Hoof horn disorders, causes and cures (Proceedings)

General principles of therapy for digital diseases are to eliminate the pain first and foremost and then to correct the underlying problem if possible. Hoof horn that is detached from underlying layers of hoof or corium should be removed. Around areas of exposed corium the wall or sole should be thinned to make the existing hoof capsule more flexible along the border of newly developing cornified epithelium. Bandages do not promote healing but may be used to control hemorrhage or to maintain some antibiotic or antiseptic in contact with a wound. Regardless of original intent, most bandages should be removed in a few days and the lesion left uncovered. Hoof blocks are an essential tool for managing painful conditions and their use should be routine. Non-steroidal anti-inflammatory drugs such as flunixin and ketoprofen should be considered to reduce the pain of some severe claw horn diseases and following surgery of the digit. Their use is not encouraged enough by most veterinary practitioners.

Basic tools for lame cow therapy include left and right hoof knives and small hoof nippers. Additional tools that are in wide use are long handled hoof nippers and electric angle grinders with carbide-toothed chipper wheels. There is a wide variety of restraint devices present on farms and still some farms have nothing. Practitioners should encourage every client to have a safe and efficient place or device for lameness work since every herd will have lame cows and most practitioners, at least in the United States, do not travel with a trimming chute to every call. Since most lameness occurs in the rear feet, simple devices for small herds should be made available to make rear limb lifting and examination easy.

White Line Abscess

The most common location is in the posterior third of the white line of the rear lateral claw. The presence of this lesion may be detected with the response to finger pressure on the bulb of the heel of the affected digit. If the abscess is near the toe tip it may be necessary to apply pressure with hoof testers to identify the location. In the fore limbs the most common site is the posterior quarter of the medial claw. Usually white line abscesses are quite obvious after a thin layer of horn has been removed. There often is dark discoloration of a portion of the white line. Sometimes the white line is fissured with manure packed into the resulting crevice which must be cleaned before the specific site of the abscess becomes visible. Relieving the pressure within the abscess provides some immediate pain relief. Abscesses near the heel may dissect between layers of sole horn to exit at the heel resulting in a transverse flap of detached horn. Much less frequently than in the horse, abscesses under the wall may erupt at the coronary band. Treatment is to remove the detached horn and trim to allow walking without pressure on the inflamed corium. Large abscesses and those at the toe tip will benefit from the use of a hoof block on the healthy digit. Bandaging is discouraged. Most cows recover uneventfully and reexamination is not necessary. Hoof blocks should be removed in about 4 weeks. Occasionally white line abscesses will extend into the soft tissue structures of the digital cushion and involve structures posterior to the distal interphalangeal joint. These conditions require surgical intervention that is described later.

Sole Ulcer

Ulceration of the sole may occur in any digit but is most common in the lateral claws of the rear feet and the medial claws of the fore limbs. Symmetrical ulcers occur in both rear or both fore limbs. The typical site for ulceration is in the corium that overlies the flexor process of the third phalanx. Ulceration at the toe tip is a less common lesion in housed cattle but the most common lesion in extensive grazing dairies of the southern hemisphere. When it occurs in housed cattle it is though to be due to either overtrimming at the toe or from wear that exceeds growth. A third location of ulceration is at the heel sole junction. This may occur secondary to severe interdigital dermatitis or as is usually seen in the medial claw of the rear foot from unknown causes. The degree of damage to the sole and underlying corium varies from slight hemorrhage visible at trimming to complete absence of a portion of the sole to extensive necrosis of the underlying corium. The term complicated sole ulcer is used for those that have necrosis extending beyond the corium to include other tissues in the hoof.

Treatment for sole ulcer is to remove weight bearing from the affected portion of the digit. Depending on the location of the lesion and its severity this may be accomplished by corrective trimming and lowering the heel horn of the affected claw. Most often a hoof block is applied to the healthy claw. If the ulcer is in the typical site or at the heel and there is sufficient heel depth of the healthy toe a "heelless" trimming method may be used. This method, described by a Japanese hoof trimmer H. Manabe, is to remove all wall and sole from the posterior half of the digit to a depth that just preserves a thin layer of sole. When the cow stands there should be space for a finger between the floor and the remaining portion of the affected area. The use of this technique eliminates the need for a block but is always dependent on the cow having sufficient heel depth on the healthy digit. Bandaging is discouraged. If the corium is intact, the swelling that is usually present throughout the posterior portion of the digit including protrusion of the coronary corium will usually subside within a few days. Reexamination in about 4 weeks is recommended to check the integrity of the hoof block and to trim the sole horn adjacent to the original lesion. Healing time for full thickness sole ulcers is about 2 months. Reoccurrence in subsequent lactations is likely. Complicated sole ulcers require surgical intervention that is described later.

Thimbling or Transverse Wall Separation

This condition results from an insult to the coronary corium that results in an interruption in growth and resulting break in continuity of the horn tubules of the hoof wall. It is not apparent until the hoof has grown sufficiently for the break point to be about 5 cm from the coronary band. It is always present in all 8 digits but usually noticed due to pain in only one. The distal portion of the hoof capsule separates from the more proximal along the entire axial, dorsal, and abaxial regions. The sole is normally attached to the younger healthy wall and the older detached wall. Pain occurs when movement of the distal portion relative to the rest of the hoof pinches the corium at the toe tip. The goals of trimming are to minimize weight bearing at the toe tip by shortening as much as possible and thinning the sole at the toe relative to the rest of the hoof. Pain may shift from one limb to another as successive thimbles become more detached from the younger hoof wall. Recovery is complete and without complications as the thimbles wear or are trimmed away.

Interdigital Fibroma

Redundant skin in the interdigital space is a hereditary condition associated with lax interdigital ligaments resulting in a splay-toed conformation. It also occurs in cattle secondary to chronic interdigital dermatitis. By itself it is not painful unless the fibroma becomes so large that the cow pinches it between the sole and floor when walking. However, fibromas predispose a risk of foot rot and are common sites of digital dermatitis in endemically infected herds. For most dairy cattle fibromas occur secondary to interdigital dermatitis and should not be treated as a specific problem but as a reflection of the poor management of hygiene or foot bathing. There exists some pressure from farmers on veterinarians and hoof trimmers to remove fibromas as part of routine procedures and this should be discouraged. Rather, address the underlying causal factors.

If the fibroma is a part of a significant painful process in a cow then surgical removal is indicated. Anesthesia is discussed in the section on digit surgery. Sharp dissection of the skin around the base of the fibroma follows normal surgical site preparation. It is considered important for prompt healing to remove the interdigital fat as well as the protruding fibroma. Care must be taken to prevent surgical injury to the distal interphalangeal joint capsules and the cruciate ligaments when removing the fat. Some antibiotic powder may be placed in the wound but no dressings or packings before bandaging the foot to prevent splaying of the toes. The bandage may be removed in a few days as granulation tissue will fill the defect. Systemic antibiotics are optional.