The influence of dietary iron and molybdenum on copper metabolism in calves.

1. Twenty heifer calves were allocated to four groups and maintained for 32 weeks on a diet based mainly on barley and straw and containing 4 mg copper/kg. The diet was supplemented with 0 or 800 mg iron/kg and 0 or 5 mg molybdenum/kg. 2. Liver and plasma Cu concentrations, erythrocyte superoxide dismutase (EC 1.15.1.1) and plasma caeruloplasmin (EC 1.16.3.1) activities decreased greatly and rapidly in all calves given the Fe or Mo supplements or both. Levels indicative of severe Cu deficiency were attained within 16 weeks. There were no significant differences in values in animals given Fe, Mo or Fe plus Mo. 3. Clinical signs of Cu deficiency developed after 20 weeks in the calves given the Mo supplement. Growth rates were reduced, skeletal lesions developed and hair texture and colour were affected. No such effects were observed in the calves given only the Fe supplement. 4. Plasma and liver Fe concentrations increased in calves given the Fe supplement but were not greatly affected by Mo, even when the calves were severely Cu-deficient. 5. The significance of the effects of Fe and Mo on Cu metabolism are discussed with special regard to the influence of soil ingestion on Cu availability and to the frequent lack of correlation between the Cu status of animals and their clinical condition.