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Effects of 5,6-Dimethylbenzimidazole, Adenine and Riboflavin on Ruminal Vitamin B₁₂ Synthesis¹

Cornell University, Ithaca, New York 14853

Abstract

Sheep fitted with duodenal reentrant cannulas were used to determine the effects of dietary 5,6-dimethylbenzimidazole, adenine and riboflavin on ruminal vitamin B₁₂ production. The addition of 5,6-dimethylbenzimidazole (DMB) to the basal diet resulted in a large and significant (P< .05) increase in vitamin B₁₂ production. The increase was apparently at the expense of B₁₂ analogues since total B₁₂ activity (non-specific assay) was not significantly affected. Two trials were performed to determine the effects of dietary riboflavin. In one trial in which dehydrated alfalfa meal was used as a roughage source B₁₂ production was unusually high and riboflavin supplementation had no effect. In the second trial ground mixed hay was used as roughage and a larger proportion of the diet consisted of ground corn. In this case there was a trend of increased vitamin B₁₂ production with increasing riboflavin, but, the differences between diets were not statistically significant. Riboflavin had no effect on total vitamin B₁₂ activity in either trial. Fifteen grade lambs randomized over three treatments — control, DMB, and adenine — were fed the supplements with a pelleted complete basal diet until they reached market weight (7 to 11 weeks). Enhancement of serum and liver B₁₂ levels was observed in the group receiving DMB but no differences in growth rate resulted.

¹ Supported in part by U.S. Public Health Service Research Grant AM14165, and by a grant from Agway, Inc.

² The authors gratefully acknowledge the assistance of Dr. J. E. Lowe, Dr. A. L. Sutton, Dr. J. Kubota, Denise Lensing, Cynthia Walters, M. F. Hedrich, G. L. Hunt and Mrs. Lynn Polan.