Vitamin B12 (cobalamin) serves as A coenzyme for methionine synthase and methylmalonyl-CoA mutase in animals. Its core function is to participate in one-carbon unit metabolism and methyl transfer, thereby ensuring hematopoietic function (preventing pernicious anemia), maintaining the integrity of nerve myelin, promoting protein and nucleic acid synthesis, and is crucial for growth, reproduction and fur health. It must be synthesized by microorganisms, so monogastric animal feed needs to be directly added (especially in high-yield, seed or purely plant-based diets), while the rumen of ruminants can synthesize it by itself but relies on an adequate supply of cobalt.