Response in Vitamin B-12 Production and Absorption to Increasing Cobalt Intake in the Sheep

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Abstract
Three sheep, fitted with intestinal reentrant and rumen cannulas, were used to estimate ruminal production of vitamin B-12 when fed diets differing in cobalt concentrations. The basal diet, which was in pelleted form, consisted of 30% ground corn, 69% ground hay and 1% sodium chloride. At daily cobalt intakes averaging 0.047, 0.41 and 0.83 mg, mean estimates of vitamin B-12 production were 37, 1006 and 1553 µg, respectively—a significant (P < 0.05) treatment effect. Multiple regression analysis of the data from this and other experiments employing the same techniques indicated that more than one-half of the observed variation in vitamin B-12 production estimates was accounted for by variations in cobalt intake, percentage roughage in diet and digestible dry matter intake. The multiple regression was highly significant (P < 0.01). Data from two sheep on apparent absorption from the small intestine, determined as the difference in flow of B-12 at the ileal and duodenal levels, were combined with data from other trials to study the effects of duodenal B-12 flow (production), rate of ileal digesta flow, and relative proportion of Ochromonas-active B-12 in duodenal B-12 activity as measured by radioassay. A highly significant (P < 0.01) multiple regression equation accounting for 57% of the observed variation in apparent absorption was computed. The data suggest that the minimum cobalt requirement of the ruminant is affected by the level of digestible dry matter intake as well as the composition of the diet.