Actinobacillosis is a sporadic, inflammatory disease of the soft tissue in cattle, sheep, goats (Swarbrick 1967, Fubini and Campbell 1983, Muhammad and others 2006, Radostits 2007) and other species (Dibb and others 1981, Carmalt and others 1999, Kennerman and others 2006). The causative organism, Actinobacillus lignieresii , is part of the oral flora (Rycroft and Garside 2000, Quinn 2002) and invades mucosal surfaces following trauma caused by abrasive ingesta or the action of the teeth during mastication (Radostits 2007). In cattle, the disease typically involves the formation of pyogranulomas in the oral cavity, tongue or fore-stomachs with subsequent spread to regional lymph nodes (Hebeler and others 1961, Mortimer 1962, Rycroft and Garside 2000), although the skin of the head, neck and, occasionally, the limbs can also be affected. An unusual presentation of the disease is reported here where extensive distal limb involvement resulted in severe lameness in 20 of 130 animals on a beef fattening unit. The cases occurred in a group of one- to two-year-old Aberdeen Angus crossbred cattle over an 11-month period from when the animals were housed in October 2009 until the following August 2010. Affected animals were housed in groups of 30 to a pen in slatted units at a stocking density of 1 animal/2 metre2. The cases presented clinically as focally extensive unilateral firm swellings distal to the elbow/stifle regions of the fore and hind limbs, resulting in significant …