Absence of a weight gain response to Vitamin B12 supplementation in weaned dairy heifers grazing pastures of marginal cobalt content

Aim. To obtain information on serum and liver vitamin B₁₂ and urinary methylmalonic acid concentrations as diagnostic tests to predict a weight gain response to supplementation with vitamin B₁₂ in young dairy cattle when grazing pasture of low cobalt content.

Methodology. Forty dairy cattle (12 Friesian, 14 Friesian × Jersey and 14 Jersey) were allocated to two equal sized groups, treated and untreated, based on liveweight. At monthly intervals for 14 months, all animals were weighed, their serum and urine sampled, their liver biopsied and the pasture sampled from the paddocks they were grazing and going to graze. Serum and liver were assayed for Vitamin B₁₂ concentrations. For the first 5 months of the trial, urine was assayed for methylmalonic acid concentrations. Both washed and unwashed pasture samples were assayed for cobalt concentrations.

Results. No weight gain response occurred to Vitamin B₁₂ supplementation in young growing cattle grazing pasture with a cobalt concentration of 0.04-0.06 mg/kg DM. For 5 months of the trial, liver Vitamin B₁₂ concentrations from untreated calves were in the range 75-220 nmol/kg and serum vitamin B₁₂ concentrations were as low as 72 pmol/1. There was no associated growth response to supplementation.

Conclusion. Further trials involving young cattle grazing pastures with cobalt concentrations less than 0.04 mg/kg DM are required to reliably determine liver and serum Vitamin B₁₂ concentrations at which growth responses to Vitamin B₁₂ or cobalt supplementation are likely under New Zealand pastoral grazing conditions.