Bovine digital dermatitis, also known as Mortellaro disease or hairy heel warts, is an infectious skin disease of the bovine foot and a significant cause of lameness in cattle worldwide. The condition primarily impacts dairy operations, causing economic losses from reduced milk production, impaired reproductive performance, and treatment costs. It manifests as painful lesions on the skin, most commonly around the heel of the hind feet.
Clinical Signs and Lesion Stages
The most apparent sign of bovine digital dermatitis is lameness, where an affected cow may favor a limb, lift its foot repeatedly, or walk on its toes to alleviate pressure on the heel. The disease’s progression is classified using an “M-stage” scoring system, which helps identify the severity and phase of the infection.
The initial M1 stage is a small, early lesion less than 2 cm in diameter that appears as a red-to-gray area and is not painful. This can progress to the M2 stage, the classic active ulcerative lesion. M2 lesions are larger than 2 cm, acutely painful, and have a raw, bright red, strawberry-like surface.
Following treatment, the lesion enters the M3 healing stage, becoming covered by a firm, dark, and painless scab. The M4 stage is a chronic phase where the lesion transforms into a thickened, rough-skinned area, sometimes with hair-like growths. Although not painful, M4 lesions can harbor bacteria and act as a reservoir for future outbreaks. A subtype, M4.1, is used to describe a chronic M4 lesion that has reactivated with a new, small M2-like ulcerative area on its surface.
Causative Agents and Transmission
Bovine digital dermatitis is a polymicrobial disease caused by a combination of bacteria. The primary bacteria implicated are spirochetes from the Treponema genus, with species like Treponema medium, T. phagedenis, and T. pedis commonly isolated. These anaerobic bacteria thrive in low-oxygen environments and invade the skin through small abrasions or hair follicles.
Wet, unhygienic conditions are a major contributor to transmission, as manure slurry creates an ideal environment for Treponema bacteria to survive and spread. Constant moisture exposure also weakens the skin’s natural barrier, making it more susceptible to invasion.
The disease spreads through contact with a contaminated environment, as shared walkways, holding pens, and bedding can become reservoirs of infectious bacteria. Contaminated equipment, particularly hoof trimming tools, can also transfer bacteria between animals if not properly disinfected. Introducing new, infected animals into a herd without an adequate quarantine period is another risk factor for spreading the disease.
Treatment of Active Infections
Treatment for bovine digital dermatitis focuses on managing active, painful infections. It can be administered to individual animals or at the herd level during a widespread outbreak. The goal is to resolve the pain and infection, allowing the lesion to heal.
For individual treatment, the affected area must be thoroughly cleaned of manure and debris to allow for clear inspection and direct contact for topical applications. After cleaning and drying the foot, a topical antibiotic, such as an oxytetracycline spray, is applied. Bandaging is not recommended as it can create an anaerobic environment that supports bacterial growth.
If a high percentage of the herd is affected, therapeutic footbaths can be used to cure existing infections. These footbaths use a higher concentration of an agent like oxytetracycline or copper sulfate to treat many animals at once. For the footbath to remain effective, the solution must be kept clean and changed frequently.
Herd Prevention and Control Strategies
Long-term management focuses on prevention and control to minimize the spread of new infections and manage chronic carriers. A strong prevention strategy relies on biosecurity, hygiene, and routine hoof care.
Biosecurity is a primary defense. New animals should be quarantined and inspected for lesions before joining the herd. Maintaining a closed herd, where no new animals are introduced, is the most secure biosecurity measure.
Environmental hygiene is important for controlling the bacterial load. Frequent scraping of alleyways to remove manure and providing clean, dry bedding reduces the feet’s exposure to wet conditions. Keeping walking surfaces as clean and dry as possible helps prevent skin from becoming compromised.
Regular, preventative footbaths are a common control measure used to disinfect feet and reduce the bacterial population on the skin. Unlike therapeutic footbaths, their purpose is to prevent new infections. Routine hoof trimming also helps maintain foot health and provides an opportunity to inspect feet and identify early-stage lesions.