This article provides a comprehensive analysis of sodium selenite's basic information, authoritative standards, core functions (antioxidant, immune enhancement, prevention of white muscle disease, etc.), precise usage plans for different animals, and safe usage guidelines. It also compares its differences with organic selenium and analyzes the industry's trend towards high purity, low toxicity, and organic formulations. As an essential feed additive, sodium selenite requires strict control over its dosage and usage procedures. Its cost advantage makes it irreplaceable in large-scale farming. - Polifar