Rumen bacteria synthesize approximately 2 to 3 mg vitamin B12 per day when provided with adequate dietary cobalt. Synthesis of competitive analogs of vitamin B12 has been reported with higher levels of grain in the diet (Walker and Elliot, 1972). Serum vitamin B12 is lower during late pregnancy and early lactation than during mid-lactation, although correlations with milk yield, grain consumption or blood glucose concentration were poor (Elliot et al., 1965). Peters and Elliot (1983) reported that vitamin B12 injections increased milk protein production but not milk yield, solids or fat production in vitamin B12-deficient ewes during early lactation. Liver capacity for gluconeogenesis from labeled propionic acid was increased in vitamin B12-treated ewes. Croom et al.(1981) did not detect any effect of supplementary vitamin B12 on milk fat synthesis in dairy cows. The authors had hypothesized that accumulation of MMA inhibits milk fat synthesis by reducing activity of lipogenic enzymes. Daugherty et al.(1986) found no beneficial effect of vitamin B12 injections on growth performance or propionate-metabolizing enzymes in the livers of feedlot lambs fed 80% concentrate diets with an ionophore. Girard et al.(1998) in a preliminary trial reported that primiparous dairy cows fed diets supplemented with both folic acid and methionine responded to vitamin B12 injections with increased milk production between 25 and 125 days of lactation. The possible interaction among vitamin B12, folic acid and methionine in lactating dairy cows requires further study. Supplemental cobalt (vitamin B12) may increase the tolerance of sheep to ryegrass toxicosis (Davies et al., 1995).
Young ruminants require supplemental vitamin B12 prior to full rumen development. Milk is a good source of vitamin B12. The NRC (1989) suggests that milk replacer for dairy calves contain 0.07 mg of cobalt per kg (0.03 g per lb).
Although dietary supplementation of cobalt is the normal means of meeting the vitamin B12 requirement of ruminants, parenteral administration is used to treat animals with apparent deficiency symptoms or the general appearance of malnutrition or poor health. Vitamin B12 is sometimes administered parenterally to incoming feedlot cattle as a prophylactic measure.
Intramuscular injection of vitamin B12, at the rate of 100 µg per week, or 150 µg every other week, produced a rapid remission of all signs of deficiency in lambs, and was equivalent to cobalt administered orally at the rate of 7 mg per week (Andrews and Anderson, 1954). For treatment of cobalt deficiency in cattle, intramuscular administration of vitamin B12 at 500 to 3,000 µg per head is recommended, which may be repeated weekly (Graham, 1991). Administration of intramuscular vitamin B12 to cobalt-deficient animals produces overnight improvement in appetite, whereas oral dosing with cobalt requires seven to 10 days to produce similar effects (MacPherson, 1982).
Many forages and concentrate feeds do not supply adequate (0.10 ppm) cobalt, and thus supplementation is required. Growth responses to supplemental cobalt have been demonstrated in steers fed finishing diets based on barley grain (Raun et al., 1968), sorghum grain and silage (Morris and Gartner, 1967).
Vitamin B12 is produced by fermentation and is available commercially as cyanocobalamin. Vitamin B12 is only slightly sensitive to heat, oxygen, moisture and pH (Gadient, 1986). Vitamin B12 has good stability in premixes with or without minerals, regardless of source of the minerals, and is little affected by pelleting (Scott, 1966; Verbeeck, 1975).