Swine C3a is a biologically active anaphylatoxin generated during activation of the complement cascade in pigs (Sus scrofa). It is produced through proteolytic cleavage of complement component C3 and functions as a potent mediator of innate immune and inflammatory responses. C3a exerts its effects by binding to the C3a receptor (C3aR) expressed on immune cells such as neutrophils, monocytes, macrophages, mast cells, and certain epithelial and endothelial cells, leading to chemotaxis, cytokine release, increased vascular permeability, smooth muscle contraction, and amplification of inflammatory signaling. In healthy swine, circulating C3a levels are typically low but increase rapidly during complement activation triggered by infection, immune complex formation, tissue injury, endotoxemia, or vaccine-induced immune responses. In veterinary and translational research, swine C3a is particularly relevant in models of sepsis, ischemia-reperfusion injury, acute lung injury, xenotransplantation, and inflammatory diseases, as pigs share important physiological similarities with humans. Measurement and characterization of swine C3a provide valuable insight into complement activation, systemic inflammation, and innate immune regulation in both agricultural and biomedical research settings.