THE MERCK VETERINARY MANUAL
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Disorders of the Interdigital Space in Cattle

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The interdigital lesions of foot-and-mouth disease can, in some instances, be confused with other diseases causing lesions of this region (see Foot-and-Mouth Disease and see Vesicular Stomatitis).

Footrot

(Interdigital phlegmon, Foul in the foot)

Footrot is a subacute or acute necrotic infection that originates in the interdigital skin, leading to cellulitis in the digital region. Footrot has a worldwide distribution and is usually sporadic but may be endemic in intensive beef or dairy cattle production units at pasture. The incidence varies according to weather, season of year, grazing periods, and housing system. Footrot is less common today than it was decades ago probably because dairy cows spend much less time at pasture. However, on average, footrot accounts for up to 15% of claw diseases.

Injury to the interdigital skin provides a portal of entry for infection. Maceration of the skin by water, feces, and urine may predispose to injuries.

Fusobacterium necrophorum is considered to be the major cause of footrot. It can be isolated from feces where it may survive as a saprophyte, which may explain why control is difficult. This organism can survive in moist soil.

F necrophorum is a gram-negative, nonspore-forming, nonflagellated, nonmotile, pleomorphic anaerobic bacteria. It has a lipopolysaccharide endotoxin that is capable of necrotizing activity. There are 3 subspecies and a number of genotypes, each of which targets different tissues. When PCR assays become more widely available, the genotypes will be more readily identifiable.

Other organisms, such as Dichelobacter nodosus, Staphylococcus aureus, Escherichia coli, Arcanobacterium pyogenes, and possibly Bacteroides melaninogenicus can also be involved.

Research suggests that the incubation period of footrot can be a week. The fore or, more commonly, the hindlimbs can be affected, but more than one foot is rarely involved at the same time in mature cows. However, footrot can occasionally develop in several feet in calves. The first sign is swelling and erythema of the soft tissues of the interdigital space and the adjacent coronary band. The inflammation may extend to the pastern and fetlock. Typically, the claws are markedly separated, and the inflammatory edema is uniformly distributed between the 2 digits. The onset of the disease is rapid, and the extreme pain leads to increasing lameness. In severe cases, the animal is reluctant to bear weight on the affected foot. Fever and anorexia are seen. The skin of the interdigital space first appears discolored; later, it fragments with exudate production. As necrosis of the skin progresses, sloughing of tissue is likely to follow. A characteristic foul odor is produced.

If the disease proceeds unchecked, weight loss is severe and milk yield is significantly reduced. Milk production may not recover during the current lactation. Open lesions can be infected with secondary invaders. If the necrotic lesion is located in the anterior region of the interdigital space, the distal interphalangeal joint can become infected.

Hematogenous infection of the tissues of the interdigital space may account for peracute cases of footrot, which are referred to as either “blind” or “super foul.” This form of footrot is characterized by the initial absence of a skin lesion, extreme pain, and the tendency to progress despite aggressive therapy.

Most treated animals recover in a few days. Good results are obtained with penicillin G, IM, for 3 days. Treatment should be administered as soon as signs are observed. However, the label dosage may be inadequate to effect a rapid resolution, and increased dosages may be needed, requiring increased withdrawal times. Treatment of “super foul” must be particularly aggressive. Early cases respond well to single doses of long-acting oxytetracycline.

Sodium sulfadimidine solution IV or trimethoprim/sulfadoxine IV or IM, bid for 3 days, can also be used. A single oral administration of a long-acting bolus containing baquiloprim/sulfadimidine may be suitable for treating beef cattle.

High concentration of an agent in the target tissues can be achieved by a regional IV injection. Positive results have been obtained with penicillin or oxytetracycline.

Local treatment is essential for some longstanding cases and in all instances in which the anterior region of the interdigital space has been compromised. The lesion must be thoroughly cleansed, but it is inadvisable to curette or otherwise remove necrotic tissue surgically. The dorsal pouch of the distal phalangeal joint is very superficial at this point. A nonirritant bacteriostatic agent (such as nitrofurazone or a sulfa preparation) should be applied as a topical dressing. The application of gauze, cotton batting, or bandages is contraindicated. However, the lesion can be protected and immobilized by binding the digits together with a bandage. The entire digital region can be protected from contamination if it is enclosed in a plastic bag that is fixed in place with an adhesive bandage. However, prolonged protection is not advocated because the enclosed lesion tends to macerate further. Bandages, if used, should be replaced daily.

Animals that are actively shedding infectious organisms should be isolated until signs of lameness have disappeared. If this is not possible, a waterproof dressing or protective boot should be applied; however, animals wearing protective boots should be monitored carefully to avoid additional damage. Boots should be disinfected between use.

Because busy traffic areas are invariably heavily contaminated, steps should be taken to ensure that areas around drinking troughs, gateways, and tracks are adequately drained. Animals at pasture might be moved to a clean, dry area, or possibly housed during periods of heavy rainfall. Contaminated concrete must be frequently cleaned and scraped free of manure.

Preventive use of a footbath with an antiseptic and astringent solution (eg, copper or zinc sulfate [7–10% in water]) has given beneficial results. Formaldehyde solution (3–5% in water) can also be used, but in some areas it is considered to be an environmental hazard if discharged into natural waterways.

Ethylenediamine dihydroiodide has been used as a feed supplement for prevention, but the results are extremely uncertain. Vaccines against F necrophorum have failed because of the weak immune response to the bacterium. High levels of zinc fed as a supplement have a beneficial effect by improving epidermal resistance to bacterial invaders.

Interdigital Dermatitis

(Stable footrot, Slurry heel, Scald)

Interdigital dermatitis is diagnosed today much less frequently than it was prior to digital dermatitis reaching epidemic proportions (see below). It is a low-grade infection of the interdigital epidermis that causes a slow erosion of the skin with discomfort but no lameness unless the lesion becomes complicated. The distribution is worldwide. Morbidity is usually high in housed animals, particularly toward the end of the winter. The disease is most commonly seen when humidity is high, in temperate climates, and under poor hygienic conditions, especially in housed dairy cattle. When animals in such herds are examined, it is not unusual for 100% to have lesions of varying degrees of severity.

In tied systems, the hindlegs are affected more often than the forelegs. In loose housing systems, the distribution between fore and hindlegs is about equal. Animals on slatted floors are affected less often than animals on solid floors.

Interdigital dermatitis is caused by a mixed bacterial infection, but Dichelobacter nodosus has been considered to be the most active component. D nodosus is an anaerobe and exceptionally proteolytic. The source of the infection is the cow itself, and the infection spreads from infected to noninfected animals through the environment. D nodosus cannot survive for more than 4 days on the ground but can persist in filth that is caked onto the claws. The bacteria invade the epidermis, but the organisms do not penetrate to the dermal layers. As the condition progresses, the border between the skin and soft heel horn disintegrates, producing lesions similar to ulcers or erosions. At this stage, the lesions cause discomfort.

The first stage of the condition appears to be an exudative dermatitis. The exudate oozes to the commissures of the interdigital space and forms a crust or scab, which may be observed occasionally on the dorsal surface of the digits. As the condition progresses, the animal shows discomfort by “paddling,” ie, constantly moving from one foot to the other. If the heels of the hindfeet are especially painful, the limbs are held further back than normal. True lameness does not develop until a complicating lesion is present. After a prolonged period, during which the animal has avoided bearing weight on the heel, the horn beneath the heel increases in thickness and some aberrations of gait result. In dairy cows, interdigital hyperplasia (corns, fibroma) may be caused by the chronic irritation of the interdigital space. Often, the fibroma develops on one side of the interdigital space.

Systemic therapy, including the use of antibiotics, is not cost effective. In severe cases, the lesions should be cleaned and dried, after which a topical bacteriostatic agent is applied, eg, a 50% mixture of sulfamethazine powder and anhydrous copper sulfate. Alternatively, an animal can be confined in a footbath for 1 hr, bid for 3 days.

Good management and housing systems to keep claws dry and clean are most important. Regular foot trimming helps avoid complications. Foot bathing, beginning in late fall and before clinical cases can be identified during high-risk periods, is essential in herds known to be infected. Weekly foot bathing may be sufficient in the late fall, but the frequency may have to be increased in late winter.

Digital Dermatitis

(Hairy warts, Papillomatous digital dermatitis)

Digital dermatitis is a highly contagious, erosive, and proliferative infection of the epidermis proximal to the skin-horn junction in the flexor region of the interdigital space. Morbidity within a herd can be >90%. It can affect any breed or age group, although young animals with a poor immune response are most susceptible. It spreads rapidly from newly acquired animals, or it may be introduced by any mechanical vector, eg, boots or hoof trimming instruments.

The condition was first reported in Italy in 1974 as a large outbreak, although it was reported in isolated animals many years before. Since 1974, the disease has spread across the dairy-producing areas of Europe and the USA. The incidence in beef cattle appears to be minimal. The incidence is highest in loose-housed herds that are not kept clean. The prevalence is highest in the fall and winter and is lowest if the animals are pastured.

Two main types of lesions are seen. The erosive/reactive form is seen more commonly in Europe while the proliferative or wart-like form is more prevalent in North America. Both forms cause varying degrees of discomfort and may give rise to severe lameness. Both forms can be seen in the same animal. The two forms likely represent different stages of the same disease process.

Explosive outbreaks can occur when affected cows are introduced to herds previously unaffected by the disease. In herds in which the disease has become established, young cattle are particularly susceptible.

The etiology of digital dermatitis is uncertain, although it is widely believed that more than one bacterium is involved. It has been postulated that the ubiquitous Dichelobacter nodosus first destroys the epidermis, allowing Treponema spp such as T phagedenis, T vincentii, and T denticola to gain entrance to deeper tissues. At all events, deep in the epidermis of erosive/reactive lesions, 2 types of spirochetes can be demonstrated using Warthin-Starry stain. One is a long, spiral, filamentous organism 12 × 0.3 μm, and the other is a shorter, thicker spirochete 5–6 × 0.1 μm. Other bacterial species isolated from lesions are Fusobacterium spp, Campylobacter spp, and Prevotella spp. Strong circumstantial evidence suggests that a virus plays a part in the pathogenesis of the disease, but none has been isolated to date.

Lesions are most common in the region of the flexor commissure of the interdigital space. Less typically, lesions have been seen on the dorsal surface of the foot as well as around the dewclaws. One or both hindfeet are most commonly involved, although forefeet can be affected.

Lesions vary considerably in size and appearance both within a herd and in different parts of the world. An “M” system has been developed to classify the stages of this disease: M0 = Normal skin. M1 = Early, small circumscribed red to gray epithelial defects of <2 cm in diameter preceding the acute stage, appearing between acute episodes, or within the margins of a chronic M4 lesion. M2 = Acute, active ulcerative (“strawberry-like”) or granulomatous (red-gray) lesions >2 cm in diameter and sometimes surrounded by white halo-like tissues, which may be slightly papillomatous. M3 = The healing stage occurring within 1–2 days after topical therapy. The lesion is covered with firm scab-like material. M4 = The chronic stage in which the epithelium is thickened and/or proliferative and several centimeters in diameter. The proliferations may be filamentous or scab-like.

Digital dermatitis is different in appearance from footrot because swelling and fever are normally absent.

Acute lesions are initially treated topically. The lesion should be scrubbed clean with a stiff brush and soapy water, rinsed, and dried. An antibiotic powder, such as oxytetracycline is applied and protected by a gauze pad or a small feminine hygiene pad held in place by a waterproof bandage or a reinforced nylon device (booties) that can be affixed with Velcro® closures. Multiple treatments are usually necessary. Oxytetracycline treatment has not resulted in detectable residual levels of the antibiotic in blood or milk. Extremely high parenteral antibiotic dosages have been reported to help resolve severe lesions.

Once a lesion has started to heal, topical dressings may be sprayed on the lesion with a pressurized backpack spray unit. Soluble oxytetracycline or lincomycin-spectinomycin (66 g and 132 g/L of water, respectively) produces the best results.

Topical sprays can be applied when the cows are recumbent. The nozzle of the wand of a portable unit can be applied directly to the lesion. This is a useful followup technique to either foot bathing or direct application of medication. With extreme care, formalin may also be used to reinforce antibiotic therapy.

The key to controlling digital dermatitis is a biosecure herd. That is, if digital dermatitis is not present, replacement animals should not be introduced and the herd should not be exposed to vectors such as unsterilized instruments or visitors' dirty boots. Slurry removal and improved standards of hygiene are also essential for control.

Footbaths containing oxytetracycline or lincomycin-spectinomycin were commonly used in the past. For optimal effect, the animals must be first walked through a bath containing clean water. Footbaths containing copper sulfate, zinc sulfate, or formalin have been found to be useful in some countries and may have a beneficial effect in reducing the prevalence of interdigital dermatitis, thus decreasing the susceptibility for digital dermatitis.

There are no effective vaccines.

Heel Horn Erosion

(Slurry heel)

Heel horn erosion is observed as a change in the appearance of the surface of the bulb of the heel. Because heel horn erosion alone does not cause lameness, the true incidence is unknown. However, subjective observations suggest that once cows have been exposed to copious slurry, the incidence of heel erosion rapidly approaches 100%. In some animals, heel horn erosion advances to a point at which complications develop and lameness may be apparent.

The etiology of heel horn erosion is not known. It is perhaps more commonly seen in herds in which subclinical laminitis has been diagnosed and in herds affected with digital dermatitis. Heel horn erosion is also more commonly seen during the winter, particularly when the claws are exposed to an unhygienic, moist environment (eg, intensively managed dairy units).

The first lesions observed are small circular erosions <0.5 cm in diameter. As the condition advances, these lesions merge and ridges form parallel to the hair line on the axial surface of the bulb. Invariably, the color of the roughened area is black. At this stage, the animal is not lame. A common lesion is a deep, black V.

In the secondary phase, the appearance of the heel varies. In some cases, there is a buildup of horn beneath the heel. Simultaneously, there may be a loss of horn under the axial part of the bulbs. The excessive accumulation of horn is often more pronounced in the lateral claw and causes the hock to turn in (cow-hocked stance). This stance resolves after therapeutic claw trimming. Generally, the condition is progressive unless corrected. The disturbance interferes with shock absorption, and the animal throws more and more weight forward. A common concurrent lesion is a sole ulcer. In other cases, erosion completely denudes the heel of horn—a process that also interferes with shock absorption and can be associated with a sole ulcer.

Both heels should be reduced to the same height by paring away excess horn. Careful attention must be paid to maintaining the bearing function of the abaxial wall and sloping the sole toward the axial border.

Attention to hygiene and the reduction of slurry are essential. The claws of dairy cows should be trimmed twice each year. A weekly footbath (where permitted, 3–5% formalin), starting no later than October in the northern hemisphere, should be provided.

Interdigital Hyperplasia

(Corns)

Interdigital hyperplasia is a firm, tumor-like mass located in the interdigital space. It is not common, except in certain breeds (eg, Herefords, in which it is considered to be heritable).

In heavy beef breeds, the condition is thought to result from stretching of the insertions of the distal interphalangeal ligament. The claws splay, and the interdigital skin is stretched. When not involved in weight bearing, the skin folds outward and subcutaneous scar tissue develops. In these cases, the mass tends to develop in the axis of the interdigital space. The mass may become so large that it touches the ground and may become necrotic. In dairy cows, in which the feet are continually exposed to slurry, chronic irritation or dermatitis in the interdigital region is seen. Organization of areas of irritated skin accounts for the development of masses close to the skin line on the dorsal commissure of the space.

Interdigital hyperplasia can be found in one or more limbs, although hindlimbs tend to be affected more frequently than forelimbs. Lameness results more often than not. As the lesion becomes larger, its surface may become excoriated, sore, and infected.

In simple cases, treatment may be unnecessary. For surgical removal, the animal should be sedated, and dorsal and flexor regional nerve blocks administered. Surgery can be performed with the animal standing or in lateral recumbency. After preparation of the surgical site, a tourniquet is applied and the claws separated manually or with retractors. The mass is removed, leaving as much of the interdigital skin as possible. If any fat protrudes when the claws are pressed together, it should be removed. Care must be taken to avoid cutting deep structures such as the distal interphalangeal ligament. After surgery, the wound should be dressed with an antibiotic powder and the claws bandaged closely together. Some field reports suggest considerable success with wiring the toe together. Movement of the wound or separation of the claws must be avoided until ∼10 days after surgery. Cryosurgery is also an option.

Last full review/revision March 2012 by Paul R. Greenough, FRCVS

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