A critical evaluation of serum methylmalonic acid and vitamin B12 for the assessment of cobalt deficiency of growing lambs in New Zealand

Tini M. Gruner, Southern Cross University
J R. Sedcole, Lincoln University, Canterbury
J M. Furlong, Lincoln University, Canterbury
A R. Sykes, Southern Cross University

Abstract

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.