A critical evaluation of serum methylmalonic acid and vitamin B12 for the assessment of cobalt deficiency of growing lambs in New Zealand
Gruner, TM, Sedcole, JR, Furlong, JM & Sykes, AR 2004, 'A critical evaluation of serum methylmalonic acid and vitamin B12 for the assessment of cobalt deficiency of growing lambs in New Zealand', New Zealand Veterinary Journal, vol. 52, no. 3, pp. 137-144.
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AIM: To derive reference ranges for serum methylmalonic acid (MMA) for the diagnosis of cobalt/vitamin B12-responsiveness in lambs and critique existing serum vitamin B12 reference ranges. METHODS: Individual animal data from earlier supplementation trials, involving 225 ewes, 106 suckling lambs, 301 lambs during the suckling and post-weaning periods and 414 weaned lambs, for which weight gain to supplementation was observed, were used to derive relationships between serum vitamin B12 and MMA, and liveweight gain. RESULTS: Serum MMA concentrations were rarely elevated above the norm of <2 >μmol/L when serum vitamin B12 concentrations were >375 pmol/L, and not elevated into the range where a liveweight response to supplementation occurred (>10 μmol/L) unless serum vitamin B12 concentrations were below 200 pmol/L. Suckling lambs were able to maintain high growth rates despite elevated serum MMA concentrations (>20 μmol/L). CONCLUSIONS: The current reference ranges used in New Zealand for serum vitamin B12 are set conservatively high. Serum MMA concentrations appear to allow better differentiation of a responsive condition than vitamin B12 concentrations. Serum MMA concentrations >13 μmol/L indicate responsiveness to supplementation whilst concentrations <7 >μmol/L indicate unresponsiveness. In the range 7–13 μmol/L, variation in response was observed and predictability of response is less certain, but supplementation is advisable. CLINICAL RELEVANCE: The current reference ranges for vitamin B12 responsiveness are conservatively high and lead to over-diagnosis of vitamin B12 defi ciency in ill-thriftiness of sheep.