EFFECTS OF LOW CONCENTRATIONS OF DIETARY COBALT ON RUMEN SUCCINATE CONCENTRATION IN SHEEP

Sheep fed diets containing less than 70 mu g Co per kg develop vitamin B-12 deficiency. When sheep were fed diets containing 20 mu g Co per kg or less, mean rumen succinate concentrations increased by more than one hundred-fold within 2 days. This increase was matched by an equim olar decrease in mean rumen propionate concentrations. When diets cont aining more than 20 mu g Co per kg were fed to sheep, no such changes occurred. The synthesis of succinyl CoA from propionyl CoA in liver is impaired in ovine cobalt deficiency. We suggested that, paradoxically , accumulation of rumen succinate could reduce the effects of vitamin B-12 deficiency on methylmalonyl CoA mutase and consequently result in lower plasma methylmalonic acid (MMA) concentrations that would arise by feeding diets that did not affect rumen succinate concentrations. This hypothesis was tested by feeding diets containing 4, 40 and 1000 mu g Co per kg to sheep for 23 weeks. However, sheep fed 40 mu g Co pe r kg did not have mean plasma MMA concentrations that were higher than those in the sheep fed 4 mu g Co per kg, indicating that rumen succin ate accumulation did not ameliorate the effects of Co deficiency.