Bovine interferon lambda 3 (IFN-λ3), also known as interleukin-28B (IL-28B), is a member of the type III interferon family (IFN-λ1/IL-29, IFN-λ2/IL-28A, IFN-λ3/IL-28B, and IFN-λ4) and functions as a key antiviral cytokine that signals through the IFNLR1 (IL-28Rα)/IL-10R2 receptor complex, activating JAK/STAT pathways and inducing interferon-stimulated genes (ISGs) that inhibit viral replication, particularly at epithelial surfaces. In cattle, IFN-λ3 plays an important role in mucosal immunity within the respiratory and gastrointestinal tracts, tissues commonly targeted by economically significant pathogens such as bovine respiratory syncytial virus (BRSV), bovine viral diarrhea virus (BVDV), parainfluenza virus type 3 (PI3), rotavirus, and coronavirus. Because type III interferons primarily act on epithelial cells and generate localized antiviral responses with less systemic inflammation than type I interferons, bovine IFN-λ3 is likely critical for controlling infection while minimizing tissue damage that can impair growth and productivity. As respiratory and enteric diseases remain major drivers of morbidity in livestock, bovine IFN-λ3 (IL-28B) is highly relevant for understanding antiviral defense mechanisms, improving vaccine strategies, and developing immunomodulatory approaches to enhance herd health and disease resilience.