Digital Dermatitis (DD), commonly known as Mortellaro’s disease, is an infectious, multifactorial skin disease of the bovine digit, characterized by painful, ulcerative, or proliferative lesions, most frequently located on the skin in the interdigital space near the heels (Döpfer et al., 1997). The etiology of the disease is closely linked to anaerobic bacteria of the genus Treponema, which penetrate the deep layers of the epidermis and dermis, complicating effective systemic and topical treatment (Evans et al., 2008).

The following overview aims to facilitate differential diagnosis in the field by hoof trimmers and veterinarians, based on the standardized “M-stage” scale, which is currently the gold standard in monitoring hoof health.

Classification of Lesions According to the M-stage Scoring System

This system, originally developed by Döpfer and subsequently modified by Berry, allows for the precise determination of disease dynamics within a herd.

Stage M0: Healthy Skin

The skin in the interdigital space is normal, without visible lesions, smooth, and non-painful upon palpation. This is the desired state aimed for in prevention programs (Berry et al., 2012).

Stage M1: Early Active Stage

The lesion is small, with a diameter of less than 2 cm (pea-sized). The epithelial defect is circumscribed, ranging in color from light red to gray. Often, this lesion is not yet painful to the animal, making it easy to overlook without a thorough inspection of the claw in the chute (Döpfer et al., 1997). M1 is a critical moment for topical intervention before the lesion progresses to the acute phase.

Stage M2: Classic Ulcerative Stage (Acute Stage)

This is the most characteristic and painful form of the disease. The lesion exceeds 2 cm in diameter, has a bright red color, and a “strawberry-like” appearance (granulation tissue). It is often surrounded by a margin of white, necrotic epithelium and erect hair (hypertrichosis) around the focal point (Read & Walker, 1998). Cows in this stage often exhibit significant lameness and offload the affected limb by standing on the toe (Refaai et al., 2013).

Stage M3: Healing Stage

Occurs shortly after treatment application (e.g., antibiotic spray under a bandage). The lesion becomes covered with a dark, firm scab. Pain disappears or significantly diminishes. Premature removal of the scab may expose healing tissue; therefore, caution during trimming is crucial (Berry et al., 2012).

Stage M4: Chronic Stage

The lesion transitions into a dyskeratotic (hyperkeratotic) or proliferative form. Hard, warty growths appear, resembling “hairs” or thickened skin. These lesions can serve as a reservoir for encysted Treponema spirochetes, posing a risk of disease recurrence (Plummer et al., 2013).

Stage M4.1: Chronic Reactivating Stage

This is a recurrence of the disease superimposed on a chronic lesion. A new, active, and painful focal point (M1) appears on the hardened, warty tissue (M4). This indicates incomplete healing or reactivation of bacteria hidden in the deeper layers of the epidermis (Berry et al., 2012).

Impact of Digital Dermatitis on the Dairy Herd

DD is not merely an animal welfare issue but one of the primary causes of economic loss in dairy cattle farming (Bruijnis et al., 2010).

• Decrease in Milk Yield: Cows with the clinical form of DD (Stage M2) exhibit a statistically significant drop in milk production. Pain and stress associated with lameness cause a reduction in Dry Matter Intake (DMI), which directly translates to lower milk yield per lactation (Relun et al., 2013). It is estimated that the loss can range from dozens to even hundreds of liters of milk per lactation per head, depending on the severity of lesions (Hernandez et al., 2002).
• Reproductive Disorders: The occurrence of DD is correlated with an extended calving interval and an increase in the number of insemination services required for successful conception. Lameness negatively affects the expression of estrus behavior, making heat detection difficult for the producer (Argáez-Rodríguez et al., 1997).
• Culling: Chronic, recurrent forms of DD (particularly stages M4 and M4.1) are a frequent cause of premature culling from the herd due to permanent loss of body condition and inability to ambulate (Cha et al., 2010).

Summary for Practitioners

Effective control of Mortellaro’s disease requires not only treating clinical cases (M2) but primarily identifying disease reservoirs (M4) and early stages (M1). Utilizing modern recording tools allows for tracking the dynamics of transitions between stages (e.g., whether M3 progresses to M0 or regresses to M4.1), which is crucial for evaluating the efficacy of footbath programs and individual treatments.

Bibliography (Sources):

• Döpfer, D., et al. (1997). Histological and bacteriological evaluation of digital dermatitis in cattle, with special reference to spirochaetes and Campylobacter faecalis. Veterinary Record.
• Evans, N.J., et al. (2008). Association of unique, isolated treponemes with bovine digital dermatitis lesions. Journal of Clinical Microbiology.
• Read, D.H., & Walker, R.L. (1998). Papillomatous digital dermatitis (footwarts) in California dairy cattle: clinical and gross pathologic findings. Journal of Veterinary Diagnostic Investigation.
• Plummer, P.J., et al. (2013). Deep Sequencing Analysis Reveals Temporal Microbiota Changes Associated with Development of Bovine Digital Dermatitis.
• Bruijnis, M.R.N., et al. (2014). Assessing economic consequences of foot disorders in dairy cattle using a dynamic stochastic simulation model. Journal of Dairy Science.
• Relun, A., et al. (2013). Association between digital dermatitis lesions and test-day milk yield of Holstein cows from 41 French dairy herds. Journal of Dairy Science.
• Hernandez, J., et al. (2002). Effect of lameness on milk yield in dairy cows. Journal of the American Veterinary Medical Association.
• Argáez-Rodríguez, F.J., et al. (1997). Papillomatous digital dermatitis on a commercial dairy farm in Mexicali, Mexico: incidence and effect on reproduction and milk production. Preventive Veterinary Medicine.
• Cha, E., et al. (2010). The cost of different types of lameness in dairy cows calculated by dynamic programming. Preventive Veterinary Medicine.