From Magnum Secretion to Egg Albumen Quality: Formation Mechanisms, Quality Assessment, and Influencing Factors—A Narrative Review

Egg albumen is an important component of the egg and a major source of high-quality protein. Its formation is closely associated with the tissue structure, cellular differentiation, and secretory function of the hen oviduct magnum. With advances in histology, molecular biology, and omics technologies, egg albumen formation and the mechanisms regulating egg albumen quality have become important topics in egg quality research. This narrative review outlines the physiological basis of egg albumen formation and the histological characteristics of the magnum, systematically summarizes the major magnum cell types and the synthesis, processing, and secretion of egg albumen proteins, describes egg albumen composition and quality evaluation indicators, and analyzes the factors affecting egg albumen quality. This review aims to deepen understanding of the mechanisms underlying egg albumen formation and quality changes, thereby supporting egg albumen quality improvement and the high-quality development of the laying hen industry.