Bovine IL-18 (Interleukin-18) is a pro-inflammatory cytokine belonging to the IL-1 family that plays a central role in innate and adaptive immune responses in cattle (Bos taurus). IL-18 is produced primarily by monocytes, macrophages, dendritic cells, and epithelial cells as an inactive precursor that requires cleavage by caspase-1 following inflammasome activation to become biologically active. Once activated, IL-18 stimulates production of interferon-γ (IFN-γ) by T cells and natural killer (NK) cells, thereby promoting Th1-type immune responses and enhancing cell-mediated immunity against intracellular pathogens. In healthy cattle, basal IL-18 expression is generally low, but levels increase during bacterial and viral infections, mastitis, respiratory disease, and inflammatory stimulation. IL-18 has been implicated in immune responses to pathogens such as Mycobacterium bovis, bovine viral diarrhea virus (BVDV), and agents of bovine respiratory disease complex. In veterinary and agricultural research, bovine IL-18 serves as a biomarker of inflammasome activation and Th1-mediated immune activation, providing insight into host–pathogen interactions, vaccine responses, and inflammatory disease mechanisms in cattle.