Animals can tolerate large excesses of vitamin B12. 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 ruminants.
Cobalt also has a low toxicity, with 10 mg per kg (4.5 mg per lb) the maximum dietary tolerable level for the common livestock species (NRC, 1980). Becker and Smith (1951) concluded that 150 mg per kg (68.2 mg per lb) on a dry diet basis, or 1,000 times normal levels, can be tolerated by sheep for many weeks without visible toxic effects. Characteristic signs of chronic cobalt toxicity in most species are reduced feed intake and body weight, emaciation, anemia, hyperchromenia, debility and increased liver cobalt (NRC, 1980). Cobalt toxicity in cattle is characterized by mild polycythemia; excessive urination, defecation and salivation; shortness of breath; and increased hemoglobin, red cell count and packed cell volume (NRC, 1996). ).
