Interdigital Dermatitis

Also known as

Stable foot rot, slurry heel, scald, heel erosion, heel necrosis

Description

Interdigital dermatitis is different from foot rot in cattle, but both conditions may occur concurrently. It is also different from digital dermatitis.

Interdigital dermatitis occurs most commonly on farms with high stocking density or where cattle traffic is high (many cattle coming and going) or cattle are housed for long periods. It is most prevalent in winter. Though this disease occurs more frequently when cattle are kept in unsanitary conditions, it has also been seen in well-managed herds.

Interdigital dermatitis appears first as a mild infection of the skin between the claws. There is an oily discharge of white foul-smelling material between the claws that oozes to both sides of the interdigital space and forms a crust or scab.

This moist, white exudate has a characteristic odor distinctly different from that of foot rot. The infection produces a mild irritation that results in underlying skin enlargement and may produce a faster growth rate of the adjacent axial (center) hoof wall (inner side of that claw).

There is rarely much swelling or lameness at this stage though the area is painful if touched.

Then the infection progresses to the heels which become raw and painful. The hoof horn beneath the heel increases in thickness. More than one foot may be affected. Eventually the animal shows discomfort and tries to shift weight off the painful area by “paddling,” or constantly moving from one foot to the other.

If the heels of the hind feet are painful, the hind limbs are positioned 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, resulting in changes in gait.

Chronic cases show changes of the hoof such as separation of the hoof horn at the heel bulb, enlargement of the interdigital tissues and muscle atrophy in the affected limb—since it hasn’t been bearing as much weight.

Chronic irritation of the skin between the claws of dairy cows is the commonest cause of corns (fibromas) developing on one side of that interdigital space. The horn may become underrun, with abnormal formation of claw horn, leading to elevated horn ridges and V-shaped fissures in the heel area.

Lesions in the sole of the claw at this location often result in sole ulcers. Later the area may also be abscessed, brittle or cracked.

In dairy cows, interdigital enlargements such as corns or fibroma may be caused by the chronic irritation of the interdigital space. Fibromas are benign tumors composed of fibrous or connective tissue.

Foot-and-mouth disease can be confused with interdigital dermatitis if the interdigital space is not examined carefully.

Signs

• Generalized lameness,
• Stiffness in affected limbs,
• Swelling in acute cases,
• Muscle atrophy in chronic cases,
• Underrun hoof,
• Gray-white discharge that forms a scab,
• Foul odor,
• Reduced milk yield,
• Weight loss,
• Slow gait (unable to walk at usual speed, drifting to the back of the herd)

Causes

Interdigital dermatitis is caused by a mixed bacterial infection, but Dichelobacter nodosus is considered to be the most active pathogen. D. nodosus is an anaerobe (thrives in an environment without oxygen) and exceptionally proteolytic (causing the breakdown of proteins).

Cattle are the source of infection (these bacteria are found in feces), and the pathogen spreads from infected to non-infected cows through the environment. D.nodosus cannot survive for more than4 days on the ground but can persist in mud and manure caked onto the claws, creating an anaerobic environment.

These bacteria first invade the epidermis (outer layer) of the skin between the claws but do not penetrate to the dermal layers. As the condition progresses, the border between the skin and soft heel horn at the posterior juncture disintegrates, producing lesions similar to ulcers or erosions.

At this stage, the lesions cause discomfort. In dairy cows in tied systems, the hind legs are affected more often than the forelimbs (due to more exposure to manure). In loose housing systems, the distribution between front and hind limbs is about equal. Animals on slatted floors are affected less often than animals on solid floors.
Prevention

Good management and housing systems that keep feet dry and clean are most important, reducing the presence of manure/slurry. Regular foot trimming helps avoid complications.

Footbaths beginning in late fall and before clinical cases are seen during high-risk periods, is essential in herds known to be infected. Weekly footbaths may be sufficient in the late fall, but frequency may have to be increased in late winter.

Control relies on prompt detection, isolation and treatment of affected cattle. Travel areas should be kept as dry as possible and slurry build-up avoided. Regular footbaths using 3% formalin, or 5%copper sulfate, or a thymol-based disinfectant can kill the main bacteria causing digital dermatitis (Dichelobacter nodosus).

Treatment

Systemic therapy with antibiotics, is costly and not very effective. In severe cases, the lesions should be cleaned and dried, after which a topical bacteriostatic agent is applied, such as a 50% mixture of sulfamethazine powder and anhydrous copper sulfate, or the animal can be confined in a 5% copper sulfate footbath for an hour, twice-daily for a number of weeks.

If there is excessive horn accumulation along the inside wall of the claw (flare toward the interdigital space) or an abnormally high region in the adjacent sole, it should be trimmed. Corrective trimming should remove all excessive horn and open the interdigital space so that it is more self-cleaning and more accessible to air.

If the infection spreads across the heels, it may erode the horny portion of the heel in irregular patterns or create a transverse crack at the heel-sole junction.