Some observations on the vitamin B12 content of rat's milk

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Abstract
1. Vitamin B12 activity in the milk of rats on various diets was measured by microbiological assay at intervals throughout lactation. The concentration of sodium and calcium in the milk was also determined.2. At all stages of lactation the milk of rats fed on commercial rat cake contained much more vitamin B12 activity than that of rats receiving a semi-synthetic diet containing at least as much vitamin B12 as the rat cake. The milk of the latter group of animals contained more vitamin B12 than that from rats fed on the same diet without added cyanocobalamin. The levels of sodium and calcium were much less variable than those of vitamin B12 and the changes did not appear to be related to differences in diet, stage of lactation or litter size.