Bovine Interleukin-12/Interleukin-23 p40 (IL-12/IL-23 p40) is a cytokine subunit that plays an important role in regulating immune responses in cattle (Bos taurus). The p40 subunit is shared by two heterodimeric cytokines, IL-12 and IL-23, where it pairs with the p35 subunit to form IL-12 and with the p19 subunit to form IL-23. These cytokines are produced primarily by activated antigen-presenting cells, including macrophages and dendritic cells, in response to microbial infection or inflammatory stimuli. Bovine IL-12/IL-23 p40 contributes to activation and differentiation of T helper cells and natural killer (NK) cells, promoting Th1-type immune responses and production of interferon-γ (IFN-γ), which are critical for defense against intracellular pathogens. Through IL-23 signaling, the p40 subunit also supports the maintenance and expansion of Th17 cells involved in inflammatory responses and host defense. In cattle, IL-12/IL-23 p40 is involved in immune responses against bacterial, viral, and parasitic infections, including important livestock pathogens such as Mycobacterium bovis, Salmonella spp., and Mycobacterium avium subsp. paratuberculosis. Due to these functions, bovine IL-12/IL-23 p40 is widely studied in veterinary immunology and translational research, particularly in models of bovine tuberculosis and Johne’s disease, where cytokine responses are used to investigate host immunity, evaluate vaccine candidates, and develop diagnostic and immunomodulatory strategies relevant to both animal health and comparative biomedical research.