The biological availability of cobalt to ruminants
McDonald, Paul Graham
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The aetiology of cobalt deficiency in ruminants is not clear and this study focussed on a crucial step in cobalt metabolism, namely its incororation, by rumen microbes, into the essential vitamin B12. Continuous cultures of rumen microbes (Rusitec) were used to study factors influencing vitamin B12 biosynthesis.An improved technique for estimating cobalamin (true vitamin B12) in biological fluids rich in vitamin B12 analogues was developed.Cobalamin and analogue production was increased, from the low levels encountered with cobalt deficient hays and barley, by infusing inorganic cobalt into the cultures. The utilisation of cobalt from cobalt deficient barley in the synthesis of cobalamin was more efficient than that from cobalt-deficient and cobalt-adequate hays, contrary to the generally held ideas. For any substrate, the synthesis of vitamin B12 analogues was far more efficient than that for cobalamin. Inorganic cobalt was incorporated into cobalamin and vitamin B12 analogues far less efficiently than that from either or hay and barley. Cobalt from four soils substantially increased cobalamin and particularly analogue synthesis. The use of monensin, a fermentation manipulator, had greater effects on digestibility and VFA production than on vitamin B12 synthesis.