Bovine Interleukin-4 (IL-4) is a Th2-associated cytokine produced primarily by activated CD4⁺ T helper 2 (Th2) cells, mast cells, and basophils in cattle (Bos taurus), where it plays a central role in regulating humoral immunity, alternative macrophage activation, and modulation of inflammatory responses. IL-4 signals through receptor complexes containing IL-4Rα paired with the common gamma chain (γc) or IL-13Rα1, activating JAK/STAT6 pathways that promote B-cell proliferation, antibody class switching, and suppression of Th1-associated cytokines such as IFN-γ. In bovine health, IL-4 is particularly important in responses to parasitic infections—including gastrointestinal nematodes and lungworms—where Th2 polarization supports parasite clearance and mucosal repair. IL-4 also influences immune balance during infections such as bovine viral diarrhea virus (BVDV), mastitis, and respiratory disease by shaping Th1/Th2 dynamics, which can affect pathogen control and disease outcome. While IL-4-mediated responses are protective in parasite defense and tissue repair, excessive Th2 skewing may impair effective cell-mediated immunity against intracellular pathogens. As a biomarker of type 2 immune activation, bovine IL-4 is relevant in vaccine evaluation, host–parasite interaction studies, and immune resilience research. Characterization of bovine IL-4 supports veterinary investigations into cytokine network regulation, disease susceptibility, and strategies to enhance cattle health and productivity through balanced immune modulation.