|Serum vitamin B12 (pmol/L)|
|Liver vitamin B12 (nmol/kg fresh tissue)|
|Pasture Co (mg/kg DM)|
1. Co is an integral part of the vitamin B12 molecule and therefore Co deficiency is really a vitamin B12 deficiency.
2. The data for lambs is very robust, based on vitamin B12 supplementation growth responses. Lambs by far are the most sensitive to Co deficiency.
3. The data for cattle and deer are based on a few good studies.
4. There are some excellent overseas studies with cattle that have observed growth responses on diets containing 0.04-0.07 mg Co/kg DM. The cattle were fed, indoors or in feedlots, diets that were high in grains. Grain diets influence the conversion of Co to vitamin B12 by the microorganisms in the reticulorumen. In the presence of grain diets, the efficiency of the conversion of Co to vitamin B12 is lower and hence the Co intakes have to be higher to synthesize the same concentrations of vitamin B12 in the reticulorumen.
5. A serum vitamin B12 concentration of 120 pmol/L reflects an adequate vitamin B12 status in cattle regardless of the diet fed.
6. Serum vitamin B12 is the best index of Co (vitamin B12) status of livestock.
7. There have been other biochemical metabolites such as plasma methylmalonic acid which have been considered as a suitable index of vitamin B12 status, but robust criteria have yet to be developed.