Digital dermatitis (DD), widely known as Mortellaro disease, is an infectious, multifactorial skin condition of the bovine digit. Anaerobic bacteria of the genus Treponema play the central role: they penetrate the deep layers of the epidermis, which is exactly what makes the disease so hard to clear.

Classifying lesions on the M-system

The system developed by Döpfer and modified by Berry lets you describe the dynamics of the disease across a herd, not just the state of one cow.

M0: healthy skin

Intact, smooth, painless. The state a prevention programme is aiming at.

M1: early active stage

A lesion under 2 cm — roughly pea-sized. Colour ranges from pale red to grey. Often gives no clinical signs at all and is easy to miss without a proper look in the crush.

M1 is the moment worth intervening — before the lesion turns acute.

M2: the classic ulcerative stage

The most recognisable and the most painful form. The lesion is over 2 cm, bright red, with the granulation tissue that gives it its "strawberry" look. Cows are usually visibly lame and unload the affected limb, standing on the toe.

M3: healing stage

After treatment the lesion covers over with a dark, firm scab. Pain disappears or drops sharply. Take care when trimming — do not lift the scab prematurely.

M4: chronic stage

Hard, wart-like proliferations and thickened skin. These can act as a reservoir of dormant Treponema, which is why a herd that looks clean can relapse.

M4.1: chronic with an active focus

A relapse on top of M4 — a fresh active M1 focus appearing on hardened tissue. It points to incomplete healing or reactivation of the bacteria.

What DD costs a herd

Lost milk

Cows with clinical DD (M2) show a statistically significant drop in milk production: pain and stress cut dry matter intake. Estimated losses run from tens to hundreds of litres per lactation per cow (Hernandez et al., 2002).

Fertility

Lameness suppresses oestrus expression, which makes heat detection harder. The result is a longer calving interval and more inseminations per conception.

Culling

Chronic, recurring DD (M4 and M4.1) is a frequent reason for premature culling, because the cow never fully regains condition.

What this means in practice

Beating Mortellaro is not only about treating the clinical M2 cases. It is about finding the reservoirs (M4) and the early lesions (M1), which are the two stages nobody notices without looking for them.

Tracking how cows move between stages — whether M3 resolves to M0 or slides back to M4.1 — is what tells you whether a footbath programme is working. That is the kind of question a digital record answers and a notebook does not.

References

Döpfer, D., et al. (1997). Veterinary Record.
Evans, N.J., et al. (2008). Journal of Clinical Microbiology.
Bruijnis, M.R.N., et al. (2014). Journal of Dairy Science.
Relun, A., et al. (2013). Journal of Dairy Science.
Hernandez, J., et al. (2002). Journal of the American Veterinary Medical Association.

Digital dermatitis (Mortellaro): signs, M-stages and herd impact