Cobalamin, or vitamin B12, has many vital functions in the body. It is involved in cellular energy production, DNA synthesis, nervous system function, amino acid and lipid metabolism, and red blood cell production. Absorption in the ileum is achieved by forming a complex with intrinsic factor (IF), however, it is now thought that passive diffusion of cobalamin may also occur in dogs and cats throughout the gastrointestinal tract1,2.