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Vitamin B₁₂ Content of Milk and Milk Products as Determined by Rat Assay

Dairy Husbandry Research Branch, Agricultural Research Service, United States Department of Agriculture, Beltsville, Maryland

A vitamin B₁₂ assay method using growth of the depleted normal rat as the criterion of potency has been described and utilized to assay milk and milk products. Assays were made of Jersey and Holstein milk collected under different conditions of feeding and subjected to different conditions of handling.

No differences in potency were observed between the two breeds or between barn-fed and pasture-fed cows. The average vitamin B₁₂ content of 10 lots of raw whole milk was found to be 7.1 µg/l. This figure corresponds to the highest values obtained by other workers using microbiological methods of assay.

Neither pasteurization by the holding or flash methods nor storage of raw milk at 0°C. for as much as three days had a significant effect on the B₁₂ potency.

Values are given for the vitamin B₁₂ content of a few samples of several milk products.