Bovine Annexin V (also known as ANXA5, Annexin A5, placental anticoagulant protein I (PAP-I), lipocortin V, or anchorin CII) is a calcium-dependent phospholipid-binding protein belonging to the annexin family, a group of conserved proteins involved in membrane organization, cellular signaling, and regulation of inflammation and apoptosis. In cattle (Bos taurus), Annexin V binds with high affinity to phosphatidylserine exposed on the outer leaflet of the plasma membrane during early apoptosis or cell damage in the presence of calcium ions. Because of this property, FITC-labeled bovine Annexin V (Annexin V–FITC) is widely used in flow cytometry and fluorescence microscopy assays to detect apoptotic cells. When conjugated to fluorescein isothiocyanate (FITC), Annexin V enables fluorescent labeling of cells exposing phosphatidylserine, allowing quantitative detection and discrimination of early apoptotic cells—often in combination with viability dyes such as propidium iodide (PI) to distinguish early apoptosis from late apoptosis or necrosis. In bovine health and research, Annexin V–FITC assays are used to study cellular responses during infections, inflammatory conditions such as mastitis, and tissue injury. It is also applied in reproductive biology to assess sperm membrane integrity and apoptosis in spermatozoa or early embryos, which is important for fertility evaluation and assisted reproductive technologies in cattle. As a sensitive biomarker of apoptosis and membrane remodeling, FITC-labeled bovine Annexin V supports studies of host–pathogen interactions, immune regulation, cell death pathways, and reproductive cell viability in veterinary and comparative biomedical research.