1. Copper deficiency was induced in five Friesian cattle offered a semi-synthetic diet containing < 1 mg Cu/kg. Changes in blood and liver Cu contents and in the Cu-containing enzymes, ferroxidase I (caeruloplasmin; EC 220.127.116.11) and monoamine oxidase (EC 18.104.22.168) of plasma and cytochrome oxidase (EC 22.214.171.124) of liver and skeletal muscle were monitored during Cu depletion.
2. Rapid decreases in blood and liver Cu and plasma ferroxidase I activity were found at least 80 d before the first appearance of overt clinical signs of deficiency. Plasma monoamine oxidase and liver cytochrome oxidase activities decreased less rapidly and thus may provide useful indices of chronic Cu depletion.
3. Although results of these assays indicated that Cu depletion was occurring and metabolic defects supervening, none facilitated the early recognition of individuals that subsequently showed marked overt clinical signs of Cu deficiency compared with those less severely affected.
4. Irrespective of their clinical appearance at slaughter, Cu-depleted cattle showed gross or microscopic lesions of the skeleton and cardiovascular system and, in some instances, lesions of the ligamentum nuchae and small intestine. The aetiology of these lesions is considered with particular respect to changes in the activities of the Cu-dependent enzymes studied and to the interpretation of field surveys based solely upon determination of blood or liver Cu content.
5. A second group of five cattle was offered the same diet supplemented with Cu to provide 8 mg Cu/kg and, later, 15 mg Cu/kg. Although no pathological lesions attributable to Cu deficiency were detected at slaughter a marked reduction in liver Cu content, a decrease in plasma ferroxidase I activity and, in four animals, the development of a diarrhoea controlled by oral administration of Cu, suggested that 8 mg Cu/kg diet did not meet their requirement for Cu.