Methylmalonic acid in the diagnosis of cobalt deficiency in barley-fed lambs.

Eight lambs were fed on a cobalt-deficient whole-barley diet supplemented with urea, vitamins and minerals. Four control lambs were fed on the same diet which had been further supplemented with Co. Plasma vitamin B12 levels in the Co-depleted group declined rapidly, falling below the normal range within 5 weeks. Differences between the live weights of the animals in the two groups approached statistical significance by week 14. However, methylmalonic acid (MMA) rose above normal levels in the Co-depleted group within 7 weeks. This suggested that an elevated plasma concentration of MMA is a comparatively early indicator of functional vitamin B12 deficiency. It is recommended that 10 mumol/l be the upper level of normality for plasma MMA concentration in barley-fed animals, in contrast with the level of 5 mumol/l for grass-fed animals. Changes in the plasma concentrations of MMA and ethylmalonic acid associated with feeding the barley-based diet per se did not significantly affect the validity of the gas-liquid chromatographic assay for MMA.