Absorption of Vitamin B12 and Factor B from the Intestine of Sheep

Sheep fed diets which would result in the ruminal synthesis of different amounts of vitamin B12 were used to determine the efficiency of absorption of 57Co-cyanocobalamin administered as a single dose at the duodenal level. Apparent absorption efficiency, estimated as percent of the dose not appearing in the feces, ranged from approximately 8 to 38%. It was higher with a diet which would result in predicted synthesis of B12 of 113 μg daily than with those with predicted synthesis in excess of 1000 μg daily. The recovery of absorbed label in urine after flushing with unlabeled B12 was less for diets with greater predicted B12 synthesis, suggesting that animals absorbing larger quantities of B12 have a greater ability to bind or otherwise store the vitamin, In a preliminary experiment 57 Co-Factor B absorption efficiency estimates in four sheep fed four diets ranged from 7 to 22%. Much less of the label was recovered in urine than was the case with B12.