Bovine Interleukin-6 (IL-6) is a multifunctional pro-inflammatory cytokine and a central member of the IL-6 cytokine family, which includes IL-6, IL-11, IL-27, IL-31, leukemia inhibitory factor (LIF), oncostatin M (OSM), ciliary neurotrophic factor (CNTF), cardiotrophin-1 (CT-1), and cardiotrophin-like cytokine factor 1 (CLCF1), all of which signal through receptor complexes utilizing the shared gp130 subunit. In cattle (Bos taurus), IL-6 plays a critical role in regulating acute-phase protein synthesis (including haptoglobin and serum amyloid A), B- and T-cell differentiation, hematopoiesis, and systemic inflammatory responses via the IL-6R/gp130-mediated JAK/STAT pathway. It is a key mediator in economically significant diseases such as bovine respiratory disease (BRD), mastitis, metritis, Johne’s disease, and other bacterial and viral infections, where elevated IL-6 levels correlate with fever, tissue inflammation, and disease severity. As a biomarker, bovine IL-6 is widely used to assess immune activation, monitor herd health, and evaluate vaccine efficacy or therapeutic interventions. In animal model and translational research, characterization of bovine IL-6 and related family members supports studies of host-pathogen interactions, inflammatory regulation in large-animal systems, comparative immunology, and the development of immunomodulatory strategies to improve livestock health, productivity, and welfare.