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Variations in the Amount and Relative Distribution of Vitamin B₁₂ and its Analog in the Bovine Rumen

Animal Science Research Division, USDA, Beltsville, Maryland 20705

ABSTRACT

The effects of various factors upon the amount and nature of vitamin B₁₂-active material in the rumen of dairy heifers were studied. Animals fed silage contained a significantly higher (1.4x to 2.7x) concentration of vitamin B₁₂ activity in their rumen contents than those fed chopped or pelleted hay; heifers fed hay-grain contained less of the vitamin. The dorsal rumen possessed more vitamin B₁₂ activity than the ventral rumen or reticulum on the wet but not dry matter basis. Depending upon the ration, sampling position, and experiment, there was a tendency for the vitamin B₁₂ concentration to increase up to a point with time of collection of sample after feeding. Amounts of the vitamin in rumen contents were 12 to 663 times those available from the food. Correlation coefficients were calculated between vitamin B₁₂ concentrations and other rumen constituents. The highest of those tested was between vitamin B₁₂ activity and total bacterial counts. Estimates of the approximate relative distribution of vitamin B₁₂ and its analogs in rumen contents indicated little variation of most of them with ration. Fifteen to 20% consisted of vitamin B₁₂ itself. The analog composition represents the net contribution of a number of various microorganisms.