The paper reports an experiment conducted with 50 Scottish Blackface and 10 South Country Cheviot ewes all suckling twin lambs and grazing, from parturition for some 18 weeks, pasture previously shown to cause a molybdenum-sulphur induced copper deficiency. The objectives were to examine the efficacy of various means of prophylaxis and the susceptibility of the two genotypes to copper deficiency.

The treatment of ewes at parturition with copper, either as an injection of 90 mg copper as copper methionate or orally with cupric oxide needles (3·2 g copper), delayed the onset of signs of copper deficiency in their lambs but did not prevent completely the development of hypocupraemia or hypocuprosis.

The treatment of lambs with a single injection of 15 mg copper as copper calcium edetate at about 6 or 10 weeks of age was not effective in preventing the development of hypocupraemia. Four injections (1 × 5 mg and 3 × 15 mg) at approximately equal intervals maintained normocupraemic values in lambs, but the most effective treatment, as judged by plasma and liver copper concentrations and by live-weight gain, was the administration of cupric oxide needles (1.6 g copper) to lambs at about 6 weeks of age.

The between-genotype comparison indicated that the Cheviot ewes and their lambs were as severely affected by the induced copper deficiency as were the Blackfaces.