The Effect of Vitamin B12 on Reproduction and Lactation in Rats Receiving Pork or Beef Diets

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Abstract
Oral supplements of crystalline vitamin B12 at the 0.1 µg per day level did not overcome the lactation failure frequently seen in rats fed roast pork as the sole source of protein, but did help in overcoming the conception lag often accompanying such a diet. Addition of a methanol liver extract (0.05 µg B12 per day) raised the lactation performance of animals on a purified diet to 100% but did not affect those on the pork diet. The failure of vitamin B12 did not seem to be due to poor absorption, as injected vitamin B12 did not produce an improvement. Substitution of dextrin for sucrose caused lactation failure in every group. Addition of 5 mg % streptomycin did not produce any improvement in the lactation of the pork-fed animals. The need to consider the influence of the diet as a whole in establishing the requirements for any one nutrient was emphasized. A method for milking rats was described and data were presented showing the variations in the amount of vitamin B12 in the milk with changes in diet. Rat milk has a high vitamin B12 activity, averaging about 20 mµg/ml. The vitamin B12 level of the milk seemed to follow the reproduction and lactation performance regardless of the level of the vitamin in the diet.