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Effect of Ratio of Roughage to Concentrate and Level of Feed Intake on Ovine Ruminal Vitamin B₁₂ Production^{1, 2,}

Department of Animal Science, New York State College of Agriculture and Life Sciences, Cornell University, Ithaca, New York 14850

Three sheep, fitted with intestinal reentrant and rumen cannulas, were used in two experiments to estimate ruminal production of vitamin B₁₂ and to assess the effects of proportion of concentrate in the diet and level of feed intake. The flow of vitamin B₁₂ through the duodenum over 24-hour periods was used as an estimate of daily production. Two vitamin B₁₂ assays were used, one of which (Ochromonas malhamensis) is quite specific for the vitamin, the other of which (radioisotope dilution) responds to at least some of the analogues of vitamin B₁₂ as well. The primary ingredients of the diets, which were ground and pelleted, were timothy hay and corn in ratios of 100:0, 70:30 and 40:60. Cobalt (0.5 ppm) was added to all diets. Average estimates of daily vitamin B₁₂ production ranged from 579 to 1195 µg. The high corn diet significantly (P < 0.05) reduced vitamin B₁₂ production. The production of analogues of B₁₂ was not, however, proportionately reduced. Consequently a smaller percentage of the intestinal flow of total vitamin B₁₂ activity was represented by the vitamin itself. This was reflected in a similar pattern in serum B₁₂ activity. Within the range of intakes studied (approx. one to two times maintenance), vitamin B₁₂ production responded in a linear fashion to changes in digestible dry matter intake. Vitamin B₁₂ represented a significantly (P < 0.05) increasing proportion of total B₁₂ activity as feed intake increased. The increased synthesis of vitamin B₁₂ appeared to be at the expense of analogues.

KEY WORDS: • vitamin B₁₂ • ruminal synthesis • ratio of roughage to concentrate • feed intake

¹ Supported in part by U. S. Public Health Service Research Grant AM14165 from the National Institute of Arthritis and Metabolic Diseases.

² Present address: Department of Animal Sciences, Purdue University, Lafayette, Indiana 47907.

³ A brief report of results was presented at the annual meeting of the North Atlantic Section, American Society of Animal Science, Storrs, Connecticut, July 11–13, 1971 (J. Animal Sci. 33: 312).

Manuscript received 8 March 1972.

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