The effects of supplementation of the diet of young steers with Mo and S on the intracellular distribution of copper in liver and on copper fractions in blood

Abstract

Young Jersey steers weighing between 100 and 200 kg were fed a basic diet supplemented with Mo, 35 ppm, and S, 0·3% of dry matter intake, for 24 weeks. Total liver copper levels, assessed from biopsy material, fell more rapidly than those of a control group fed the basic diet. While the copper levels declined in all the subcellular fractions examined, that is nuclear, mitochondrial and cytosol; the decrease was most marked in the nuclear fraction. Moderate supplementation (5 ppm Cu) of the controls increased liver copper values, particularly in the nuclear fraction. Total plasma copper levels rose initially in the Mo and S supplemented animals, but the most striking feature was the appearance of a TCA-insoluble copper fraction in plasma. Levels of TCA-insoluble copper were highest in the first month of supplementation, afterwards levels declined. Caeruloplasmin activities were related to the levels of TCA-soluble Cu in plasma. In the Mo and S supplemented animals activities fell whereas in the control animals caeruloplasmin was unaffected. There was some correlation between the copper in the TCA-soluble plasma fraction and total liver copper ( r = 0·7928) and a better correlation ( r = 0·8448) between the TCA-insoluble plasma fraction and the copper of the nuclear fraction in liver. Regression equations were derived from the data which relate the total copper in liver and in the nuclear fraction to copper levels in these plasma fractions.