Studies with copper-67 and copper-64 in conditioned copper-deficient ruminants: Preliminary results

Conditioned copper deficiency was induced in ruminants by feeding a diet of ground alfalfa hay containing, on a dried matter basis, 50 ppm of molybdenum and 0.4% of sulphhate in the diet for cattle and 75 ppm of molybdenum and a similar level of sulphate in the diet for sheep. Several parameters of copper metabolism were studied in control and deficient animals by means of 67Cu and 64Cu. The plasma clearance of 67Cu showed that deficient animals removed the tracer at a slower rate than control animals, particularly in cattle. Normal cattle evidenced a higher rate of ceruloplasmin production than normal sheep, although the half-time of ceruloplasmin in the circulation of cattle seems to be shorter than in sheep. These differences in the kinetics of ceruloplasmin between cattle and sheep could explain the higher susceptibility of cattle to dietary molybdenum and sulphate. Apparent absorption of 67Cu from the gut of control and deficient sheep was similar, but the endogenous excretion of the injected tracer was higher in the deficient sheep. These results agree with previous data obtained with 64Cu, nevertheless further determinations are needed before drawing definitive conclusions on this aspect of copper metabolism. The intracellular distribution of 64Cu in the liver samples of control and deficient steers, as well as in normal sheep, showed differences among several fractions. The lack of previous data in normal animals, as well as the limited number of animals studied in the present work, do not allow a valid interpretation of these results. However, such data suggest that further studies in this field could explain the disturbances of copper metabolism in the liver demonstrated in previous research. (author)