Addition of vitamin B12 to feed in amounts far in excess of need or absorbability appears to be without hazard. Dietary levels of at least several hundred times the requirement are suggested as safe for the mouse (NRC, 1987). No data are available pertaining to vitamin B12 safety in cats.
Although frank vitamin B12 toxicity has not been described in the dog, in one report Pshonik and Gribanov (1961) noted disturbances of reflex activity in the form of reduction in size of vascular conditioned reflexes and exaggeration of unconditioned reflexes when vitamin B12 was injected subcutaneously in doses of 2 to 33 µg per kg (0.91 to 15 µg per lb) of body weight.
