Systemic granulomatous disease of unknown origin in cattle: epidemiologic investigation of a clustered outbreak

Abstract Systemic granulomatous disease in cattle is most commonly associated with hypersensitivity to ingested Vicia villosa . Cases occurring in the absence of recognized dietary causes or feed additives have rarely been reported. Here we describe an outbreak of systemic granulomatous disease of unknown cause in dairy and beef cattle in southern Brazil. Affected cattle underwent autopsy, histopathology, and epidemiologic assessment. Between November 2021 and January 2022, 14 cases were diagnosed, both in dairy (12 cases, 86%) and beef (2 cases, 14%) cattle in several farms. These cases represented 36.8% of the diagnoses issued by our laboratory during the same period. A few months later, between April and June 2022, five additional cases were diagnosed in dairy cattle. Known causative agents, such as citric pulp, Vicia sp., citrinine, dicyandiamide, formalin-based additives, and viruses were ruled out. All cattle had moderate-to-severe systemic granulomatous inflammation. Commercial mineral premixes were the only common exposure identified during the epidemiologic investigation; however, causation could not be established. Detailed investigation of feed ingredients, suppliers, and formulation changes was not possible.