Cobalt metabolism in horse. Serum level and biosynthesis of vitamin B12.

The levels of serum vitamin B₁₂ were determined on 16 mature partly warm-blooded, partly Finnish rural-race horses by the radioisotopic competitive inhibition assay method. The mean value from three samplings carried out in dupli- or triplicate was 1.54 ± 0.16 ng/ml. The utilization of serum inorganic cobalt for cyanocobalamin synthesis was studied on two geldings, which received a dose of 200 µCi ⁵⁸CoGl₂ i.v. A Sephadex G-100 gel filtration was carried out with the serum proteins from serial blood samplings at different time intervals 15 min. to 48 hrs. after administration. The gel filtration showed the presence of two labelled proteins in the serum, one of them appearing some time after administration and disappearing almost completely towards the end of the experimental period. The two elution peaks are considered to represent inorganic ⁵⁸Co and ⁵⁸Co labelled vitamin B₁₂. The appearance of labelling in serum vitamin B₁₂ indicates the passing of cobalt into the intestine, and reabsorption into blood in the form of vitamin B₁₂.