Digital dermatitis (DD) is a highly contagious bacterial skin infection that causes painful lesions on the feet of cattle, representing a worldwide challenge for livestock production. Commonly called “hairy heel warts,” DD is a major cause of lameness and significant animal welfare concern. The resulting discomfort reduces feed intake and mobility, diminishing milk yield and reproductive performance. Due to its high prevalence in dairy and beef herds, DD is an economically impactful condition, placing a substantial burden on the industry through control and treatment costs.
Defining Digital Dermatitis: Clinical Presentation
DD lesions are most frequently observed on the hind feet, typically located in the skin between the heel bulbs and above the heel horn junction. The characteristic lesion begins as a raw, red, oval ulcer, often described as having a strawberry-like or granular surface. This intense pain causes affected animals to walk on their toes or exhibit noticeable lameness. Diagnosis and monitoring use the standardized M-stages system, which describes the disease’s progression.
The initial healthy skin is M0, transitioning to the M1 stage, an early, small, red-gray lesion less than two centimeters. The most acute and painful phase is the M2 stage, a larger, active ulcerative lesion exceeding two centimeters, characterized by a raw, often bleeding surface. After successful treatment or natural regression, the lesion enters the M3 stage, covered by a firm, scab-like material.
The chronic, persistent form is the M4 stage, presenting as a thickened, proliferative, or “warty” lesion with a black, dyskeratotic appearance. In M4, bacteria can become encysted deep within the skin, creating a reservoir of infection prone to reactivation. A recurring lesion is sometimes classified as M4.1, indicating a chronic M4 lesion with a small, active M1 lesion developing within its border.
Causation and Environmental Transmission
Digital dermatitis is a polymicrobial disease involving multiple types of bacteria. The primary causative agents are anaerobic bacteria from the Treponema genus, particularly phylotypes like Treponema phagedenis-like, Treponema medium/vincentii-like, and Treponema denticola-like. These invasive spirochetes penetrate deep into the dermal layers, making permanent cure difficult. They release enzymes that cause tissue damage, hemorrhage, and the intense pain associated with active lesions.
Transmission is heavily facilitated by specific environmental conditions. The bacteria thrive in wet, low-oxygen environments contaminated by manure and urine. Consistently wet walking surfaces, such as in holding pens and alleyways, macerate the skin, making it susceptible to bacterial invasion. Poor hygiene, inadequate drainage, and abrasive flooring create favorable entry points for the pathogens. Infected animals are the main reservoir, and introducing new, infected animals without quarantine is a major route for spreading the disease between herds.
Treatment Protocols for Active Lesions
Treatment for active DD lesions focuses on topical application of antibacterial agents directly to the affected area. Effective treatment requires lifting the foot, thoroughly cleaning the lesion to remove debris, and gently drying the area. This preparation allows the medication to penetrate and maximize effectiveness.
The most common topical treatments involve licensed antibiotic sprays, often containing oxytetracycline or tetracycline. Repeat applications may be required for several consecutive days, with M2 lesions sometimes needing daily treatment for up to five days. Bandaging is generally discouraged as it creates a moist environment that harbors bacteria and may lead to chemical burns. Non-antibiotic alternatives, such as chelated copper gels or salicylic acid pastes, are also used to spot-treat individual lesions.
Systemic antibiotics are reserved for severe or refractory cases due to concerns about cost, milk withhold times, and antibiotic resistance. Therapeutic footbaths can be used as a mass treatment approach during an outbreak, though individual treatment is the gold standard for active lesions. These footbaths utilize disinfectant solutions, such as copper sulfate (around five percent) or formalin (two to five percent), to reduce the bacterial load. The solution must be replaced frequently—typically after 150 to 200 animal passages—to maintain concentration and efficacy.
Prevention and Long-Term Management Strategies
Long-term management relies on minimizing environmental factors that enable the disease to proliferate. This requires maintaining a consistently dry and clean environment, which reduces the survival and transmission of Treponema bacteria. Frequent scraping of alleys and walkways removes manure and minimizes the time animals spend standing in slurry. Optimizing drainage is also important to eliminate pooling of water and urine in high-traffic areas.
Regular, preventive footbaths are a standard component of a control program, acting as a herd-level hygiene measure to prevent new infections and reduce chronic lesion recurrence. These footbaths should be used multiple times a week, with frequency adjusted based on the herd’s infection prevalence. Copper sulfate and formalin are common choices, but alternatives like zinc sulfate, acidified copper sulfate, or commercial quaternary ammonium compounds are also implemented.
Routine functional hoof trimming supports foot health by maintaining proper weight bearing and removing potential sites for bacterial entry. Nutritional management also plays a supportive role; adequate levels of trace minerals like zinc and copper support skin and hoof integrity. Finally, strict biosecurity protocols, including the quarantine and inspection of all incoming animals, are necessary to prevent the introduction of new sources of infection into the resident herd.