Abstract Actinobacillus lignieresii is a normal part of the oral bacterial flora of cattle, but may cause infection if the mucosal barrier is interrupted. Here, we report a case of diffuse myocellulitis in the nasal planum without development of granulomas on its surface. A Jersey cow was presented with hypersalivation and a firm, painless, diffuse almost symmetrical swelling of the nasal planum with moderate hyperaemia. The cow was slaughtered and the head was examined. Histopathology of the nasal planum revealed widespread severe pyogranulomatous inflammation with clusters of bacteria and Splendore–Hoeppli material with extensive diffuse fibrosis and loss of muscle tissue. A. lignieresii was isolated in monoculture by bacteriology. The appearance of the condition differed from previously reported cases, as protruding granulomas were not present and the tissue reaction affected the entire nasal planum in a uniform way. Actinobacillosis should be considered in cases of firm enlargement of the nasal planum in cattle.