse intensity. The normal horn of the sole and frog is destroyed and replaced by a white, frondlike version of abnormal horn that is described as looking like crabmeat and bleeds easily.

A presumptive diagnosis of canker in horses is usually based on the characteristic appearance of the affected tissue. A biopsy and histological examination are necessary for definitive diagnosis; however, these diagnostic tests are rarely performed.

Differential diagnoses for canker include thrush and exuberant granulation tissue.

Canker in horses may be treated with chemical, surgical, and medical approaches, singly or in combination.

Chemical treatment of canker consists of soaking the foot in a chlorine dioxide solution in a closed-bag system for approximately 45 minutes per treatment session. This process may be repeated every 24–48 hours, usually for several treatments. Chemical treatment is generally quite successful, and it is minimally invasive.

Surgical debridement of the affected tissue in cases of canker can usually be performed in a sedated standing horse with perineural analgesia. Debridement may require general anesthesia, depending on the temperament of the horse and severity of the canker. The goal of surgical excision is to remove all the affected tissue without disrupting the germinal layer of the epidermis. Affected tissue is commonly removed with a combination of hoof knives and scalpels.

Carbon dioxide laser treatment and cryotherapy have also both been used for removal of affected tissue in cases of canker in horses. Rongeur forceps are useful for removing tissue that is difficult to excise with hoof knives or scalpels. Depending on the depth of debridement, a tourniquet may be necessary. Cryotherapy has also been used on affected tissue; however, that use is somewhat controversial because of the potential for damage to germinal tissue.

Medical treatment for canker in horses consists of applying topical medications after surgical debridement. Antimicrobials such as metronidazole and oxytetracycline are commonly used. Application of a solution of 10% benzoyl peroxide dissolved in acetone has also been reported to have good results. These topicals are held against the desired area by a hoof bandage or treatment plate shoe and are changed daily during the early treatment stage. NSAIDs may be necessary for pain management after debridement.

It is important that a horse with canker be kept in a clean, dry environment while the tissue is healing. Regular rechecks are recommended to closely monitor for any recurrence of diseased tissue. Treatment should result in marked improvement within 2 weeks. 

Because the response to canker treatment in horses varies, the initial prognosis is guarded. Complete recovery with normal horn growth is possible with appropriate treatment and housing management.

• Also see pet health content regarding canker in horses.