Duration of effective benefit from administration of graded oral doses of cobalt to sheep.

The rapidity and duration of the response of sheep to graded oral doses of cobalt, given as the sulphate or as a cobalt-supplemented anthelmintic Panacur SC, was assessed by the determination of serum vitamin B12 and methylmalonic acid concentrations. The rapidity of the response to the treatments, which ranged from 1 to 250 mg cobalt, was unaffected by dose rate but the effective duration was dose related. There was some evidence of a cumulative effect from repeat treatments of the anthelmintic at three weekly intervals. It is suggested that the optimum inclusion rate for cobalt in anthelmintics lies within the range 21 to 100 mg/treatment.