Absence of a weight gain response to vitamin B₁₂ supplementation in weaned beef cattle grazing pastures of marginal cobalt content

Abstract

Forty female Angus crossbred calves aged 8 months were allocated to 2 groups based on liver vitamin B₁₂ levels and bodyweight. The treatment group was given monthly subcutaneous injections of 2000 μg hydroxycobalamin. From each group, 5 animals were liver biopsied and 10 animals: serum and urine sampled at monthly intervals for 10 months. Pasture cobalt content in washed and unwashed samples averaged 0.051 mg/kg (0.866 μgmol/kg) and 0.061 mg/kg (1.04 p.mollkg) DM respectively over the trial period. Mean liver vitamin B 12 levels of the untreated group dropped during the spring and summer to 400 nmollkg, while the treated group remained above 640 nmollkg. Serum vitamin B₁₂ levels of the untreated group during the spring and summer averaged 87 pmolllitre, with the lowest mean monthly level of 73 pmolllitre occurring in November. Mean urinary methyl malonic acid remained low (less than 36 p.molllitre) in both groups. There was no weight gain response to vitamin B₁₂ treatment.

Keywords:

• cobalt
• vitamin B₁₂
• methyl malonic acid
• liver
• serum
• urine
• pasture
• cattle
• weight gain