Bovine CCL1 (C-C motif chemokine ligand 1), also known as I-309, is a member of the CC chemokine family that plays a role in regulating leukocyte trafficking and immune responses in cattle (Bos taurus). CCL1 is produced primarily by activated T lymphocytes, monocytes, macrophages, and endothelial cells in response to inflammatory stimuli, and it functions mainly through the CCR8 receptor to recruit monocytes, T cells, and other immune effector cells to sites of inflammation. In healthy cattle, basal CCL1 expression is typically low, but levels can increase during infection, tissue injury, or immune activation. Elevated CCL1 expression has been associated with inflammatory and infectious conditions such as mastitis, respiratory disease, enteric infections, and parasitic challenges, reflecting its role in coordinating cellular immune responses. In veterinary and agricultural research, bovine CCL1 serves as a biomarker of immune activation and leukocyte recruitment, providing insight into host–pathogen interactions, vaccine responses, and inflammatory regulation in cattle.