Vitamin K₃ MSB, i.e., Menadione Sodium Bisulfite, is a synthetic addition compound of vitamin K₃ and sodium bisulfite. It is the most widely used source of vitamin K₃ in the feed industry – compared with natural vitamins K₁/K₂ and plain menadione, it offers superior water solubility and processing stability. It appears as a white to off‑white crystalline powder, readily soluble in water, but is hygroscopic and light‑sensitive; it should be stored in a sealed container, protected from light and moisture. Feed‑grade products comply with the standard GB/T 7294‑2009, and the mainstream commercial specification is MSB96 (Menadione Sodium Bisulfite content ≥96%, equivalent to menadione ≥50.0%, moisture ≤13.0%, free sodium bisulfite ≤5.0%).

In animals, MSB is converted to active vitamin K₂ (menaquinone‑4). Its core role is to serve as a coenzyme for vitamin K‑dependent carboxylase, catalysing the activation of coagulation factors II (prothrombin), VII, IX, and X, thereby ensuring normal blood clotting and preventing subcutaneous and visceral haemorrhage in livestock and poultry. It also participates in the γ‑carboxylation of osteocalcin, promoting calcium deposition in bone, which is crucial for the skeletal development of rapidly growing broilers and piglets. Additionally, supplementary MSB during coccidiosis treatment, concurrent use of sulfonamides, beak trimming, and other stress conditions helps reduce intestinal bleeding, accelerates wound healing, and enhances stress tolerance.